Harvesting the complex pathways of antibiotic production and resistance of soil bacilli for optimizing plant microbiome

Eco-friendly Biocontrol of Ralstonia solanacearum and Plant Growth Promotion in Tobacco Using Garbage Enzyme and Bacillus velezensis A1

Ralstonia solanacearum, the causative agent of bacterial wilt disease, poses a significant threat to agriculture. The demand for safe and high-quality food has increased interest in biological control agents (BCAs), despite challenges related to stability and cost. Garbage enzymes (GEs) are a promising alternative, rich in beneficial microbes and organic compounds. In this study, four types of GEs (onion, garlic, ginger, and mixed fruit) were individually tested against R. solanacearum in vitro, with only onion GE showing significant inhibition. Filtered onion GE, which lacked any microbes, also showed inhibition; however, its heat-treated form exhibited a reduced inhibitory effect, indicating the role of heat-sensitive compounds in inhibiting R. solanacearum. An antagonistic bacterial strain A1, isolated from onion GE, inhibited pathogen growth by up to 75% through volatile compounds. Cell-free culture filtrate of the strain A1 also inhibited R. solanacearum in vitro. Strain A1 exhibited nitrogen fixation, siderophore production, indole acetic acid (IAA) synthesis, and extracellular enzyme production, positioning it as a potent biocontrol agent. The genome analysis of the strain A1 revealed the presence of several plant growth-promoting genes. In vivo studies with GE, GE-filtered, and strain A1 demonstrated significant pathogen inhibition and promoted tobacco plant growth. Disease incidence was reduced to 26.6% with GE, 46.67% with microbe-free GE, and 40% with strain A1. Overall, these treatments positively impacted plant root and shoot lengths as well as both fresh and dry weights. Our findings highlight onion GE as a potential, environmentally friendly method for controlling bacterial wilt and enhancing plant development, offering an alternative approach to traditional chemical controls in agriculture.

Niche differentiation shaped the evolution of rhizobacterial antibiotic resistance in paddy fields: Evidences from spatial-temporal and chemical-biological scaling

The rhizosphere serves as both a hotspot and an entry point for the proliferation and transformation of antibiotic resistance genes (ARGs). However, the ecological mechanisms governing the evolution of ARGs in rhizosphere soils remain poorly understood. This study showed that ARGs associated with efflux pumps were found to be significantly enriched in the rice rhizosphere, compared to bulk soils, with a deterministic assembly process. Notably, soil habitat specialization, dominated by turnover processes and the accelerated succession of microbial evolution in rhizosphere soils, profoundly influenced the spatial-temporal composition and expression of ARGs. Furthermore, ARGs involved in carbohydrate and proton transport showed higher activity in the rhizosphere, conductive to the adaptation of chemical niche differentiation. The genetic-level impacts stemming from biological niche warfare significantly shaped the evolutionary trajectory of ARG. Overall, rhizosphere effects led to 20.2-41.3 % of ARGs been enriched or depleted across various rice growth and under different irrigation conditions. These findings offer a comprehensive understanding of the essential ecological roles of ARGs evolution in rhizosphere soils, which is critical for ARGs risks analysis in the context of plant recruitment and growth promotion.

The chemical ecology and physiological functions of type I polyketide natural products: the emerging picture

Covering: up to 2024.For many years, the value of complex polyketides lay in their medical properties, including their antibiotic and antifungal activities, with little consideration paid to their native functions. However, more recent evidence gathered from the study of inter-organismal interactions has revealed the influence of these metabolites upon the ecological adaptation and distribution of their hosts, as well as their modes of communication. The increasing number of sequenced genomes and associated transcriptomes has also unveiled the widespread occurrence of the underlying biosynthetic enzymes across all kingdoms of life, and the important contributions they make to physiological events specific to each organism. This review depicts the diversity of roles fulfilled by type I polyketides, particularly in light of studies carried out during the last decade, providing an initial overall picture of their diverse functions.

