Biotechnological Potential of Bdellovibrio and Like Organisms and Their Secreted Enzymes

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.

Investigation of the marine bacterial community along the coastline of the Gulf of Thailand

The Gulf of Thailand provides many services to the Thai population, and human activities may influence the diversity of microorganisms in the seawater. Information of the microorganisms' profile which inhabit the coastline can be used to monitor the water quality. This study aimed to investigate the bacterial community in the waters along the coastline provinces, including Rayong, Chonburi, Prachuap Kiri Khan, and Nakhon Sri Thammarat. Seawater samples were collected at each site, and the conductivity, pH, salinity, temperature, and turbidity were measured. The samples were subjected to whole DNA extraction, 16S rRNA amplification, next-generation sequencing, and statistical analysis to identify the bacterial diversity and analyse the effects of water parameters on the bacterial community. The dominant bacterial phyla found were Proteobacteria, Bacteroidota, and Cyanobacteria. Spearman rank correlation analysis revealed a high correlation of Pseudoalteromonas, the NS5 marine group, Lachnospiraceae, Marinobacterium, Mariviven, and Vibrio with the seawater parameters. The predatory bacteria Peredibacter and Halobacteriovorax were reported among these bacterial communities for the first time in the Gulf of Thailand. Interestingly, Akkermansia, a novel candidate for next-generation probiotics to improve human health, was also found in the sample from Nakhon Sri Thammarat Province. Although the rich-ness and diversity of the bacterial communities differed among sampling sites, it is a possible source of many valuable bacteria for future use.

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.

Natronospira bacteriovora sp. nov., and Natronospira elongata sp. nov., extremely salt-tolerant predatory proteolytic bacteria from soda lakes and proposal to classify the genus Natronospira into Natronospiraceae fam. nov., and Natronospirales ord. nov., within the class Gammaproteobacteria

The genus Natronospira is represented by a single species of extremely salt-tolerant aerobic alkaliphilic proteolytic bacterium, isolated from hypersaline soda lakes. When cells of Gram-positive cocci were used as a substrate instead of proteins at extremely haloalkaline conditions, two new members of this genus were enriched and isolated in pure culture from the same sites. Strains AB-CW1 and AB-CW4 are obligate aerobic heterotrophic proteolytic bacteria able to feed on both live and dead cells of staphylococci and a range of proteins and peptides. Similar to the type species, N. proteinivora, the isolates are extremely salt-tolerant obligate alkaliphiles. However, N. proteinivora was unable to use bacterial cells as a substrate. Electron microscopy showed direct contact between the prey and predator cells. Functional analysis of the AB-CW1 and AB-CW4 genomes identified two sets of genes coding for extracellular enzymes potentially involved in the predation and proteolysis, respectively. The first set includes several copies of lysozyme-like GH23 peptidoglycan-lyase and murein-specific M23 [Zn]-di-peptidase enabling the cell wall degradation. The second set features multiple copies of secreted serine and metallopeptidases apparently allowing for the strong proteolytic phenotype. Phylogenomic analysis placed the isolates into the genus Natronospira as two novel species members, and furthermore indicated that this genus forms a deep-branching lineage of a new family (Natronospiraceae) and order (Natronospirales) within the class Gammaproteobacteria. On the basis of distinct phenotypic and genomic properties, strain AB-CW1T (JCM 335396 = UQM 41579) is proposed to be classified as Natronospira elongata sp. nov., and AB-CW4T (JCM 335397 = UQM 41580) as Natronospira bacteriovora sp. nov.

Elucidating potential bioindicators from insights in the diversity and assembly processes of prokaryotic and eukaryotic communities in the Mekong River

Drivers for spatio-temporal distribution patterns of overall planktonic prokaryotes and eukaryotes in riverine ecosystems are generally not fully understood. This study employed amplicon metabarcoding to investigate the distributions and assembly mechanisms of bacterial and eukaryotic communities in the Mekong River. The prevailing bacteria taxa were found to be Betaproteobacteria, Actinobacteria, and Bacteroidetes, while the dominant eukaryotic organisms were cryptophytes, chlorophytes, and diatoms. The community assemblages were influenced by a combination of stochastic and deterministic processes. Drift (DR) and dispersal limitation (DL), signifying the stochastic mechanism, were the main processes shaping the overall prokaryotic and eukaryotic communities. However, homogeneous selection (HoS), indicating deterministic mechanism, played a major role in the assembly process of core prokaryotic communities, especially in the wet season. In contrast, the core eukaryotic communities including Opisthokonta, Sar, and Chlorophyta were dominated by stochastic processes. The significance of HoS within prokaryotic communities was also found to exhibit a decreasing trend from the upstream sampling sites (Chiang Saen and Chiang Khan, Nong Khai) towards the downstream sites (Mukdahan, and Khong Chiam) of the Mekong River. The environmental gradients resulting from the site-specific variations and the gradual decrease in elevation along the river may have a potential influence on the role of HoS in community assembly. Crucial environmental factors that shape the phylogenetic structure within distinct bins of the core prokaryotic communities including water depth, temperature, chloride, sodium, and sulphate were identified, as inferred by their correlation with the beta Net Relatedness Index (betaNRI) during the wet season. Overall, these findings enhance understanding of the complex mechanisms governing the spatio-temporal dynamics of prokaryotic and eukaryotic communities in the Mekong River. Finally, insights gained from this study could provide information on further use of specific core bacteria as microbial-based bioindicators that are effective for the assessment and conservation of the Mekong River ecosystem.

