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Although nitrogen removal by partial nitritation and anammox is more cost-effective than conventional nitrification and denitrification, one downside is the production and accumulation of nitrous oxide (N2O). The potential exploitation of N2O-reducing bacteria, which are resident members of anammox microbial communities, for N2O mitigation would require more knowledge of their ecophysiology. This study investigated the phylogeny of resident N2O-reducing bacteria in an anammox microbial community and quantified individually the processes of N2O production and N2O consumption. An up-flow column-bed anammox reactor, fed with NH4+ and NO2- and devoid of oxygen, emitted N2O at an average conversion ratio (produced N2O: influent nitrogen) of 0.284%. Transcriptionally active and highly abundant nosZ genes in the reactor biomass belonged to the Burkholderiaceae (clade I type) and Chloroflexus genera (clade II type). Meanwhile, less abundant but actively transcribing nosZ strains were detected in the genera Rhodoferax, Azospirillum, Lautropia, and Bdellovibrio and likely act as an N2O sink. A novel 15N tracer method was adapted to individually quantify N2O production and N2O consumption rates. The estimated true N2O production rate and true N2O consumption rate were 3.98 ± 0.15 and 3.03 ± 0.18 mgN·gVSS-1·day-1, respectively. The N2O consumption rate could be increased by 51% (4.57 ± 0.51 mgN·gVSS-1·day-1) with elevated N2O concentrations but kept comparable irrespective of the presence or absence of NO2-. Collectively, the approach allowed the quantification of N2O-reducing activity and the identification of transcriptionally active N2O reducers that may constitute as an N2O sink in anammox-based processes.

Bdellovibrio and like organisms (BALOs) are Gram-negative obligate predators of other bacteria in a range of environments. The recent discovery of BALOs in the circulatory system of cultured spiny lobster P. ornatus warrants more investigation. We used a combination of co-culture agar and broth assays and transmission electron microscopy to show a Halobacteriovorax sp. strain Hbv preyed upon the model prey bacterium Vibrio sp. strain Vib. The haemolymph microbiome of juvenile P. ornatus was characterised following injection of phosphate buffered saline (control) or prey and/or predator bacteria for 3 d. The predator Hbv had no effect on survival compared to the control after 3 d. However, when compared to the prey only treatment group, lobsters injected with both prey and predator showed significantly lower abundance of genus Vibrio in the haemolymph bacterial community composition. This study indicates that predatory bacteria are not pathogenic and may assist in controlling microbial population growth in the haemolymph of lobsters.

A fundamental question in community ecology is the role of predator–prey interactions in food-web stability and species coexistence. Although microbial microcosms offer powerful systems to investigate it, interrogating the environment is much more arduous. Here, we show in a 1-year survey that the obligate predators Bdellovibrio and like organisms (BALOs) can regulate prey populations, possibly in a density-dependent manner, in the naturally complex, species-rich environments of wastewater treatment plants. Abundant as well as rarer prey populations are affected, leading to an oscillating predatory landscape shifting at various temporal scales in which the total population remains stable. Shifts, along with differential prey range, explain co-existence of the numerous predators through niche partitioning. We validate these sequence-based findings using single-cell sorting combined with fluorescent hybridization and community sequencing. Our approach should be applicable for deciphering community interactions in other systems., Studying the role of predator–prey interactions in food-web stability and species coexistence in the environment is arduous. Here, Cohen et al. use a combination of community and single-cell analyses to show that bacterial predators can regulate prey populations in the species-rich environments of wastewater treatment plants.

It was previously demonstrated that predatory bacteria are able to efficiently eliminate Gram-negative pathogens including antibiotic-resistant and biofilm-associated bacteria. In this proof-of-concept study we evaluated whether two species of predatory bacteria, Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus, were able to alter the survival of Gram-negative pathogens on the ocular surface. Clinical keratitis isolates of Pseudomonas aeruginosa (strain PAC) and Serratia marcescens (strain K904) were applied to the ocular surface of NZW rabbits followed by application of predatory bacteria. At time intervals, surviving pathogenic bacteria were enumerated. In addition, B. bacteriovorus and S. marcescens were applied to porcine organ culture corneas under contact lenses, and the ocular surface was examined by scanning electron microscopy. The ocular surface epithelial layer of porcine corneas exposed to S. marcescens, but not B. bacteriovorus was damaged. Using this model, neither pathogen could survive on the rabbit ocular surface for longer than 24 h. M. aeruginosavorus correlated with a more rapid clearance of P. aeruginosa but not S. marcescens from rabbit eyes. This study supports previous evidence that predatory bacteria are well tolerated by the cornea, but suggest that predatory bacteria do not considerably change the ability of the ocular surface to clear the tested Gram-negative bacterial pathogens from the ocular surface.

