Evaluation of the application potential of Bdellovibrio sp. YBD-1 isolated from Yak faeces.

Studies on Bdellovibrio and like organisms (BALOs), obligate predatory bacteria, have highlighted the possibility of regulating bacteria and biofilms; however, yak-derived BALOs are yet to be reported. We aimed to characterize the BALOs isolated and identified from yak (Bos grunniens) feces and examine application potential. BALOs were isolated from healthy yak fecal samples, with Escherichia coli (ATCC 25922) as prey using the double-layer agar method, identified by transmission electron microscopy (TEM), and the specific 16S rDNA sequencing analysis. Sequencing of the 16S rDNA gene indicated that this isolate was 91% similar to the Bdellovibrio sp. NC01 reference strain and was named YBD-1. Proportion of YBD-1 lysed bacteria is 12/13. The YBD-1 showed best growth at 25-40°C, 0-0.25% (w/v) NaCl, and pH 6.5-7.5. YBD-1 significantly reduced the planktonic cells and biofilms of E.coli in co-culture compared to the E.coli group. Additionally, SEM analysis indicated that YBD-1 significantly reduced biofilm formation in E. coli. Furthermore, quantitative Real Time-polymerase chain reaction (qRT-PCR) showed that the expression of the virulence genes fim and iroN and the genes pgaABC involved in biofilm formation went down significantly. We concluded that YBD-1 may have the potential to control bacterial growth and biofilm-associated bacterial illnesses.

Lifecycle of a predatory bacterium vampirizing its prey through the cell envelope and S-layer.

Predatory bacteria feed upon other bacteria in various environments. Bdellovibrio exovorus is an obligate epibiotic predator that attaches on the prey cell surface, where it grows and proliferates. Although the mechanisms allowing feeding through the prey cell envelope are unknown, it has been proposed that the prey's proteinaceous S-layer may act as a defensive structure against predation. Here, we use time-lapse and cryo-electron microscopy to image the lifecycle of B. exovorus feeding on Caulobacter crescentus. We show that B. exovorus proliferates by non-binary division, primarily generating three daughter cells. Moreover, the predator feeds on C. crescentus regardless of the presence of an S-layer, challenging its assumed protective role against predators. Finally, we show that apparently secure junctions are established between prey and predator outer membranes.

Prey killing without invasion by Bdellovibrio bacteriovorus defective for a MIDAS-family adhesin.

The bacterium Bdellovibrio bacteriovorus is a predator of other Gram-negative bacteria. The predator invades the prey's periplasm and modifies the prey's cell wall, forming a rounded killed prey, or bdelloplast, containing a live B. bacteriovorus. Redundancy in adhesive processes makes invasive mutants rare. Here, we identify a MIDAS adhesin family protein, Bd0875, that is expressed at the predator-prey invasive junction and is important for successful invasion of prey. A mutant strain lacking bd0875 is still able to form round, dead bdelloplasts; however, 10% of the bdelloplasts do not contain B. bacteriovorus, indicative of an invasion defect. Bd0875 activity requires the conserved MIDAS motif, which is linked to catch-and-release activity of MIDAS proteins in other organisms. A proteomic analysis shows that the uninvaded bdelloplasts contain B. bacteriovorus proteins, which are likely secreted into the prey by the Δbd0875 predator during an abortive invasion period. Thus, secretion of proteins into the prey seems to be sufficient for prey killing, even in the absence of a live predator inside the prey periplasm.

Unbalanced predatory communities and a lack of microbial degraders characterize the microbiota of a highly sewage-polluted Eastern-Mediterranean stream.

