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The biodegradable (polybutylene adipate terephthalate: PBAT) and conventional (polyethylene: PE) microplastics (MPs) at 0.5 %, 1 %, and 2 % dosages (w/w) were added into soils with and without Serratia marcescens ZY01 (ZY01, a tet-host strain) to understand their different effects on the dissipation of oxytetracycline (OTC) and tet. The results showed that the dosages of PBAT MP exhibited different inhibition degrees of OTC biodegradation in soils regardless of ZY01, while the dosages of PE MP did not change the enhancement degree of OTC biodegradation in soils without ZY01. These differences were due to the higher adsorption capacity of OTC on PBAT MP and the stronger toxicity of PBAT MP to microorganisms. Besides soil organic matter, pH and total phosphorus were important factors regulating specific tet-host bacteria in soils with MPs (e.g., the nitrogen-cycling bacteria Steroidobacter and Nitrospira) and MPs + ZY01 (e.g., the phosphorus-cycling bacteria Saccharimonadales and Haliangium), respectively. Regardless of ZY01, a stronger selective harboring of tet-host bacteria in PE MP treatments than PBAT MP treatments was observed at the MP dosage of 1 % (w/w), while the opposite trend was true at the MP dosages of 0.5 % and 2 % (w/w). Some specific genera belonging to Actinobacteriota strongly associated with the class 1 integron-integrase gene (intI1), playing a critical role in the horizontal gene transfer of tet in soils especially for the co-existence of MPs and ZY01. This study will be helpful for understanding on how biodegradable and conventional MPs as hotspots affect the environmental behavior of antibiotics and ARGs in soil., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Transferrin (Tsf) is a highly conserved multifunctional protein involved in insect physiology, defense and development that has been developed as a novel RNA interference (RNAi)-based target for pest control. The function study of the Tsf gene in Odontotermes formosanu (Shiraki) was evaluated for synergistic control of this agroforestry pest with Serratia marcescens (SM1), Bacillus thuringiensis (Bt) or Beauveria bassiana (Bb). The Tsf gene of O. formosanus was identified and characterized. Real-time fluorescent quantitative PCR (qPCR) analysis demonstrated that OfTsf was most highly expressed in the male dealate of O. formosanus, and OfTsf was highly expressed in the hemolymph. OfTsf expression was considerably elevated after SM1, Bt or Bb infection. Furthermore, dsOfTsf treatment was effective in increasing the virulence of entomopathogens to O. formosanus. In addition, OfTsf expression was markedly upregulated in O. formosanus fed with oxidative stress inducers; reactive oxygen species (ROS) levels were significantly increased after dsOfTsf treatment. Therefore, OfTsf gene played an important role in defending against entomopathogen infection and antioxidant stress. Most importantly, our work suggested OfTsf as a potential RNAi target for the control of O. formosanus., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Objectives: The aim of this study was to investigate interspecies transfer of resistance gene bla NDM-1 and intraspecies transfer of resistance gene bla KPC-2 in Serratia marcescens, and explore the epidemical and evolutionary characteristics of carbapenemase-producing S. marcescens (CPSM) regionally and globally., Methods: Interspecies and intraspecies transfer of bla KPC-2 - or bla NDM-1 were identified by antimicrobial susceptibility testing, plasmid conjugation and curing, discovery of transposable units (TUs), outer membrane vesicles (OMVs), qPCR, whole-genome sequencing (WGS) and bioinformatic analysis. The genomic evolution of CPSM strains was explored by cgSNP and maximum-likelihood phylogenetic tree., Results: CPSM S50079 strain, co-carrying bla KPC-2 and bla NDM-1 on one plasmid, was isolated from the blood of a patient with acute pancreatitis and could generate TUs carrying either bla KPC-2 or bla NDM-1 . The interspecies transfer of bla NDM-1 -carrying plasmid from Providencia rettgeri P50213, producing the identical bla NDM-1 -carrying TUs, to S. marcescens S50079K, an S50079 variant via plasmid curing, was identified through bla NDM-1 -harbouring plasmid conjugation and OMVs transfer. Moreover, the intraspecies transfer of bla KPC-2 , mediated by IS26 from plasmid to chromosome in S50079, was also identified. In another patient, who underwent lung transplantation, interspecies transfer of bla NDM-1 carried by IncX3 plasmid was identified among S. marcescens and Citrobacter freundii as well as Enterobacter hormaechei via plasmid transfer. Furthermore, 11 CPSM from 349 non-repetitive S. marcescens strains were identified in the same hospital, and clonal dissemination, with carbapenemase evolution from bla KPC-2 to both bla KPC-2 and bla NDM-1 , was found in the 8 CPSM across 4 years. Finally, the analysis of 236 global CPSM from 835 non-repetitive S. marcescens genomes, retrieved from the NCBI database, revealed long-term spread and evolution worldwide, and would cause the convergence of more carbapenemase genes., Conclusions: Interspecies transfer of resistance gene bla NDM-1 and intraspecies transfer of resistance gene bla KPC-2 in CPSM were identified. Nosocomial and global dissemination of CPSM were revealed and more urgent surveillance was acquired., (Copyright © 2024 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.)

Bacteria are major drivers of organic matter decomposition and play crucial roles in global nutrient cycling. Although the degradation of dead fungal biomass (necromass) is increasingly recognized as an important contributor to soil carbon (C) and nitrogen (N) cycling, the genes and metabolic pathways involved in necromass degradation are less characterized. In particular, how bacteria degrade necromass containing different quantities of melanin, which largely control rates of necromass decomposition in situ , is largely unknown. To address this gap, we conducted a multi-timepoint transcriptomic analysis using three Gram-negative, bacterial species grown on low or high melanin necromass of Hyaloscypha bicolor . The bacterial species, Cellvibrio japonicus, Chitinophaga pinensis , and Serratia marcescens , belong to genera known to degrade necromass in situ . We found that while bacterial growth was consistently higher on low than high melanin necromass, the CAZyme-encoding gene expression response of the three species was similar between the two necromass types. Interestingly, this trend was not shared for genes encoding nitrogen utilization, which varied in C. pinensis and S. marcescens during growth on high vs low melanin necromass. Additionally, this study tested the metabolic capabilities of these bacterial species to grow on a diversity of C and N sources and found that the three bacteria have substantially different utilization patterns. Collectively, our data suggest that as necromass changes chemically over the course of degradation, certain bacterial species are favored based on their differential metabolic capacities.IMPORTANCEFungal necromass is a major component of the carbon (C) in soils as well as an important source of nitrogen (N) for plant and microbial growth. Bacteria associated with necromass represent a distinct subset of the soil microbiome and characterizing their functional capacities is the critical next step toward understanding how they influence necromass turnover. This is particularly important for necromass varying in melanin content, which has been observed to control the rate of necromass decomposition across a variety of ecosystems. Here we assessed the gene expression of three necromass-degrading bacteria grown on low or high melanin necromass and characterized their metabolic capacities to grow on different C and N substrates. These transcriptomic and metabolic studies provide the first steps toward assessing the physiological relevance of up-regulated CAZyme-encoding genes in necromass decomposition and provide foundational data for generating a predictive model of the molecular mechanisms underpinning necromass decomposition by soil bacteria., Competing Interests: The authors declare no conflict of interest.

Background: We describe the investigations for control of two consecutive Serratia marcescens outbreaks in neonatology unit of Singapore General Hospital., Methods: Epidemiological investigations, environmental sampling and risk-factors analysis were performed to guide infection control measures. Active surveillance sampling of nasopharyngeal aspirate and/or stool from neonates was conducted during both outbreaks. Whole-genome-sequencing was done to determine clonal links. Retrospective case-control study was conducted for second outbreak to identify risk factors for S marcescens acquisition., Results: In 2022, two genetically unrelated S marcescens outbreaks were managed involving five neonates in March 2022 (outbreak 1) and eight neonates in November 2022 (outbreak 2). A link to positive isolates from sinks in intensive care units and milk preparation room was identified during outbreak 1. Neonatal jaundice (aOR, 16.46; p-value= 0.023) and non-formula milk feeding (aOR, 13.88; p-value= 0.02) were identified as risk factors during second outbreak. Multiple interventions adopted were cohorting of positive cases, carriage-screening, enhanced environmental cleaning, and emphasis on alcohol-based handrubs for hand-hygiene., Conclusion: The two outbreaks were likely due to infection prevention practices lapses and favourable environmental conditions. Nosocomial S marcescens outbreaks in neonatology units are difficult to control and require multidisciplinary approach with strict infection prevention measures to mitigate risk factors., (Copyright © 2024 Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved.)