Antibiotic Resistance: Do We Need Only Cutting-Edge Methods, or Can New Visions Such as One Health Be More Useful for Learning from Nature?

Antibiotic resistance is an increasing global problem for public health, and focusing on biofilms has provided further insights into resistance evolution in bacteria. Resistance is innate in many bacterial species, and many antibiotics are derived from natural molecules of soil microorganisms. Is it possible that nature can help control AMR diffusion? In this review, an analysis of resistance mechanisms is summarized, and an excursus of the different approaches to challenging resistance spread based on natural processes is presented as "lessons from Nature". On the "host side", immunotherapy strategies for bacterial infections have a long history before antibiotics, but continuous new inputs through biotechnology advances are enlarging their applications, efficacy, and safety. Antimicrobial peptides and monoclonal antibodies are considered for controlling antibiotic resistance. Understanding the biology of natural predators is providing new, effective, and safe ways to combat resistant bacteria. As natural enemies, bacteriophages were used to treat severe infections before the discovery of antibiotics, marginalized during the antibiotic era, and revitalized upon the diffusion of multi-resistance. Finally, sociopolitical aspects such as education, global action, and climate change are also considered as important tools for tackling antibiotic resistance from the One Health perspective.

Translating eco-evolutionary biology into therapy to tackle antibiotic resistance

Antibiotic resistance is currently one of the most important public health problems. The golden age of antibiotic discovery ended decades ago, and new approaches are urgently needed. Therefore, preserving the efficacy of the antibiotics currently in use and developing compounds and strategies that specifically target antibiotic-resistant pathogens is critical. The identification of robust trends of antibiotic resistance evolution and of its associated trade-offs, such as collateral sensitivity or fitness costs, is invaluable for the design of rational evolution-based, ecology-based treatment approaches. In this Review, we discuss these evolutionary trade-offs and how such knowledge can aid in informing combination or alternating antibiotic therapies against bacterial infections. In addition, we discuss how targeting bacterial metabolism can enhance drug activity and impair antibiotic resistance evolution. Finally, we explore how an improved understanding of the original physiological function of antibiotic resistance determinants, which have evolved to reach clinical resistance after a process of historical contingency, may help to tackle antibiotic resistance.

Predatory bacteria as potential biofilm control and eradication agents in the food industry

Biofilms are a major concern within the food industry since they have the potential to reduce productivity in situ (within the field), impact food stability and storage, and cause downstream food poisoning. Within this review, predatory bacteria as potential biofilm control and eradication agents are discussed, with a particular emphasis on the intraperiplasmic Bdellovibrio-and-like organism (BALO) grouping. After providing a brief overview of predatory bacteria and their activities, focus is given to how BALOs fulfill four attributes that are essential for biocontrol agents to be successful in the food industry: (1) Broad spectrum activity against pathogens, both plant and human; (2) Activity against biofilms; (3) Safety towards humans and animals; and (4) Compatibility with food. As predatory bacteria possess all of these characteristics, they represent a novel form of biofilm biocontrol that is ripe for use within the food industry.

On the emergence of eukaryotes and other enigmas

The origin of eukaryotes is one of the most fundamental problems in the entire history of life. How did eukaryotes arise? Previous attempts to solve the problem are very far from an answer, at best they propose a solution to one of the various innovations that ended up culminating in eukaryotes. Based on a hypothetical-deductive methodology, as usual in evolutionary issues, I propose that eukaryotes emerged from the endosymbiotic association between a flagellate parasite and its host, of which the sperm is the main vestige. The hypothesis unifies the solution to the vast array of acquisitions shared by eukaryotes that differentiate them from other beings, remarkably cell nucleus, mitosis, meiosis and sexual reproduction. The solution has a deep impact on understanding the origin and functioning of all complex life forms.

Resistance, Tolerance, Virulence and Bacterial Pathogen Fitness-Current State and Envisioned Solutions for the Near Future

The current antibiotic crisis and the global phenomena of bacterial resistance, inherited and non-inherited, and tolerance-associated with biofilm formation-are prompting dire predictions of a post-antibiotic era in the near future. These predictions refer to increases in morbidity and mortality rates as a consequence of infections with multidrug-resistant or pandrug-resistant microbial strains. In this context, we aimed to highlight the current status of the antibiotic resistance phenomenon and the significance of bacterial virulence properties/fitness for human health and to review the main strategies alternative or complementary to antibiotic therapy, some of them being already clinically applied or in clinical trials, others only foreseen and in the research phase.