Wastewater pollution of water resources takes a heavy toll on humans and on the environment. In highly polluted water bodies, self-purification is impaired, as the capacity of the riverine microbes to regenerate the ecosystem is overwhelmed. To date, information on the composition, dynamics and functions of the microbial communities in highly sewage-impacted rivers is limited, in particular in arid and semi-arid environments. In this year-long study of the highly sewage-impacted Al-Nar/Kidron stream in the Barr al-Khalil/Judean Desert east of Jerusalem, we show, using 16S and 18S rRNA gene-based community analysis and targeted qPCR, that both the bacterial and micro-eukaryotic communities, while abundant, exhibited low stability and diversity. Hydrolyzers of organics compounds, as well as nitrogen and phosphorus recyclers were lacking, pointing at reduced potential for regeneration. Furthermore, facultative bacterial predators were almost absent, and the obligate predators Bdellovibrio and like organisms were found at very low abundance. Finally, the micro-eukaryotic predatory community differed from those of other freshwater environments. The lack of essential biochemical functions may explain the stream's inability to self-purify, while the very low levels of bacterial predators and the disturbed assemblages of micro-eukaryote predators present in Al-Nar/Kidron may contribute to community instability and disfunction.

Bdellovibrio svalbardensis sp. nov., a newly described predator isolated from Svalbard, Norway.

Identified as a newly described species from a biocrust in Svalbard, Norway (78° 54' 8.27″ N 12° 01' 20.34″ E), isolate PAP01T has different characteristics from any known predatory bacteria. The isolate was vibrio-shaped strain that employed flagellar motility. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the isolate clustered within the genus Bdellovibrio in the family Bdellovibrionaceae. 16S rRNA gene sequence similarities between strain PAP01T and the type strain (Bdellovibrio bacteriovorus HD100) was 95.7 %. The PAP01T genome has a size of 3.898 Mbp and possesses 3732 genes and a G+C content of 45.7 mol%. The results of genetic and physiological tests indicated the phenotypic differentiation of strain PAP01T from the two other Bdellovibrio species with validly published names. Based on the physiological and phylogenetic data, as well as the prey range spectrum and osmolality sensitivities, isolate PAP01T represents a novel species within the genus Bdellovibrio, for which the name Bdellovibrio svalbardensis sp. nov. is proposed. The type strain is PAP01T (=KCTC 92583T=DSM 115080T).

Ecological succession and community assembly of mixed microbial culture polyhydroxyalkanoate production systems: Drivers of polyhydroxyalkanoate synthesis and Bdellovibrio predation.

The production of polyhydroxyalkanoate (PHA) by mixed microbial culture (MMC) can reduce the pollution of plastics. Ecophysiological study of the microbial community assembly and succession is helpful for comprehensive understanding the MMC PHA production process. The operation mode of sequential aerobic dynamic discharge - aerobic dynamic feeding (ADD-ADF) was applied and the operation can be divided into acclimation phase and maturation phase. Deterministic process caused by selective pressure dominated the community assembly throughout the operation. In the acclimation phase, the physical selective pressure recovered the settling capacity of the system, and settling ability of the MMC was closely related to function of PHA synthesis. However, in the maturation phase, stochastic process caused sludge bulking, making the settling ability and PHA synthesis function of the MMC independent on each other. Stochastic process led to the succession of the dominant PHA-producing bacteria, for example, the predation of Paracoccus and Thauera by Bdellovibrio.

Chromosome structure and DNA replication dynamics during the life cycle of the predatory bacterium Bdellovibrio bacteriovorus.

Bdellovibrio bacteriovorus, an obligate predatory Gram-negative bacterium that proliferates inside and kills other Gram-negative bacteria, was discovered more than 60 years ago. However, we have only recently begun to understand the detailed cell biology of this proficient bacterial killer. Bdellovibrio bacteriovorus exhibits a peculiar life cycle and bimodal proliferation, and thus represents an attractive model for studying novel aspects of bacterial cell biology. The life cycle of B. bacteriovorus consists of two phases: a free-living nonreplicative attack phase and an intracellular reproductive phase. During the reproductive phase, B. bacteriovorus grows as an elongated cell and undergoes binary or nonbinary fission, depending on the prey size. In this review, we discuss: (1) how the chromosome structure of B. bacteriovorus is remodeled during its life cycle; (2) how its chromosome replication dynamics depends on the proliferation mode; (3) how the initiation of chromosome replication is controlled during the life cycle, and (4) how chromosome replication is spatiotemporally coordinated with the proliferation program.

