Biocontrol of Burkholderia cepacia complex bacteria and bacterial phytopathogens by Bdellovibrio bacteriovorus

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

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

Harnessing fungal endophytes for natural management: a biocontrol perspective

In the ever-evolving realm of agriculture, the convoluted interaction between plants and microorganisms have assumed paramount significance. Fungal endophytes, once perceived as mere bystanders within plant tissues, have now emerged as dynamic defenders of plant health. This comprehensive review delves into the captivating world of fungal endophytes and their multifaceted biocontrol mechanisms. Exploring their unique ability to coexist with their plant hosts, fungal endophytes have unlocked a treasure trove of biological weaponry to fend off pathogens and enhance plant resilience. From the synthesis of bioactive secondary metabolites to intricate signaling pathways these silent allies are masters of biological warfare. The world of fungal endophytes is quite fascinating as they engage in a delicate dance with the plant immune system, orchestrating a symphony of defense that challenges traditional notions of plant-pathogen interactions. The journey through the various mechanisms employed by these enigmatic endophytes to combat diseases, will lead to revelational understanding of sustainable agriculture. The review delves into cutting-edge research and promising prospects, shedding light on how fungal endophytes hold the key to biocontrol and the reduction of chemical inputs in agriculture. Their ecological significance, potential for bioprospecting and avenues for future research are also explored. This exploration of the biocontrol mechanisms of fungal endophytes promise not only to enrich our comprehension of plant-microbe relationships but also, to shape the future of sustainable and ecofriendly agricultural practices. In this intricate web of life, fungal endophytes are indeed the unsung heroes, silently guarding our crops and illuminating a path towards a greener, healthier tomorrow.

Biopesticides: a Green Approach Towards Agricultural Pests

Biopesticides are biological products or organisms which are potential candidates for eco-friendly pest management and crop protection over the chemical pesticides. The so-called biopesticides include viruses, bacteria, fungi, predators, parasites, and pheromones exhibiting a variety of modes of actions. They are less toxic, rapidly degradable, and more targeted to specific pests. However, it is noted that the formulation of biopesticides plays a crucial link between production and application, and the former dictates economy, longer shelf life, ease of application, and enhanced field efficacy. Moreover, there is an urgent need for organic farmers to gain more proficiency in using biopesticides. Even though biopesticides have more advantages, the main challenge is the marketing of biopesticides. Advances in biopesticide research and development significantly reduce the environmental damage caused by the residues of synthetic insecticides and support sustainable agriculture. Numerous products have been developed since the introduction of biopesticides, some of which have taken the lead in the agro-market after being registered and released. The types of biopesticides; their mode of action; formulation strategies; recent advancements of biopesticides focusing mainly on improvement of its action spectra, to thereby replace chemical pesticides; and finally, the future aspects of biopesticides have been discussed in this review.

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.

Effective combination of arugula vermicompost, chitin and inhibitory bacteria for suppression of the root-knot nematode Meloidogyne javanica and explanation of their beneficial properties based on microbial analysis

Root-knot nematodes (Meloidogyne spp.) are dangerous parasites of many crops worldwide. The threat of chemical nematicides has led to increasing interest in studying the inhibitory effects of organic amendments and bacteria on plant-parasitic nematodes, but their combination has been less studied. One laboratory and four glasshouse experiments were conducted to study the effect on M. javanica of animal manure, common vermicompost, shrimp shells, chitosan, compost and vermicompost from castor bean, chinaberry and arugula, and the combination of arugula vermicompost with some bacteria, isolated from vermicompost or earthworms. The extract of arugula compost and vermicompost, common vermicompost and composts from castor bean and chinaberry reduced nematode egg hatch by 12-32% and caused 13-40% mortality of second-stage juveniles in vitro. Soil amendments with the combination vermicompost of arugula + Pseudomonas. resinovorans + Sphingobacterium daejeonense + chitosan significantly increased the yield of infected tomato plants and reduced nematode reproduction factor by 63.1-76.6%. Comparison of chemical properties showed that arugula vermicompost had lower pH, EC, and C/N ratio than arugula compost. Metagenomics analysis showed that Bacillus, Geodermatophilus, Thermomonas, Lewinella, Pseudolabrys and Erythrobacter were the major bacterial genera in the vermicompost of arugula. Metagenomics analysis confirmed the presence of chitinolytic, detoxifying and PGPR bacteria in the vermicompost of arugula. The combination of arugula vermicompost + chitosan + P. resinovorans + S. daejeonense could be an environmentally friendly approach to control M. javanica.