Advances in cellular and molecular predatory biology of Bdellovibrio bacteriovorus six decades after discovery

Since its discovery six decades ago, the predatory bacterium Bdellovibrio bacteriovorus has sparked recent interest as a potential remedy to the antibiotic resistance crisis. Here we give a comprehensive historical overview from discovery to progressive developments in microscopy and molecular mechanisms. Research on B. bacteriovorus has moved from curiosity to a new model organism, revealing over time more details on its physiology and fascinating predatory life cycle with the help of a variety of methods. Based on recent findings in cryo-electron tomography, we recapitulate on the intricate molecular details known in the predatory life cycle including how this predator searches for its prey bacterium, to how it attaches, grows, and divides all from within the prey cell. Finally, the newly developed B. bacteriovorus progeny leave the prey cell remnants in the exit phase. While we end with some unanswered questions remaining in the field, new imaging technologies and quantitative, systematic advances will likely help to unravel them in the next decades.

Bacterial defences: mechanisms, evolution and antimicrobial resistance

Throughout their evolutionary history, bacteria have faced diverse threats from other microorganisms, including competing bacteria, bacteriophages and predators. In response to these threats, they have evolved sophisticated defence mechanisms that today also protect bacteria against antibiotics and other therapies. In this Review, we explore the protective strategies of bacteria, including the mechanisms, evolution and clinical implications of these ancient defences. We also review the countermeasures that attackers have evolved to overcome bacterial defences. We argue that understanding how bacteria defend themselves in nature is important for the development of new therapies and for minimizing resistance evolution.

Expanding therapeutic potential of Bdellovibrio bacteriovorus against multidrug-resistant pathogens

Novel treatments toward Gram-negative bacteria are urgently needed to prevent even higher mortality levels associated with resistant bacterial infections. Predatory bacteria have been studied as a new type of treatment against pathogenic bacteria, including resistant species. However, because of limitations related to eradication efficacy, combination therapy using predatory bacteria with other agents has also been tested. Here, we discuss recent advances in the use of predatory bacteria to treat infections and propose novel combinatory strategies with antivirulence compounds. Teaser: The increasing number of resistant bacteria requires the implementation of new strategies to avoid mortality. Studies about predatory bacteria indicate a field to be explored in different ways that can lead to new treatment solutions.

Environmental predictors of electroactive bacterioplankton in small boreal lakes

Extracellular electron transfer (EET) by electroactive bacteria in anoxic soils and sediments is an intensively researched subject, but EET's function in planktonic ecology has been less considered. Following the discovery of an unexpectedly high prevalence of EET genes in a bog lake's bacterioplankton, we hypothesized that the redox capacities of dissolved organic matter (DOM) enrich for electroactive bacteria by mediating redox chemistry. We developed the bioinformatics pipeline FEET (Find EET) to identify and summarize predicted EET protein-encoding genes from metagenomics data. We then applied FEET to 36 bog and thermokarst lakes and correlated gene occurrence with environmental data to test our predictions. Our results provide indirect evidence that DOM may participate in bacterioplankton EET. We found a similarly high prevalence of genes encoding putative EET proteins in most of these lakes, where oxidative EET strongly correlated with DOM. Numerous novel clusters of multiheme cytochromes that may enable EET were identified. Taxa previously not considered EET-capable were found to carry EET genes. We propose that EET and DOM interactions are of ecologically important to bacterioplankton in small boreal lakes, and that EET, particularly by methylotrophs and anoxygenic phototrophs, should be further studied and incorporated into methane emission models of melting permafrost.

The potential of facultative predatory Actinomycetota spp. and prospects in agricultural sustainability

Actinomycetota in the phylum of bacteria has been explored extensively as a source of antibiotics and secondary metabolites. In addition to acting as plant growth-promoting agents, they also possess the potential to control various plant pathogens; however, there are limited studies that report the facultative predatory ability of Actinomycetota spp. Furthermore, the mechanisms that underline predation are poorly understood. We assessed the diversity of strategies employed by predatory bacteria to attack and subsequently induce the cell lysing of their prey. We revisited the diversity and abundance of secondary metabolite molecules linked to the different predation strategies by bacteria species. We analyzed the pros and cons of the distinctive predation mechanisms and explored their potential for the development of new biocontrol agents. The facultative predatory behaviors diverge from group attack "wolfpack," cell-to-cell proximity "epibiotic," periplasmic penetration, and endobiotic invasion to degrade host-cellular content. The epibiotic represents the dominant facultative mode of predation, irrespective of the habitat origins. The wolfpack is the second-used approach among the Actinomycetota harboring predatory traits. The secondary molecules as chemical weapons engaged in the respective attacks were reviewed. We finally explored the use of predatory Actinomycetota as a new cost-effective and sustainable biocontrol agent against plant pathogens.

Potential of Predatory Bacteria to Colonize the Duckweed Microbiome and Change Its Structure: A Model Study Using the Obligate Predatory Bacterium, Bacteriovorax sp. HI3

Modifying the duckweed microbiome is a major challenge for enhancing the effectiveness of duckweed-based wastewater treatment and biomass production technologies. We herein examined the potential of the exogenous introduction of predatory bacteria to change the duckweed microbiome. Bacteriovorax sp. HI3, a model predatory bacterium, colonized the core of the Lemna microbiome, and its predatory behavior changed the microbiome structure, which correlated with colonization density. These results reveal that bacterial predatory interactions may be important drivers that shape the duckweed microbiome, suggesting their potential usefulness in modifying the microbiome.