The assembly of gut microbiota implicates shrimp acute hepatopancreas necrosis disease progression.

Ample evidence shows dysbiosis in the gut microbiota when comparing healthy shrimp with those affected by severe acute hepatopancreatic necrosis disease (AHPND). However, the static comparison used in available studies leads to the uncertainties regarding how and to what extent the gut microbiota responds to the progressive severity of AHPND. In addition, shrimp AHPND is featured by rapid and massive mortality, thus the initiation of AHPND must be diagnosed for preemptive therapy. For these reasons, we explored the ecological assembly of gut microbiota over shrimp AHPND progression. Increasing AHPND severity was associated with linear increase in the copies of pirAB genes, relative abundance of gut Vibrio and potentially pathogenic, and reduction in the gut bacterial diversity, stability, and relative abundance of Bdellovibrio. Negative and significant association between gut Vibrio and Bdellovibrio were noted, indicating that compromised predation exerts a role in AHPND progression. Notably, the extents of departure to the healthy shrimp gut microbiota were positively coupled with the increasing severity of AHPND. After controlling the temporal variation in the gut microbiota as healthy shrimp age, we constructed a diagnosis model that accurately diagnosed the initial, progressed or moribund stages of AHPND, with an overall accuracy of 86.5%. Shrimp AHPND induced more stochastic gut microbiotas as a consequence of the attenuated ability of diseased shrimp to select their commensals, resulting in convergent bacterial communities between gut and rearing water over AHPND progression. Collectively, our findings provide important step toward the ecological assembly of gut microbiota implicating in AHPND etiology and in diagnosing AHPND stages. KEY POINTS: • The departure of shrimp gut microbiota positively linked with AHPND severity. • The diagnosis model accurately diagnosed the stages of AHPND. • Shrimp AHPND induced more stochastic gut microbiota.

Bdellovibrio predation cycle characterized at nanometre-scale resolution with cryo-electron tomography.

Bdellovibrio bacteriovorus is a microbial predator that offers promise as a living antibiotic for its ability to kill Gram-negative bacteria, including human pathogens. Even after six decades of study, fundamental details of its predation cycle remain mysterious. Here we used cryo-electron tomography to comprehensively image the lifecycle of B. bacteriovorus at nanometre-scale resolution. With high-resolution images of predation in a native (hydrated, unstained) state, we discover several surprising features of the process, including macromolecular complexes involved in prey attachment/invasion and a flexible portal structure lining a hole in the prey peptidoglycan that tightly seals the prey outer membrane around the predator during entry. Unexpectedly, we find that B. bacteriovorus does not shed its flagellum during invasion, but rather resorbs it into its periplasm for degradation. Finally, following growth and division in the bdelloplast, we observe a transient and extensive ribosomal lattice on the condensed B. bacteriovorus nucleoid.

Binary or Nonbinary Fission? Reproductive Mode of a Predatory Bacterium Depends on Prey Size.