Background: The healthcare water environment is a potential reservoir of carbapenem-resistant organisms (CROs)., Aim: To report the role of the water environment as a reservoir and the infection control measures applied to suppress a prolonged outbreak of Klebsiella pneumoniae carbapenemase-producing Serratia marcescens (KPC-SM) in two intensive care units (ICUs)., Methods: The outbreak occurred in the ICUs of a tertiary hospital from October 2020 to July 2021. Comprehensive patient contact tracing and environmental assessments were conducted, and a case-control study was performed to identify factors associated with the acquisition of KPC-SM. Associations among isolates were assessed via pulsed-field gel electrophoresis (PFGE). Antibiotic usage was analysed., Findings: The outbreak consisted of two waves involving a total of 30 patients with KPC-SM. Multiple environmental cultures identified KPC-SM in a sink, a dirty utility room, and a communal bathroom shared by the ICUs, together with the waste bucket of a continuous renal replacement therapy (CRRT) system. The genetic similarity of the KPC-SM isolates from patients and the environment was confirmed by PFGE. A retrospective review of 30 cases identified that the use of CRRT and antibiotics was associated with acquisition of KPC-SM (P < 0.05). There was a continuous increase in the use of carbapenems; notably, the use of colistin has increased since 2019., Conclusion: Our study demonstrates that CRRT systems, along with other hospital water environments, are significant potential sources of resistant micro-organisms, underscoring the necessity of enhancing infection control practices in these areas., (Copyright © 2024 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.)

Host-microbe interactions are virtually bidirectional, but how the host affects their microbiome is poorly understood. Here, we report that the host is a critical modulator to regulate the lifestyle switch and pathogenicity heterogeneity of the opportunistic pathogens Serratia marcescens utilizing the Drosophila and bacterium model system. First, we find that Drosophila larvae efficiently outcompete S. marcescens and typically drive a bacterial switch from pathogenicity to commensalism toward the fly. Furthermore, Drosophila larvae reshape the transcriptomic and metabolic profiles of S. marcescens characterized by a lifestyle switch. More importantly, the host alters pathogenicity and heterogeneity of S. marcescens in the single-cell resolution. Finally, we find that larvae-derived AMPs are required to recapitulate the response of S. marcescens to larvae. Altogether, our findings provide an insight into the pivotal roles of the host in harnessing the life history and heterogeneity of symbiotic bacterial cells, advancing knowledge of the reciprocal relationships between the host and pathogen., Competing Interests: ZW, SL, SZ, TZ, YW, AL, KW, XJ, HC, YZ, ET, YW, YW, WL No competing interests declared, (© 2024, Wang, Li et al.)

Opportunistic pathogens are environmental microbes that are generally harmless and only occasionally cause disease. Unlike obligate pathogens, the growth and survival of opportunistic pathogens do not rely on host infection or transmission. Their versatile lifestyles make it challenging to decipher how and why virulence has evolved in opportunistic pathogens. The coincidental evolution hypothesis postulates that virulence results from exaptation or pleiotropy, i.e. traits evolved for adaptation to living in one environment that have a different function in another. In particular, adaptation to avoid or survive protist predation has been suggested to contribute to the evolution of bacterial virulence (the training ground hypothesis). Here, we used experimental evolution to determine how the selective pressure imposed by a protist predator impacts the virulence and fitness of a ubiquitous environmental opportunistic bacterial pathogen that has acquired multidrug resistance: Serratia marcescens. To this aim, we evolved S. marcescens in the presence or absence of generalist protist predator, Tetrahymena thermophila. After 60 d of evolution, we evaluated genotypic and phenotypic changes by comparing evolved S. marcescens with the ancestral strain. Whole-genome shotgun sequencing of the entire evolved populations and individual isolates revealed numerous cases of parallel evolution, many more than statistically expected by chance, in genes associated with virulence. Our phenotypic assays suggested that evolution in the presence of a predator maintained virulence, whereas evolution in the absence of a predator resulted in attenuated virulence. We also found a significant correlation between virulence, biofilm formation, growth, and grazing resistance. Overall, our results provide evidence that bacterial virulence and virulence-related traits are maintained by selective pressures imposed by protist predation., Competing Interests: Conflict of Interest None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of Society for Molecular Biology and Evolution.)

The aim of this study is to evaluate the antimicrobial susceptibility of invasive isolates of Serratia marcescens, associated with blood stream infections (BSIs) in patients hospitalized in Varna University Hospital, Bulgaria, as well as to identify the genetic mechanisms responsible for 3rd generation cephalosporin and carbapenem-resistance among these isolates. A total of 45 consecutive S. marcescens isolates, obtained from blood cultures of 45 patients with BSIs, hospitalized during an 8-year period (2016-2023) were included. Species identification and antimicrobial susceptibility testing were done by Phoenix (BD, USA) and Vitek 2 (BioMerieux, France) systems and the results were interpreted according to EUCAST guidelines. The genetic mechanisms of beta-lactam resistance were studied by PCR. During the study period, a total of 45 patients were diagnosed with S. marcescens-associated BSIs. All infections were defined as nosocomial, predominantly intensive care unit-acquired (42.2%) and 28.8% were central venous catheter-associated. The following antimicrobial resistance rates were found: ceftriaxone, piperacillin/tazobactam, 57.8%; ceftazidime, 55.6%; cefepime, trimethoprime/sulfamethoxazole, 53.3%; gentamicin, 48.8%; ciprofloxacin, 44.5%; amikacin, 15.6%; carbapenems, 2.2%. The blaCTX-M was identified in 88.9% of the tested 3rd generation cephalosporin resistant isolates. Among these, 50% were also blaTEM positive. The single carbapenem-resistant isolate harboured blaKPC, blaCTX-M1/9, blaCMY-2 and blaTEM. This study demonstrates S. marcescens as a problematic nosocomial pathogen and we report a KPC-producing S. marcescens clinical isolate from a BSI in Bulgaria.

Objectives: To describe the in vivo emergence of ceftazidime-avibactam resistance in GES-type carbapenemases and to characterize an unusual outbreak of GES-6-producing Serratia marcescens during the COVID-19 pandemic in Spain., Methods: Retrospective study to describe a GES-CPSM outbreak based on whole genome sequencing and antimicrobial susceptibility testing (AST). Transferability of bla GES -carrying plasmid was assessed by conjugation experiments., Results: In December 2020, we identified a cluster of S. marcescens harbouring bla GES-6 involving 9 patients. Whole-genome sequence analysis revealed a clonal relationship (≤3 SNPs) between the first isolates identified in each of the evolved patients and environmental samples with GES-CPSM detection. Plasmid analysis showed that the bla GES-6 gene was located in an IncQ3-type plasmid. Triparental mating experiments using a helper plasmid demonstrated mobilization of the bla GES-6 -carrying plasmid. Our results also demonstrate within-host evolution in S. marcescens isolates, leading to a transition from bla GES-6 to the new bla GES-55 , caused by the P162S mutation, in a subsequent infection in one of the affected patients. In bla GES-55 we identified emergence of ceftazidime-avibactam resistance along with an increase of carbapenems susceptibility. This patient had been treated with a 14-day course of ceftazidime-avibactam. AST of the transformants bearing bla GES-6 and bla GES-55 plasmids, confirmed susceptibility variation affecting ceftazidime-avibactam and carbapenems., Conclusions: We report an unusual outbreak of GES-6 whose incidence is becoming increasing. Transition from GES-6 to GES-55 may readily occur in vivo leading to ceftazidime-avibactam resistance, which brings to the fore the critical need for developing more accurate diagnosis tools for detection of GES β-lactamases and optimise the use of antimicrobials., (Copyright © 2024 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.)

Background: Serratia marcescens is known to cause outbreaks in neonatal intensive care units (NICUs). Traditionally epidemiological data, antimicrobial resistance patterns and epidemiological typing have been used to guide infection prevention methods. Whole-genome sequencing (WGS) applications such as core-genome multi-locus sequence typing (cgMLST) applied during an outbreak would potentially yield more information., Aim: To use cgMLST to acquire detailed information on the source and spread of bacteria, enabling more efficient control measures during an S. marcescens outbreak at a NICU., Methods: Neonates admitted to the NICU of the Leiden University Medical Center (LUMC) during an outbreak between September 2023 and January 2024, with S. marcescens being cultured, were included. Environmental samples were taken to search for a common source, antibiotic susceptibility testing was performed, and antimicrobial resistance genes were analysed., Findings: S. marcescens strains from 17 of the 20 positive patients were available for molecular typing. The cgMLST scheme revealed five different complex types consisting of four separate clusters. Multiple clusters made an unidentified persistent environmental source as cause of the outbreak less likely, leading to a quick downscaling of infection prevention measures. Differences were shown in aminoglycoside resistance patterns of isolates within the same complex types and patients., Conclusion: The use of ad-hoc cgMLST provided timely data for rational decision-making during an S. marcescens outbreak at the NICU. Antibiotic phenotyping alone was found not to be suitable for studying clonal spread during this outbreak with S. marcescens., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Serratia marcescens is an opportunistic human pathogen that produces a vibrant red pigment called prodigiosin. Prodigiosin has implications in virulence of S. marcescens and promising clinical applications. We discovered that addition of the virulent flagellotropic bacteriophage χ (Chi) to a culture of S. marcescens stimulates a greater than fivefold overproduction of prodigiosin. Active phage infection is required for the effect, as a χ-resistant strain lacking flagella does not respond to phage presence. Via a reporter fusion assay, we have determined that the addition of a χ-induced S. marcescens cell lysate to an uninfected culture causes a threefold increase in transcription of the pig operon, containing genes essential for pigment biosynthesis. Replacement of the pig promoter with a constitutive promoter abolished the pigmentation increase, indicating that regulatory elements present in the pig promoter likely mediate the phenomenon. We hypothesize that S. marcescens detects the threat of phage-mediated cell death and reacts by producing prodigiosin as a stress response. Our findings are of clinical significance for two main reasons: (i) elucidating complex phage-host interactions is crucial for development of therapeutic phage treatments, and (ii) overproduction of prodigiosin in response to phage could be exploited for its biosynthesis and use as a pharmaceutical., (© 2024. The Author(s).)