Bacterium-Phage Symbiosis Facilitates the Enrichment of Bacterial Pathogens and Antibiotic-Resistant Bacteria in the Plastisphere

The plastisphere, defined as the ecological niche for microbial colonization of plastic debris, has been recognized as a hotspot of pathogenic and antibiotic-resistant bacteria. However, the interactions between bacteria and phages facilitated by the plastisphere, as well as their impact on microbial risks to public health, remain unclear. Here, we analyzed public metagenomic data from 180 plastisphere and environmental samples, stemming from four different habitats and two plastic types (biodegradable and nonbiodegradable plastics) and obtained 611 nonredundant metagenome-assembled genomes (MAGs) and 4061 nonredundant phage contigs. The plastisphere phage community exhibited decreased diversity and virulent proportion compared to those found in environments. Indexes of phage-host interaction networks indicated significant associations of phages with pathogenic and antibiotic-resistant bacteria (ARB), particularly for biodegradable plastics. Known phage-encoded auxiliary metabolic genes (AMGs) were involved in nutrient metabolism, antibiotic production, quorum sensing, and biofilm formation in the plastisphere, which contributed to enhanced competition and survival of pathogens and ARB hosts. Phages also carried transcriptionally active virulence factor genes (VFGs) and antibiotic resistance genes (ARGs), and could mediate their horizontal transfer in microbial communities. Overall, these discoveries suggest that plastisphere phages form symbiotic relationships with their hosts, and that phages encoding AMGs and mediating horizontal gene transfer (HGT) could increase the source of pathogens and antibiotic resistance from the plastisphere.

Whole Genome Sequencing and Biocontrol Potential of Streptomyces luteireticuli ASG80 Against Phytophthora Diseases

Phytophthora-induced crop diseases, commonly known as "plant plagues", pose a significant threat to global food security. In this study, strain ASG80 was isolated from sisal roots and demonstrated a broad-spectrum antagonistic activity against several Phytophthora species and fungal pathogens. Strain ASG80 was identified as Streptomyces luteireticuli via phylogenetic analysis, digital DNA-DNA hybridization (dDDH), and average nucleotide identity (ANI). Whole-genome sequencing identified 40 biosynthetic gene clusters (BGCs) related to secondary metabolite production, including antimicrobial compounds. Strain ASG80 extract exhibited broad-spectrum inhibitory activity against Phytophthora nicotianae, P. vignae, P. cinnamomi, and P. sojae. Pot experiments showed that strain ASG80 extract significantly reduced sisal zebra disease incidence, with an efficacy comparable to the fungicide metalaxyl. These findings suggest that strain ASG80 is a promising biocontrol agent with substantial potential for managing Phytophthora-related diseases in agriculture.

Bacterial epigenetics and its implication for agriculture, probiotics development, and biotechnology design

In their natural habitats, organisms encounter numerous external stimuli and must be able to sense and adapt to those stimuli to survive. Unlike mutations, epigenetic changes do not alter the underlying DNA sequence. Instead, they create modifications that promote or silence gene expression. Bacillus subtilis has long been a model organism in studying genetics and development. It is beneficial for numerous biotechnological applications where it is included as a probiotic, in fermentation, or in bio-concrete design. This bacterium has also emerged recently as a model organism for studying bacterial epigenetic adaptation. In this review, we examine the evolving knowledge of epigenetic regulation (restriction-modification systems (RM), orphan methyltransferases, and chromosome condensation) in B. subtilis and related bacteria, and utilize it as a case study to test their potential roles and future applications in genetic engineering and microbial biotechnology. Finally, we suggest how the implementation of these fundamental findings promotes the design of synthetic epigenetic memory circuits and their future applications in agriculture, medicine, and biotechnology.