As microbiologists and public health officials scramble for weapons to combat antibiotic resistance, they may end up including an unlikely ally in their arsenal: other bacteria. The prime candidate right now is a predatory bacterium known as Bdellovibrio bacteriovorus . Researchers have started to evaluate predatory bacteria such as Bdellovibrio —shown here in a false-color transmission electron microscopy image at 50,000× magnification—as a means of treating intractable, antibiotic-resistant infections. Image credit: Science Source/ALFRED PASIEKA. Found in soils and water globally, B. bacteriovorus are free-living, harmless bacteria—harmless to humans, at least. In the microbial world, they’re voracious predators of gram-negative bacteria, a group that includes Salmonella , Escherichia coli , and several other pathogens. Bdellovibrio punch a hole in the membranes of their prey, enter and consume their contents, then burst out again to find their next meal. “They’re a very efficient killing machine,” says Daniel Kadouri, an associate professor at the Rutgers School of Dental Medicine in Newark, NJ. “They act kind of like the creature in the movie Alien .” Researchers are now beginning to evaluate Bdellovibrio and other similar predatory bacteria as a route to treating intractable, antibiotic-resistant infections. They’re starting to learn how these predators work in different organs and against different pathogens. As they examine various infection scenarios, they are also discovering how these microbes work in concert with the native microbiome and immune cells. Pills full of predatory bacteria won’t replace antibiotics at pharmacies anytime soon. But studying these microbes could help prepare for a future when many antibiotics fail to treat multi-drug-resistant infections. “Right now, the idea that a single injection of live bacteria could be used as therapy seems quite extreme to people,” says microbiologist Elizabeth Sockett of the University of Nottingham in the United Kingdom. “But as we run out of other …

AIMS The Mediterranean fruit fly (the medfly) causes major losses of agricultural fruits. Its microbiome is mainly composed of various Enterobacteriaceae that contribute to nutrient acquisition and are associated with the fly's development. Moreover, the performance of males produced by the sterile insect technique is improved by providing mass-reared insects with specific gut bacteria. Bdellovibrio and like organisms (BALOs) are obligate predators of Gram-negative bacteria that efficiently preys upon diverse Enterobacteriaceae, making it a potential disruptor of the fly's microbiome. We hypothesized that the fly's microbiome can be targeted to control the insect. METHODS AND RESULTS Inoculation of B. bacteriovorus as free-swimming or encapsulated cells into gut extracts significantly reduced gut bacterial abundance, sustaining predator survival. Similar treatments applied to adult flies showed that the predators also survived in the gut environment. While addition of the predators did not affect total gut bacterial abundance and end-point fly mortality, a shift in the gut community structure, measured by high-throughput community sequencing was observed. CONCLUSIONS The bacterial predator of bacteria B. bacteriovorus can prey and survive in vivo in the medfly gut. SIGNIFICANCE AND IMPACT OF THE STUDY This study establishes the potential of BALOs to affect the microbiome of insect hosts.

Bdellovibrio bacteriovorus is an environmentally-ubiquitous bacterium that uses unique adaptations to kill other bacteria. The best-characterized strain, HD100, has a multistage lifestyle, with both a free-living attack phase and an intraperiplasmic growth and division phase inside the prey cell. Advances in understanding the basic biology and regulation of predation processes are paving the way for future potential therapeutic and bioremediation applications of this unusual bacterium.

Bdellovibrio bacteriovorus is an environmentally-ubiquitous bacterium that uses unique adaptations to kill other bacteria. The best-characterized strain, HD100, has a multistage lifestyle, with both a free-living attack phase and an intraperiplasmic growth and division phase inside the prey cell. Advances in understanding the basic biology and regulation of predation processes are paving the way for future potential therapeutic and bioremediation applications of this unusual bacterium.

Trophic interactions are crucial for carbon cycling in food webs. Traditionally, eukaryotic micropredators are considered the major micropredators of bacteria in soils, although bacteria like myxobacteria and Bdellovibrio are also known bacterivores. Until recently, it was impossible to assess the abundance of prokaryotes and eukaryotes in soil food webs simultaneously. Using metatranscriptomic three-domain community profiling we identified pro- and eukaryotic micropredators in 11 European mineral and organic soils from different climes. Myxobacteria comprised 1.5–9.7% of all obtained SSU rRNA transcripts and more than 60% of all identified potential bacterivores in most soils. The name-giving and well-characterized predatory bacteria affiliated with the Myxococcaceae were barely present, while Haliangiaceae and Polyangiaceae dominated. In predation assays, representatives of the latter showed prey spectra as broad as the Myxococcaceae. 18S rRNA transcripts from eukaryotic micropredators, like amoeba and nematodes, were generally less abundant than myxobacterial 16S rRNA transcripts, especially in mineral soils. Although SSU rRNA does not directly reflect organismic abundance, our findings indicate that myxobacteria could be keystone taxa in the soil microbial food web, with potential impact on prokaryotic community composition. Further, they suggest an overlooked, yet ecologically relevant food web module, independent of eukaryotic micropredators and subject to separate environmental and evolutionary pressures.