Respiratory pathogens, commonly colonizing nasopharynx, are among the leading causes of death due to antimicrobial resistance. Yet, antibiotic resistance determinants within nasopharyngeal microbial communities remain poorly understood. In this prospective cohort study, we investigate the nasopharynx resistome development in preterm infants, assess early antibiotic impact on its trajectory, and explore its association with clinical covariates using shotgun metagenomics. Our findings reveal widespread nasopharyngeal carriage of antibiotic resistance genes (ARGs) with resistomes undergoing transient changes, including increased ARG diversity, abundance, and composition alterations due to early antibiotic exposure. ARGs associated with the critical nosocomial pathogen Serratia marcescens persist up to 8-10 months of age, representing a long-lasting hospitalization signature. The nasopharyngeal resistome strongly correlates with microbiome composition, with inter-individual differences and postnatal age explaining most of the variation. Our report on the collateral effects of antibiotics and prolonged hospitalization underscores the urgency of further studies focused on this relatively unexplored reservoir of pathogens and ARGs., (© 2024. The Author(s).)

Serratia marcescens is utilized as a significant enterobacteria in the production of various high-value secondary metabolites. Acetoin serves as a crucial foundational compound of development and finds application in a broad range of fields. Furthermore, S. marcescens HBQA-7 is capable of utilizing xylose as its exclusive carbon source for acetoin production. The objective of this study was to utilize a constitutive promoter screening strategy to enhance both xylose utilization and acetoin production in S. marcescens HBQA-7. By utilizing RNA-seq, we identified the endogenous constitutive promoter P6 that is the most robust, which facilitated the overexpression of the sugar transporter protein Glf L445I , α-acetyl lactate synthase, and α-acetyl lactate decarboxylase, respectively. The resultant recombinant strains exhibited enhanced xylose utilization rates and acetoin yields. Subsequently, a recombinant plasmid, denoted as pBBR1MCS-P6-glf L445I alsSalsD, was constructed, simultaneously expressing the aforementioned three genes. The resulting recombinant strain, designated as S3, demonstrated a 1.89-fold boost in xylose consumption rate compared with the original strain during shake flask fermentation. resulting in the accumulation of 7.14 g/L acetoin in the final fermentation medium. Subsequently, in a 5 L fermenter setup, the acetoin yield reached 48.75 g/L, corresponding to a xylose-to-acetoin conversion yield of 0.375 g/g., (© 2024 International Union of Biochemistry and Molecular Biology, Inc.)

Polymerase chain reaction (PCR) is an important tool for exogenous gene acquisition and recombinants identification. There exist two problems when using Serratia marcescens as a template for PCR amplification: amplified PCR products are rapidly degraded, and the results of PCR amplification are unstable. The aim of the present work was to elucidate the reasons for this. By mixing PCR products amplified from Escherichia coli DH5α with S. marcescens supernatant or pellet, we found that the DNA-degrading substance in S. marcescens is thermally resistant and present both intracellularly and extracellularly. We then determined that it is protein, and most likely S. marcescens nuclease, that degrades PCR products since the addition of SDS and EDTA can effectively inhibit or block the degradation of PCR products. By knocking out the S. marcescens nuclease encoding gene, nucA, we confirmed that the nuclease is responsible for the degradation of PCR products and the instability of PCR amplification. This work is the first to show that the S. marcescens nuclease is temporarily and partially inhibited by high temperatures during PCR and recovers rapidly at room temperature after PCR., (© 2024 John Wiley & Sons Ltd.)

In 2022, an outbreak with severe bloodstream infections caused by Serratia marcescens occurred in an adult intensive care unit (ICU) in Hungary. Eight cases, five of whom died, were detected. Initial control measures could not stop the outbreak. We conducted a matched case-control study. In univariable analysis, the cases were more likely to be located around one sink in the ICU and had more medical procedures and medications than the controls, however, the multivariable analysis was not conclusive. Isolates from blood cultures of the cases and the ICU environment were closely related by whole genome sequencing and resistant or tolerant against the quaternary ammonium compound surface disinfectant used in the ICU. Thus, S. marcescens was able to survive in the environment despite regular cleaning and disinfection. The hospital replaced the disinfectant with another one, tightened the cleaning protocol and strengthened hand hygiene compliance among the healthcare workers. Together, these control measures have proved effective to prevent new cases. Our results highlight the importance of multidisciplinary outbreak investigations, including environmental sampling, molecular typing and testing for disinfectant resistance.

Introduction: Serratia marcescens is an opportunistic pathogen found ubiquitously in the environment and associated with a wide range of nosocomial infections. This multidrug-resistant bacterium has been a cause of concern for hospitals and healthcare facilities due to its ability to spread rapidly and cause outbreaks. Next generation sequencing genotyping of bacterial isolates has proven to be a valuable tool for tracking the spread and transmission of nosocomial infections. This has allowed for the identification of outbreaks and transmission chains, as well as determining whether cases are due to endogenous or exogenous sources. Evidence of nosocomial transmission has been gathered through genotyping methods. The aim of this study was to investigate the genetic diversity of carbapenemase-producing S. marcescens in an outbreak at a public hospital in Cuiaba, MT, Brazil., Methodology: Ten isolates of S. marcenses were sequenced and antibiotic resistance profiles analyzed over 12 days., Results: The isolates were clonal and multidrug resistant. Gentamycin and tigecycline had sensitivity in 90% and 80% isolates, respectively. Genomic analysis identified several genes that encode β-lactamases, aminoglycoside-modifying enzymes, efflux pumps, and other virulence factors., Conclusions: Systematic surveillance is crucial in monitoring the evolution of S. marcescens genotypes, as it can lead to early detection and prevention of outbreaks., Competing Interests: No Conflict of Interest is declared, (Copyright (c) 2024 Thalita PPS Cruz, Francisco KSF Azevedo, Marco A Pepato, Paula S Rizzo, Francisco JD Souto, Bertram Brenig, Aristóteles Góes-Neto, Siomar C Soares, Rommel TJ Ramos, Vasco AC Azevedo, Mateus M Costa, Leonardo Broetto, Luciano Nakazato, Valéria Dutra.)

OxyR, a LysR family transcriptional regulator, plays vital roles in bacterial oxidative stress response. In this study, we found that the deletion of oxyR not only inhibited the antioxidant capacity of S. marcescens FS14, but also decreased the production of prodigiosin. Further study revealed that OxyR activated the prodigiosin biosynthesis at the transcriptional level. Complementary results showed that not only the wild-type OxyR but also the reduced form OxyR C199S could activate the prodigiosin biosynthesis. We further demonstrated that reduced form of wild type OxyR could bind to the promoter of pig gene cluster, and identified the binding sites which is different from oxidized OxyR binding sites in E. coli. Our results demonstrated that OxyR in FS14 uses oxidized form to regulate the expression of the antioxidant related genes and utilizes reduced form to activate prodigiosin production. Further in silico analysis suggested that the activation of prodigiosin biosynthesis by reduced OxyR should be general in S. marcesencs. To our knowledge, this is the first report to show that OxyR uses the reduced form to activate the gene's expression, therefore, our results provide a novel regulation mechanism of OxyR., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Serratiopeptidase, a proteolytic enzyme serves as an important anti-inflammatory and analgesic medication. Present study reports the production and purification of extracellular serratiopeptidase from an endophyte, Serratia marcescens MES-4, isolated from Morus rubra. Purification of the enzyme by Ion exchange chromatography led to the specific activity of 13,030 U/mg protein of serratiopeptidase, showcasing about 3.1 fold enhanced activity. The catalytic domain of the purified serratiopeptidase, composed of Zn coordinated with three histidine residues (His 209, His 213, and His 219), along with glutamate (Glu 210) and tyrosine (Tyr 249). The molecular mass, as determined by SDS-PAGE was ∼51 kDa. The purified serratiopeptidase displayed optimal activity at pH 9.0, temperature 50°C. Kinetic studies revealed V max and K m values of 33,333 U/mL and 1.66 mg/mL, respectively. Further, optimized conditions for the production of serratiopeptidase by Taguchi design led to the productivity of 87 U/mL/h with 87.9 fold enhanced production as compared to the previous conditions., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Asha Chaubey reports financial support and administrative support were provided by Council of Scientific & Industrial Research Indian Institute of Integrative Medicine. Dr Asha Chaubey reports a relationship with Council of Scientific & Industrial Research Indian Institute of Integrative Medicine that includes: employment. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