Exploring the Darobactin Class of Antibiotics: A Comprehensive Review from Discovery to Recent Advancements

The prevalence of antimicrobial resistance in Gram-negative bacteria poses a greater challenge due to their intrinsic resistance to many antibiotics. Recently, darobactins have emerged as a novel class of antibiotics originating from previously unexplored Gram-negative bacterial species such as Photorhabdus, Vibrio, Pseudoalteromonas and Yersinia. Darobactins belong to the ribosomally synthesized and post-translationally modified peptide (RiPP) class of antibiotics, exhibiting selective activity against Gram-negative bacteria. They target the β-barrel assembly machinery (BAM), which is crucial for the maturation and insertion of outer membrane proteins in Gram-negative bacteria. The dar operon in the producer's genome encodes for the synthesis of darobactins, which are characterized by a fused ring system connected via an alkyl-aryl ether linkage (C-O-C) and a C-C cross-link. The enzyme DarE, using the radical S-adenosyl-l-methionine (rSAM), facilitates the formation of these bonds. Biosynthetic manipulation of the darobactin gene cluster, along with its expression in a surrogate host, has enabled access to diverse darobactin analogues with variable antibiotic activities. Recently, two independent research groups successfully achieved the total synthesis of darobactin, employing Larock heteroannulation to construct the bicyclic structure. This paper presents a comprehensive review of darobactins, encompassing their discovery through to the most recent advancements.

The Utilization of Bacillus subtilis to Design Environmentally Friendly Living Paints with Anti-Mold Properties

The anti-fungal properties of the probiotic bacterium Bacillus subtilis have been studied extensively in agriculture and ecology, but their applications in the built environment remain to be determined. Our work aims to utilize this biological component to introduce new diverse anti-mold properties into paint. "Mold" refers to the ubiquitous fungal species that generate visible multicellular filaments commonly found in household dust. The development of mold leads to severe health problems for occupants, including allergic response, hypersensitivity pneumonitis, and asthma, which have significant economic and clinical outcomes. We here demonstrate the robust effect of a commercial paint enhanced with Bacillus subtilis cells against the common mold agent, Aspergillus niger, and identify three biosynthetic clusters essential for this effect. Our results lay the foundation for bio-convergence and synthetic biology approaches to introduce renewable and environmentally friendly bio-anti-fungal agents into the built environment.

Biocontrol mechanisms of Bacillus: Improving the efficiency of green agriculture

Species of the genus Bacillus have been widely used for the biocontrol of plant diseases in the demand for sustainable agricultural development. New mechanisms underlying Bacillus biocontrol activity have been revealed with the development of microbiome and microbe-plant interaction research. In this review, we first briefly introduce the typical Bacillus biocontrol mechanisms, such as the production of antimicrobial compounds, competition for niches/nutrients, and induction of systemic resistance. Then, we discussed in detail the new mechanisms of pathogen quorum sensing interference and reshaping of the soil microbiota. The "cry for help" mechanism was also introduced, in which plants can release specific signals under pathogen attack to recruit biocontrol Bacillus for root colonization against invasion. Finally, two emerging strategies for enhancing the biocontrol efficacy of Bacillus agents, including the construction of synthetic microbial consortia and the application of rhizosphere-derived prebiotics, were proposed.

The roles of calcium signaling and calcium deposition in microbial multicellularity

Calcium signaling is an essential mediator of signal-controlling gene expression in most developmental systems. In addition, calcium has established extracellular functions as a structural component of biogenic minerals found in complex tissues. In bacteria, the formation of calcium carbonate structures is associated with complex colony morphology. Genes promoting the formation of biogenic minerals are essential for proper biofilm development and protection against antimicrobial solutes and toxins. Here we review recent findings on the role of calcium and calcium signaling as emerging regulators of biofilm formation in beneficial bacteria, as well as essential mediators of biofilm formation and virulence in human pathogens. The presented analysis concludes that the new understanding of calcium signaling may help to improve the performance of beneficial strains for sustainable agriculture, microbiome manipulation, and sustainable construction. Unraveling the roles of calcium may also promote the development of novel therapies against biofilm infections that target calcium uptake, calcium sensors, and calcium carbonate deposition.