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.

Bdellovibrio reynosensis sp. nov., from a Mexico soil sample

A novel predatory bacterium, strain LBG001T, has been isolated from Reynosa, Mexico. The 16S rRNA shares approximately 97 % sequence identity with many reported strains in the genus Bdellovibrio including the type strain Bdellovibrio bacteriovorus HD100T. Phylogenetic trees based on the 16S rRNA gene and on 30 concatenated housekeeping genes or core genes showed that LBG001T is on a separate branch from the B. bacteriovorus group. LBG0001T has a genome size of 3 582 323 bp with a G+C content of 43.1 mol %. The average nucleotide identity, average amino acid identity and digital DNA-DNA hybridization values with other members of the genus Bdellovibrio (<79, <72 and <17 %, respectively) qualifies the strain to represent a new species in the genus. Strain LBG001T formed visible plaques on all 10 tested Gram-negative bacterial species. The phenotypic characteristics, phylogenetic analysis and genomic taxonomic studies support the classification of the strain as representing a new species for which the name Bdellovibrio reynosensis sp. nov. is proposed. The type strain is LBG001T(=ATCC TSD-288T =CM-CNRG 0932T).

Complete Genome Sequences of Two Predatory Bacterial Strains, Bacteriovorax sp. HI3 and Myxococcus sp. MH1, Isolated from a Freshwater Pond

We report the complete genome sequences of two predatory bacterial strains, Bacteriovorax sp. HI3 and Myxococcus sp. MH1, which were isolated from a freshwater pond. These two strains are grouped with the Bdellovibrio and like organisms and myxobacteria, respectively. Their genomes expand our knowledge of the characteristics of predatory bacteria.

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.

Characterization of Two Novel Predatory Bacteria, Bacteriovorax stolpii HI3 and Myxococcus sp. MH1, Isolated from a Freshwater Pond: Prey Range, and Predatory Dynamics and Efficiency

Predatory bacteria, which prey on other bacteria, have significant functions in microbial ecosystems and have attracted increasing attention for their biotechnological use. However, knowledge of the characteristics of wild-type environmental predatory bacteria remains limited. This study isolated two predatory bacteria, Bacteriovorax stolpii HI3 and Myxococcus sp. MH1, from a freshwater pond and characterized their predation capabilities. Determination of the prey range using 53 potential prey strains, including 52 environmental strains, revealed that B. stolpii HI3 and Myxococcus sp. MH1 could prey on a wide spectrum of Gram-negative bacteria and a broader range of bacteria, irrespective of phylogeny, in accordance with the common characteristics of Bdellovibrio and like organisms and myxobacteria, respectively. Liquid culture assays also found that although predation by B. stolpii HI3 rapidly and largely occurred, the prey bacteria regrew, possibly through plastic phenotypic resistance to predation. In contrast, predation by Myxococcus sp. MH1 occurred at relatively low efficiency but was longer lasting. The two strains exhibited slightly distinct temperature preferences but commonly preferred slightly alkaline pH. The novel findings of this study provide evidence for the coexistence of predatory bacteria with diverse predation capabilities in the natural aquatic environment.

Influence of temperature on aerobic granular sludge formation and stability treating municipal wastewater with high nitrogen loadings

This study investigated the influence of temperature (20 and 30 °C) on the formation and stability of aerobic granules in sequential batch reactors (SBR). Therefore, two lab-scale SBRs operated at 20 and 30 °C (SBR₂₀ and SBR₃₀) were used. The reactors were fed with municipal wastewater (COD_t:TN:TP 100:15:1.7), leading to mean organic loading rates (OLR) of 1.3 ± 0.4 kgCOD_t m^-3 day^-1. Both reactors had the same height/diameter ratio of 4.2 and were inoculated with activated sludge from a municipal wastewater treatment plant. The operational conditions were also the same for both temperatures and lasted in stable process parameters for over 100 days. By optimizing the aeration and oxygen concentration, a high removal efficiency of NH₄-N (∼99%) and COD (∼90%) was achieved in both reactors, despite the poor C:N:P ratio at the influent. Furthermore, a relatively low oxygen concentration of 2 mg L^-1 was defined as the set point for the control strategy. Nevertheless, granulation at 30 °C was significantly faster, resulting in more stable sludge volume index (SVI) values (SVI₁₀/SVI₃₀ < 1.1). The granules formed at 30 °C were also larger, more compact, and considerably more stable against system disturbances. However, at higher temperatures, larger granules might be required for nitrate removal because of the increased oxygen diffusion rates. Finally, microbiological 16S rRNA gene amplicon analysis for both systems indicated major differences relatively to the inoculum sludge only for nitrogen-degrading organisms.

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.

