Bdellovibrio And Like Organisms Research Articles

Sludge biolysis pretreatment to reduce antibiotic resistance genes (ARGs): Insight into the relationship between potential ARGs hosts and BALOs' preferred prey

As an important reservoir of antibiotic resistance genes (ARGs), the sludge discharged from wastewater treatment plants is the key intermediate for ARG transport into the environment. Bdellovibrio-and-like organisms (BALOs) are predatory bacteria that are expected to attack antibiotic-resistant bacteria (ARB). In this study, the screened BALOs (C3 & D15) were mixed with the sludge for biolysis to achieve the satisfying removal efficiencies of six tet genes, two sul genes, and one mobile genetic element (intl 1). Among them, tet(Q) demonstrated the highest reduction rate in relative abundance at 87.3 ± 1.0 %, while tet(X) displayed the lowest of 11.7 ± 0.2 %. The microorganisms, including Longilinea, Methanobacterium, Acetobacterium, Sulfurimonas, allobaculum, Gaiella, AAP99, Ellin6067, Rhodoferax, Ferruginibacter and Thermomonas, were expected to play a dual role in the reduction of ARGs by serving as ARB and BALOs’ preferred prey. Meanwhile, BALOs consortium improved ARGs reduction efficiency via the expansion of the prey profile. Additionally, BALOs decreased the relative abundance of not only pathogens (Shinella, Rickettsia, Burkholderia, Acinetobacter, Aeromonas, Clostridium, Klebsiella and Pseudomonas), but also the ARGs' host pathogens (Mycobacterium, Plesiocystis, Burkholderia, and Bacteroides). Therefore, the application of BALOs for sludge biolysis are promising to decrease the sludge's public health risks via limiting the spread of ARGs and pathogens into the environment.

Predatory Bdellovibrio-and-like organism mixtures on efficient MBR in-situ membrane fouling diminishment and mechanisms

ABSTRACT Membrane fouling is a major hindrance that restricts the application of membrane bioreactors (MBRs). Bdellovibrio-and-like organisms (BALOs), as obligatory parasitic bacteria, prey upon various bacteria. In this study, the BALO mixtures were screened and found more effective in membrane fouling mitigation compared to the single BALO species and extended the membrane filtration period by as long as 33.3%. The higher BALO diversity reduced the potential foulants generation in the activated sludge by decreasing the sludge viscosity as high as 13.8 ± 0.6% than the pure culture of BALO. Meanwhile, the mixed BALOs demonstrated superior biofilm predation capabilities, with the content of soluble microbial products and extracellular polymeric substances on the biofilm decreasing by 26.1 ± 0.5% and 38.3 ± 0.2% as the most compared to the single BALO species involved system. Additionally, the BALO mixtures expanded the single strains’ host lysis spectrum of both the activated sludge and biofilm. The abundance of membrane-fouling-related bacteria such as Flavobacterium, Rhodobacter, and Labilithrix and pioneer bacteria such as Sphingorhabdus and Pseudomonas was significantly reduced. In summary, this study disclosed the significantly better membrane fouling mitigation effects of the BALOs with higher diversity, suggesting that the expansion of the host range is crucial for the further application of BALOs to enhance the anti-fouling performance of the MBR system.

Effect of predatory bacterial mixtures on biolysis of waste activated sludge to improve dewatering performance

ABSTRACTThe generation of surplus sludge during biological wastewater treatment has become a prevalent issue, necessitating the development of a dewatering approach that is efficient, economically feasible, and ecologically sound. Bdellovibrio-and-like-organisms (BALOs) are obligatory parasitic bacteria that prey on an array of bacteria. In this study, different BALO strains were isolated and purified from waste activited sludge (WAS). Anti-predation host strains were applied to screen the BALO strains with different host-range to minimize the overlap of the biolysis prey spectrum. In addition, the BALO strains with different host preferences were mixed for sludge biolysis treatment efficiency comparison. The results indicated that the capillary suction time and the bound water content in the WAS treated with the mixed BALOs were significantly decreased by 25.9% ± 1.7% and 5.2% ± 1.2%, respectively, compared to those treated with the single BALO strain. The soluble chemical oxygen demand concentration in the mixed BALOs treated group was increased by 31.2% ± 0.7% than that treated with the single strain. The findings indicate that the mixed strains used in the treatment process resulted in a notable enhancement of both sludge dewatering performance and lysis degree. In addition, the abundance of Proteobacteria treated with the BALO mixtures decreased by 69.1% than the single strain treated one which demonstrated that the BALO mixture expanded the sludge host lysis spectrum. This study revealed the different effects of single and mixed strains on sludge community structure, suggesting that the BALO host-range expansion is crucial to further improve sludge dewatering performances.