The dynamics and transmission of antibiotic resistance associated with plant microbiomes

Antibiotic resistance genes (ARGs) have been widely found and studied in soil and water environments. However, the propagation of ARGs in plant microbiomes has attracted insufficient attention. Plant microbiomes, especially the rhizosphere microorganisms, are closely connected with water, soil, and air, which allows ARGs to spread widely in ecosystems and pose a threat to human health after entering the human body with bacteria. Therefore, it is necessary to deeply understand and explore the dynamics and the transmission of ARGs in rhizosphere microorganisms and endophytes of plants. In this review, the transmission and influencing factors of ARGs in the microorganisms associated with plants, especially the influence of root exudates on plant microbiomes, are analyzed. Notably, the role of intrinsic genes of plants in determining root exudates and their potential effects on ARGs are proposed and analyzed. The important role of phyllosphere microorganisms and endophytes in the transmission of ARGs and co-resistance of antibiotics and other substances are also emphasized. The proliferation and transmission of ARGs associated with plant microbiomes addressed in this review is conducive to revealing the fate of ARGs in plant microorganisms and alleviating ARG pollution.

Herbicolin A production and its modulation by quorum sensing in a Pantoea agglomerans rhizobacterium bioactive against a broad spectrum of plant‐pathogenic fungi

Global population growth makes it necessary to increase agricultural production yields. However, climate change impacts and diseases caused by plant pathogens are challenging modern agriculture. Therefore, it is necessary to look for alternatives to the excessive use of chemical fertilizers and pesticides. The plant microbiota plays an essential role in plant nutrition and health, and offers enormous potential to meet future challenges of agriculture. In this context, here we characterized the antifungal properties of the rhizosphere bacterium Pantoea agglomerans 9Rz4, which is active against a broad spectrum of plant pathogenic fungi. Chemical analyses revealed that strain 9Rz4 produces the antifungal herbicolin A and its biosynthetic gene cluster was identified and characterized. We found that the only acyl-homoserine lactone-based quorum sensing system of 9Rz4 modulates herbicolin A gene cluster expression. No role of plasmid carriage in the production of herbicolin A was observed. Plant assays revealed that herbicolin A biosynthesis does not affect the root colonization ability of P. agglomerans 9Rz4. Current legislative restrictions are aimed at reducing the use of chemical pesticides in agriculture, and the results derived from this study may lay the foundations for the development of novel biopesticides from rhizosphere microorganisms.

Explainable Machine Learning for Longitudinal Multi-Omic Microbiome

Over the years, research studies have shown there is a key connection between the microbial community in the gut, genes, and immune system. Understanding this association may help discover the cause of complex chronic idiopathic disorders such as inflammatory bowel disease. Even though important efforts have been put into the field, the functions, dynamics, and causation of dysbiosis state performed by the microbial community remains unclear. Machine learning models can help elucidate important connections and relationships between microbes in the human host. Our study aims to extend the current knowledge of associations between the human microbiome and health and disease through the application of dynamic Bayesian networks to describe the temporal variation of the gut microbiota and dynamic relationships between taxonomic entities and clinical variables. We develop a set of preprocessing steps to clean, filter, select, integrate, and model informative metagenomics, metatranscriptomics, and metabolomics longitudinal data from the Human Microbiome Project. This study accomplishes novel network models with satisfactory predictive performance (accuracy = 0.648) for each inflammatory bowel disease state, validating Bayesian networks as a framework for developing interpretable models to help understand the basic ways the different biological entities (taxa, genes, metabolites) interact with each other in a given environment (human gut) over time. These findings can serve as a starting point to advance the discovery of novel therapeutic approaches and new biomarkers for precision medicine.