The genus Serratia harbors opportunistic pathogenic species, among which Serratia marcescens is pathogenic for honeybees although little studied. Recently, virulent strains of S. marcescens colonizing the Varroa destructor mite's mouth were found vectored into the honeybee body, leading to septicemia and death. Serratia also occurs as an opportunistic pathogen in the honeybee's gut with a low absolute abundance. The Serratia population seems controlled by the host immune system, but its presence may represent a hidden threat, ready to arise when honeybees are weakened by biotic and abiotic stressors. To shed light on the Serratia pathogen, this research aims at studying Serratia 's development dynamics in the honeybee body and its interactions with the co-occurring fungal pathogen Vairimorpha ceranae . Firstly, the degree of pathogenicity and the ability to permeate the gut epithelial barrier of three Serratia strains, isolated from honeybees and belonging to different species ( S. marcescens , Serratia liquefaciens , and Serratia nematodiphila ), were assessed by artificial inoculation of newborn honeybees with different Serratia doses (10 4 , 10 6 , and 10 8 cells/mL). The absolute abundance of Serratia in the gut and in the hemocoel was assessed in qPCR with primers targeting the luxS gene. Moreover, the absolute abundance of Serratia was assessed in the gut of honeybees infected with V. ceranae at different development stages and supplied with beneficial microorganisms and fumagillin. Our results showed that all tested Serratia strains could pass through the gut epithelial barrier and proliferate in the hemocoel, with S. marcescens being the most pathogenic. Moreover, under cage conditions, Serratia better proliferates when a V. ceranae infection is co-occurring, with a positive and significant correlation. Finally, fumagillin and some of the tested beneficial microorganisms could control both Serratia and Vairimorpha development. Our findings suggest a correlation between the two pathogens under laboratory conditions, a co-occurring infection that should be taken into consideration by researches when testing antimicrobial compounds active against V. ceranae , and the related honeybees survival rate. Moreover, our findings suggest a positive control of Serratia by the environmental microorganism Apilactobacillus kunkeei in a in vivo model, confirming the potential of this specie as beneficial bacteria for honeybees., Competing Interests: Author DS is/was employed by the company Advance Science Forbairt Eolaiochta Teo Limited. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Braglia, Alberoni, Garrido, Porrini, Baffoni, Scott, Eguaras, Di Gioia and Mifsud.)

Gram-negative bacteria (GNB) are a major cause of neonatal sepsis in low- and middle-income countries (LMICs). Although the World Health Organization (WHO) reports that over 80% of these sepsis deaths could be prevented through improved treatment, the efficacy of the currently recommended first- and second-line treatment regimens for this condition is increasingly affected by high rates of drug resistance. Here we assess three well known antibiotics, fosfomycin, flomoxef and amikacin, in combination as potential antibiotic treatment regimens by investigating the drug resistance and genetic profiles of commonly isolated GNB causing neonatal sepsis in LMICs. The five most prevalent bacterial isolates in the NeoOBS study (NCT03721302) are Klebsiella pneumoniae, Acinetobacter baumannii, E. coli, Serratia marcescens and Enterobacter cloacae complex. Among these isolates, high levels of ESBL and carbapenemase encoding genes are detected along with resistance to ampicillin, gentamicin and cefotaxime, the current WHO recommended empiric regimens. The three new combinations show excellent in vitro activity against ESBL-producing K. pneumoniae and E. coli isolates. Our data should further inform and support the clinical evaluation of these three antibiotic combinations for the treatment of neonatal sepsis in areas with high rates of multidrug-resistant Gram-negative bacteria., (© 2024. The Author(s).)

Serratia marcescens is an opportunistic pathogen historically associated with sudden outbreaks in intensive care units (ICUs) and the spread of carbapenem-resistant genes. However, the ecology of S. marcescens populations in the hospital ecosystem remains largely unknown. We combined epidemiological information of 1,432 Serratia spp. isolates collected from sinks of a large ICU that underwent demographic and operational changes (2019-2021) and 99 non-redundant outbreak/non-outbreak isolates from the same hospital (2003-2019) with 165 genomic data. These genomes were grouped into clades (1-4) and subclades (A and B) associated with distinct species: Serratia nematodiphila (1A), S. marcescens (1B), Serratia bockelmannii (2A), Serratia ureilytica (2B), S. marcescens / Serratia nevei (3), and S. nevei (4A and 4B). They may be classified into an S. marcescens complex (SMC) due to the similarity between/within subclades (average nucleotide identity >95%-98%), with clades 3 and 4 predominating in our study and publicly available databases. Chromosomal AmpC β-lactamase with unusual basal-like expression and prodigiosin-lacking species contrasted classical features of Serratia . We found persistent and coexisting clones in sinks of subclades 4A (ST92 and ST490) and 4B (ST424), clonally related to outbreak isolates carrying bla VIM-1 or bla OXA-48 on prevalent IncL/pB77-CPsm plasmids from our hospital since 2017. The distribution of SMC populations in ICU sinks and patients reflects how Serratia species acquire, maintain, and enable plasmid evolution in both "source" (permanent, sinks) and "sink" (transient, patients) hospital patches. The results contribute to understanding how water sinks serve as reservoirs of Enterobacterales clones and plasmids that enable the persistence of carbapenemase genes in healthcare settings, potentially leading to outbreaks and/or hospital-acquired infections.IMPORTANCEThe "hospital environment," including sinks and surfaces, is increasingly recognized as a reservoir for bacterial species, clones, and plasmids of high epidemiological concern. Available studies on Serratia epidemiology have focused mainly on outbreaks of multidrug-resistant species, overlooking local longitudinal analyses necessary for understanding the dynamics of opportunistic pathogens and antibiotic-resistant genes within the hospital setting. This long-term genomic comparative analysis of Serratia isolated from the ICU environment with isolates causing nosocomial infections and/or outbreaks within the same hospital revealed the coexistence and persistence of Serratia populations in water reservoirs. Moreover, predominant sink strains may acquire highly conserved and widely distributed plasmids carrying carbapenemase genes, such as the prevalent IncL-pB77-CPsm (pOXA48), persisting in ICU sinks for years. The work highlights the relevance of ICU environmental reservoirs in the endemicity of certain opportunistic pathogens and resistance mechanisms mainly confined to hospitals., Competing Interests: The authors declare no conflict of interest.

Serratia marcescens is an emerging health-threatening, gram-negative opportunistic pathogen associated with a wide variety of localized and life-threatening systemic infections. One of the most crucial virulence factors produced by S. marcescens is serratiopeptidase, a 50.2-kDa repeats-in-toxin (RTX) family broad-specificity zinc metalloprotease. RTX family proteins are functionally diverse exoproteins of gram-negative bacteria that exhibit calcium-dependent structural dynamicity and are secreted through a common type-1 secretion system (T1SS) machinery. To evaluate the impact of various divalent ligands on the folding and maturation of serratiopeptidase zymogen, the protein was purified and a series of structural and functional investigations were undertaken. The results indicate that calcium binding to the C-terminal RTX domain acts as a folding switch, triggering a disordered-to-ordered transition in the enzyme's conformation. Further, the auto-processing of the 16-amino acid N-terminal pro-peptide results in the maturation of the enzyme. The binding of calcium ions to serratiopeptidase causes a highly cooperative conformational transition in its structure, which is essential for the enzyme's activation and maturation. This conformational change is accompanied by an increase in solubility and enzymatic activity. For efficient secretion and to minimize intracellular toxicity, the enzyme needs to be in an unfolded extended form. The calcium-rich extracellular environment favors the folding and processing of zymogen into mature serratiopeptidase, i.e., the holo-form required by S. marcescens to establish infections and survive in different environmental niches., (© 2024 Federation of European Biochemical Societies.)

MicroRNAs (miRNAs) are noncoding small regulatory RNAs involved in diverse biological processes. Odontotermes formosanus (Shiraki) is a polyphagous pest that causes economic damage to agroforestry. Serratia marcescens is a bacterium with great potential for controlling this insect. However, knowledge about the miRNA pathway and the role of miRNAs in O. formosanus defense against SM1 is limited. In this study, OfAgo1, OfDicer1 and OfDrosha were differentially expressed in different castes and tissues. SM1 infection affected the expression of all three genes in O. formosanus. Then, we used specific double-stranded RNAs to silence OfAgo1, OfDicer1 and OfDrosha. Knockdown of these genes enhanced the virulence of SM1 to O. formosanus, suggesting that miRNAs were critical in the defense of O. formosanus against SM1. Furthermore, we sequenced miRNAs from SM1-infected and uninfected O. formosanus. 33 differentially expressed (DE) miRNAs were identified, whereby 22 were upregulated and 11 were downregulated. Finally, the miRNA-mRNA networks were constructed, which further suggested the important role of miRNAs in the defense of O. formosanus against SM1. Totally, O. formosanus miRNA core genes defend against SM1 infection by regulating miRNA expression. This study elucidates the interactions between O. formosanus and SM1 and provides new theories for biological control., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Objectives: bla KPC -carrying Enterobacterales have post great challenges to global healthcare systems. In this study, we reported the evolution and spread of bla KPC between Serratia marcescens and Klebsiella pneumoniae., Methods: Four S. marcescens and one K. pneumoniae strains were isolated from the sputum samples of the patient. Antimicrobial susceptibility tests and whole genome sequencing were performed to investigate the phenotype & genotype of strains. Conjugation assays, cloning experiment and kinetic parameters measuring were performed to explore the spread and antimicrobial resistance mechanisms., Results: The evolution and transmission of bla KPC-2 occurred during the treatment of ceftazidime-avibactam and trimethoprim-sulfamethoxazole. Analysis of the antimicrobial susceptibility and genetic profiles of the clinical strains showed that bla KPC-2 evolved into bla KPC-71 and bla KPC-44 , together with resistance to ceftazidime-avibactam and carbapenems susceptibility recovery under antimicrobial pressure. Cloning and expression of bla KPC-44 & bla KPC-71 in E. coli DH5α showed that KPC-44 and KPC-71 resulted in a 64∼128-fold increase in the MIC value for ceftazidime-avibactam. Meanwhile, the kinetic assays also showed that the enzyme activity of KPC-44 and KPC-71 towards carbapenems was destroyed and couldn't be inhibited by avibactam. Based on the conjugation assay and whole genome sequence analyses, we provided evolutionary insights into the transmission pathway trace of bla KPC -bearing plasmids between S. marcescens and K. pneumoniae., Conclusions: Mixed-species co-infection is one of the risk factors leading to the spread of plasmids carrying carbapenem-resistant genes, and increased surveillance of multidrug-resistant Enterobacterales is urgently needed., (Copyright © 2024 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.)