In this study, two bacterial strains, IRP7 and IRP8, were selected to induce resistance against pine wilt disease (PWD). Foliar application with these strains to nematode-inoculated pine seedlings significantly reduced PWD severity. The effect of nematode inoculation and bacterial treatment on the rhizosphere bacterial community was investigated. The results indicated that the rhizosphere of nematode-inoculated seedlings contained a lower relative abundance of beneficial microbes such as Paraburkholderia, Bradyrhizobium, Rhizobacter, Lysobacter, and Caballeronia. Bacterial treatment resulted in significant changes in the microbes that were represented in relatively low relative abundance. Treatment with IRP7 resulted in an increase in the relative abundance of Nitrospirillum, Bacillus, and Luteibacter, which might be useful for protection against infection. Treatment with IRP8 resulted in an increase in the relative abundance of obligate bacterial predators of the Bdellovibrio genus that were previously shown to control several bacterial phytopathogens and may have a role in the management of nematode-carried bacteria. The selected bacteria were identified as Pseudomonas koreensis IRP7 and Lysobacter enzymogenes IRP8 and are suggested as a potential treatment for induced resistance against PWD. To our knowledge, this is the first report on the effect of foliar treatment with resistance-inducing bacteria on the rhizosphere microbiota.

Antimicrobial resistance (AMR) is a global health and economic crisis. With too few antibiotics in development to meet current and anticipated needs, there is a critical need for new therapies to treat Gram-negative infections. One potential approach is the use of living predatory bacteria, such as Bdellovibrio bacteriovorus (small Gram-negative bacteria that naturally invade and kill Gram-negative pathogens of humans, animals and plants). Moving toward the use of Bdellovibrio as a ‘living antibiotic’ demands the investigation and characterization of these bacterial predators in biologically relevant systems. We review the fundamental science supporting the feasibility of predatory bacteria as alternatives to antibiotics.

Background and Objectives: The microbial contamination of wastewater is associated with health risks. The aim of this study was to use the autochthonous Bdellovibrio potential to prey Gram-negative pathogenic bacteria as a bio-control agent to treat urban wastewater. Materials and Methods: Thirty-six raw sewage samples were collected for isolation of Bdellovibrio. Double layer plaque assay was used for isolation and the isolates were identified by microscopic examination and molecular analysis. To evaluate the predatory potential for decrease number of Gram-negative pathogenic bacteria, plaque perdition assay, reduction in host cells viability by colony-forming unit (CFU) counting, reduction in optical density (OD) in co-cultures and assay of killing efficiency were carried out. Also, the raw wastewater was treated by Bdellovibrio then the reduction in CFU counting and reduction in OD was evaluated. Results: Four strains of Bdellovibrio were isolated and were registered in Gene Bank. Clear plaques were observed after 3-6 days of incubation for all prey cells. The CFU enumerations of all preys were decreased after 48 hrs in co-cultures and raw wastewater. Also, OD was decreased down to 0.2 nm after 48 hrs. Conclusion: These autochthonous Bdellovibrio strains are proposed to use for bio-control of Gram-negative pathogenic bacteria in wastewater and reuse it for irrigation in arid regions.

We report the complete genome sequence of the predatory bacterium Bdellovibrio sp. strain KM01, isolated from soil collected near a pond. The genome is 3,961,288 bp long with 45.5% GC content. Comparative genomics among Bdellovibrio strains will help us understand how genotypic differences affect differences in predatory phenotypes.

© 2020 Herencias et al., In this study we analyze the growth-phase dependent metabolic states of Bdellovibrio bacteriovorus by constructing a fully compartmented, mass and charge-balanced genome-scale metabolic model of this predatory bacterium (iCH457). Considering the differences between life cycle phases driving the growth of this predator, growth-phase condition-specific models have been generated allowing the systematic study of its metabolic capabilities. Using these computational tools, we have been able to analyze, from a system level, the dynamic metabolism of the predatory bacteria as the life cycle progresses. We provide computational evidences supporting potential axenic growth of B. bacteriovorus’s in a rich medium based on its encoded metabolic capabilities. Our systems-level analysis confirms the presence of “energy-saving” mechanisms in this predator as well as an abrupt metabolic shift between the attack and intraperiplasmic growth phases. Our results strongly suggest that predatory bacteria’s metabolic networks have low robustness, likely hampering their ability to tackle drastic environmental fluctuations, thus being confined to stable and predictable habitats. Overall, we present here a valuable computational testbed based on predatory bacteria activity for rational design of novel and controlled biocatalysts in biotechnological/clinical applications., This work was supported by the Spanish Ministry of Economy and Competitiveness through the grants BIO2014-59528-JIN (JN), BIO2013-44878-R, and BIO2017-83448-R and H2020 Engicoin no 760994 (MAP). CH was supported by a FPI (Contratos predoctorales para la formación de doctores) fellowship (BES-2014-070856). SSB was supported by a FPU (Ayuda para la formación de profesorado universitario) fellowship (FPU17/03978) from the Spanish Ministry of Universities.

