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Hafnia sp. was one of the specific spoilage bacteria in aquatic products, and the aim of the study was to investigate the inhibition ability of the silver nanoparticles (AgNPs) biosynthesis by an aqueous extract of Prunus persica leaves toward the spoilage-related virulence factors of Hafnia sp. The synthesized P-AgNPs were spherical, with a mean particle size of 36.3 nm and zeta potential of 21.8 ± 1.33 mV. In addition, the inhibition effects of P-AgNPs on the growth of two Hafnia sp. strains and their quorum sensing regulated virulence factors, such as the formation of biofilm, secretion of N-acetyl-homoserine lactone (AHLs), proteases, and exopolysaccharides, as well as their swarming and swimming motilities were evaluated. P-AgNPs had a minimum inhibitory concentration (MIC) of 64 μg ml-1 against the two Hafnia sp. strains. When the concentration of P-AgNPs was below MIC, it could inhibit the formation of biofilms by Hafnia sp at 8-32 μg ml-1, but it promoted the formation of biofilms by Hafnia sp at 0.5-4 μg ml-1. P-AgNPs exhibited diverse inhibiting effects on AHLs and protease production, swimming, and swarming motilities at various concentrations., (© The Author(s) 2024. Published by Oxford University Press on behalf of Applied Microbiology International.)

Quorum sensing (QS) is a communication pattern between bacteria, hence the inhibition of bacterial QS system could be used as a new strategy to the control the spoilage caused by bacteria, and to some extent could avoid the bacteria drug resistance. In the study, dandelion water extract mediated biosynthesis Ag nanoparticles (D-AgNPs) was prepared with AgN03 as silver source and dandelion water extract as reducing agent. Its structure was characterized by ultraviolet visible absorption spectroscopy (UV-vis), dynamic light scattering (DLS), Zeta potential, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray energy spectrum (EDS). It was found that the synthesized D-AgNPs were spherical, with an average particle size of 13.9 nm and Zeta potential of (-14.07±0.25) mV. The effects of D-AgNPs on the growth of two Hafnia strains and quorum sensing regulated virulence factors such as biofilm, AHLs, proteases, exopolysaccharides, swimming and swarming motilities were determined. It was found that the minimum inhibitory concentration of D-AgNPs against Hafnia was 128 |g/mL, and could inhibit the formation of the biofilms of Hafnia at 1/16-1/2 MIC (8-64 |g/mL), whereas promoted its biofilm formation at 1/128-1/32 MIC (1-4 µg/mL). D-AgNPs showed different inhibition abilities on the AHLs and protease production, as well as swimming and swarming motilities; however, sub-MIC D-AgNPs promoted the production of exopolysaccharides. It is proved that D-AgNPs could be used as quorum sensing inhibitor. [ABSTRACT FROM AUTHOR]

Lactic acid bacteria (LAB) and yeasts are the dominant microorganisms in the fermentation process of pickled vegetables, and their relationship and fermentation characteristics are important factors affecting the quality of products. In the study, high-yield AI-2 LAB and aroma-producing yeasts were screened from commercial pickled vegetable using Vibrio harveyi BB170 report method and total ester titration method. The mixed fermentation conditions of LAB and yeast were further optimized by orthogonal test. The differences in AI-2 production, acid production rate, acid resistance, salt tolerance, and nitrite degradation between the mixed strains and LAB alone fermentation were compared. Effect of yeasts on the fermentation characteristics of LAB with high production AI-2 was explored. These results showed that Lactobacillus plantarum SR with high yield of AI-2 and Pichia membranaceus S-0-1 with ester content of 0.6 g/L were obtained. The mixed fermentation conditions were as follows: inoculation amount 2%, inoculation ratio 1 : 1 (SR: S-0-1), culture temperature 28 °C. Under optimized fermentation conditions, compared with L. plantarum SR alone fermentation, the AI-2 synthesis ability, acid tolerance rate (pH = 3) and the salt tolerance rate at 5% of the mixed strains was increased by 1.4 times, 4.8 times and 24.66%, respectively. Meanwhile, the acid production rate of the mixed strains was increased. but there was no significant change in the degradation rate of nitrite of the mixed strains, which basically maintained at 98%. The above results indicated that Pichia membranaceus S-0-1 could increase the yield of AI-2 signal molecules in L. plantarum SR, result in enhancing the fermentation characteristics of the LAB and yeasts. This study aimed to provide a theoretical basis for further exploring the mutual regulation mechanism of AI-2 / LuxS quorum sensing in mixed fermentation system of LAB and yeasts. [ABSTRACT FROM AUTHOR]