Newborns admitted to neonatal intensive care units (NICU) are at increased risk of health care-associated infections. Serratia marcescens represent the third most common pathogen in NICU outbreaks. Here we present an outbreak investigation performed using Whole Genome Sequencing (WGS) analyses and the control measures implemented to limit the spread of S. marcescens in the NICU of an Italian hospital. In February 2023 S. marcescens was isolated from six newborns, when in 2022 this pathogen was isolated only from two samples in the same ward. Measures for infection prevention were adopted. Routinary surveillance screening, performed with rectal swabs collected at admission and weekly thereafter, was implemented to search for S. marcescens presence. Environmental samples were collected. All the isolates, obtained from the conjunctival swab of six newborns, from rectal swab of two newborns who did not develop infections, as well as from the aerators of two faucets, were sequenced. WGS analyses showed no correlation between the isolates from newborns and environmental isolates. The implementation of the measures for infection prevention and control had enabled us to successfully control the outbreak within a short period. WGS analyses proved to be crucial in outbreak investigation to limit the spreading of the pathogens., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background/aim: Given the characteristics of Serratia marcescens (S. marcescens), this study aimed at investigating its presence in the hands and contact lens cases of orthokeratology wearers, along with the status of bacterial contamination., Patients and Methods: The 39 patients received the questionnaires about the background of orthokeratology and hygiene habits. A total of 39 contact lens cases and 39 hand samples from the patients were collected at Show Chwan Memorial Hospital from June to August in 2020 and sent to National Chung Cheng University for DNA extraction and PCR identification., Results: The results indicated a detection rate of 5.13% for S. marcescens in the contact lens cases and 12.82% in the hand samples. Additionally, 66.67% of contact lens case samples and 30.77% of hand samples found positive for 16s bacterial amplicons. The relationship between hand contamination and the duration of contact lens usage were revealed for both S. marcescens (p=0.021) and 16s bacterial amplicons (p=0.048)., Conclusion: The results indicated that hand hygiene is more critical than focusing on contact lens hygiene when it comes to preventing S. marcescens infections. Nevertheless, both proper hand and contact lens hygiene practices can reduce the detection of bacterial eye pathogens, especially a common intestinal bacterium., (Copyright © 2024, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Behavioral avoidance of parasites is a widespread strategy among animal hosts and in human public health. Avoidance has repercussions for both individual and population-level infection risk. Although most cases of parasite avoidance are viewed as adaptive, there is little evidence that the basic assumptions of evolution by natural selection are met. This study addresses this gap by testing whether there is a heritable variation in parasite avoidance behavior. We quantified behavioral avoidance of the bacterial parasite Serratia marcescens for 12 strains of the nematode host Caenorhabditis elegans. We found that these strains varied in their magnitude of avoidance, and we estimated the broad-sense heritability of this behavior to be in the range of 11%-26%. We then asked whether avoidance carries a constitutive fitness cost. We did not find evidence of one. Rather, strains with higher avoidance had higher fitness, measured as population growth rate. Together, these results direct future theoretical and empirical work to identify the forces maintaining genetic variation in parasite avoidance., (© The Author(s) 2024. Published by Oxford University Press on behalf of The Society for the Study of Evolution (SSE). All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Bacterial species often comprise well-separated lineages, likely emerged and maintained by genetic isolation and/or ecological divergence. How these two evolutionary actors interact in the shaping of bacterial population structure is currently not fully understood. In this study, we investigate the genetic and ecological drivers underlying the evolution of Serratia marcescens, an opportunistic pathogen with high genomic flexibility and able to colonise diverse environments. Comparative genomic analyses reveal a population structure composed of five deeply-demarcated genetic clusters with open pan-genome but limited inter-cluster gene flow, partially explained by Restriction-Modification (R-M) systems incompatibility. Furthermore, a large-scale research on hundred-thousands metagenomic datasets reveals only a partial habitat separation of the clusters. Globally, two clusters only show a separate gene composition coherent with ecological adaptations. These results suggest that genetic isolation has preceded ecological adaptations in the shaping of the species diversity, an evolutionary scenario coherent with the Evolutionary Extended Synthesis., (© 2024. The Author(s).)

Reticulitermes chinensis Snyder is an important pest in forestry and construction and is widely distributed in China. We found that Serratia marcescens Bizio strain SM1 has insecticidal activity to R. chinensis , but the pathogenic mechanism of SM1 to R. chinensis is not clear. Therefore, full-length transcriptome sequencing was performed on R. chinensis infected with SM1 and the control group. A total of 230 differentially expressed genes were identified by comparing SM1 infection group and the control group, among which 103 were downregulated and 127 were upregulated. We found downregulated genes in nine metabolic pathway categories, among which carbohydrate metabolism had the most downregulated genes, followed by energy metabolism and amino acid metabolism. We also found that some downregulated genes were related to pattern recognition receptors, cellular immunity, and humoral immunity, indicating that R. chinensis immunity was negatively affected by SM1 infection. In addition, some genes in signal transduction and genetic information processing pathways were downregulated. In this study, high-throughput full-length transcriptome analysis was used to analyse the pathogenic mechanism of SM1 to R. chinensi s. The results of this study provide useful information for exploring the relationship between SM1 and R. chinensis , and provide theoretical support for the future application of SM1 and the prevention and treatment of R. chinensis .

Serratia marcescens is an environmental gram-negative bacterium that causes invasive disease in rare cases. During 2020-2022, an outbreak of 21 invasive Serratia infections occurred in a prison in California, USA. Most (95%) patients had a history of recent injection drug use (IDU). We performed whole-genome sequencing and found isolates from 8 patients and 2 pieces of IDU equipment were closely related. We also identified social interactions among patients. We recovered S. marcescens from multiple environmental samples throughout the prison, including personal containers storing Cell Block 64 (CB64), a quaternary ammonium disinfectant solution. CB64 preparation and storage conditions were suboptimal for S. marcescens disinfection. The outbreak was likely caused by contaminated CB64 and propagated by shared IDU equipment and social connections. Ensuring appropriate preparation, storage, and availability of disinfectants and enacting interventions to counteract disease spread through IDU can reduce risks for invasive Serratia infections in California prisons.

Microbial biotransformation is a recommended and reliable method in face of formidable tetracycline (TC) with broad-spectrum antibacterial activity. Herein, comprehensive characteristics of a newfound strain and its molecular mechanism in process of TC bioremediation were involved in this study. Specifically, Serratia marcescens MSM2304 isolated from pig manure sludge grew well in presence of TC and achieved optimal removal efficiency of 61% under conditions of initial TC concentration of 10 mg/L, pH of 7.0, cell inoculation amount of 5%, and tryptone of 10 g/L as additional carbon. The pathways of biotransformation include EPS biosorption, cell surface biosorption and biodegradation, which enzymatic processes of biodegradation were occurred through TC adsorbed by biofilms was firstly broken down by extracellular enzymes and part of TC migrated towards biofilm interior and degraded by intracellular enzymes. Wherein extracellular polysaccharides in extracellular polymeric substances (EPS) from biofilm of strain MSM2304 mainly performed extracellular adsorption, and changes in position and intensity of CO, =CH and C-O-C/C-O of EPS possible further implied TC adsorption by it. Biodegradation accounting for 79.07% played a key role in TC biotransformation and could be fitted well by first-order model that manifesting rapid and thorough removal. Potential biodegradation pathway including demethylation, dihydroxylation, oxygenation, and ring opening possibly involved in TC disposal process of MSM2304, TC-degrading metabolites exhibited lower toxicity to indicator bacteria relative to parent TC. Whole genome sequencing as underlying molecular evidence revealed that TC resistance genes, dehydrogenases-encoding genes, monooxygenase-encoding genes, and methyltransferase-encoding genes of strain MSM2304 were positively related to TC biodegradation. Collectively, these results favored a theoretical evaluation for Serratia marcescens MSM2304 as a promising TC-control agent in environmental bioremediation processes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Spodoptera frugiperda , the fall armyworm (FAW), is a highly invasive polyphagous insect pest that is considered a source of severe economic losses to agricultural production. Currently, the majority of chemical insecticides pose tremendous threats to humans and animals besides insect resistance. Thus, there is an urgent need to develop new pest management strategies with more specificity, efficiency, and sustainability. Chitin-degrading enzymes, including chitinases, are promising agents which may contribute to FAW control. Chitinase-producing microorganisms are reported normally in bacteria and fungi. In the present study, Serratia marcescens was successfully isolated and identified from the larvae of Spodoptera frugiperda . The bacterial strain NRC408 displayed the highest chitinase enzyme activity of 250 units per milligram of protein. Subsequently, the chitinase gene was cloned and heterologously expressed in E. coli BL21 (DE3). Recombinant chitinase B was overproduced to 2.5-fold, driven by the T7 expression system. Recombinant chitinase B was evaluated for its efficacy as an insecticidal bioagent against S. frugiperda larvae, which induced significant alteration in subsequent developmental stages and conspicuous malformations. Additionally, our study highlights that in silico analyses of the anticipated protein encoded by the chitinase gene (ChiB) offered improved predictions for enzyme binding and catalytic activity. The effectiveness of (ChiB) against S. frugiperda was evaluated in laboratory and controlled field conditions. The results indicated significant mortality, disturbed development, different induced malformations, and a reduction in larval populations. Thus, the current study consequently recommends chitinase B for the first time to control FAW.