Microbial Consortia for Plant Protection against Diseases: More than the Sum of Its Parts

Biological plant protection presents a promising and exciting alternative to chemical methods for safeguarding plants against the increasing threats posed by plant diseases. This approach revolves around the utilization of biological control agents (BCAs) to suppress the activity of significant plant pathogens. Microbial BCAs have the potential to effectively manage crop disease development by interacting with pathogens or plant hosts, thereby increasing their resistance. However, the current efficacy of biological methods remains unsatisfactory, creating new research opportunities for sustainable plant cultivation management. In this context, microbial consortia, comprising multiple microorganisms with diverse mechanisms of action, hold promise in terms of augmenting the magnitude and stability of the overall antipathogen effect. Despite scientific efforts to identify or construct microbial consortia that can aid in safeguarding vital crops, only a limited number of microbial consortia-based biocontrol formulations are currently available. Therefore, this article aims to present a complex analysis of the microbial consortia-based biocontrol status and explore potential future directions for biological plant protection research with new technological advancements.

Optimization of Constitutive Promoters Using a Promoter-Trapping Vector in Burkholderia pyrrocinia JK-SH007

Selecting suitable promoters to drive gene overexpression can provide significant insight into the development of engineered bacteria. In this study, we analyzed the transcriptome data of Burkholderia pyrrocinia JK-SH007 and identified 54 highly expressed genes. The promoter sequences were located using genome-wide data and scored using the prokaryotic promoter prediction software BPROM to further screen out 18 promoter sequences. We also developed a promoter trap system based on two reporter proteins adapted for promoter optimization in B. pyrrocinia JK-SH007: firefly luciferase encoded by the luciferase gene set (Luc) and trimethoprim (TP)-resistant dihydrofolate reductase (TP^r). Ultimately, eight constitutive promoters were successfully inserted into the probe vector and transformed into B. pyrrocinia JK-SH007. The transformants were successfully grown on Tp antibiotic plates, and firefly luciferase expression was determined by measuring the relative light unit (RLU). Five of the promoters (P4, P9, P10, P14, and P19) showed 1.01-2.51-fold higher activity than the control promoter λ phage transcriptional promoter (PRPL). The promoter activity was further validated via qPCR analysis, indicating that promoters P14 and P19 showed stable high transcription levels at all time points. Then, GFP and RFP proteins were overexpressed in JK-SH007. In addition, promoters P14 and P19 were successfully used to drive gene expression in Burkholderia multivorans WS-FJ9 and Escherichia coli S17-1. The two constitutive promoters can be used not only in B. pyrrocinia JK-SH007 itself to gene overexpression but also to expand the scope of application.

Effects of Bdellovibrio bacteriovorus HD100 on experimental periodontitis in rats

AIM

The aim of this study was to evaluate the effects of Bdellovibrio bacteriovorus HD100 on experimental periodontitis (EP) in rats.

METHODS

Thirty-two rats were divided into four groups: control, C-HD100 (B. bacteriovorus), EP, and EP-HD100. On day 0, EP was induced by the placement of cotton ligatures around the mandibular first molars (MFMs) in the EP and EP-HD100 groups. In the C-HD100 and EP-HD100 groups, suspensions containing 1 × 10⁹  PUF/ml of B. bacteriovorus HD100 were topically administered to the subgingival region of MFMs on days 0, 3, and 7. Animals were euthanized on day 14. Morphometrics analyses were performed in hemimandibles. The levels of tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, monocyte chemoattractant protein (MCP)-1, IL-10, IL-1β, transforming growth factor beta (TGF-β), macrophage colony-stimulating factor (M-CSF) and regulated on activation and normal T cell expressed and secreted (RANTES) were determined by enzymatic immunoassays in gingival tissues. Beta defensin (BD)-1, BD-2, and BD-3, Toll-like receptors (TLR)-2 and TLR-4, and a cluster of differentiation (CD)-4, CD-8 and CD-57 were analyzed by immunohistochemistry in hemimandibles. Data were statistically analyzed.