Most bacteria, including model organisms such as Escherichia coli, Bacillus subtilis, and Caulobacter crescentus, reproduce by binary fission. However, some bacteria belonging to various lineages, including antibiotic-producing Streptomyces and predatory Bdellovibrio, proliferate by nonbinary fission, wherein three or more chromosome copies are synthesized and the resulting multinucleoid filamentous cell subdivides into progeny cells. Here, we demonstrate for the first time that the predatory bacterium Bdellovibrio bacteriovorus reproduces through both binary and nonbinary fission inside different prey bacteria. Switching between the two modes correlates with the prey size. In relatively small prey cells, B. bacteriovorus undergoes binary fission; the FtsZ ring assembles in the midcell, and the mother cell splits into two daughter cells. In larger prey cells, B. bacteriovorus switches to nonbinary fission and creates multiple asynchronously assembled FtsZ rings to produce three or more daughter cells. Completion of bacterial cell cycle critically depends on precise spatiotemporal coordination of chromosome replication with other cell cycle events, including cell division. We show that B. bacteriovorus always initiates chromosome replication at the invasive pole of the cell, but the spatiotemporal choreography of subsequent steps depends on the fission mode and/or the number of progeny cells. In nonbinary dividing filaments producing five or more progeny cells, the last round(s) of replication may also be initiated at the noninvasive pole. Altogether, we find that B. bacteriovorus reproduces through bimodal fission and that extracellular factors, such as the prey size, can shape replication choreography, providing new insights about bacterial life cycles. IMPORTANCE Most eukaryotic and bacterial cells divide by binary fission, where one mother cell produces two progeny cells, or, rarely, by nonbinary fission. All bacteria studied to date use only one of these two reproduction modes. We demonstrate for the first time that a predatory bacterium, Bdellovibrio bacteriovorus, exhibits bimodal fission and the mode of division depends on the size of the prey bacterium inside which B. bacteriovorus grows. This work provides key insights into the mode and dynamics of B. bacteriovorus proliferation in different pathogens that pose a major threat to human health due to their emerging antibiotic resistance (Proteus mirabilis, Salmonella enterica, and Shigella flexneri). The use of predatory bacteria such as B. bacteriovorus is currently regarded as a promising strategy to kill antibiotic-resistant pathogens. We find that B. bacteriovorus employs different chromosome replication choreographies and division modes when preying on those pathogens. Our findings may facilitate the design of efficient pathogen elimination strategies.

Cleave a Septum, Leave a Cell: Bdellovibrio bacteriovorus Secretes a Specialized Lytic Transglycosylase to Clear Prey Cell Septum Obstruction.

Predatory microbes like Bdellovibrio feed on other bacteria by invading their periplasm, replicating within the bacterial shell that is now a feeding trough, and ultimately lysing the prey and disseminating. A new study by E. J. Banks, C. Lambert, S. Mason, J. Tyson, et al. (J Bacteriol 205:e00475-22, 2023, https://doi.org/10.1128/jb.00475-22) highlights the great lengths to which Bdellovibrio must go to affect host cell remodeling: A secreted cell wall lytic enzyme with specificity for the host septal cell wall maximizes the size of the attacker's meal and the size of the restaurant in which it can spread out. This study provides novel insights into bacterial predator-prey dynamics and showcases elegant co-option of an endogenous cell wall turnover enzyme refurbished as a warhead to enhance prey consumption.

An MltA-Like Lytic Transglycosylase Secreted by Bdellovibrio bacteriovorus Cleaves the Prey Septum during Predatory Invasion.

Lytic transglycosylases cut peptidoglycan backbones, facilitating a variety of functions within bacteria, including cell division, pathogenesis, and insertion of macromolecular machinery into the cell envelope. Here, we identify a novel role of a secreted lytic transglycosylase associated with the predatory lifestyle of Bdellovibrio bacteriovorus strain HD100. During wild-type B. bacteriovorus prey invasion, the predator rounds up rod-shaped prey into spherical prey bdelloplasts, forming a spacious niche within which the predator grows. Deleting the MltA-like lytic transglycosylase Bd3285 still permitted predation but resulted in three different, invaded prey cell shapes: spheres, rods, and "dumbbells." Amino acid D321 within the catalytic C-terminal 3D domain of Bd3285 was essential for wild-type complementation. Microscopic analyses revealed that dumbbell-shaped bdelloplasts are derived from Escherichia coli prey undergoing cell division at the moment of Δbd3285 predator invasion. Prelabeling of E. coli prey peptidoglycan prior to predation with the fluorescent D-amino acid HADA showed that the dumbbell bdelloplasts invaded by B. bacteriovorus Δbd3285 contained a septum. Fluorescently tagged Bd3285, expressed in E. coli, localized to the septum of dividing cells. Our data indicate that B. bacteriovorus secretes the lytic transglycosylase Bd3285 into the E. coli periplasm during prey invasion to cleave the septum of dividing prey, facilitating prey cell occupation. IMPORTANCE Antimicrobial resistance is a serious and rapidly growing threat to global health. Bdellovibrio bacteriovorus can prey upon an extensive range of Gram-negative bacterial pathogens and thus has promising potential as a novel antibacterial therapeutic and is a source of antibacterial enzymes. Here, we elucidate the role of a unique secreted lytic transglycosylase from B. bacteriovorus which acts on the septal peptidoglycan of its prey. This improves our understanding of mechanisms that underpin bacterial predation.