Serratia marcescens has garnered increasing attention as a promising host for valuable compound production. However, the lack of an efficient gene regulation toolkit severely hampers its applications. Here, a library of stationary phase promoters was screened in S. marcescens HBA7 using RNA-seq and RT-qPCR, revealing a 43-fold regulatory range with the red fluorescent protein mKate2 as the reporter. The β-galactosidase was employed to demonstrate the universality in driving the expression of different proteins. The wide-ranging utility of these promoters in different hosts was demonstrated in Escherichia coli . Moreover, to assess their potential application, the strongest promoter, P2, was employed to express the swrW gene, resulting in a roughly 20-fold increase in serrawettin W1 production in S. marcescens HBQA7Δ swrW . In summary, this study successfully constructed a gradient-strength stationary phase promoter library, providing an effective toolkit for gene regulation and secondary metabolite production in diverse prokaryotes, including S. marcescens and E . coli .

Antibiotic-resistant Serratia marcescens (Sm) is known to cause bloodstream infections, pneumonia, etc. The nod-like receptor family, pyrin domain-containing 3 (NLRP3), has been implicated in various lung infections. Yet, its role in Sm-induced pneumonia was not well understood. In our study, we discovered that deletion of Nlrp3 in mice significantly improved Sm-induced survival rates, reduced bacterial loads in the lungs, bronchoalveolar lavage fluid (BALF), and bloodstream, and mitigated the severity of acute lung injury (ALI) compared to wild-type (WT) mice. Mechanistically, we observed that 24 h post-Sm infection, NLRP3 inflammasome activation occurred, leading to gasdermin D NH2-terminal (GSDMD-NT)-induced pyroptosis in macrophages and IL-1β secretion. The NLRP3 or NLRP3 inflammasome influenced the expression PD-L1 and PD-1, as well as the count of PD-L1 or PD-1-expressing macrophages, alveolar macrophages, interstitial macrophages, PD-L1-expressing neutrophils, and the count of macrophage receptors with collagenous structure (MARCO)-expressing macrophages, particularly MARCO + alveolar macrophages. The frequency of MARCO + alveolar macrophages, PD-1 expression, particularly PD-1 + interstitial macrophages were negatively or positively correlated with the Sm load, respectively. Additionally, IL-1β levels in BALF correlated with three features of acute lung injury: histologic score, protein concentration and neutrophil count in BALF. Consequently, our findings suggest that Nlrp3 deletion offers protection agaisnt acute Sm pneumonia in mice by inhibiting inflammasome activation and reducing Sm infection-induced PD-L1/PD-1 or MARCO expression, particularly in macrophages. This highlights potential therapeutic targets for Sm and other gram-negative bacteria-induced acute pneumonia., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Serratia marcescens is a global opportunistic pathogen. In vitro cytotoxicity of this bacterium is mainly related to metalloprotease serralysin (PrtS) activity. Proteolytic capability varies among the different isolates. Here, we characterized protease production and transcriptional regulators at 37°C of two S. marcescens isolates from bronchial expectorations, HU1848 and SmUNAM836. As a reference strain the insect pathogen S. marcescens Db10 was included. Zymography of supernatant cultures revealed a single (SmUNAM836) or double proteolytic zones (HU1848 and Db10). Mass spectrometry confirmed the identity of PrtS and the serralysin-like protease SlpB from supernatant samples. Elevated proteolytic activity and prtS expression were evidenced in the HU1848 strain through azocasein degradation and qRT-PCR, respectively. Evaluation of transcriptional regulators revealed higher eepR expression in HU1848, whereas cpxR and hexS transcriptional levels were similar between studied strains. Higher eepR expression in HU1848 was further confirmed through an in vivo transcriptional assay. Moreover, two putative CpxR binding motifs were identified within the eepR regulatory region. EMSA validated the interaction of CpxR with both motifs. The evaluation of eepR transcription in a cpxR deletion strain indicated that CpxR negatively regulates eepR . Sequence conservation suggests that regulation of eepR by CpxR is common along S. marcescens species. Overall, our data incorporates CpxR to the complex regulatory mechanisms governing eepR expression and associates the increased proteolytic activity of the HU1848 strain with higher eepR transcription. Based on the global impact of EepR in secondary metabolites production, our work contributes to understanding virulence factors variances across S. marcescens isolates., (© 2024 Karla L. De Anda-Mora et al., published by Sciendo.)

Background: Serratia marcescens is a gram-negative bacterium that is widespread in the environment. S. marcescens bacteremia can be fatal during pregnancy and cause persistent chorioamnionitis. This study reports an outbreak of Serratia marcescens bloodstream infection (BSI) among high-risk pregnant women in an obstetric ward. The purpose of this study is to report our experience with the usefulness of the ATP test in hospital environmental management and to confirm that bloodstream infections of patients with the same strain were correlated by WGS testing., Methods: This retrospective study collected the data of inpatients with S. marcescens bacteremia in obstetric ward for high-risk pregnant women from August 22, 2021, to October 14, 2021. We performed: an adenosine triphosphate (ATP) bioluminescence test in the environment with a high-contact area; environmental culture; on-site monitoring and staff education; and whole-genome sequencing (WGS) to evaluate genetic relationships among S. marcescens isolates., Results: S. marcescens BSI occurred in four consecutive patients. None of the patients had central venous catheters. An ATP bioluminescence test revealed that high-contact areas and areas for injection preparation were not clean (≥ 1000 relative light units). However, S. marcescens was not identified in the environmental cultures, likely due to intensive environmental cleaning and discarding of potentially contaminated specimens before the culture test. On-site monitoring and education were conducted for 1 month. There were no further reports of BSI until 6 months after the last patient was discharged. WGS performed on three isolates from three patients indicated that the isolated S. marcescens was likely from the same strain., Conclusions: We controlled an S. marcescens outbreak by improving environmental cleaning as well as education of and behavior changes in healthcare workers. Using the ATP bioluminescence test can provide feedback on environmental cleaning and education. WGS played a role in determining the spread of BSI caused by the same strain., (© 2024. The Author(s).)

Background: The increasing cases of bloodstream infections among children at neonatal intensive care units (NICUs) led this work to investigate biofilm production, antibiotics and the presence of ESβL genes in Serratia marcescens (S. marcescens) strains isolated from blood., Methods: Twenty S. marcescens strains were isolated and identified by the VITEK-2 system over 7 months from late 2022 to mid-2023 from Ibn Al-Balady Hospital in Baghdad. Kirby-Bauer test was used to measure antibiotic susceptibility., Results: The results revealed that 95% of twenty S. marcescens isolates were non-susceptible to Ampicillin and Amoxicillin-clavulanic. Furthermore, S. marcescens isolates showed a high sensitivity rate 70% toward Imipenem. All S. marcescens strains 100% were produced biofilm. This work clarifies that, out of 20 S. marcescens strains, 80% were harbored ESβL genes. The coexistence of blaTEM, blaCTX and blaSHV genes was shown in 43.75% of strains, while 56.25% of S. marcescens strains harbored single ES[Formula: see text]L genes. The biofilm values increase with the accuracy of EsβL genes. Phylogenetic analyses based on the sequence of blaCTX-M and blaTEM were done with closely related genes in the GenBank using MEGA6 software., Conclusions: The distribution of blaTEM, blaCTX and blaSHV genes among local S. marcescens strains may be attributed to the indiscriminate use of antibiotics. The results confirmed the spread of ESβL genes in S. marcescens from blood infections among newborn infants., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Pyrroloquinoline quinone (PQQ) is a redox cofactor with numerous important physiological functions, and the type VI secretion system (T6SS) is commonly found in Gram-negative bacteria and plays important roles in physiological metabolism of the bacteria. In this study, we found that the deletion of pqqF enhanced the secretion of Hcp-1 in Serratia marcesens FS14 in M9 medium. Transcriptional analysis showed that the deletion of pqqF almost had no effect on the expression of T6SS-1. Further study revealed that the increased secretion of Hcp-1 was altered by the pH changes of the culture medium through the reaction catalyzed by the glucose dehydrogenases in FS14. Finally, we demonstrated that decreased pH of culture medium has similar inhibition effects as PQQ induced on the secretion of T6SS-1. This regulation mode on T6SS by pH in FS14 is different from previously reported in other bacteria. Therefore, our results suggest a novel pH regulation mode of T6SS in S. marcesens FS14, and would broaden our knowledge on the regulation of T6SS secretion., (© The Author(s) 2024. Published by Oxford University Press on behalf of FEMS.)