Appropriate use and specific primers are important in assessing the diversity and abundance of microbial groups of interest. Bdellovibrio and like organisms (BALOs), that refer to obligate Gram-negative bacterial predators of other Gram-negative bacteria, evolved in terms of taxonomy and classification over the past two decades. Hence, some former primers have become inadequate while others are yet to be designed, for both PCR (especially with the advent of NGS) and qPCR approaches. Thus, to study BALOs' abundance and diversity in a variety of aquatic ecosystems, we designed in silico specific primer sets for each BALO genera and tested them in vitro on a variety of cultures and environmental samples. Also, we performed Sanger and Nano Miseq sequencing to reveal the exact degree of specificity of the most promising primers set. Here we report our success in designing specific primers for some BALOs genera, i.e. Bdellovibrio (PCR), Bacteriovorax (qPCR), Peredibacter (PCR).

Acanthamoeba castellanii is a protist that has a high predation efficiency for bacteria in a number of monoxenic culture experiments. However, the role of A. castellanii in the microbial community is still unknown because of the lack of studies on multiple-species interactions. The aim of this study was to investigate the change of bacterial composition after A. castellanii emerges in a water environment. We added A. castellanii to an environmental water sample and incubated it for two days. Then, we performed 16S ribosomal RNA sequencing techniques to analyze the changes in bacterial composition. In this study, A. castellanii slightly increased the relative abundance of a few opportunistic pathogens, such as Legionella, Roseomonas, and Haemophilus. This result may be related to the training ground hypothesis. On the other hand, the growth of some bacteria was inhibited, such as Cyanobacteria and Firmicutes. Although A. castellanii did not drastically change the whole bacterial community, we surprisingly found the dissolved oxygen concentration was increased after incubation with A. castellanii. We applied environmental water at the laboratory scale to investigate the interactions among A. castellanii, complex microbial communities and the environment. We identified the bacteria that are sensitive to A. castellanii and further found the novel relationship between dissolved oxygen and microbial interaction. Our results helped to clarify the role of A. castellanii in microbial communities.

Bacteria are preyed upon by diverse microbial predators, including bacteriophage and predatory bacteria, such as Bdellovibrio bacteriovorus While bacteriophage are used as antimicrobial therapies in Eastern Europe and are being applied for compassionate use in the United States, predatory bacteria are only just beginning to reveal their potential therapeutic uses. However, predation by either predator type can falter due to different adaptations arising in the prey bacteria. When testing poultry farm wastewater for novel Bdellovibrio isolates on Escherichia coli prey lawns, individual composite plaques were isolated containing both an RTP (rosette-tailed-phage)-like-phage and a B. bacteriovorus strain and showing central prey lysis and halos of extra lysis. Combining the purified phage with a lab strain of B. bacteriovorus HD100 recapitulated haloed plaques and increased killing of the E. coli prey in liquid culture, showing an effective side-by-side action of these predators compared to their actions alone. Using approximate Bayesian computation to select the best fitting from a variety of different mathematical models demonstrated that the experimental data could be explained only by assuming the existence of three prey phenotypes: (i) sensitive to both predators, (ii) genetically resistant to phage only, and (iii) plastic resistant to B. bacteriovorus only. Although each predator reduces prey availability for the other, high phage numbers did not abolish B. bacteriovorus predation, so both predators are competent to coexist and are causing different selective pressures on the bacterial surface while, in tandem, controlling prey bacterial numbers efficiently. This suggests that combinatorial predator therapy could overcome problems of phage resistance.IMPORTANCE With increasing levels of antibiotic resistance, the development of alternative antibacterial therapies is urgently needed. Two potential alternatives are bacteriophage and predatory bacteria. Bacteriophage therapy has been used, but prey/host specificity and the rapid acquisition of bacterial resistance to bacteriophage are practical considerations. Predatory bacteria are of interest due to their broad Gram-negative bacterial prey range and the lack of simple resistance mechanisms. Here, a bacteriophage and a strain of Bdellovibrio bacteriovorus, preyed side by side on a population of E. coli, causing a significantly greater decrease in prey numbers than either alone. Such combinatorial predator therapy may have greater potential than individual predators since prey surface changes selected for by each predator do not protect prey against the other predator.