RESULTS

The EP group showed greater alveolar bone loss than EP-HD100 (p < .05). The EP-HD100 group showed higher levels of MCP-1, RANTES, IL-10, and TGF-β, lower levels of TNF-α than the EP group (p < .05). No differences were observed in IL-1β, IL-6, and M-CSF levels between EP and EP-HD100 groups. The C-HD100 group had higher IL-6, TNF-α, RANTES, and MCP-1 levels than the control group (p < .05). Regarding BD, the EP-HD100 group showed a larger immunolabeling pattern for BD-1, BD-2, and BD-3 than the EP group (p < .05). No significant differences in the immunolabeling pattern were observed for TLR-2, TLR-4, CD-4, CD-8, and CD-57 between EP and EP-HD100 groups.

CONCLUSION

The topical use of B. bacteriovorus HD100 reduces alveolar bone loss, increases expression of BD, and modulates the cytokines levels on periodontal tissues in rats with EP.

Use of Ecological Theory to Understand the Efficacy and Mechanisms of Multistrain Biological Control

Since the 1970s, over 6,500 articles have been published about microbial biocontrols and over 200 microbial isolates have been registered for commercial use. However, many of these solutions have seen limited use due to limitations with their in-field efficacy. Even when multiple biocontrol agents are combined to create multistrain biocontrols, the resulting combinations can be less effective than the individual agents. One likely contributor is due to how multistrain microbial biocontrols are created. Multistrain microbial biocontrols are generally produced under controlled settings that are divorced from the ecological conditions they will need to function under. Traditionally, researchers culture, identify, and screen isolates for pathogen suppression traits. Then these researchers will combine the most promising isolates in an attempt to create more effective solutions. This approach, while effective for identifying suppressive isolates and determining the mechanisms of pathogen suppression, does not take into consideration the variability of natural environments, nor the complex ecological interactions that occur between plant hosts, pathogens, and component biocontrol agents, thus limiting the range of circumstances that these multistrain solutions can reliably succeed. To address these limitations, we suggest the application of relevant ecological theory to determine which isolates should be combined to create more reliable multistrain biocontrols. In this synthesis, we build on prior work focused on addressing plant pathogens through the use of multistrain microbial biocontrols, but we argue that viewing this work through the lens of ecology reveals key "design principles" from natural communities that are stable, functioning, and comprise multiple species.

Endophytes and their potential in biotic stress management and crop production

Biotic stress is caused by harmful microbes that prevent plants from growing normally and also having numerous negative effects on agriculture crops globally. Many biotic factors such as bacteria, fungi, virus, weeds, insects, and nematodes are the major constrains of stress that tends to increase the reactive oxygen species that affect the physiological and molecular functioning of plants and also led to the decrease in crop productivity. Bacterial and fungal endophytes are the solution to overcome the tasks faced with conventional farming, and these are environment friendly microbial commodities that colonize in plant tissues without causing any damage. Endophytes play an important role in host fitness, uptake of nutrients, synthesis of phytohormone and diminish the injury triggered by pathogens via antibiosis, production of lytic enzymes, secondary metabolites, and hormone activation. They are also reported to help plants in coping with biotic stress, improving crops and soil health, respectively. Therefore, usage of endophytes as biofertilizers and biocontrol agent have developed an eco-friendly substitute to destructive chemicals for plant development and also in mitigation of biotic stress. Thus, this review highlighted the potential role of endophytes as biofertilizers, biocontrol agent, and in mitigation of biotic stress for maintenance of plant development and soil health for sustainable agriculture.

Emerging Research Topics in the Vibrionaceae and the Squid-Vibrio Symbiosis

The Vibrionaceae encompasses a cosmopolitan group that is mostly aquatic and possesses tremendous metabolic and genetic diversity. Given the importance of this taxon, it deserves continued and deeper research in a multitude of areas. This review outlines emerging topics of interest within the Vibrionaceae. Moreover, previously understudied research areas are highlighted that merit further exploration, including affiliations with marine plants (seagrasses), microbial predators, intracellular niches, and resistance to heavy metal toxicity. Agarases, phototrophy, phage shock protein response, and microbial experimental evolution are also fields discussed. The squid-Vibrio symbiosis is a stellar model system, which can be a useful guiding light on deeper expeditions and voyages traversing these "seas of interest". Where appropriate, the squid-Vibrio mutualism is mentioned in how it has or could facilitate the illumination of these various subjects. Additional research is warranted on the topics specified herein, since they have critical relevance for biomedical science, pharmaceuticals, and health care. There are also practical applications in agriculture, zymology, food science, and culinary use. The tractability of microbial experimental evolution is explained. Examples are given of how microbial selection studies can be used to examine the roles of chance, contingency, and determinism (natural selection) in shaping Earth's natural history.

