Bdellovibrio and like organisms: current understanding and knowledge gaps of the smallest cellular hunters of the microbial world.

Almost sixty years ago, Bdellovibrio and like organisms (BALOs) were discovered as the first obligate bacterial predators of other bacteria known to science. Since then, they were shown to be diverse and ubiquitous in the environment, and to bear astonishing ecological, physiological, and metabolic capabilities. The last decade has seen important strides made in understanding the mechanistic basis of their life cycle, the dynamics of their interactions with prey, along with significant developments towards their use in medicine, agriculture, and industry. This review details these achievements, identify current understanding and knowledge gaps to encourage and guide future BALO research.

Insights into Bdellovibrio spp. mechanisms of action and potential applications.

Recent studies investigating Bdellovibrio spp. have found that although this predator predominantly preys on Gram-negative organisms, under certain conditions (nutrient/prey limitation), it will adapt to survive and grow axenically (without prey) or in the presence of Gram-positive bacterial prey. These advances in the understanding of predatory bacteria have stimulated a renewed interest in these organisms and the potential applications of Bdellovibrio spp. to the benefit of society. Early studies primarily focused on the application of predatory bacteria as "live antibiotics" in the medical field, probiotics in aquaculture and veterinary medicine and their use in agriculture. Additionally, studies have investigated their prevalence in wastewater and environmental sources. However, comprehending that Bdellovibrio spp. may also prey on and target Gram-positive organisms, implies that these predators could specifically be applied for the bioremediation or removal of mixed bacterial communities. Recent studies have also indicated that Bdellovibrio spp. may be useful in controlling food spoilage organisms and subsequently decrease our reliance on food additives. This review will thus highlight recent developments in understanding Bdellovibrio spp. predation strategies and focus on potential new applications of these organisms for water treatment, food preservation, enhancement of industrial processes, and in combination therapies with bacteriophages and/or antibiotics to combat multi-drug resistant organisms.

From the Inside Out: an Epibiotic Bdellovibrio Predator with an Expanded Genomic Complement.

Bdellovibrio and like organisms are abundant environmental parasitoids of prokaryotes that show diverse predation strategies. The vast majority of studied Bdellovibrio bacteria and like organisms deploy intraperiplasmic replication inside the prey cell, while few isolates with smaller genomes consume their prey from the outside in an epibiotic manner. The novel parasitoid "Candidatus Bdellovibrio qaytius" was isolated from a eutrophic freshwater pond in British Columbia, where it was a continual part of the microbial community. "Ca Bdellovibrio qaytius" was found to preferentially prey on the betaproteobacterium Paraburkholderia fungorum without entering the periplasm. Despite its epibiotic replication strategy, "Ca Bdellovibrio" encodes a large genomic complement more similar to that of complex periplasmic predators. Functional genomic annotation further revealed several biosynthesis pathways not previously found in epibiotic predators, indicating that "Ca Bdellovibrio" represents an intermediate phenotype and at the same time narrowing down the genomic complement specific to epibiotic predators. In phylogenetic analysis, "Ca Bdellovibrio qaytius" occupies a widely distributed, but poorly characterized, basal cluster within the genus Bdellovibrio This suggests that epibiotic predation might be a common predation type in nature and that epibiotic predation could be the ancestral predation type in the genus.IMPORTANCEBdellovibrio and like organisms are bacteria that prey on other bacteria and are widespread in the environment. Most of the known Bdellovibrio species enter the space between the inner and outer prey membrane, where they consume their prey cells. However, one Bdellovibrio species has been described that consumes its prey from the outside. Here, we describe "Ca Bdellovibrio qaytius," a novel member of the genus Bdellovibrio that also remains outside the prey cell throughout its replication cycle. Unexpectedly, the genome of "Ca Bdellovibrio" is much more similar to the genomes of intracellular predators than to the species with a similar life cycle. Since "Ca Bdellovibrio" is also a basal representative of this genus, we hypothesize that extracellular predation could be the ancestral predation strategy.