Antibiotic resistance genes removals in stormwater bioretention cells with three kinds of environmental conditions

Recently, increasing attention has been paid to antibiotic resistance genes (ARGs) in stormwater runoff. However, there is still no available literature about ARGs removals through stormwater bioretention cells. Batch experiments were conducted to investigate target ARGs (bla_TEM, tetR and aphA) removals under three environmental conditions, including substrate (weight ratios of sand to soil), hydraulic loading rate (HLR) and submerged area depth. The target ARGs removals were the largest (more than 5 log in the bottom outlets) in bioretention cells with 8:2 ratio of sand to soil, HLR 0.044 cm³/cm²/min and 150 mm of submerged area depth. The proportion for both iARGs and eARGs had little effect on target ARGs removals (expect extracellular bla_TEM), although distributions of target ARGs were different in substrate layers. Adsorption behavior tests indicated that both kinetics and isotherms of target ARGs adsorption by biofilms were more suitable to explain their best removals for bioretention cells with 8:2 ratio of sand to soil than that by substrate. At phylum and genus levels, there were respectively 6 dominant microflora related significantly to target ARGs levels, and their relationships changed obviously under different environmental conditions, suggesting that regulating the dominant microflora (like Verrucomicrobia and Actinobacteria) could be feasible to change ARGs removals.

β-Lactam Resistance in Azospirillum baldaniorum Sp245 Is Mediated by Lytic Transglycosylase and β-Lactamase and Regulated by a Cascade of RpoE7→RpoH3 Sigma Factors

Bacterial resistance to β-lactam antibiotics is often mediated by β-lactamases and lytic transglycosylases. Azospirillum baldaniorum Sp245 is a plant-growth-promoting rhizobacterium that shows high levels of resistance to ampicillin. Investigating the molecular basis of ampicillin resistance and its regulation in A. baldaniorum Sp245, we found that a gene encoding lytic transglycosylase (Ltg1) is organized divergently from a gene encoding an extracytoplasmic function (ECF) σ factor (RpoE7) in its genome. Inactivation of rpoE7 in A. baldaniorum Sp245 led to increased ability to form cell-cell aggregates and produce exopolysaccharides and biofilm, suggesting that rpoE7 might contribute to antibiotic resistance. Inactivation of ltg1 in A. baldaniorum Sp245, however, adversely affected its growth, indicating a requirement of Ltg1 for optimal growth. The expression of rpoE7, as well that of as ltg1, was positively regulated by RpoE7, and overexpression of RpoE7 conferred ampicillin sensitivity to both the rpoE7::km mutant and its parent. In addition, RpoE7 negatively regulated the expression of a gene encoding a β-lactamase (bla1). Out of the 5 paralogs of RpoH encoded in the genome of A. baldaniorum Sp245, RpoH3 played major roles in conferring ampicillin sensitivity and in the downregulation of bla1. The expression of rpoH3 was positively regulated by RpoE7. Collectively, these observations reveal a novel regulatory cascade of RpoE7-RpoH3 σ factors that negatively regulates ampicillin resistance in A. baldaniorum Sp245 by controlling the expression of a β-lactamase and a lytic transglycosylase. In the absence of a cognate anti-sigma factor, addressing how the activity of RpoE7 is regulated by β-lactams will unravel new mechanisms of regulation of β-lactam resistance in bacteria. IMPORTANCE Antimicrobial resistance is a global health problem that requires a better understanding of the mechanisms that bacteria use to resist antibiotics. Bacteria inhabiting the plant rhizosphere are a potential source of antibiotic resistance, but their mechanisms controlling antibiotic resistance are poorly understood. A. baldaniorum Sp245 is a rhizobacterium that is known for its characteristic resistance to ampicillin. Here, we show that an AmpC-type β-lactamase and a lytic transglycosylase mediate resistance to ampicillin in A. baldaniorum Sp245. While the gene encoding lytic transglycosylase is positively regulated by an ECF σ-factor (RpoE7), a cascade of RpoE7 and RpoH3 σ factors negatively regulates the expression of β-lactamase. This is the first evidence showing involvement of a regulatory cascade of σ factors in the regulation of ampicillin resistance in a rhizobacterium.