Predatory Bacteria: A Novel Approach to Antibiotic Substitution

Antibiotics are an effective means of treating infectious bacterial diseases. However, the extensive use of antibiotics in the recent past has resulted in antibiotic-resistant bacteria which interfere with disease treatment and recovery. There is an urgent need for novel medicines to treat Gram-negative infections because there are not enough antibiotics in development to address projected and present demands. One novel approach to antibiotic alternatives is the use of living predatory bacteria which can naturally prey upon other Gram-negative bacteria. These predators are ubiquitous in a wide variety of manmade and natural environments and depending upon their feeding habits are classified as obligatory or facultative predators. All the obligate predators are classified under the umbrella terminology Bdellovibrio and like organisms (BALOs). Bdellovibrio bacteriovorus is by far the most studied BALOs and have long been recognized as a potential therapeutic, water clean-up, and biocontrol agent and source for discovering novel biotechnological tools for research. Antibiotics won’t be replaced by pills containing predatory microorganisms any time soon. However, understanding these bacteria could help us prepare for a time when many medications cannot treat infections that are multi-drug resistant. A paradigm change is necessary since it may appear counterintuitive to cure a bacterial infection by giving another bacterium. The burden of an infection on the host must be taken into account while evaluating the prospective implications of treating a Gram-negative bacterial infection with the administration of a live predatory bacterium.

Outer Membrane Porin F in E. coli Is Critical for Effective Predation by Bdellovibrio.

Bdellovibrio and like organisms (BALOs) are a unique bacterial group that live by predating on other bacteria, consuming them from within to grow and replicate before the progeny come out to complete the life cycle. The mechanisms by which these predators recognize their prey and differentiate them from nonprey bacteria, however, are still not clear. Through genetic knockout and complementation studies in different Escherichia coli strains, we found that Bdellovibrio bacteriovorus strain 109J recognizes outer membrane porin F (OmpF) on the E. coli surface and that the activity of the E. coli EnvZ-OmpR regulatory system significantly impacts predation kinetics. OmpF is not the only signal by which BALOs recognize their prey, however, as B. bacteriovorus could eventually predate on the E. coli ΔompF mutant after prolonged incubation. Furthermore, recognizing OmpF as a prey surface structure was dependent on the prey strain, as knocking out OmpF protein homologues in other prey species, including Escherichia fergusonii, Klebsiella pneumoniae, and Salmonella enterica, did not always reduce the predation rate. Consequently, although OmpF was found to be an important surface component used by Bdellovibrio to efficiently recognize and attack E. coli, future work is needed to determine what other prey surface structures are recognized by these predators. IMPORTANCE Bdellovibrio bacteriovorus and like organisms (BALOs) are Gram-negative predatory bacteria that attack other Gram-negative bacteria by penetrating their periplasm and consuming them from within to obtain the nutrients necessary for the predator's growth and replication. How these predators recognize their prey, however, has remained a mystery. Here, we show that the outer membrane porin F (OmpF) in E. coli is recognized by B. bacteriovorus strain 109J and that the loss of this protein leads to severely delayed predation. However, predation of several other prey species was not dependent on the recognition of this protein or its homologues, indicating that there are other structures recognized by the predators on the prey surface that are yet to be discovered.

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.

A Comparative Study of the Dynamics and Diversity of Bdellovibrio and Like Organisms in Lakes Annecy and Geneva.