Community assembly of the native C. elegans microbiome is influenced by time, substrate and individual bacterial taxa.

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.

Potential Control of Potato Soft Rot Disease by the Obligate Predators Bdellovibrio and Like Organisms.

Bacterial soft rot diseases caused by Pectobacterium spp. and Dickeya spp. affect a wide range of crops, including potatoes, a major food crop. As of today, farmers mostly rely on sanitary practices, water management, and plant nutrition for control. We tested the bacterial predators Bdellovibrio and like organisms (BALOs) to control potato soft rot. BALOs are small, motile predatory bacteria found in terrestrial and aquatic environments. They prey on a wide range of Gram-negative bacteria, including animal and plant pathogens. To this end, BALO strains HD100, 109J, and a ΔmerRNA derivative of HD100 were shown to efficiently prey on various rot-causing strains of Pectobacterium and Dickeya solani BALO control of maceration caused by a highly virulent strain of Pectobacterium carotovorum subsp. brasilense was then tested in situ using a potato slice assay. All BALO strains were highly effective at reducing disease, up to complete prevention. Effectivity was concentration dependent, and BALOs applied before P. carotovorum subsp. brasilense inoculation performed significantly better than those applied after the disease-causing agent, maybe due to in situ consumption of glucose by the prey, as glucose metabolism by live prey bacteria was shown to prevent predation. Dead predators and the supernatant of BALO cultures did not significantly prevent maceration, indicating that predation was the major mechanism for the prevention of the disease. Finally, plastic resistance to predation was affected by prey and predator population parameters, suggesting that population dynamics affect prey response to predation.IMPORTANCE Bacterial soft rot diseases caused by Pectobacterium spp. and Dickeya spp. are among the most important plant diseases caused by bacteria. Among other crops, they inflict large-scale damage to potatoes. As of today, farmers have few options to control them. The bacteria Bdellovibrio and like organisms (BALOs) are obligate predators of bacteria. We tested their potential to prey on Pectobacterium spp. and Dickeya spp. and to protect potato. We show that different BALOs can prey on soft rot-causing bacteria and prevent their growth in situ, precluding tissue maceration. Dead predators and the supernatant of BALO cultures did not significantly prevent maceration, showing that the effect is due to predation. Soft rot control by the predators was concentration dependent and was higher when the predator was inoculated ahead of the prey. As residual prey remained, we investigated what determines their level and found that initial prey and predator population parameters affect prey response to predation.

Bdellovibrio and Like Organisms Are Predictors of Microbiome Diversity in Distinct Host Groups.

Biodiversity is generally believed to be a main determinant of ecosystem functioning. This principle also applies to the microbiome and could consequently contribute to host health. According to ecological theory, communities are shaped by top predators whose direct and indirect interactions with community members cause stability and diversity. Bdellovibrio and like organisms (BALOs) are a neglected group of predatory bacteria that feed on Gram-negative bacteria and can thereby influence microbiome composition. We asked whether BALOs can predict biodiversity levels in microbiomes from distinct host groups and environments. We demonstrate that genetic signatures of BALOs are commonly found within the 16S rRNA reads from diverse host taxa. In many cases, their presence, abundance, and especially richness are positively correlated with overall microbiome diversity. Our findings suggest that BALOs can act as drivers of microbial alpha-diversity and should therefore be considered candidates for the restoration of microbiomes and the prevention of dysbiosis.

Effects of Acanthamoeba castellanii on the dissolved oxygen and the microbial community under the experimental aquatic model.

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.

Bacterial predation under changing viscosities.