Parallel Evolution in Predatory Bdellovibrio sp. NC01 during Long-Term Coculture with a Single Prey Strain.

Experimental evolution provides a powerful tool for examining how Bdellovibrio evolves in response to unique selective pressures associated with its predatory lifestyle. We tested how Bdellovibrio sp. NC01 adapts to long-term coculture with Pseudomonas sp. NC02, which is less susceptible to predation compared to other Gram-negative bacteria. Analyzing six replicate Bdellovibrio populations across six time points spanning 40 passages and 2,880 h of coculture, we detected 30 to 40 new mutations in each population that exceeded a frequency of 5%. Nonsynonymous substitutions were the most abundant type of new mutation, followed by small indels and synonymous substitutions. After completing the final passage, we detected 20 high-frequency (>75%) mutations across all six evolved Bdellovibrio populations. Eighteen of these alter protein sequences, and most increased in frequency rapidly. Four genes acquired a high-frequency mutation in two or more evolved Bdellovibrio populations, reflecting parallel evolution and positive selection. The genes encode a sodium/phosphate cotransporter family protein (Bd2221), a metallophosphoesterase (Bd0054), a TonB family protein (Bd0396), and a hypothetical protein (Bd1601). Tested prey range and predation efficiency phenotypes did not differ significantly between evolved Bdellovibrio populations and the ancestor; however, all six evolved Bdellovibrio populations demonstrated enhanced starvation survival compared to the ancestor. These results suggest that, instead of evolving improved killing of Pseudomonas sp. NC02, Bdellovibrio evolved to better withstand nutrient limitation in the presence of this prey strain. The mutations identified here point to genes and functions that may be important for Bdellovibrio adaptation to the different selective pressures of long-term coculture with Pseudomonas. IMPORTANCE Bdellovibrio attack and kill Gram-negative bacteria, including drug-resistant pathogens of animals and plants. This lifestyle is unusual among bacteria, and it imposes unique selective pressures on Bdellovibrio. Determining how Bdellovibrio evolve in response to these pressures is valuable for understanding the mechanisms that govern predation. We applied experimental evolution to test how Bdellovibrio sp. NC01 evolved in response to long-term coculture with a single Pseudomonas strain, which NC01 can kill, but with low efficiency. Our experimental design imposed different selective pressures on the predatory bacteria and tracked the evolutionary trajectories of replicate Bdellovibrio populations. Using genome sequencing, we identified Bdellovibrio genes that acquired high-frequency mutations in two or more populations. Using phenotype assays, we determined that evolved Bdellovibrio populations did not improve their ability to kill Pseudomonas, but rather are better able to survive starvation. Overall, our results point to functions that may be important for Bdellovibrio adaptation.

Biological control of soft rot in potato by κ-carrageenan carriers encapsulated microbial predators.

The Pectobacterium and Dickeya pectinolytic bacteria are phytopathogens responsible for several macerating diseases on a wide range of crops and ornamental plants. Recently, bacterial predators belonging to the Bdellovibrio and like organisms (BALOs) were shown to efficiently prey on these rot-causing bacteria and reduce soft rot-induced potato slice maceration. In the current research, our novel approach aimed at developing and studying a κ-carrageenan-based encapsulation system for fast-release of entrapped B. bacteriovorus HD100 in high numbers to prevent bacterial soft-rot infections. κ-carrageenan-dried carriers swelled and dissolved upon immersion in water due to a loss of potassium ions which are the main cross-linking agents. Survival rates of the predators after drying were higher for immobilized bdelloplasts (e.g., predator inside the host) compared to attack phase (host-searching, AP) cells, and with the addition of the osmoprotectant trehalose to the carriers. Released encapsulated predators preyed efficiently on soft rot bacteria, with bdelloplasts performing better as compared to AP cells. However, predation dynamics were influenced by the type of added osmoprotectant. Carrageenan-trehalose carriers encapsulating predators were able to reduce soft-rot disease in situ using a potato slice assay. To our knowledge, this research is the first to explore the potential of encapsulated BALOs against phytopathogens. KEY POINTS: • Dissolution of the carriers was affected by potassium concentration in the system. • Encapsulation of bdelloplasts with trehalose best maintained the predator viability. • The encapsulated predators efficiently controlled soft rot in vitro and in situ.