Bdellovibrio and like organisms (BALOs) are obligate bacterial predators of other Gram-negative bacteria. Here, we used quantitative PCR (qPCR) and recently developed specific primers which target the 16S rRNA gene to explore the abundance and distribution of three families of BALO belonging to the Oligoflexia class (i.e., Bdellovibrionaceae, Peredibacteraceae and Bacteriovoracaceae) over one year in the epilimnion and hypolimnion of Lakes Annecy and Geneva. Peredibacteraceae was the dominant group at all sampling points except at the bottom of Lake Geneva, where Bdellovibrionaceae was found in higher number. In addition, the abundance of BALOs increased significantly during the warmer months. Using high-throughput sequencing (Illumina Miseq), hundreds of OTUs were identified for Bdellovibrionaceae and Peredibacteraceae. Phylogenetic analysis suggests that Bdellovibrionaceae are more diverse than Peredibacteraceae and that some OTUs belong to new species of Bdellovibrionaceae. We also found that dominant OTUs were present simultaneously in the two lakes, while some others were specific to each lake, suggesting an adaptive pattern. Finally, both abundance and diversity of BALOs were poorly associated with abiotic factors except temperature, suggesting the importance of studying biotic relationships, assumed to play a greater role than physico-chemical variables in BALOs’ dynamics and distribution.

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-β1 (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.

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.

Ubiquitous and promising: new potential biocontrol BALOs (Bdellovibrio and like organisms) species, isolated from water and soil samples in Iran

Ubiquitous and promising: new potential biocontrol BALOs (Bdellovibrio and like organisms) species, isolated from water and soil samples in Iran

Predatory bacteria in the haemolymph of the cultured spiny lobster Panulirus ornatus.

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.

Interactions between Bdellovibrio and like organisms and bacteria in biofilms: beyond predator-prey dynamics.

Bdellovibrio and like organisms (BALOs) prey on Gram-negative bacteria in the planktonic phase as well as in biofilms, with the ability to reduce prey populations by orders of magnitude. During the last few years, evidence has mounted for a significant ecological role for BALOs, with important implications for our understanding of microbial community dynamics as well as for applications against pathogens, including drug-resistant pathogens, in medicine, agriculture and aquaculture, and in industrial settings for various uses. However, our understanding of biofilm predation by BALOs is still very fragmentary, including gaps in their effect on biofilm structure, on prey resistance, and on evolutionary outcomes of both predators and prey. Furthermore, their impact on biofilms has been shown to reach beyond predation, as they are reported to reduce biofilm structures of non-prey cells (including Gram-positive bacteria). Here, we review the available literature on BALOs in biofilms, extending known aspects to potential mechanisms employed by the predators to grow in biofilms. Within that context, we discuss the potential ecological significance and potential future utilization of the predatory and enzymatic possibilities offered by BALOs in medical, agricultural and environmental applications.

Short-Term Dynamics of Bdellovibrio and Like Organisms in Lake Geneva in Response to a Simulated Climatic Extreme Event.

The short time-scale dynamics of three families of Bdellovibrio and like organisms (i.e. Bdellovibrionaceae, Peredibacteraceae, and Bacteriovoracaceae) were studied on the surface waters of Lake Geneva in summer. Using mesocosms deployed nearshore in July 2019, we simulated an extreme climatic event (an input of carbon from the watershed in response to runoff from the catchment, light reduction, and mixing in response to stormy conditions) and aimed to study the impact of both abiotic and biotic factors on their dynamics. The three families of Bdellovibrio and like organisms (BALOs) showed different dynamics during the experiment. Peredibacteraceae was the most abundant group, whereas Bacteriovoracaceae was the least abundant. Compared with the other two families, the abundance of Bdellovibrionaceae did not fluctuate, remaining relatively stable over time. Environmental variables only partially explained the dynamics of these families; in particular, temperature, pH, and chloride concentrations were positively correlated with Bacteriovoracaceae, Bdellovibrionaceae, and Peredibacteraceae abundance, respectively. Prokaryote-like particles (PLPs), such as those with high DNA content (HDNA), were strongly and positively correlated with Peredibacteraceae and Bacteriovoracaceae. In contrast, no relationships were found between Bdellovibrionaceae and PLP abundance, nor between the virus-like particles (VLPs) and the different BALOs. Overall, the experiment revealed that predation was stable in the face of the simulated climatic events. In addition, we observed that Peredibacteraceae and Bacteriovoracaceae share common traits, while Bdellovibrionaceae seems to constitute a distinct category.