New opportunities in plant microbiome engineering for increasing agricultural sustainability under stressful conditions

Plant microbiome (or phytomicrobiome) engineering (PME) is an anticipated untapped alternative strategy that could be exploited for plant growth, health and productivity under different environmental conditions. It has been proven that the phytomicrobiome has crucial contributions to plant health, pathogen control and tolerance under drastic environmental (a)biotic constraints. Consistent with plant health and safety, in this article we address the fundamental role of plant microbiome and its insights in plant health and productivity. We also explore the potential of plant microbiome under environmental restrictions and the proposition of improving microbial functions that can be supportive for better plant growth and production. Understanding the crucial role of plant associated microbial communities, we propose how the associated microbial actions could be enhanced to improve plant growth-promoting mechanisms, with a particular emphasis on plant beneficial fungi. Additionally, we suggest the possible plant strategies to adapt to a harsh environment by manipulating plant microbiomes. However, our current understanding of the microbiome is still in its infancy, and the major perturbations, such as anthropocentric actions, are not fully understood. Therefore, this work highlights the importance of manipulating the beneficial plant microbiome to create more sustainable agriculture, particularly under different environmental stressors.

Harnessing intercellular signals to engineer the soil microbiome

Covering: Focus on 2015 to 2020Plant and soil microbiomes consist of diverse communities of organisms from across kingdoms and can profoundly affect plant growth and health. Natural product-based intercellular signals govern important interactions between microbiome members that ultimately regulate their beneficial or harmful impacts on the plant. Exploiting these evolved signalling circuits to engineer microbiomes towards beneficial interactions with crops is an attractive goal. There are few reports thus far of engineering the intercellular signalling of microbiomes, but this article argues that it represents a tremendous opportunity for advancing the field of microbiome engineering. This could be achieved through the selection of synergistic consortia in combination with genetic engineering of signal pathways to realise an optimised microbiome.

Bacteriophage-Mediated Control of Phytopathogenic Xanthomonads: A Promising Green Solution for the Future

Xanthomonads, members of the family Xanthomonadaceae, are economically important plant pathogenic bacteria responsible for infections of over 400 plant species. Bacteriophage-based biopesticides can provide an environmentally friendly, effective solution to control these bacteria. Bacteriophage-based biocontrol has important advantages over chemical pesticides, and treatment with these biopesticides is a minor intervention into the microflora. However, bacteriophages’ agricultural application has limitations rooted in these viruses’ biological properties as active substances. These disadvantageous features, together with the complicated registration process of bacteriophage-based biopesticides, means that there are few products available on the market. This review summarizes our knowledge of the Xanthomonas-host plant and bacteriophage-host bacterium interaction’s possible influence on bacteriophage-based biocontrol strategies and provides examples of greenhouse and field trials and products readily available in the EU and the USA. It also details the most important advantages and limitations of the agricultural application of bacteriophages. This paper also investigates the legal background and industrial property right issues of bacteriophage-based biopesticides. When appropriately applied, bacteriophages can provide a promising tool against xanthomonads, a possibility that is untapped. Information presented in this review aims to explore the potential of bacteriophage-based biopesticides in the control of xanthomonads in the future.

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.

Potential Use of Beneficial Microorganisms for Soil Amelioration, Phytopathogen Biocontrol, and Sustainable Crop Production in Smallholder Agroecosystems