Biocontrol treatment: Application of Bdellovibrio bacteriovorus HD100 against burn wound infection caused by Pseudomonas aeroginosa in mice.

Owing to the high level of resistance to various antibiotics in bacteria causing burn wound infections, the alternative therapeutics is highly demanded. Bdellovibrio and like organisms (BALOs) seem to be a superb choice. In the present study, Bdellovibrio bacteriovorus HD100 was selected for treating burn wound infection caused by Pseudomonas aeruginosa strain PAO1 in a mouse model. In this experiment, two treatments, meropenem as antibiotic and B. bacteriovorus, were employed. Histopathology indicated an accelerated healing rate in both treatments in comparison with the control. Moreover, quantitative reverse transcription PCR (qRT-PCR) was applied to investigate the expression of tnf-α (tumor necrosis factor alpha), pdgf (platelet-derived growth factor), tgf-ß1 (transforming growth factor beta1), ifn-γ (interferon gamma), vegf (vascular endothelial group factor), and col1 (collagen type 1). The results demonstrated that treating burn wound areas with Bdellovibrio not only decrease the inflammatory phase period, but also may improve the characteristics of proliferative phases of wound healing. In addition, a significant difference was explored between the two treatment groups in the regulation of all genes, except for pdgf revealed a significant up regulation in both treatment groups. The results disclose that Bdellovibrio attenuates P. aeruginosa in burn wounds infections and improves the wound healing process.

Use of Resazurin To Rapidly Enumerate Bdellovibrio and Like Organisms and Evaluate Their Activities.

A method to rapidly quantify predatory bacterial cell populations using resazurin reduction to resorufin and its resulting fluorescence kinetics (dF/dt) are described. The reliability of this method to measure the predatory populations was demonstrated with the type strain, Bdellovibrio bacteriovorus HD100, as well as B. bacteriovorus 109J and two natural isolates, Halobacteriovorax strains JA-1 and JA-3, with clear correlation when densities were between 107 and 109 PFU/ml. Resazurin was also used to evaluate how B. bacteriovorus HD100 and Halobacteriovorax strain JA-1 respond to harmful conditions, i.e., exposure to sodium dodecyl sulfate (SDS), with both the dF/dt and PFU/ml indicating Halobacteriovorax strain JA-1 is more sensitive to this surfactant. Tests were also performed using media of different osmolalities, with the dF/dt values matching the 24-h predatory activities reasonably well. Finally, this method was successfully applied in near real-time analyses of predator-prey dynamics and, when coupled with SDS, was capable of differentiating between the predatory and prey populations. All of these tests serve to prove this method is (i) very rapid, needing only 15 min from start to finish; (ii) very reliable with different predatory bacterial species; and (iii) very versatile as it can be easily adapted to measure predatory numbers and activities in a range of experiments. IMPORTANCEBdellovibrio and like organisms are predatory bacteria that are capable of attacking, killing, and consuming many bacterial pathogens, including multidrug-resistant strains. These qualities have led to them being labeled as "living antibiotics." Research work with these remarkable strains, however, has been hampered by long growth times needed to quantify the predatory populations through plaque assays, which typically take 4 days to develop. Here, we describe a fluorescence-based method using the conversion of resazurin (low fluorescence) to resorufin (high fluorescence) after it is reduced by the predators' NADH. Not only do we show that the fluorescence correlates strongly with the predatory concentration and that we can use it to evaluate if the predators are viable, but the entire procedure from start to finish takes only 15 min, drastically reducing the time researchers need to quantify the predatory numbers. Employing this technique will greatly advance research related to predatory bacteria and their potential applications.