The microbiome of a bacterivorous marine choanoflagellate contains a resource-demanding obligate bacterial associate

Microbial predators such as choanoflagellates are key players in ocean food webs. Choanoflagellates, which are the closest unicellular relatives of animals, consume bacteria and also exhibit marked biological transitions triggered by bacterial compounds, yet their native microbiomes remain uncharacterized. Here we report the discovery of a ubiquitous, uncultured bacterial lineage we name Candidatus Comchoanobacterales ord. nov., related to the human pathogen Coxiella and physically associated with the uncultured marine choanoflagellate Bicosta minor. We analyse complete ‘Comchoano’ genomes acquired after sorting single Bicosta cells, finding signatures of obligate host-dependence, including reduction of pathways encoding glycolysis, membrane components, amino acids and B-vitamins. Comchoano encode the necessary apparatus to import energy and other compounds from the host, proteins for host-cell associations and a type IV secretion system closest to Coxiella’s that is expressed in Pacific Ocean metatranscriptomes. Interactions between choanoflagellates and their microbiota could reshape the direction of energy and resource flow attributed to microbial predators, adding complexity and nuance to marine food webs.

Choanoflagellates are the closest living unicellular relatives of animals and are important bacterivorous predators in the ocean. Here the authors show that the microbiome of this predator includes an obligate, host resource-dependent bacterial associate.

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.

Biological Control of Acinetobacter baumannii: In Vitro and In Vivo Activity, Limitations, and Combination Therapies

The survival, proliferation, and epidemic spread of Acinetobacter baumannii (A. baumannii) in hospital settings is associated with several characteristics, including resistance to many commercially available antibiotics as well as the expression of multiple virulence mechanisms. This severely limits therapeutic options, with increased mortality and morbidity rates recorded worldwide. The World Health Organisation, thus, recognises A. baumannii as one of the critical pathogens that need to be prioritised for the development of new antibiotics or treatment. The current review will thus provide a brief overview of the antibiotic resistance and virulence mechanisms associated with A. baumannii’s “persist and resist strategy”. Thereafter, the potential of biological control agents including secondary metabolites such as biosurfactants [lipopeptides (surfactin and serrawettin) and glycolipids (rhamnolipid)] as well as predatory bacteria (Bdellovibrio bacteriovorus) and bacteriophages to directly target A. baumannii, will be discussed in terms of their in vitro and in vivo activity. In addition, limitations and corresponding mitigations strategies will be outlined, including curtailing resistance development using combination therapies, product stabilisation, and large-scale (up-scaling) production.

Sludge dewaterability enhancement under low temperature condition with cold-tolerant Bdellovibrio sp. CLL13

The dewatering performance of waste activated sludge (WAS) is generally deteriorated under low temperature due to the increase of viscosity, which would exacerbate the difficulties in sludge treatment and disposal. In this study, the cold-tolerant Bdellovibrio sp. CLL13 was successfully screened for efficient sludge biolysis, and it dramatically improved the sludge dewaterability while no significant biolysis effects were observed for the mesophilic BALO strain at 12 °C. The reduction rates of the sludge capillary suction time (CST), the specific resistance of filtration (SRF), the sludge dry weight, and the fecal coliform bacteria concentration at the optimal reaction time of 14 h were 40.1 ± 0.2%, 69.6 ± 0.7%, 7.7 ± 0.4%, and 78.5 ± 0.4%, respectively, when the mixed liquid suspended solids (MLSS) content was between 10.8 and 29.6 g/L, the input dosage of CLL13 was 8.8 × 10⁶ PFU/mL sludge, and the DO level was 1.2 mg/L. Meanwhile, the viscosity reduction rate, the relative hydrophobicity increasement rate, and the bound water reduction rate were 20.3 ± 1.2%, 6.9 ± 0.7%, and 29.4 ± 1.0%, respectively. The ratios of protein content to polysaccharides content in the extracellular polymeric substances (EPS) decreased significantly. In addition, the degradation of the macromolecular substances in EPS and the increase of the soluble chemical oxygen demand, the total nitrogen, the total phosphorus, and the lactate dehydrogenase levels were observed. Therefore, the cold-tolerant CLL13 induced the sludge biolysis and compromised the negative effects of low temperature on the sludge dewatering performance, which should be beneficial for the efficient WAS biolysis treatment application in the near future under low temperature.

Interaction of Bdellovibrio bacteriovorus with Gram-Negative and Gram-Positive Bacteria in Dual Species and Polymicrobial Communities

The interaction of Bdellovibrio bacteriovorus PF13 with mixed bacterial communities, consisting of Gram-negative (Pseudomonas fluorescens and Klebsiella pneumoniae) and Gram-positive (Staphylococcus aureus and Enterococcus faecium) bacteria, was investigated to determine if this wild-type predator preferentially preys on certain bacteria and whether the presence of Gram-positive organisms influences its predation efficiency. In co-culture with P. fluorescens and K. pneumoniae, the cell counts (PFU/mL) of PF13 increased by 5.79 and 5.17 logs (48 h), respectively, while in the dual species assay (P. fluorescens, K. pneumoniae and PF13), the cell counts of PF13 increased by 1.95 logs (24 h). Using ethidium monoazide bromide quantitative polymerase chain reaction (EMA-qPCR), the concentration of PF13 increased by 1.25 to 3.62 logs in the co-culture experiments, by 1.41 to 5.05 logs in dual species cultures and by 2.65 logs in a polymicrobial culture. However, PF13 preferentially preyed on K. pneumoniae in the dual species and polymicrobial cultures, highlighting that the presence of Gram-positive bacteria did not affect the predation efficiency of PF13. This is significant as it implies that the predator can be applied in mixed microbial communities to target Gram-negative pathogens which may pose a health risk to patients, consumers or for the treatment of contaminated water.