Resolving the conflict between antibiotic production and rapid growth by recognition of peptidoglycan of susceptible competitors

Microbial communities employ a variety of complex strategies to compete successfully against competitors sharing their niche, with antibiotic production being a common strategy of aggression. Here, by systematic evaluation of four non-ribosomal peptides/polyketide (NRPs/PKS) antibiotics produced by Bacillus subtilis clade, we revealed that they acted synergistically to effectively eliminate phylogenetically distinct competitors. The production of these antibiotics came with a fitness cost manifested in growth inhibition, rendering their synthesis uneconomical when growing in proximity to a phylogenetically close species, carrying resistance against the same antibiotics. To resolve this conflict and ease the fitness cost, antibiotic production was only induced by the presence of a peptidoglycan cue from a sensitive competitor, a response mediated by the global regulator of cellular competence, ComA. These results experimentally demonstrate a general ecological concept - closely related communities are favoured during competition, due to compatibility in attack and defence mechanisms.

Imaging flow cytometry reveals a dual role for exopolysaccharides in biofilms: To promote self-adhesion while repelling non-self-community members

In nature, bacteria frequently reside in differentiated communities or biofilms. These multicellular communities are held together by self-produced polymers that allow the community members to adhere to the surface as well as to neighbor bacteria. Here, we report that exopolysaccharides prevent Bacillus subtilis from co-aggregating with a distantly related bacterium Bacillus mycoides, while maintaining their role in promoting self-adhesion and co-adhesion with phylogenetically related bacterium, Bacillus atrophaeus. The defensive role of the exopolysaccharides is due to the specific regulation of bacillaene. Single cell analysis of biofilm and free-living bacterial cells using imaging flow cytometry confirmed a specific role for the exopolysaccharides in microbial competition repelling B. mycoides. Unlike exopolysaccharides, the matrix protein TasA induced bacillaene but inhibited the expression of the biosynthetic clusters for surfactin, and therefore its overall effect on microbial competition during floating biofilm formation was neutral. Thus, the exopolysaccharides provide a dual fitness advantage for biofilm-forming cells, as it acts to promote co-aggregation of related species, as well as, a secreted cue for chemical interference with non-compatible partners. These results experimentally demonstrate a general assembly principle of complex communities and provides an appealing explanation for how closely related species are favored during community assembly. Furthermore, the differential regulation of surfactin and bacillaene by the extracellular matrix may explain the spatio-temporal gradients of antibiotic production within biofilms.

Biological Control of Plant Diseases: An Evolutionary and Eco-Economic Consideration

Biological control is considered as a promising alternative to pesticide and plant resistance to manage plant diseases, but a better understanding of the interaction of its natural and societal functions is necessary for its endorsement. The introduction of biological control agents (BCAs) alters the interaction among plants, pathogens, and environments, leading to biological and physical cascades that influence pathogen fitness, plant health, and ecological function. These interrelationships generate a landscape of tradeoffs among natural and social functions of biological control, and a comprehensive evaluation of its benefits and costs across social and farmer perspectives is required to ensure the sustainable development and deployment of the approach. Consequently, there should be a shift of disease control philosophy from a single concept that only concerns crop productivity to a multifaceted concept concerning crop productivity, ecological function, social acceptability, and economical accessibility. To achieve these goals, attempts should make to develop “green” BCAs used dynamically and synthetically with other disease control approaches in an integrated disease management scheme, and evolutionary biologists should play an increasing role in formulating the strategies. Governments and the public should also play a role in the development and implementation of biological control strategies supporting positive externality.