Background: Psychrophilic bacteria can survive in a unique living environment., Objective: To explore the mechanism of low temperature adaptation and the physiological function of thermophilic metabolic genes., Method: Serratia marcescens strain F13 stored in microbial laboratory was cultured at 5∘C, 10∘C and 25∘C respectively, and the obtained strains were sequenced by high-throughput transcriptome. Serratia marcescens strain CAV1761 was used as the reference strain. The data produced by transcriptome sequencing were statistically analyzed by biostatistics software such as soapnuke, soap and edger. The differentially expressed genes were found based on the gene expression, and analyzed by Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis., Results: The results showed that there were 718 differential genes in F13-10 vs F13-5 comparison group, 1614 differential genes in F13-25 vs F13-5 comparison group and 1636 differential genes in F13-25 vs F13-10 comparison group. GO function enrichment analysis showed that the GO term mainly enriched by different genes in the three comparison groups was mostly related to the migration and transport of cellular or subcellular components, cell localization and transmembrane transporter activity, as well as cilia or flagella dependent cell movement. In the enrichment analysis of KEGG pathway, the three comparison groups all enriched the largest number of differential genes in the branch pathway of KEGG metabolism, followed by the branch pathway of environmental information processing., Conclusion: In F13-10 vs F13-5, the differential genes were mainly concentrated in 20 pathways such as ATP-binding cassette transport (ABC) transporters, thiamine metabolism and flagella assembly; In F13-25 vs F13-5, the differential genes are mainly concentrated in 20 pathways, such as (ABC) transporters, arginine and proline metabolism, two-component system and so on; In F13-25 vs F13-10, the differential genes are mainly concentrated in 20 pathways such as various types of glycan synthesis, two-component system and arginine metabolism.

Phospholipase A1 (PlaA) plays a pivotal role in diverse applications within the food and biochemical medical industries. Herein, we investigate the impact of the accessory protein encoded by plaS from Serratia marcescens on PlaA activity in Escherichia coli. Notably, PlaS demonstrates the ability to enhance PlaA activity while concurrently exhibiting inhibitory effects on the growth of E. coli BL21 (DE3). Our study revolves around probing the inhibitory action of PlaS on E. coli BL21 (DE3). PlaS exhibits a propensity to heighten both the permeability of outer and inner cell membranes, leading to concomitant reductions in membrane fluidity and surface hydrophobicity. This phenomenon is validated through scanning electron microscopy (SEM) analysis, which highlights PlaS's capacity to compromise membrane integrity. Moreover, through a comprehensive comparative transcriptomic sequencing approach, we identify four down-regulated genes (galM, ybhC, ldtC, and kdpB) alongside two up-regulated genes (rbsB and degP). These genes are intricately associated with processes such as cell membrane synthesis and modification, energy metabolism, and transmembrane transport. Our investigation unveils the intricate gene-level mechanisms underpinning PlaS-mediated growth inhibition and membrane disruption. Consequently, our findings serve as a significant reference for the elucidation of membrane protein mechanisms, shedding light on potential avenues for future exploration., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Objectives: To evaluate the clinical and epidemiological impact of a new molecular surveillance strategy based on qPCR to control an outbreak by Serratia marcescens in a Neonatal Intensive Care Unit (NICU)., Methods: We design a specific qPCR for the detection of S. marcescens in rectal swabs of patients admitted to a NICU. We divided the surveillance study into two periods: (a) the pre-PCR, from the outbreak declaration to the qPCR introduction, and (b) the PCR period, from the introduction of the qPCR until the outbreak was solved. In all cases, S. marcescens isolates were recovered and their clonal relationship was analysed by PFGE. Control measures were implemented during the outbreak. Finally, the number of bloodstream infections (BSI) was investigated in order to evaluate the clinical impact of this molecular strategy., Results: Nineteen patients colonized/infected by S. marcescens were detected in the pre-PCR period (October 2020-April 2021). On the contrary, after the PCR implementation, 16 new patients were detected. The PFGE revealed 24 different pulsotypes belonging to 7 different clonal groups, that were not overlapping at the same time. Regarding the clinical impact, 18 months after the qPCR implementation, no more outbreaks by S. marcescens have been declared in the NICU of our hospital, and only 1 episode of BSI has occurred, compared with 11 BSI episodes declared previously to the outbreak control., Conclusions: The implementation of this qPCR strategy has proved to be a useful tool to control the nosocomial spread of S. marcescens in the NICU., (© 2023. The Author(s).)

Background: Nine surgical site infections caused by Serratia marcescens were diagnosed in neurosurgical patients in a 3500-bed hospital between 2 nd February and 6 th April 2022., Objective: To trace the source of infections caused by S. marcescens to expedite termination of the outbreak and prevent future epidemics., Methods: A review of all surgical procedures and cultures yielding S. marcescens since February 2022 was conducted. Samples were collected from patients and environmental sources. S. marcescens isolates were characterized by antibiotic susceptibility testing. Whole-genome sequencing (WGS) was used to investigate genetic relationships. Resistance genes, virulence genes and plasmid replicons were identified., Results: S. marcescens was isolated from patients' puncture fluid, cerebrospinal fluid and other secretions, and was also cultured from the barbers' haircutting tools, including leather knives, slicker scrapers and razors. In total, 15 isolates were obtained from patients and eight isolates were obtained from haircutting tools. All isolates exhibited identical antibiotic resistance patterns. WGS revealed close clustering among the 23 isolates which differed significantly from previous strains. Three resistance genes and nine virulence-associated genes were detected in all isolates, and 19 of 23 isolates harboured an MOBP-type plasmid. The results confirmed an outbreak of S. marcescens, which was traced to contaminated haircutting tools in the hospital barber shop. The outbreak ended after extensive reinforcement of infection control procedures and re-education of the barbers., Conclusions: These results highlight the risk of postoperative infections related to pre-operative skin preparation, and demonstrate the value of next-generation sequencing tools to expedite outbreak investigations., (Copyright © 2023 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.)

The raising concern of drug resistance, having substantial impacts on public health, has instigated the search of new natural compounds with substantial medicinal activity. In order to find out a natural solution, the current study has utilized prodigiosin, a linear tripyrrole red pigment, as an active ingredient to control bacterial proliferation and prevent cellular oxidation caused by ROS (Reactive Oxygen Species). A prodigiosin-producing bacterium BRL41 was isolated from the ancient Barhind soil of BCSIR Rajshahi Laboratories, Bangladesh, and its morphological and biochemical characteristics were investigated. Whole genome sequencing data of the isolate revealed its identity as Serratia sp. and conferred the presence of prodigiosin gene cluster in the bacterial genome. "Prodigiosin NRPS", among the 10 analyzed gene clusters, showed 100% similarity with query sequences where pigC, pigH, pigI, and pigJ were identified as fundamental genes for prodigiosin biosynthesis. Some other prominent clusters for synthesis of ririwpeptides, yersinopine, trichrysobactin were also found in the chromosome of BRL41, whilst the rest displayed less similarity with query sequences. Except some first-generation beta-lactam resistance genes, no virulence and resistance genes were found in the genome of BRL41. Structural illumination of the extracted red pigment by spectrophotometric scanning, Thin-Layer Chromatography (TLC), Fourier Transform Infrared Spectroscopy (FTIR), and change of color at different pH solutions verified the identity of the isolated compound as prodigiosin. Serratia sp. BRL41 attained its maximum productivity 564.74 units/cell at temperature 30˚C and pH 7.5 in two-fold diluted nutrient broth medium. The compound exhibited promising antibacterial activity against Gram-positive and Gram-negative bacteria with MIC (Minimum Inhibitory Concentration) and MBC (Minimum Bactericidal Concentration) values ranged from 3.9 to15.62 μg/mL and 7.81 to 31.25 μg/mL respectively. At concentration 500 μg/mL, except in Salmonella enterica ATCC-10708, prodigiosin significantly diminished biofilm formed by Listeria monocytogens ATCC-3193, Pseudomonas aeruginosa ATCC-9027, Escherichia coli (environmental isolate), Staphylococcus aureus (environmental isolate). Cellular glutathione level (GSH) was elevated upon application of 250 and 500 μg/mL pigment where 125 μg/mL failed to show any free radical scavenging activity. Additionally, release of cellular components in growth media of both Gram-positive and Gram-negative bacteria were facilitated by the extract that might be associated with cell membrane destabilization. Therefore, the overall findings of antimicrobial, antibiofilm and antioxidant activities suggest that in time to come prodigiosin might be a potential natural source to treat various diseases and infections., Competing Interests: All authors have declared that they have no competing interests., (Copyright: © 2023 Boby et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Analysis of virulence genes (PhlA, ShlA, FlhD) sequencing of Serratia marcescens including collection of two hundred twenty samples from sputum & wound infection of the period from April-June in 2021 of the patients in some hospitals in Baghdad - Iraq. These specimens were collected from central hospitals in Iraq. After laboratory diagnosis of these specimens by detecting morphological and biochemical tests on bacteria that were cultured on selective and enriched media, VITEK- 2 compact system. There are 40 bacterial isolates of Serratia marcescens from total samples (220) in percentage (18.18%). The genome of these bacteria was extracted to investigate target virulence genes that were amplified by specific forward and specific primers. The product size of virulence genes was Ph1A (207 bp), Sh1A (217 bp), and FlhD virulence gene (307 bp). The results exhibited that these isolates contained these genes at different levels. Sequencing of these genes was carried out and analyzed through BLAST in NCBI and Geneious version -9. The results explained the top identity of sequencing these virulence genes (PhlA, ShlA, FlhD) between local Iraqi bacteria. In addition, there are misidentify or dissimilarities in different levels between Iraqi S. marcescens and global strain recorded in NCBI. These results consider scientific evidence to find new variations of these virulence genes in Iraqi S. marcescens in comparison with the global strain. These new Iraqi bacterial variation sequencing registered in the global database in NCBI under accession numbers including (Ph1A virulence gene LC647828.1 & LC647829.1), (Sh1A virulence gene LC647830.1 & LC647831.1) & (F1hD virulence gene LC647826.1, LC647827.1). The results of analysis sequencing exhibited different percentages in genetic identity distance, which refer to these bacteria new variation in Pathogenicity Island. These results explained the ability of these bacteria to produce different levels of virulence factors that lead to an increase in pathogenicity and spreading of infection.