Microbial community characterization in advanced water reclamation for potable reuse

This study investigated the microbial community structure and composition across two treatment steps used in advanced water reclamation for potable reuse applications, namely Coagulation/Flocculation/Clarification/Granular Media Filtration (CFCGMF) and Ozone-Biological Activated Carbon filtration (O₃/BAC). The study examined the richness, variations, and similarities of the microorganisms involved at each treatment step to better understand the role of ecology and the dynamics on unit process performance and the microbial community developed within it. The bacterial microbiomes at each treatment step were independently characterized using 16S metagenomic sequencing. Combining both treatment steps, a total of 3801 species were detected. From the total species detected, 38% and 98% were identified at CFCGMF and O₃/BAC, respectively. The most abundant phyla were Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes in both treatment steps. The identified species were classified based on their preferences to free-living style (59%) vs attached-living style (22%) showing a relatively low richness in the BAC media, but higher diversities. At the taxonomic class level, Betaproteobacteria was the predominant in both system processes. Additionally, a list of eight genera were identified as potential bacterial pathogens present in both process effluents. They are Aeromonas, Clostridium, Enterobacter, Escherichia, Flavobacterium, Legionella, Mycobacterium, and Pseudomonas. CFCGMF effluent yielded less pathogenic bacteria than both the ozone and BAC filter effluent from the O₃/BAC process unit; their relative abundance accounted for about 2% and 8% for CFCGMF and O₃/BAC, respectively. Detailed studies to characterize the microbial communities are crucial in interpreting the mechanisms and synergies between processes performance and microorganisms by identifying the needs and best practices to ensure public health protection. Key points • Microbial communities of two treatment processes are characterized using 16S rRNA sequencing. • Organisms that can tolerate ozone and form biofilms define microbial community in subsequent biofilters. • In relatively low abundances, potential pathogenic bacteria are detected in the treated water.

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.

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.

Predatory and biocontrol potency of Bdellovibrio bacteriovorus toward phytopathogenic strains of Pantoea sp. and Xanthomonas campestris in the presence of exo-biopolymers: in vitro and in vivo assessments

Bdellovibrios are predatory bacteria that invade other live Gram-negative bacterial cells for growth and reproduction. They have recently been considered as potential living antibiotics and biocontrol agents. In this study, the predatory activity and biocontrol potency of Bdellovibrio bacteriovorus strain SOIR-1 against Pantoea sp. strain BCCS and Xanthomonas campestris, two exo-biopolymer-producing phytopathogens, was evaluated. Plaque formation assays and lysis analysis in the broth co-cultures were used for the in vitro evaluation of bacteriolytic activity of strain SOIR-1. The in vivo biocontrol potential of strain SOIR-1 was evaluated by pathogenicity tests on the onion bulbs and potato tuber slices. The phytopathogens were also recovered from the infected plant tissues and confirmed using biochemical tests and PCR-based 16S rRNA gene sequence analysis. Typical bdellovibrios plaques were developed on the lawn cultures of Pantoea sp. BCCS and X. campestris. The killing rate of strain SOIR-1 toward Pantoea sp. BCCS and X. campestris was 84.3% and 76.3%, respectively. Exo-biopolymers attenuated the predation efficiency of strain SOIR-1 up to 10.2-18.2% (Pantoea sp. BCCS) and 12.2-17.3% (X. campestris). The strain SOIR-1 significantly reduced rotting symptoms in the onion bulbs caused by Pantoea sp. BCCS (69.0%) and potato tuber slices caused by X. campestris (73.1%). Although more field assessments are necessary, strain SOIR-1 has the preliminary potential as a biocontrol agent against phytopathogenic Pantoea sp. BCCS and X. campestris, especially in postharvest storage. Due to the particular physicochemical properties of evaluated exo-biopolymers, they can be used in the designing encapsulation systems for delivery of bdellovibrios.

Bdellovibrio bacteriovorus: a potential 'living antibiotic' to control bacterial pathogens

Bdellovibrio bacteriovorus is a small Deltaproteobacterium which, since its discovery, has distinguished itself for the unique ability to prey on other Gram-negative bacteria. The studies on this particular "predatory bacterium", have gained momentum in response to the rising problem of antibiotic resistance, because it could be applied as a potential probiotic and antibiotic agent. Hereby, we present recent advances in the study of B. bacteriovorus, comprehending fundamental aspects of its biology, obligatory intracellular life cycle, predation resistance, and potential applications. Furthermore, we discuss studies that pave the road towards the use of B. bacteriovorus as a "living antibiotic" in human therapy, focussing on its interaction with biofilms, the host immune response, predation susceptibility and in vivo application models. The available data imply that it will be possible to upgrade this predator bacterium from a predominantly academic interest to an instrument that could confront antibiotic resistant infections.