Promotion and mechanisms of Bdellovibrio sp. Y38 on membrane fouling alleviation in membrane bioreactor.

Membrane fouling is a major bottleneck limiting the widespread application of membrane bioreactors (MBR). In this study, Bdellovibrio sp. Y38, an obligate bacteriophage bacterium of Bdellovibrio-and-like organisms (BALOs), was enriched into highly concentrated culture medium (106-107 PFU/mL), and daily dosed into the MBR to investigate its effects on membrane fouling mitigation. The strain Y38 prolonged the membrane fouling cycle from 73 days to 90 days, indicating its membrane fouling alleviation potentials. The concentration of BALOs was increased 625 times higher than the control group after the whole operation, resulting in the concentration of chemical oxygen demand and nucleic acids in the liquid phase of the MBR system being significantly increased by 169.8 ± 1.5% and 126.7 ± 2.2%, respectively. The biomass growth rate was reduced by 27.2 ± 0.7% from day 0 to day 54. These results indicated the predation potential of Bdellovibrio sp. Y38 on the microorganisms in the sludge. The improvement of homogenized sludge and filtration and settling performance by the strain Y38 alleviated the membrane fouling. Compared with the control group, the macromolecular proteins in SMP and EPS were partially declined, and the polysaccharide in EPS decreased by 14.0 ± 3.9%, and the ratios of protein content to polysaccharide content (PN/PS) in SMP and EPS significantly increased by 35.6 ± 16.8% and 57.8 ± 6.1% at the middle stage, respectively, indicating the strain Y38 could alleviate membrane fouling by reducing and modifying SMP and EPS. Furthermore, the relative abundance of γ-proteobacteria decreased from 13.2% to 5.1% at the pre-middle stage, and Planctomycetes decreased from 1.5% to 0.8% at the end-stage, which were probably responsible for the membrane fouling mitigation. In addition, the strain Y38 had few impacts on the water treatment performance of MBR. There findings provide a promising strategy for in situ membrane pollution mitigation via exogenous additions of BALOs.

Strain-specific predation of Bdellovibrio bacteriovorus on Pseudomonas aeruginosa with a higher range for cystic fibrosis than for bacteremia isolates.

This work aimed to evaluate the predatory activity of Bdellovibrio bacteriovorus 109J on clinical isolates of Pseudomonas aeruginosa selected from well-characterized collections of cystic fibrosis (CF) lung colonization (n = 30) and bloodstream infections (BSI) (n = 48) including strains selected by genetic lineage (frequent and rare sequence types), antibiotic resistance phenotype (susceptible and multidrug-resistant isolates), and colony phenotype (mucoid and non-mucoid isolates). The intraspecies predation range (I-PR) was defined as the proportion of susceptible strains within the entire collection. In contrast, the predation efficiency (PE) is the ratio of viable prey cells remaining after predation compared to the initial inoculum. I-PR was significantly higher for CF (67%) than for BSI P. aeruginosa isolates (35%) probably related to an environmental origin of CF strains whereas invasive strains are more adapted to humans. I-PR correlation with bacterial features such as mucoid morphotype, genetic background, or antibiotic susceptibility profile was not detected. To test the possibility of increasing I-PR of BSI isolates, a polyhydroxyalkanoate depolymerase deficient B. bacteriovorus bd2637 mutant was used. Global median I-PR and PE values remained constant for both predators, but 31.2% of 109J-resistant isolates were susceptible to the mutant, and 22.9% of 109J-susceptible isolates showed resistance to predation by the mutant, pointing to a predator-prey specificity process. The potential use of predators in the clinical setting should be based on the determination of the I-PR for each species, and the PE of each particular target strain.