Aim of the Study: The rising instances of multidrug-resistant pathogens are rapidly evolving into a global healthcare crisis. Identifying new ways of synthesis of antibiotics is both time-consuming and expensive. Repurposing existing drugs for the treatment of such antimicrobial-resistant pathogens has also been explored., Methods and Results: In the current study, ebselen was screened for antibacterial and antibiofilm activity against Serratia marcescens. Various antibacterial studies such as minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time-kill curves, intracellular reactive oxygen species (ROS) quantification, and colony-forming unit assays were performed. The antibiofilm potential was assayed by biofilm inhibition, cell surface hydrophobicity assay, eradication, quantification of extracellular DNA (eDNA), and extracellular polymeric substance (EPS) layer and scanning electron microscopy (SEM) analysis were performed. Anti-quorum sensing assay was validated by quantifying the virulence factors production. Further molecular docking of ebselen with two quorum sensing (QS) specific proteins was also carried out. Antibacterial susceptibility tests showed potent antimicrobial activity of ebselen against S. marcescens with MIC 50 of 14 μg/mL. Ebselen's ability to disturb the redox environment by inducing significant ROS generation led to bacterial death. It also showed concentration-dependent bactericidal activity as indicated by reduced bacterial growth and colony-forming unit propagation. Ebselen was also found to prevent biofilm attachment by altering the cell surface hydrophobicity while also being effective against preformed biofilms as validated by scanning electron microscopy (SEM) analysis. Additionally, ebselen showed reduced virulence factors like urease enzyme activity and prodigiosin pigment production indicating its promising anti-quorum sensing potential. Molecular docking analysis validated the strong binding of ebselen with QS-specific proteins (1Joe and PigG) with binding energies of - 6.6 and - 8.1kj/mol through hydrogen bonds and aromatic interactions. These results show that ebselen has potent antibiofilm potential that can be explored to identify treatment against bacterial infections., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Plasmids play important roles in bacterial genome diversification. In the Serratia marcescens complex (SMC), a notable contribution of plasmids to genome diversification was also suggested by our recent analysis of >600 draft genomes. As accurate analyses of plasmids in draft genomes are difficult, in this study we analysed 142 closed genomes covering the entire complex, 67 of which were obtained in this study, and identified 132 plasmids (1.9-244.4 kb in length) in 77 strains. While the average numbers of plasmids in clinical and non-clinical strains showed no significant difference, strains belonging to clade 2 (one of the two hospital-adapted lineages) contained more plasmids than the others. Pangenome analysis revealed that of the 28 954 genes identified, 12.8 % were plasmid-specific, and 1.4 % were present in plasmids or chromosomes depending on the strain. In the latter group, while transposon-related genes were most prevalent (31.4 % of the function-predicted genes), genes related to antimicrobial resistance and heavy metal resistance accounted for a notable proportion (22.7 %). Mash distance-based clustering separated the 132 plasmids into 23 clusters and 50 singletons. Most clusters/singletons showed notably different GC contents compared to those of host chromosomes, suggesting their recent or relatively recent appearance in the SMC. Among the 23 clusters, 17 were found in only clinical or only non-clinical strains, suggesting the possible preference of their distribution on the environmental niches of host strains. Regarding the host strain phylogeny, 16 clusters were distributed in two or more clades, suggesting their interclade transmission. Moreover, for many plasmids, highly homologous plasmids were found in other species, indicating the broadness of their potential host ranges, beyond the genus, family, order, class or even phylum level. Importantly, highly homologous plasmids were most frequently found in Klebsiella pneumoniae and other species in the family Enterobacteriaceae , suggesting that this family, particularly K. pneumoniae , is the main source for plasmid exchanges with the SMC. These results highlight the power of closed genome-based analysis in the investigation of plasmids and provide important insights into the nature of plasmids distributed in the SMC.

Metallo-β-lactamases (MβLs) are the primary mechanism of resistance to carbapenem antibiotics. To elucidate how MβLs have evolved with the introduction and use of antibiotics, the mutation and evolution of SMB-1 from Serratia marcescens were investigated in microbial evolution plates containing discontinuous meropenem (MEM) concentration gradients. The results revealed 2-point mutations, A242G and S257R; 1 double-site mutation, C240G/E258G; and 3 frameshift mutations, M5, M12, and M13, which are all missense mutations situated at the C-terminus. Compared with that of the wild-type (WT), the minimum inhibitory concentrations (MICs) of MEM for A242G, C240G/E258G, M5, M12, and M13 increased at least 120-fold, and that of S257R increased 8-fold. The catalytic efficiency k cat /K m increased by 365% and 647%, respectively. Concerning the structural changes, the structure at the active site changed from an ordered structure to an unordered conformation. Simultaneously, the flexibility of loop 1 was enhanced. These changes increased the volume of the active site cavity; thus, this was more conducive to exposing the Zn 2+ site, facilitating substrate binding and conversion to products. In A242G, structural changes in Gly-242 can be transmitted to the active region via a network of interactions between the side chains of Gly-242 and the amino acid side chains near the active pocket. Together, these results pointed to the process of persistent drug tolerance and resistance, the SMB-1 enzyme evolved into a more exquisite structure with increased flexibility and stability, and stronger hydrolysis activity via genetic mutations and structural changes., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Prodigiosin (2-methyl-3-pentyl-6-methoxyprodiginine) is a valuable medicinal and edible natural pigment derived from Serratia marcescens . How prodigiosin synthesis is suppressed by environmental factors has not been investigated. Previous studies described a low level of prodigiosin production in the presence of yeast extracts. However, we have observed that S. marcescens SDSPY-136 did not synthesize prodigiosin in yeast extract culture. In this study, transcriptome sequencing of yeast extract cultures was used to estimate the metabolic control of the synthetic prodigiosin pathway in S. marcescens . Key phosphorylation enzymes in the glycolysis pathway, 6-phosphofructokinase, and glyceraldehyde 3-phosphate dehydrogenase, were downregulated by yeast extract and other carbon metabolism pathway genes were enhanced. Genes related to ribosomes, amino acid metabolism, and aminoacyl-tRNA biosynthesis were also highly up-regulated. The presence of metal ions in yeast extracts and the accumulation of fermentation metabolites alter the two-component signaling system, which regulated metabolism to various degrees. The results of metal ion testing suggested that prodigiosin inhibition could be caused by metal ions, such as zinc ion. The findings indicate that yeast extract may affect metabolism through multiple pathways in S. marcescens . This research sheds light on the mechanism of prodigiosin regulatory inhibition.

Microorganisms have recently gained recognition as efficient biological tool for reducing heavy metal toxicity in crops. In this experiment, we isolated a potent heavy metal (As, Ni, and Cr) resistant rhizobacterium Serratia marcescens DB1 and detected its plant growth promoting traits such as phosphate solubilization, gibberellin synthesis, organic acid production and amino acid regulation. Based on these findings, DB1 was further investigated for application in a rice var. Hwayeongbyeo subjected to 1 mM As, 4 mM Ni, and 4 mM Cr stress. The rice plants treated with Cr and Ni appeared healthy but were lethal, indicating unfitness for consumption due to toxic metal deposition, whereas the plants treated with > 1 mM As instantaneously died. Our results showed that DB1 inoculation significantly decreased metal accumulation in the rice shoots. Particularly, Cr uptake dropped by 16.55% and 22.12% in (Cr + DB1) and (Cr + As + Ni + DB1), respectively, As dropped by 48.90% and 35.82% in (As + DB1) and (Cr + As + Ni + DB1), respectively, and Ni dropped by 7.95% and 19.56% in (Ni + DB1) and (Cr + As + Ni + DB1), respectively. These findings were further validated by gene expression analysis results, which showed that DB1 inoculation significantly decreased the expression of OsPCS1 (a phytochelatin synthase gene), OsMTP1 (a metal transporting gene), and OsMTP5 (a gene for the expulsion of excess metal). Moreover, DB1 inoculation considerably enhanced the morphological growth of rice through modulation of endogenous phytohormones (abscisic acid, salicylic acid, and jasmonic acid) and uptake of essential elements such as K and P. These findings indicate that DB1 is an effective biofertilizer that can mitigate heavy metal toxicity in rice crops., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)