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.

Phylogenomic Insights into Distribution and Adaptation of Bdellovibrionota in Marine Waters

Bdellovibrionota is composed of obligate predators that can consume some Gram-negative bacteria inhabiting various environments. However, whether genomic traits influence their distribution and marine adaptation remains to be answered. In this study, we performed phylogenomics and comparative genomics studies using 132 Bdellovibrionota genomes along with five metagenome-assembled genomes (MAGs) from deep sea zones. Four phylogenetic groups, Oligoflexia, Bdello-group1, Bdello-group2 and Bacteriovoracia, were revealed by constructing a phylogenetic tree, of which 53.84% of Bdello-group2 and 48.94% of Bacteriovoracia were derived from the ocean. Bacteriovoracia was more prevalent in deep sea zones, whereas Bdello-group2 was largely distributed in the epipelagic zone. Metabolic reconstruction indicated that genes involved in chemotaxis, flagellar (mobility), type II secretion system, ATP-binding cassette (ABC) transporters and penicillin-binding protein were necessary for the predatory lifestyle of Bdellovibrionota. Genes involved in glycerol metabolism, hydrogen peroxide (H2O2) degradation, cell wall recycling and peptide utilization were ubiquitously present in Bdellovibrionota genomes. Comparative genomics between marine and non-marine Bdellovibrionota demonstrated that betaine as an osmoprotectant is probably widely used by marine Bdellovibrionota, and all the marine genomes have a number of genes for adaptation to marine environments. The genes encoding chitinase and chitin-binding protein were identified for the first time in Oligoflexia, which implied that Oligoflexia may prey on a wider spectrum of microbes. This study expands our knowledge on adaption strategies of Bdellovibrionota inhabiting deep seas and the potential usage of Oligoflexia for biological control.

A Metataxonomic Approach Reveals Diversified Bacterial Communities in Antarctic Sponges

Marine sponges commonly host a repertoire of bacterial-associated organisms, which significantly contribute to their health and survival by producing several anti-predatory molecules. Many of these compounds are produced by sponge-associated bacteria and represent an incredible source of novel bioactive metabolites with biotechnological relevance. Although most investigations are focused on tropical and temperate species, to date, few studies have described the composition of microbiota hosted by Antarctic sponges and the secondary metabolites that they produce. The investigation was conducted on four sponges collected from two different sites in the framework of the XXXIV Italian National Antarctic Research Program (PNRA) in November-December 2018. Collected species were characterized as Mycale (Oxymycale) acerata, Haliclona (Rhizoniera) dancoi, Hemigellius pilosus and Microxina sarai by morphological analysis of spicules and amplification of four molecular markers. Metataxonomic analysis of these four Antarctic sponges revealed a considerable abundance of Amplicon Sequence Variants (ASVs) belonging to the phyla Proteobacteria, Bacteroidetes, Actinobacteria and Verrucomicrobia. In particular, M. (Oxymycale) acerata, displayed several genera of great interest, such as Endozoicomonas, Rubritalea, Ulvibacter, Fulvivirga and Colwellia. On the other hand, the sponges H. pilosus and H. (Rhizoniera) dancoi hosted bacteria belonging to the genera Pseudhongella, Roseobacter and Bdellovibrio, whereas M. sarai was the sole species showing some strains affiliated to the genus Polaribacter. Considering that most of the bacteria identified in the present study are known to produce valuable secondary metabolites, the four Antarctic sponges could be proposed as potential tools for the discovery of novel pharmacologically active compounds.

Using autochthonous Bdellovibrio as a predatory bacterium for reduction of Gram-negative pathogenic bacteria in urban wastewater and reuse it

Background and Objectives:

The microbial contamination of wastewater is associated with health risks. The aim of this study was to use the autochthonous Bdellovibrio potential to prey Gram-negative pathogenic bacteria as a bio-control agent to treat urban wastewater.

Materials and Methods:

Thirty-six raw sewage samples were collected for isolation of Bdellovibrio. Double layer plaque assay was used for isolation and the isolates were identified by microscopic examination and molecular analysis. To evaluate the predatory potential for decrease number of Gram-negative pathogenic bacteria, plaque perdition assay, reduction in host cells viability by colony-forming unit (CFU) counting, reduction in optical density (OD) in co-cultures and assay of killing efficiency were carried out. Also, the raw wastewater was treated by Bdellovibrio then the reduction in CFU counting and reduction in OD was evaluated.

Results:

Four strains of Bdellovibrio were isolated and were registered in Gene Bank. Clear plaques were observed after 3–6 days of incubation for all prey cells. The CFU enumerations of all preys were decreased after 48 hrs in co-cultures and raw wastewater. Also, OD was decreased down to 0.2 nm after 48 hrs.

Conclusion:

These autochthonous Bdellovibrio strains are proposed to use for bio-control of Gram-negative pathogenic bacteria in wastewater and reuse it for irrigation in arid regions.

Predatory bacteria as living antibiotics - where are we now?