A novel bacterial strain, designated YN101T, was isolated from a marine solar saltern in the coast of Weihai, Shandong Province, China. Strain YN101T was Gram-stain negative, facultatively anaerobic, oxidase and catalase negative bacterium with the ability to prey on other microbes. A cross-streaking culture method was utilized to analyze the predatory activity of strain YN101T. The results showed strain YN101T could prey on various bacteria, either Gram-stain negative or Gram-stain positive. According to the predatory assays, different species in the same genus may behave differently when attacked by strain YN101T. The predatory behavior of strain YN101T to four typical species was analyzed, and furthermore, predation to Algoriphagus marinus am2T were quantitatively studied by fluorogenic quantitative PCR, and the gene copies decreased over two magnitudes. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain YN101T shared the greatest sequence similarity of 93.9% to Bradymonas sediminis FA350T. The complete genome sequence of strain YN101T was 8,047,306 bp in size and the genomic DNA G + C content was 63.8 mol%. The digital DNA-DNA hybridization (dDDH) values and average nucleotide identity (ANI) values between strain YN101T and B. sediminis FA350T were 13.9 and 74.0%. The genetic features showed that the biosynthesis of many important compounds was deficient in genome of strain YN101T, which may lead to its predation. Moreover, its genome encoded many genes affiliated with type IV pili, secretion system, membrane proteins and transduction proteins. Similar with myxobacteria and Bdellovibrio and like organisms (BALOs), these genes should play important roles in motility, adhesion or virulence to attack prey cells during predation. The predominant polar lipid profile of strain YN101T consisted of phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), and one unidentified aminophospholipid (APL). The major cellular fatty acid of strain YN101T was iso-C17:0, and the sole respiratory quinone was MK-7. Based on the chemotaxonomic, physiological and biochemical characteristics, strain YN101T represents a novel species of a novel genus in the family Bradymonadaceae, for which the name Persicimonas caeni gen. nov., sp. nov. is proposed. The type strain is YN101T (=KCTC 72083T = MCCC 1H00374T).

Bacterial predation, as exemplified by the periplasm-invading model predator Bdellovibrio bacteriovorus, is a fascinating multistage process facilitated by several adaptations to ‘regular’ bacterial lifestyles. We are beginning to understand more about such adaptations at the molecular level, particularly those concerning processes near the beginning of the predatory lifecycle (recognition, invasion, prey cell wall manipulation). In this review we highlight recent advances in investigating predation and tie these into some of the classical observations and phenotypes that make this two-cell system such an interesting case study in evolution.

To seek how soil biotic and abiotic factors which might shape the Bdellovibrio-and-like-organisms community, we sampled paddy soils under different fertilization treatments including fertilization without nitrogen (Control), the nitrogen use treatment (N) and the nitrogen overuse one (HNK) at three rice growing stages. The abundances of BALOs were impacted by the rice-growing stages but not the fertilization treatments. The abundances of Bdellovibrionaceae-like were positively associated with soil moisture, which showed a negative relationship with Bacteriovoracaceae-like bacteria. High-throughput sequencing analysis of the whole bacterial community revealed that the α-diversity of BALOs was not correlated with any soil properties data. Network analysis detected eight families directly linked to BALOs, namely, Pseudomonadaceae, Peptostreptococcaceae, Flavobacteriaceae, Sediment-4, Verrucomicrobiaceae, OM27, Solirubrobacteraceae and Roseiflexaceae. The richness and composition of OTUs in the eight families were correlated with different soil properties, while the evenness of them had a positive effect on the predicted BALO biomass. These results highlighted that the bottom-up control of BALOs in paddy soil at least partially relied on the changes of soil water content and the diversity of bacteria directly linked to BALOs in the microbial network.

Bdellovibrio-and-like organisms (BALOs) are a small group of bacteria that actively predate on other Gram-negative bacterial species. Although viewed mostly in a positive light, such as their potential use as living antibiotics to reduce pathogenic strain populations, several studies have also highlighted the need to control their activities, such as in the production of biodiesel. Consequently, this mini-review discusses research being conducted to characterize compounds and environmental settings that influence predation rates and the mechanisms by which they accomplish this, with a heavy emphasis on studies published within the last decade.Key points• This review discusses bacterial predators and factors impacting their activities. • Emphasis is on recent articles, particularly those discussing prey metabolites. • The implications on possible applications of bacterial predators are discussed.