Smallholder agroecosystems play a key role in the world's food security providing more than 50% of the food produced globally. These unique agroecosystems face a myriad of challenges and remain largely unsupported, yet they are thought to be a critical resource for feeding the projected increasing human population in the coming years. The new challenge to increase food production through agricultural intensification in shrinking per capita arable lands, dwindling world economies, and unpredictable climate change, has led to over-dependence on agrochemical inputs that are often costly and hazardous to both human and animal health and the environment. To ensure healthy crop production approaches, the search for alternative ecofriendly strategies that best fit to the smallholder systems have been proposed. The most common and widely accepted solution that has gained a lot of interest among researchers and smallholder farmers is the use of biological agents; mainly plant growth promoting microorganisms (PGPMs) that provide essential agroecosystem services within a holistic vision of enhancing farm productivity and environmental protection. PGPMs play critical roles in agroecological cycles fundamental for soil nutrient amelioration, crop nutrient improvement, plant tolerance to biotic and abiotic stresses, biocontrol of pests and diseases, and water uptake. This review explores different research strategies involving the use of beneficial microorganisms, within the unique context of smallholder agroecosystems, to promote sustainable maintenance of plant and soil health and enhance agroecosystem resilience against unpredictable climatic perturbations.

Insight into the Possible Use of the Predator Bdellovibrio bacteriovorus as a Probiotic

The gut microbiota is a complex microbial ecosystem that coexists with the human organism in the intestinal tract. The members of this ecosystem live together in a balance between them and the host, contributing to its healthy state. Stress, aging, and antibiotic therapies are the principal factors affecting the gut microbiota composition, breaking the mutualistic relationship among microbes and resulting in the overgrowth of potential pathogens. This condition, called dysbiosis, has been linked to several chronic pathologies. In this review, we propose the use of the predator Bdellovibrio bacteriovorus as a possible probiotic to prevent or counteract dysbiotic outcomes and look at the findings of previous research.

Biotechnological Potential of Bdellovibrio and Like Organisms and Their Secreted Enzymes

Bdellovibrio and like organisms (BALOs) are obligate predatory bacteria that selectively prey on a broad range of Gram-negative bacteria, including multidrug-resistant human pathogens. Due to their unique lifestyle, they have been long recognized as a potential therapeutic and biocontrol agent. Research on BALOs has rapidly grown over the recent decade, resulting in many publications concerning molecular details of bacterial predation as well as applications thereof in medicine and biotechnology. This review summarizes the current knowledge on biotechnological potential of obligate predatory bacteria and their secreted enzymes.

Shedding Light on the Cell Biology of the Predatory Bacterium Bdellovibrio bacteriovorus

Bdellovibrio bacteriovorus is a predatory bacterium that feeds upon and proliferates inside other Gram-negative bacteria. Upon entry into the periplasmic space of the prey envelope, B. bacteriovorus initiates an exquisite developmental program in which it digests the host resources and grows as a filament, which eventually divides in a non-binary manner, releasing a variable number of daughter cells. The progeny then escape from the prey ghost to encounter new victims and resume the predation cycle. Owing to its unique biology, B. bacteriovorus undoubtedly represents an attractive model to unravel novel mechanisms of bacterial cell cycle control and cellular organization. Yet, the molecular factors behind the sophisticated lifestyle of this micro-predator are still mysterious. In particular, the spatiotemporal dynamics of proteins that control key cellular processes such as transmission of the genetic information, cell growth and division remain largely unexplored. In this Perspective article, I highlight outstanding fundamental questions related to these aspects and arising from the original biology of this bacterium. I also discuss available insights and potential cell biology approaches based on quantitative live imaging techniques, in combination with bacterial genetics and biochemistry, to shed light on the intracellular organization of B. bacteriovorus in space and time.

A Riboflavin Transporter in Bdellovibrio exovorous JSS

The ImpX transporters of the drug/metabolite transporter superfamily were first proposed to transport riboflavin (RF; vitamin B2) based on findings of a cis-regulatory RNA element responding to flavin mononucleotide (an FMN riboswitch). Bdellovibrio exovorous JSS has a homolog belonging to this superfamily. It has 10 TMSs and shows 30% identity to the previously characterized ImpX transporter from Fusobacterium nucleatum. However, the ImpX homolog is not regulated by an FMN-riboswitch. In order to test the putative function of the ImpX homolog from B. exovorous (BexImpX), we cloned and heterologously expressed its gene. We used functional complementation, growth inhibition experiments, direct uptake experiments and inhibition studies, suggesting a high degree of specificity for RF uptake. The EC50 for growth with RF was estimated to be in the range 0.5-1 µM, estimated from the half-maximal RF concentration supporting the growth of a RF auxotrophic Escherichia coli strain, but the Khalf for RF uptake was 20 µM. Transport experiments suggested that the energy source is the proton motive force but that NaCl stimulates uptake. Thus, members of the ImpX family members are capable of RF uptake, not only in RF prototrophic species such as F.  nucleatum, but also in the B2 auxotrophic species, B. exovorous.