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

Metataxonomic profiling of bacterial communities and their predictive functional profiles in traditionally preserved meat products of Sikkim state in India

Traditionally preserved meat products are common food items in Sikkim state of India. We studied the high-throughput sequencing of four traditionally preserved meat products viz. beef kargyong, pork kargyong, yak satchu and khyopeh to profile the bacterial communities and also inferred their predictive functional profiles. Overall abundant OTUs in samples showed that Firmicutes was the abundant phylum followed by Proteobacteria and Bacteroidetes. Abundant species detected in each product were Psychrobacter pulmonis in beef kargyong, Lactobacillus sakei in pork kargyong, Bdellovibrio bacteriovorus and Ignatzschinera sp. in yak satchu and Lactobacillus sakei and Enterococcus sp. in khyopeh. Several genera unique to each product, based on analysis of shared OTUs contents, were observed among the samples except in khyopeh. Goods coverage recorded to 1.0 was observed, which reflected the maximum bacterial diversity in the samples. Alpha diversity metrics showed a maximum bacterial diversity in khyopeh and lowest in pork kargyong Community dissimilarities in the products were observed by PCoA plot. A total of 133 KEGG predictive functional pathways was observed in beef kargyong, 131 in pork kargyong, 125 in yak satchu and 101 in khyopeh. Metagenome contribution of the OTUs was computed using PICTRUSt2 and visualized by BURRITO software to predict the metabolic pathways. Several predictive functional profiles were contributed by abundant OTUs represented by Enterococcus, Acinetobacter, Agrobacterium, Bdellovibrio, Chryseobacterium, Lactococcus, Leuconostoc, Psychrobacter, and Staphylococcus.

Vibrio parahaemolyticus control in mussels by a Halobacteriovorax isolated from the Adriatic sea, Italy

This study evaluated the application of a Halobacteriovorax isolated from water of the Adriatic Sea (Italy) in controlling V. parahaemolyticus in mussels (Mytilus galloprovincialis). Two 72 h laboratory-scale V. parahaemolyticus decontamination experiments of mussels were performed. The test microcosm of experiment 1 was prepared using predator/prey free mussels experimentally contaminated with Halobacteriovorax/V. parahaemolyticus at a ratio of 10³ PFU/10⁵ CFU per ml, while that of experiment 2 using mussels naturally harbouring Halobacteriovorax that were experimentally contaminated with 10⁵ CFU per ml of V. parahaemolyticus. For experiment 1, was also tested a control microcosm only contaminated with 10⁵ CFU per ml of V. parahaemolyticus.. Double layer agar plating and pour plate techniques were used to enumerate Halobacteriovorax and V. parahaemolyticus, respectively. 16 S rRNA analysis was used to identify Halobacteriovorax. For both experiments in the test microcosm the concentration of prey remained at the same level as that experimentally added, i.e. 5 log for the entire analysis period. In experiment 1, V. parahaemolyticus counts in mussels were significantly lower in the test microcosm than the control with the maximum difference of 2.2 log at 24 h. Results demonstrate that Halobacteriovorax can modulate V. parahaemolyticus level in the mussels. The public impact of V. parahaemolyticus in bivalves is relevant and current decontamination processes are not always effective. Halobacteriovorax is a suitable candidate in the development of a biological approach to the purification of V. parahaemolyticus in mussels.

The antibiotic crisis: How bacterial predators can help

Discovery of antimicrobials in the past century represented one of the most important advances in public health. Unfortunately, the massive use of these compounds in medicine and other human activities has promoted the selection of pathogens that are resistant to one or several antibiotics. The current antibiotic crisis is creating an urgent need for research into new biological weapons with the ability to kill these superbugs. Although a proper solution requires this problem to be addressed in a variety of ways, the use of bacterial predators is emerging as an excellent strategy, especially when used as whole cell therapeutic agents, as a source of new antimicrobial agents by awakening silent metabolic pathways in axenic cultures, or as biocontrol agents. Moreover, studies on their prey are uncovering mechanisms of resistance that can be shared by pathogens, representing new targets for novel antimicrobial agents. In this review we discuss potential of the studies on predator-prey interaction to provide alternative solutions to the problem of antibiotic resistance.

Promising Therapeutic Strategies Against Microbial Biofilm Challenges

Biofilms are communities of microorganisms that are attached to a biological or abiotic surface and are surrounded by a self-produced extracellular matrix. Cells within a biofilm have intrinsic characteristics that are different from those of planktonic cells. Biofilm resistance to antimicrobial agents has drawn increasing attention. It is well-known that medical device- and tissue-associated biofilms may be the leading cause for the failure of antibiotic treatments and can cause many chronic infections. The eradication of biofilms is very challenging. Many researchers are working to address biofilm-related infections, and some novel strategies have been developed and identified as being effective and promising. Nevertheless, more preclinical studies and well-designed multicenter clinical trials are critically needed to evaluate the prospects of these strategies. Here, we review information about the mechanisms underlying the drug resistance of biofilms and discuss recent progress in alternative therapies and promising strategies against microbial biofilms. We also summarize the strengths and weaknesses of these strategies in detail.