Bdellovibrio and like organisms (BALOs) are largely distributed in soils and in water bodies obligate predators of gram-negative bacteria that can affect bacterial communities. Potential applications of BALOs include biomass reduction, their use against pathogenic bacteria in agriculture, and in medicine as an alternative against antibiotic-resistant pathogens. Such different environments and uses mean that BALOs should be active under a range of viscosities. In this study, the predatory behaviour of two strains of the periplasmic predator B. bacteriovorus and of the epibiotic predator Micavibrio aeruginosavorus was examined in viscous polyvinylpyrrolidone (PVP) solutions at 28 and at 37°C, using fluorescent markers and plate counts to track predator growth and prey decay. We found that at high viscosities, although swimming speed was largely decreased, the three predators reduced prey to levels similar to those of non-viscous suspensions, albeit with short delays. Prey motility and clumping did not affect the outcome. Strikingly, under low initial predator concentrations, predation dynamics were faster with increasing viscosity, an effect that dissipated with increasing predator concentrations. Changes in swimming patterns and in futile predator-predator encounters with viscosity, as revealed by path analysis under changing viscosities, along with possible PVP-mediated crowding effects, may explain the observed phenomena.

Variation in genome content and predatory phenotypes between Bdellovibrio sp. NC01 isolated from soil and B. bacteriovorus type strain HD100.

Defining phenotypic and associated genotypic variation among Bdellovibrio may further our understanding of how this genus attacks and kills different Gram-negative bacteria. We isolated Bdellovibrio sp. NC01 from soil. Analysis of 16S rRNA gene sequences and average amino acid identity showed that NC01 belongs to a different species than the type species bacteriovorus. By clustering amino acid sequences from completely sequenced Bdellovibrio and comparing the resulting orthologue groups to a previously published analysis, we defined a 'core genome' of 778 protein-coding genes and identified four protein-coding genes that appeared to be missing only in NC01. To determine how horizontal gene transfer (HGT) may have impacted NC01 genome evolution, we performed genome-wide comparisons of Bdellovibrio nucleotide sequences, which indicated that eight NC01 genomic regions were likely acquired by HGT. To investigate how genome variation may impact predation, we compared protein-coding gene content between NC01 and the B. bacteriovorus type strain HD100, focusing on genes implicated as important in successful killing of prey. Of these, NC01 is missing ten genes that may play roles in lytic activity during predation. Compared to HD100, NC01 kills fewer tested prey strains and kills Escherichia coli ML35 less efficiently. NC01 causes a smaller log reduction in ML35, after which the prey population recovers and the NC01 population decreases. In addition, NC01 forms turbid plaques on lawns of E. coli ML35, in contrast to clear plaques formed by HD100. Linking phenotypic variation in interactions between Bdellovibrio and Gram-negative bacteria with underlying Bdellovibrio genome variation is valuable for understanding the ecological significance of predatory bacteria and evaluating their effectiveness in clinical applications.

Increasing the autotrophic growth of Chlorella USTB-01 via the control of bacterial contamination by Bdellovibrio USTB-06.

AIMS: (i) To obtain and identify the predatory bacteria for the control of contaminated bacteria and to promote the autotrophic growth of Chlorella USTB-01. (ii) To identify and measure the different cell numbers in microalgal culture using flow cytometer. METHODS AND RESULTS: A predatory bacterial strain was isolated using Escherichia coli BL21 as a sole prey host, which was identified as Bdellovibrio USTB-06 by the analysis of 16S rDNA sequence. A flow cytometer was successfully used to identify and measure the cell numbers of Chlorella USTB-01, the contaminated bacteria and Bdellovibrio USTB-06 simultaneously in the autotrophic culture of Chlorella USTB-01 according to the identification of the different cell sizes. With the addition of Bdellovibrio USTB-06 at initial 104 plaque-forming units per ml, the contaminated bacteria severely decreased by about five counts (in log10  CFU per ml) and the growth of Chlorella USTB-01 was greatly increased by 37·0% compared with those of control respectively. CONCLUSIONS: Bdellovibrio USTB-06 could effectively promote the growth of Chlorella USTB-01 via the killing of the contaminated bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: Our study reveals a good biotechnology method to increase the growth of Chlorella USTB-01 which is very important in the industry of microalgal culture.

Bacterial Therapy and Mitochondrial Therapy.