26 p.-4 fig.-2 tab. The Ecology of Predation at the Microscale pp 173-194, This chapter reviews the potential of the predatory bacteria Bdellovibrio bacteriovorus, an obligate predator of other gram-negative bacteria, as a biotechnological tool. Due to the unique lifestyle and the different applications, predatory bacteria have awakened interest to be developed as a lytic tool. The lack of physiological and metabolic information makes difficult this development. However, in the last years, different approaches have been described in order to understand the physiology, morphology, and metabolism of the predators, as well as the population dynamics of the prey-predator interactions. Besides its potential of “living antibiotic”, predatory bacteria have been proposed as a biocontrol agent in the food industry or aquaculture. A recent work using B. bacteriovorus as a biological lytic tool for the recovery of intracellular bioproducts highlighted the potential use of predators in industrial bioprocesses. The bottlenecks of using other Bdellovibrio and like organisms (BALOs) have been also considered and discussed during this chapter., This work was supported by the European Union’s Horizon 2020 Research and Innovation Programme, grant agreement no. 760994-2 (ENGICOIN), the Spanish Ministry of Science, Innovation and Universities (BIO2017-83448-R) and the Community of Madrid (P2018/ NMT4389).

International audience; When considering microbial biotic interactions, viruses as well as eukaryotic grazers are known to be important components of aquatic microbial food webs. It might be the same for bacterivorous bacteria but these groups have been comparatively less studied. This is typically the case of the Bdellovibrio and like organisms (BALOs), which are obligate bacterial predators of other bacteria. Recently, the abundance and distribution of three families of this functional group were investigated in perialpine lakes, revealing their presence and quantitative importance. Here, a more in-depth analysis is provided for Lake Geneva regarding the diversity of these bacterial predators at different seasons, sites and depths. We reveal a seasonal and spatial (vertical) pattern for BALOs. They were also found to be relatively diverse (especially Bdellovibrionaceae) and assigned to both known and unknown phylogenetic clusters. At last we found that most BALOs were positively correlated to other bacterial groups, mainly Gram-negative, in particular Myxococcales (among which many are predators of other microbes). This study is the first shedding light on this potentially important bacterial killing group in a large and deep lake.

In this paper, we firstly reviewed the diseases and antibiotic resistance problems facing the aquaculture industry, and introduced the probiotic concept and the use of Bdellovibrio and like organisms (BALOs) as a probiotic/biological agent to control pathogens or potential pathogens in a sustainable aquaculture. Then we reviewed, in greater details, the antibacterial activities of BALOs in aquaculture. As a special group of predator prokaryotic bacteria, BALOs are increasingly being regarded as an alternative biocontrol agent in the field of aquaculture, in China in particular. We have comprehensively evaluated relevant high quality documentations and discovered that BALOs are not only capable of lysing a wide range of Gram-negatives, but also some Gram-positives, depending on the strain/isolate specificities. Various challenge tests confirmed that BALOs do have protective effects on the organisms tested against the challenged pathogens. Furthermore, Pearson correlation coefficient analyses revealed that BALOs have significantly negative correlations with total bacterial and vibrio counts in rearing waters and the guts of reared organisms (p < 0.01), and positive correlations with their growth (body length and weight gains) and survival (p < 0.01). Finally, we concluded that BALOs do possess strong antibacterial activities against various bacteria, including vibrios, and have a very strong application potential in aquaculture practices.

Intensive studies have focused on external factors governing the gut microbiota-disease relationship. It remains unknown how internal gut microbial components, especially interkingdom predators — phagotrophs and Bdellovibrio and like organisms (BALOs) — are linked to host health. Herein, we integrated the holistic gut microbiome including pathogens, bacteria, protists, predators, functional pathways, and shrimp immune potentials, to identify the gut microbial components that were indicative of shrimp white feces syndrome (WFS) onset. Both diversities and structures of the gut BALOs and phagotrophs communities differed significantly at the WFS onset stage, but not of the gut bacterial and protistan counterparts. Pathogens dynamics were best predicted by the gut BALOs or phagotrophs. Notably, nine WFS discriminatory phagotrophic taxa contributed 78.6% diagnose accuracy of shrimp health status at the WFS onset stage. The differential functional pathways were intimately associated with BALOs. There were intensive interactions among pathogens, gut BALOs, phagotrophs, and shrimp immune potentials. Specifically, shrimp activate multiple signaling pathways in response to WFS. However, pathogens encode virulence factors that neutralize and evade shrimp immune clearance, thereby leading to WFS outbreak. Collectively, we proposed a conceptual model to infer the etiology of shrimp WFS. Our findings bridge the interplay among interkingdom predator-prey interactions, pathogens invasion, host immune feedbacks, and disease progression, which greatly broaden our understanding of shrimp WFS etiology from ecological and molecular perspectives.