objective: Pseudomonas fluorescens is the dominant spoilage organism in frozen foods, and its spoilage-caus¬ing genes are regulated by quorum sensing system. In order to accurately quantify the expression of spoilage genes and thus investigate the mechanism of quorum sensing regulation in food spoilage, it is required to screen reference genes of Pseudomonas fluorescens. Methods: Using Pseudomonas fluorescens PF-08 as the research object, eight common reference genes (dsbA, carA, rpsL, gyrB, atpD, rpoD, gltA, 16S rRNA) were selected and their gene expression was measured by quantitative real-time PCR (qPCR) after incubation with different types of quorum sensing signal molecules. geNorm, Normfinder, BestKeeper and RefFinder were used to evaluate the expression stability of the candidate reference genes and to screen out the most appropriate reference genes. Results: Under different types of exogenous signal molecules incuba¬tion, the least change in Ct value of Pseudomonas fluorescens was gltA and the Ct value of 16S rRNA was too low. The most stable reference genes by geNorm analysis were atpD and rpoD and the combination of the two could more accu¬rately quantify the expression levels of target genes. gltA was the most stable reference gene analyzed by Normfinder and BestKeeper. Further comprehensive evaluation with RefFinder showed rpoD and gltA were the most stable reference genes. Conclusion: Both rpoD and gltA were stably expressed in Pseudomonas fluorescens after incubation with different QS sig¬nal molecules. They could be used for the subsequent study of Pseudomonas fluorescens spoilage gene expression, and could also provide reference genes for studying the expression of QS-related genes in other spoilage bacteria. [ABSTRACT FROM AUTHOR]

In this study, quorum-sensing quenching activity of Lactobacillus crustorum ZHG2-1 was verified with the Chromobacterium violaceum CV026 as a indicator strain. Based on the change of biofilm, phenotypes of spoilage factors and the expression levels of related genes, the quorum sensing quenching mechanism of Lb. crustorum ZHG2-1 on P. fluoresces was detected. The results showed that the degradation rate of cell-free supernatant from strain ZHG2-1 to P. fluoresces AHLs reached 100%. The sub-inhibitory concentration (1.0, 2.0, 3.0 mg/mL) of strain ZHG2-1 crude extract could inhibit and remove the biofilm of P. fluoresces, and the inhibition rate and clearance rate reached 9.66%-31.32% and 28.62%-62.82%, respectively. In addition, the inhibition rate of strain ZHG2-1 crude extract with sub-inhibitory concentration on P. fluoresces spoilage factors (exopolysaccharides, proteases, lipases, biogenic amines) reached 7.23%- 100%. Meanwhile, the inhibition rate was mass concentration-dependent. Scanning electron microscope showed that the sub-inhibitory concentration of strain ZHG2-1 crude extract treatment significantly reduced the amount of biofilm and the bacterial colonies were in a dispersed state. The results of qRT-PCR showed that the crude extract of strain ZHG2-1 down-regulated the quorum-sensing genes rhlI and rhlR of P. fluoresces by 0.93 and 0.99, respectively, and the expression levels of aprX, algA, orm, flgA, ldcA and other biofilm and spoilage genes was significantly inhibited. The results indicated that Lb. crustorum interfered with the expression of quorum-sensing genes of P. fluoresces, thereby affecting the production of biofilm and spoilage factors. [ABSTRACT FROM AUTHOR]

Other genes identified in PF08 included some general stress response-related genes, including the antioxidant protein-coding gene I ahpC i , glutathione peroxidase-coding gene I bsaA i , starvation stringent protein-coding genes I sspA i and I sspB i , and heavy metal detoxification-related genes I cusS i and I merR i . Effects of Quorum Sensing System on the Transcription of Spoilage-Related Genes in PF08 An overnight culture of I P. fluorescens i PF08 (OD SB 595 sb = 1) was diluted 1:100 in fresh LB broth (pH 7.0 ± 0.2). Moreover, the QS system in PF08 was inhibited or activated by cinnamaldehyde or C SB 4 sb -HSL in this study and the regulatory effect of the QS system on spoilage-related genes in PF08 was evaluated by analyzing the changes of transcription level of these key genes. Keywords: Pseudomonas fluorescens PF08; complete genome; spoilage ability; quorum sensing; specific spoilage organism EN Pseudomonas fluorescens PF08 complete genome spoilage ability quorum sensing specific spoilage organism 1 13 13 04/21/22 20220418 NES 220418 Introduction Food spoilage is a complex process that is caused mainly by the metabolic activities of specific spoilage organisms (SSOs). [Extracted from the article]

[Display omitted] • The maximum capture rate of HalR (His-tag) protein by functionalized magnetic nanoparticles is 97.4%. • Functional magnetic nanoparticles can be reused for 5 times. • The screening method requires low cost and simple operation. • The screening method has the advantages of high efficiency, accuracy and high throughput. Using effective quorum sensing inhibitors (QSIs) is an important way to mitigate microbial contamination. The traditional QSI screening method is time-consuming and of low accuracy. To solve this, a more efficient and accurate method, ligand fishing-bound HPLC-MS-coupled molecular dynamics technology, was developed. In its early stages, Fe 3 O 4 @PS-ANTA-Ni2+ magnetic nanoparticles (MNPs) were prepared, to which the maximum adsorption rate of HalR (His-tag) protein was as high as 97.4%. Notably, Fe 3 O 4 @PS-ANTA-Ni2+ MNPs still exhibited good adsorption performance after being reused five times. Phytol was isolated from laurel extract by the functionalized MNPs due to its specific binding with HalR protein. To ensure the accuracy of phytol as QSI, molecular dynamics simulations were used to evaluate the specific binding between phytol and the HalR protein. The results showed that phytol has great potential as a QSI. Moreover, the subsequent quorum sensing verification experiments proved that phytol is an effective QSI. In summary, this work provides researchers with an efficient and accurate scheme for finding effective QSIs. [ABSTRACT FROM AUTHOR]