Current methods for treatment of cellular and organ pathologies are extremely diverse and constantly evolving, going beyond the use of drugs, based on chemical interaction with biological targets to normalize the functions of the system. Because pharmacological approaches are often untenable, recent strategies in the therapy of different pathological conditions are of particular interest through introducing into the organism of some living system or its components, in particular, bacteria or isolated subcellular structures such as mitochondria. This review describes the most interesting and original examples of therapy using bacteria and mitochondria, which in perspective can dramatically change our views on the principles for the treatment of many diseases. Thus, we analyze such therapeutic effects from the perspective of the similarities between mitochondria and bacteria as the evolutionary ancestors of mitochondria.

Isolation of Bdellovibrio and like organisms and potential to reduce acute hepatopancreatic necrosis disease caused by Vibrio parahaemolyticus.

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.

An Extended Cyclic Di-GMP Network in the Predatory Bacterium Bdellovibrio bacteriovorus.

UNLABELLED: Over the course of the last 3 decades the role of the second messenger cyclic di-GMP (c-di-GMP) as a master regulator of bacterial physiology was determined. Although the control over c-di-GMP levels via synthesis and breakdown and the allosteric regulation of c-di-GMP over receptor proteins (effectors) and riboswitches have been extensively studied, relatively few effectors have been identified and most are of unknown functions. The obligate predatory bacterium Bdellovibrio bacteriovorus has a peculiar dimorphic life cycle, in which a phenotypic transition from a free-living attack phase (AP) to a sessile, intracellular predatory growth phase (GP) is tightly regulated by specific c-di-GMP diguanylate cyclases. B. bacteriovorus also bears one of the largest complement of defined effectors, almost none of known functions, suggesting that additional proteins may be involved in c-di-GMP signaling. In order to uncover novel c-di-GMP effectors, a c-di-GMP capture-compound mass-spectroscopy experiment was performed on wild-type AP and host-independent (HI) mutant cultures, the latter serving as a proxy for wild-type GP cells. Eighty-four proteins were identified as candidate c-di-GMP binders. Of these proteins, 65 did not include any recognized c-di-GMP binding site, and 3 carried known unorthodox binding sites. Putative functions could be assigned to 59 proteins. These proteins are included in metabolic pathways, regulatory circuits, cell transport, and motility, thereby creating a potentially large c-di-GMP network. False candidate effectors may include members of protein complexes, as well as proteins binding nucleotides or other cofactors that were, respectively, carried over or unspecifically interacted with the capture compound during the pulldown. Of the 84 candidates, 62 were found to specifically bind the c-di-GMP capture compound in AP or in HI cultures, suggesting c-di-GMP control over the whole-cell cycle of the bacterium. High affinity and specificity to c-di-GMP binding were confirmed using microscale thermophoresis with a hypothetical protein bearing a PilZ domain, an acyl coenzyme A dehydrogenase, and a two-component system response regulator, indicating that additional c-di-GMP binding candidates may be bona fide novel effectors. IMPORTANCE: In this study, 84 putative c-di-GMP binding proteins were identified in B. bacteriovorus, an obligate predatory bacterium whose lifestyle and reproduction are dependent on c-di-GMP signaling, using a c-di-GMP capture compound precipitation approach. This predicted complement covers metabolic, energy, transport, motility and regulatory pathways, and most of it is phase specific, i.e., 62 candidates bind the capture compound at defined modes of B. bacteriovorus lifestyle. Three of the putative binders further demonstrated specificity and high affinity to c-di-GMP via microscale thermophoresis, lending support for the presence of additional bona fide c-di-GMP effectors among the pulled-down protein repertoire.

Bacterial predator-prey dynamics in microscale patchy landscapes.