For comprehensive insights into the effects of disinfection strategy on antibiotic resistance genes (ARGs) in pipe wall biofilm to ensure the biosafety of domestic hot water system (DHWS), this study investigated the occurrence, removal and interactions of ARGs, as well as their potential hosts. The shifts in biofilm community composition and microbial functions (level three) were observed under different disinfection strategies. A total of 40 ARG subtypes within seven antibiotic types were predicted. The total gene counts ranged from 6.10 × 104 to 2.31 × 105, and decreased after the chlorine, chlorine dioxide, silver ions (Ag+), ultraviolet (UV), and Ag+-UV disinfection. The ARGs in samples under different disinfection strategies were divided into four groups, and the removal and enrichment of the same ARGs in each group were almost consistent. The complex interactions among ARGs were weakened and altered by disinfection (edges decreased from 237 to 178), with yebQ and marC as the hub ARGs, but positive correlations were still dominant. Moreover, 36 nonpathogenic bacteria, including high- (Blastocatella), mid- (Ornatilinea) and low-abundant genera (Bdellovibrio), as well as 18 potential pathogens (Vibrio and Bacillus) were identified as the potential hosts harboring ARGs. Overall, this study provides some new insights into the occurrence of ARGs and their fate under eight disinfection strategies, which is of great significance for a comprehensive understanding and control of ARGs in DHWS.

Modification of essential bacterial peptidoglycan (PG) containing cell walls can lead to antibiotic resistance, for example β-lactam resistance by L,D-transpeptidase activities. Predatory Bdellovibrio bacteriovorus are naturally antibacterial and combat infections by traversing, modifying and finally destroying walls of Gram-negative prey bacteria, modifying their own PG as they grow inside prey. Historically, these multi-enzymatic processes on two similar PG walls have proved challenging to elucidate. Here, with a PG labelling approach utilizing timed pulses of multiple fluorescent D-amino acids (FDAAs), we illuminate dynamic changes that predator and prey walls go through during the different phases of bacteria:bacteria invasion. We show formation of a reinforced circular port-hole in the prey wall; L,D-transpeptidaseBd mediated D-amino acid modifications strengthening prey PG during Bdellovibrio invasion and a zonal mode of predator-elongation. This process is followed by unconventional, multi-point and synchronous septation of the intracellular Bdellovibrio, accommodating odd- and even-numbered progeny formation by non-binary division.

Acute hepatopancreatic necrosis disease, a severe disease of shrimp, is caused by Vibrio parahaemolyticus (AHPND Vp), a halophilic bacterium harboring a plasmid that contains toxin genes homologous to Photorhabdus insect-related toxins. We obtained 9 isolates of Bdellovibrio and like organisms (BALOs) from water and sediment samples in Thailand. Using 16S rRNA sequencing, all of the organisms were identified as Bacteriovorax spp. and were able to attack all tested AHPND Vp isolates. In addition, their various susceptible hosts, including Gram-positive and Gram-negative bacteria, were observed. The optimal ratio for interaction between the Bacteriovorax isolate BV-A and AHPND Vp was determined to be 1:10. The suitable conditions applied for co-culture between BV-A and AHPND Vp were 30°C, 2% NaCl, and pH 7.6. The capability of BV-A to reduce numbers of AHPND Vp in vitro was observed in co-culture after incubation for 2 d and continued until the end of the incubation period. In vivo, BV-A was able to reduce mortality of shrimp post-larvae infected with AHPND Vp. In addition, BV-A significantly decreased the formation of biofilm by AHPND Vp. These findings provide evidence for using Bacteriovorax as a biocontrol of AHPND Vp in shrimp aquaculture.

Obligate predatory bacteria, i.e. bacteria requiring a Gram negative prey cell in order to complete their cell cycle, belong to the polyphyletic group referred to as the Bdellovibrio And Like Organisms (BALO). Predatory interactions between bacteria are complex, yet their dynamics and impact on bacterial communities in the environment are becoming better understood. BALO have unique life cycles: they grow epibiotically with the predator remaining attached to the prey's envelope, dividing in a binary manner or periplasmically, i.e. by penetrating the prey's periplasm to generate a number of progeny cells. The periplasmic life cycle includes unique gene and protein patterns and unique signaling features. These ecological and cellular features, along with applications of the BALO in the medical, agricultural and environmental fields are surveyed.

Predatory bacteria are ubiquitously distributed in nature in including in aquatic environments, sewage, intestinal tracts of animals and humans, rhizophere and, soils. However, our understanding of their evolutionary history is limited. Results of recent studies have shown that acquiring novel genes is a major force driving bacterial evolution. Therefore, to gain a better understanding of the impact of gene gain and loss in the evolution of bacterial predators, this study employed comparative genomic approaches to identify core-set gene families and species-specific gene families, and model gene gain and loss events among 11 genomes that represented diverse lineages. In total, 1977 gene families were classified. Of these 509 (pattern 11111111111) were present all of the 11 species. Among the non-core set gene families, 52 were present only in saltwater bacteria predators and had no ortholog in the other genomes. Similarly 109 and 44 were present only in the genomes of Micavibrio spp. and Bdellovibrio spp., respectively. In this study, the gain loss mapping engine GLOOME was selected to analyze and estimate the expectations and probabilities of both gain and loss events in the predatory bacteria. In total, 354 gene families were involved in significant gene gain events, and 407 gene families were classified into gene loss events with high supported value. Moreover, 18 families from the core set gene family were identified as putative genes under positive selection. The results of this study suggest that acquisition of particular genes that encode functional proteins in metabolism and cellular processes and signaling, especially ABC systems, may help bacterial predators adapt to surrounding environmental changes and present different predation strategies for survival in their habitats.