Community and single cell analyses reveal complex predatory interactions between bacteria in high diversity systems

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.

Secretion systems play a critical role in resistance to predation by Bdellovibrio bacteriovorus

Bdellovibrio bacteriovorus, a Gram-negative predatory bacterium belonging to the Bdellovibrio and like organisms (BALOs), predates on Gram-negative bacteria. BALO strains differ in prey range but so far, the genetic basis of resistance against BALO predation is hardly understood. We developed a loss-of-function approach to screen for sensitive mutants in a library of strain M6, a predation-resistant strain of the plant pathogen Acidovorax citrulli. The screen is based on tracking the growth of a B. bacteriovorus strain expressing the fluorescent reporter Tdtomato in mutant pools to reveal predation-sensitive variants. Two independent loci were identified in mutant strains exhibiting significant levels of susceptibility to the predator. Genes in the two loci were analysed using both protein sequence homology and protein structure modeling. Both were secretion-related proteins and thus associated to the bacterial cell wall. Successful complementation of gspK, a gene encoding for a minor pseudopilin protein confirmed the involvement of the type II secretion system in A. citrulli M6 resistance. This proof of concept study shows that our approach can identify key elements of the BALO-prey interaction, and it validates the hypothesis that mutational changes in a single gene can drastically impact prey resistance to BALO predation.

Gut interkingdom predator-prey interactions are key determinants of shrimp health

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.

In vivo predation and modification of the Mediterranean fruit fly Ceratitis capitata (Wiedemann) gut microbiome by the bacterial predator Bdellovibrio bacteriovorus.

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. 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. The bacterial predator of bacteria B. bacteriovorus can prey and survive invivo in the medfly gut. This study establishes the potential of BALOs to affect the microbiome of insect hosts.

Characterization of the first highly predatory Bdellovibrio bacteriovorus from Iran and its potential lytic activity against principal pathogenic Enterobacteriaceae.

Objective(s): Bdellovibrio-and-like organisms (BALOs) are predatory prokaryotes that attack and kill other Gram-negative bacteria for growth and reproduction. This study describes the isolation, identification, biological properties, and bacteriolytic activity of the first Bdellovibrio bacteriovorus with a broad prey range from Iran.Materials and Methods:One BALO strain with high predatory potency was isolated from the rhizosphere soil using Enteropathogenic Escherichia coli as prey. It was identified and designated as Bdellovibrio bacteriovorus strain SOIR-1 through plaque assays, transmission electron microscopy (TEM), Bdellovibrio-specific PCRs, and 16S rRNA gene sequence analysis. Biological characterization and analysis of bacteriolytic activity were also performed.Results:TEM and Bdellovibrio-specific PCRs confirmed that the strain SOIR-1 belongs to the genus Bdellovibrio. Analysis of the 16S rRNA gene sequence revealed its close phylogenetic relationship with strains of Bdellovibrio bacteriovorus. The strain SOIR-1 grew within the temperature range of 25–37 °C and the pH range of 6.0–8.0, with the optimal predatory activity at 30 °C and pH 7.4. It had the highest and lowest bacteriolytic activity toward Shigella dysenteriae and Pseudomonas aeruginosa with a killing rate of 89.66% and 74.83%, respectively. Conclusion:Considering the hypothesis of bdellovibrios heterogeneity, identification of new isolates contributes to a deeper understanding of their diversity, their ecological roles, and their promising potential as living antibiotics or biocontrol agents. Bdellovibrios with broad bacteriolytic nature has not previously been reported in sufficient detail from Iran. The results of this study showed the great potential of native B. bacteriovorus strain SOIR-1 in the control and treatment of diseases caused by pathogenic Enterobacteriaceae.

The species evenness of “prey” bacteria correlated with Bdellovibrio-and-like-organisms (BALOs) in the microbial network supports the biomass of BALOs in a paddy soil

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.

New 16S rRNA primers to uncover Bdellovibrio and like organisms diversity and abundance

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).