Defining and combating antibiotic resistance from One Health and Global Health perspectives

Several interconnected human, animal and environmental habitats can contribute to the emergence, evolution and spread of antibiotic resistance, and the health of these contiguous habitats (the focus of the One Health approach) may represent a risk to human health. Additionally, the expansion of resistant clones and antibiotic resistance determinants among human-associated, animal-associated and environmental microbiomes have the potential to alter bacterial population genetics at local and global levels, thereby modifying the structure, and eventually the productivity, of microbiomes where antibiotic-resistant bacteria can expand. Conversely, any change in these habitats (including pollution by antibiotics or by antibiotic-resistant organisms) may influence the structures of their associated bacterial populations, which might affect the spread of antibiotic resistance to, and among, the above-mentioned microbiomes. Besides local transmission among connected habitats-the focus of studies under the One Health concept-the transmission of resistant microorganisms might occur on a broader (even worldwide) scale, requiring coordinated Global Health actions. This Review provides updated information on the elements involved in the evolution and spread of antibiotic resistance at local and global levels, and proposes studies to be performed and strategies to be followed that may help reduce the burden of antibiotic resistance as well as its impact on human and planetary health.

Mode of Action of Microbial Biological Control Agents Against Plant Diseases: Relevance Beyond Efficacy

Microbial biological control agents (MBCAs) are applied to crops for biological control of plant pathogens where they act via a range of modes of action. Some MBCAs interact with plants by inducing resistance or priming plants without any direct interaction with the targeted pathogen. Other MBCAs act via nutrient competition or other mechanisms modulating the growth conditions for the pathogen. Antagonists acting through hyperparasitism and antibiosis are directly interfering with the pathogen. Such interactions are highly regulated cascades of metabolic events, often combining different modes of action. Compounds involved such as signaling compounds, enzymes and other interfering metabolites are produced in situ at low concentrations during interaction. The potential of microorganisms to produce such a compound in vitro does not necessarily correlate with their in situ antagonism. Understanding the mode of action of MBCAs is essential to achieve optimum disease control. Also understanding the mode of action is important to be able to characterize possible risks for humans or the environment and risks for resistance development against the MBCA. Preferences for certain modes of action for an envisaged application of a MBCA also have impact on the screening methods used to select new microbials. Screening of MBCAs in bioassays on plants or plant tissues has the advantage that MBCAs with multiple modes of action and their combinations potentially can be detected whereas simplified assays on nutrient media strongly bias the selection toward in vitro production of antimicrobial metabolites which may not be responsible for in situ antagonism. Risks assessments for MBCAs are relevant if they contain antimicrobial metabolites at effective concentration in the product. However, in most cases antimicrobial metabolites are produced by antagonists directly on the spot where the targeted organism is harmful. Such ubiquitous metabolites involved in natural, complex, highly regulated interactions between microbial cells and/or plants are not relevant for risk assessments. Currently, risks of microbial metabolites involved in antagonistic modes of action are often assessed similar to assessments of single molecule fungicides. The nature of the mode of action of antagonists requires a rethinking of data requirements for the registration of MBCAs.

Controlling Bdellovibrio bacteriovorus Gene Expression and Predation Using Synthetic Riboswitches

Bdellovibrio bacteriovorus is a predatory bacterium that feeds on Gram-negative bacteria including a wide range of pathogens and thus has potential applications as a biocontrol agent. Owing to its unique life cycle, however, there are limited tools that enable genetic manipulation of B. bacteriovorus. This work describes our first steps toward engineering the predatory bacterium for practical applications by developing basic genetic parts to control gene expression. Specifically, we evaluated four robust promoters that are active during the attack phase of B. bacteriovorus. Subsequently, we tested several synthetic riboswitches that have been reported to function in Escherichia coli, and identified theophylline-activated riboswitches that function in B. bacteriovorus. Finally, we inserted the riboswitch into the bacterial chromosome to regulate expression of the flagellar sigma factor fliA, which was previously predicted to be essential for predation, and observed that the engineered strain shows a faster predation kinetics in the presence of theophylline.