Bacillus subtilis Colonization of Arabidopsis thaliana Roots Induces Multiple Biosynthetic Clusters for Antibiotic Production

Beneficial and probiotic bacteria play an important role in conferring immunity of their hosts to a wide range of bacterial, viral, and fungal diseases. Bacillus subtilis is a Gram-positive bacterium that protects the plant from various pathogens due to its capacity to produce an extensive repertoire of antibiotics. At the same time, the plant microbiome is a highly competitive niche, with multiple microbial species competing for space and resources, a competition that can be determined by the antagonistic potential of each microbiome member. Therefore, regulating antibiotic production in the rhizosphere is of great importance for the elimination of pathogens and establishing beneficial host-associated communities. In this work, we used B. subtilis as a model to investigate the role of plant colonization in antibiotic production. Flow cytometry and imaging flow cytometry (IFC) analysis supported the notion that Arabidopsis thaliana specifically induced the transcription of the biosynthetic clusters for the non-ribosomal peptides surfactin, bacilysin, plipastatin, and the polyketide bacillaene. IFC was more robust in quantifying the inducing effects of A. thaliana, considering the overall heterogeneity of the population. Our results highlight IFC as a useful tool to study the effect of association with a plant host on bacterial gene expression. Furthermore, the common regulation of multiple biosynthetic clusters for antibiotic production by the plant can be translated to improve the performance and competitiveness of beneficial members of the plant microbiome.

Effects of integrated biocontrol on bacterial wilt and rhizosphere bacterial community of tobacco

Bacterial wilt as a soil-borne disease was caused by Ralstonia solanacearum, and seriously damages the growth of tobacco. Integrated biocontrol method was explored to control bacterial wilt. Nevertheless, the long-term effects of the integrated biocontrol method on soil bacterial community, soil physicochemical properties and the incidence of bacterial wilt are not well understood. In this study, B. amyoliquefaciens ZM9, calcium cyanamide and rice bran were applied to tobacco fields in different ways. The disease index and incidence of tobacco bacterial wilt (TBW), soil physicochemical properties, colonization ability of B. amyoliquefaciens ZM9, and rhizopshere bacterial community were investigated. The results showed that the integrated application of B. amyoliquefaciens ZM9, rice bran and calcium cyanamide had the highest control efficiency of TBW and bacteria community diversity. Additionally, the integrated biocontrol method could improve the colonization ability of B. amyoliquefaciens ZM9. Furthermore, the integrated biocontrol method could effectively suppress TBW by regulating soil physicochemical properties, promoting beneficial bacteria and antagonistic bacteria of rhizopshere soil. This strategy has prospect of overcoming the defects in application of a single antagonistic bacteria and provides new insights to understand how to improve the colonization capacity of antagonistic bacteria and control efficacy for TBW.

Emerging Roles of Functional Bacterial Amyloids in Gene Regulation, Toxicity, and Immunomodulation

Bacteria often reside in multicellular communities, called biofilms, held together by an extracellular matrix. In many bacteria, the major proteinaceous component of the biofilm are amyloid fibers. Amyloids are highly stable and structured protein aggregates which were known mostly to be associated with neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's diseases. In recent years, microbial amyloids were identified also in other species and shown to play major roles in microbial physiology and virulence. For example, amyloid fibers assemble on the bacterial cell surface as a part of the extracellular matrix and are extremely important to the scaffolding and structural integrity of biofilms, which contribute to microbial resilience and resistance. Furthermore, microbial amyloids play fundamental nonscaffold roles that contribute to the development of biofilms underlying numerous persistent infections. Here, we review several nonscaffold roles of bacterial amyloid proteins, including bridging cells during collective migration, acting as regulators of cell fate, as toxins against other bacteria or against host immune cells, and as modulators of the hosts' immune system. These overall points on the complexity of the amyloid fold in encoding numerous activities, which offer approaches for the development of a novel repertoire of antivirulence therapeutics.