Soil is a microenvironment with a fragmented (patchy) spatial structure in which many bacterial species interact. Here, we explore the interaction between the predatory bacterium Bdellovibrio bacteriovorus and its prey Escherichia coli in microfabricated landscapes. We ask how fragmentation influences the prey dynamics at the microscale and compare two landscape geometries: a patchy landscape and a continuous landscape. By following the dynamics of prey populations with high spatial and temporal resolution for many generations, we found that the variation in predation rates was twice as large in the patchy landscape and the dynamics was correlated over shorter length scales. We also found that while the prey population in the continuous landscape was almost entirely driven to extinction, a significant part of the prey population in the fragmented landscape persisted over time. We observed significant surface-associated growth, especially in the fragmented landscape and we surmise that this sub-population is more resistant to predation. Our results thus show that microscale fragmentation can significantly influence bacterial interactions.

Effect of Bdellovibrio bacteriovorus HD100 on multispecies oral communities.

The predation of Bdellovibrio bacteriovorus on different periodontal pathogens has already been described. However, it is necessary to consider the polymicrobial nature of periodontal disease. The current study explores the predation of Bdellovibrio on oral pathogens organized in multispecies communities. The effect of the predator was evaluated on in vitro six species communities with microbial culturing. Additionally, the effect on ex vivo subgingival plaque and saliva samples from periodontitis patients was assessed. In the latter experiment results were examined with microbial culturing, quantitative polymerase chain reaction (qPCR) and denaturing gradient gel electrophoresis (DGGE). The latter technique was used to get an overview of the whole mixed microbial population. Results showed that even in more complex models, B. bacteriovorus was still able to predate on Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans. However predation on Prevotella intermedia and Porphyromonas gingivalis could not be validated in multispecies models. The effect of Bdellovibrio was not restricted to the target bacteria. Changes in the overall ecology of the different models were evident. It could be concluded that the efficiency of predation decreased when complexity of the models increased. However, B. bacteriovorus was able to attack two important oral pathogens, F. nucleatum, and A. actinomycetemcomitans, even when present in ex vivo clinical samples. These effects still have to be validated in in vivo models to see the impact of Bdellovibrio on the whole bacterial ecology.

Bdellovibrio and like organisms enhanced growth and survival of Penaeus monodon and altered bacterial community structures in its rearing water.

In this study, a 96-h laboratory reduction test was conducted with strain BDHSH06 (GenBank accession no. EF011103) as the test strain for Bdellovibrio and like organisms (BALOs) and 20 susceptible marine bacterial strains forming microcosms as the targets. The results showed that BDHSH06 reduced the levels of approximately 50% of prey bacterial strains within 96 h in the seawater microcosms. An 85-day black tiger shrimp (Penaeus monodon) rearing experiment was performed. The shrimp survival rate, body length, and weight in the test tanks were 48.1% ± 1.2%, 99.8 ± 10.0 mm, and 6.36 ± 1.50 g, respectively, which were values significantly (P < 0.05) higher than those for the control, viz., 31.0% ± 2.1%, 86.0 ± 11.1 mm, and 4.21 ± 1.56 g, respectively. With the addition of BDHSH06, total bacterial and Vibrio numbers were significantly reduced (P < 0.05) by 1.3 to 4.5 log CFU · ml(-1) and CFU · g(-1) in both water and shrimp intestines, respectively, compared to those in the control. The effect of BDHSH06 on bacterial community structures in the rearing water was also examined using PCR amplification of the 16S rRNA gene and denaturing gradient gel electrophoresis (DGGE). The DGGE profiles of rearing water samples from the control and test tanks revealed that the amounts of 44% of the bacterial species were reduced when BDHSH06 was added to the rearing water over the 85-day rearing period, and among these, approximately 57.1% were nonculturable. The results of this study demonstrated that BDHSH06 can be used as a biocontrol/probiotic agent in P. monodon culture.

Bdellovibrio bacteriovorus HD100 guards against Pseudomonas tolaasii brown-blotch lesions on the surface of post-harvest Agaricus bisporus supermarket mushrooms.