Summary Microbiome communities are complex assemblages of bacteria. The dissection of their assembly dynamics is challenging because it requires repeated sampling of both host and source communities. We used the nematode Caenorhabditis elegans as a model to study these dynamics. We characterized microbiome variation from natural worm populations and their substrates for two consecutive years using 16S rDNA amplicon sequencing. We found conservation in microbiome composition across time at the genus, but not amplicon sequencing variant (ASV) level. Only three ASVs were consistently present across worm samples (Comamonas ASV10859, Pseudomonas ASV7162 and Cellvibrio ASV9073). ASVs were more diverse in worms from different rather than the same substrates, indicating an influence of the source community on microbiome assembly. Surprisingly, almost 50% of worm-associated ASVs were absent in corresponding substrates, potentially due to environmental filtering. Ecological network analysis revealed strong effects of bacteria–bacteria interactions on community composition: While a dominant Erwinia strain correlated with decreased alpha-diversity, predatory bacteria of the Bdellovibrio and like organisms associated with increased alpha-diversity. High alpha-diversity was further linked to high worm population growth, especially on species-poor substrates. Our results highlight that microbiomes are individually shaped and sensitive to dramatic community shifts in response to particular competitive species.

New strategies are needed to combat multidrug-resistant bacterial infections. Application of the predatory bacterium Bdellovibrio bacteriovorus, which kills other bacteria, including pathogens, is considered promising for combating bacterial infections. The B. bacteriovorus life cycle consists of two phases, a free-living, invasive attack phase and an intracellular reproductive phase, in which this predatory bacterium degrades the host’s macromolecules and reuses them for its own growth. To understand the use of B. bacteriovorus as a “living antibiotic,” it is first necessary to dissect its life cycle, including chromosome replication. Here, we present a real-time investigation into subcellular localization of chromosome replication in a single cell of B. bacteriovorus. This process initiates at the invasion pole of B. bacteriovorus and proceeds until several copies of the chromosome have been completely synthesized. Interestingly, we demonstrate that some cells of B. bacteriovorus require two prey cells sequentially to complete their life cycle., Bdellovibrio bacteriovorus is a small Gram-negative, obligate predatory bacterium that is largely found in wet, aerobic environments (e.g., soil). This bacterium attacks and invades other Gram-negative bacteria, including animal and plant pathogens. The intriguing life cycle of B. bacteriovorus consists of two phases: a free-living nonreplicative attack phase, in which the predatory bacterium searches for its prey, and a reproductive phase, in which B. bacteriovorus degrades a host’s macromolecules and reuses them for its own growth and chromosome replication. Although the cell biology of this predatory bacterium has gained considerable interest in recent years, we know almost nothing about the dynamics of its chromosome replication. Here, we performed a real-time investigation into the subcellular localization of the replisome(s) in single cells of B. bacteriovorus. Our results show that in B. bacteriovorus, chromosome replication takes place only during the reproductive phase and exhibits a novel spatiotemporal arrangement of replisomes. The replication process starts at the invasive pole of the predatory bacterium inside the prey cell and proceeds until several copies of the chromosome have been completely synthesized. Chromosome replication is not coincident with the predator cell division, and it terminates shortly before synchronous predator filament septation occurs. In addition, we demonstrate that if this B. bacteriovorus life cycle fails in some cells of Escherichia coli, they can instead use second prey cells to complete their life cycle. IMPORTANCE New strategies are needed to combat multidrug-resistant bacterial infections. Application of the predatory bacterium Bdellovibrio bacteriovorus, which kills other bacteria, including pathogens, is considered promising for combating bacterial infections. The B. bacteriovorus life cycle consists of two phases, a free-living, invasive attack phase and an intracellular reproductive phase, in which this predatory bacterium degrades the host’s macromolecules and reuses them for its own growth. To understand the use of B. bacteriovorus as a “living antibiotic,” it is first necessary to dissect its life cycle, including chromosome replication. Here, we present a real-time investigation into subcellular localization of chromosome replication in a single cell of B. bacteriovorus. This process initiates at the invasion pole of B. bacteriovorus and proceeds until several copies of the chromosome have been completely synthesized. Interestingly, we demonstrate that some cells of B. bacteriovorus require two prey cells sequentially to complete their life cycle.