BACKGROUND: Pseudomonas tolaasii is a problematic pathogen of cultured mushrooms, forming dark brown 'blotches' on mushroom surfaces and causing spoilage during crop growth and post-harvest . Treating P. tolaasii infection is difficult, as other, commensal bacterial species such as Pseudomonas putida are necessary for mushroom growth, so treatments must be relatively specific. RESULTS: We have found that P. tolaasii is susceptible to predation in vitro by the δ-proteobacterium Bdellovibrio bacteriovorus. This effect also occurred in funga, where B. bacteriovorus was administered to post-harvest mushroom caps before and after administration of the P. tolaasii pathogen. A significant, visible improvement in blotch appearance, after incubation, was observed on administration of Bdellovibrio. A significant reduction in viable P. tolaasii cell numbers, recovered from the mushroom tissue, was detected. This was accompanied by a more marked reduction in blotch severity on Bdellovibrio administration. We found that there was in some cases an accompanying overgrowth of presumed-commensal, non-Pseudomonas bacteria on post-harvest mushroom caps after Bdellovibrio-treatment. These bacteria were identified (by 16SrRNA gene sequencing) as Enterobacter species, which were seemingly resistant to predation. We visualised predatory interactions occuring between B. bacteriovorus and P. tolaasii on the post-harvest mushroom cap surface by Scanning Electron Microscopy, seeing predatory invasion of P. tolaasii by B. bacteriovorus in funga. This anti-P. tolaasii effect worked well in post-harvest supermarket mushrooms, thus Bdellovibrio was not affected by any pre-treatment of mushrooms for commercial/consumer purposes. CONCLUSIONS: The soil-dwelling B. bacteriovorus HD100 preys upon and kills P. tolaasii, on mushroom surfaces, and could therefore be applied to prevent spoilage in post-harvest situations where mushrooms are stored and packaged for sale.

Predatory lifestyle of Bdellovibrio bacteriovorus.

Bdellovibrio species are naturally predatory, small, motile, Deltaproteobacteria that invade the periplasm of other larger gram-negative bacteria, killing and digesting them. Bdellovibrio grows and divides inside the prey cell, in a structure called a bdelloplast, which then lyses, releasing the Bdellovibrio to prey upon more bacteria. This capability makes Bdellovibrio a potential therapeutic agent, but since its discovery in the 1960s it has not been applied in this way. This review considers what is known postgenomically about Bdellovibrio and its predatory lifestyle, drawing also from what was learned by the excellent microbial physiology work of the early Bdellovibrio researchers. Recent work on the diversity and evolution of predatory bdellovibrios, the role of surface structures in predation, and the ongoing questions about how Bdellovibrio switches between axenic and predatory growth and how its predatory activities may be tempered in the wild, as well as suggestions for future research priorities, are discussed.

Shedding light on microbial predator-prey population dynamics using a quantitative bioluminescence assay.

This study assessed the dynamics of predation by Bdellovibrio bacteriovorus HD 100. Predation tests with two different bioluminescent strains of Escherichia coli, one expressing a heat-labile bacterial luciferase and the other a heat-stable form, showed near identical losses from both, indicating that protein expression and stability are not responsible for the "shutting-off" of the prey bioluminescence (BL). Furthermore, it was found that the loss in the prey BL was not proportional with the predator-to-prey ratio (PPR), with significantly greater losses seen as this value was increased. This suggests that other factors also play a role in lowering the prey BL. The loss in BL, however, was very consistent within nine independent experiments to the point that we were able to reliably estimate the predator numbers within only 1 h when present at a PPR of 6 or higher, Using a fluorescent prey, we found that premature lysis of the prey occurs at a significant level and was more prominent as the PPR ratio increased. Based upon the supernatant fluorescent signal, even a relatively low PPR of 10-20 led to approximately 5% of the prey population being prematurely lysed within 1 h, while a PPR of 90 led to nearly 15% lysis. Consequently, we developed a modified Lotka-Volterra predator-prey model that accounted for this lysis and is able to reliably estimate the prey and bdelloplast populations for a wide range of PPRs.