Chemical interplay and complementary adaptative strategies toggle bacterial antagonism and co-existence

Adaptive laboratory evolution reveals regulators involved in repressing biofilm development as key players in Bacillus subtilis root colonization

Root-associated microorganisms play an important role in plant health, such as plant growth-promoting rhizobacteria (PGPR) from the Bacillus and Pseudomonas genera. Although bacterial consortia including these two genera would represent a promising avenue to efficient biofertilizer formulation, we observed that Bacillus subtilis root colonization is decreased by the presence of Pseudomonas fluorescens and Pseudomonas protegens. To determine if B. subtilis can adapt to the inhibitory effect of Pseudomonas on roots, we conducted adaptative laboratory evolution experiments with B. subtilis in mono-association or co-cultured with P. fluorescens on tomato plant roots. Evolved isolates with various colony morphology and stronger colonization capacity of both tomato plant and Arabidopsis thaliana roots emerged rapidly from the two evolution experiments. Certain evolved isolates also had better fitness on the root in the presence of other Pseudomonas species. In all independent lineages, whole-genome resequencing revealed non-synonymous mutations in genes ywcC or sinR encoding regulators involved in repressing biofilm development, suggesting their involvement in enhanced root colonization. These findings provide insights into the molecular mechanisms underlying B. subtilis adaptation to root colonization and highlight the potential of directed evolution to enhance the beneficial traits of PGPR.IMPORTANCEIn this study, we aimed to enhance the abilities of the plant-beneficial bacterium Bacillus subtilis to colonize plant roots in the presence of competing Pseudomonas bacteria. To achieve this, we conducted adaptive laboratory experiments, allowing Bacillus to evolve in a defined environment. We successfully obtained strains of Bacillus that were more effective at colonizing plant roots than the ancestor strain. To identify the genetic changes driving this improvement, we sequenced the genomes of these evolved strains. Interestingly, mutations that facilitated the formation of robust biofilms on roots were predominant. Many of these evolved Bacillus isolates also displayed the remarkable ability to outcompete Pseudomonas species. Our research sheds light on the mutational paths selected in Bacillus subtilis to thrive in root environments and offers exciting prospects for improving beneficial traits in plant growth-promoting microorganisms. Ultimately, this could pave the way for the development of more effective biofertilizers and sustainable agricultural practices.

Bacillus sp. G2112 Detoxifies Phenazine-1-carboxylic Acid by N5 Glucosylation

Microbial symbionts of plants constitute promising sources of biocontrol organisms to fight plant pathogens. Bacillus sp. G2112 and Pseudomonas sp. G124 isolated from cucumber (Cucumis sativus) leaves inhibited the plant pathogens Erwinia and Fusarium. When Bacillus sp. G2112 and Pseudomonas sp. G124 were co-cultivated, a red halo appeared around Bacillus sp. G2112 colonies. Metabolite profiling using liquid chromatography coupled to UV and mass spectrometry revealed that the antibiotic phenazine-1-carboxylic acid (PCA) released by Pseudomonas sp. G124 was transformed by Bacillus sp. G2112 to red pigments. In the presence of PCA (>40 µg/mL), Bacillus sp. G2112 could not grow. However, already-grown Bacillus sp. G2112 (OD600 > 1.0) survived PCA treatment, converting it to red pigments. These pigments were purified by reverse-phase chromatography, and identified by high-resolution mass spectrometry, NMR, and chemical degradation as unprecedented 5N-glucosylated phenazine derivatives: 7-imino-5N-(1'β-D-glucopyranosyl)-5,7-dihydrophenazine-1-carboxylic acid and 3-imino-5N-(1'β-D-glucopyranosyl)-3,5-dihydrophenazine-1-carboxylic acid. 3-imino-5N-(1'β-D-glucopyranosyl)-3,5-dihydrophenazine-1-carboxylic acid did not inhibit Bacillus sp. G2112, proving that the observed modification constitutes a resistance mechanism. The coexistence of microorganisms-especially under natural/field conditions-calls for such adaptations, such as PCA inactivation, but these can weaken the potential of the producing organism against pathogens and should be considered during the development of biocontrol strategies.

Competition for iron shapes metabolic antagonism between Bacillus subtilis and Pseudomonas marginalis

Siderophores have long been implicated in sociomicrobiology as determinants of bacterial interrelations. For plant-associated genera, like Bacillus and Pseudomonas, siderophores are well known for their biocontrol functions. Here, we explored the functional role of the Bacillus subtilis siderophore bacillibactin (BB) in an antagonistic interaction with Pseudomonas marginalis. The presence of BB strongly influenced the outcome of the interaction in an iron-dependent manner. The BB producer B. subtilis restricts colony spreading of P. marginalis by repressing the transcription of histidine kinase-encoding gene gacS, thereby abolishing production of secondary metabolites such as pyoverdine and viscosin. By contrast, lack of BB restricted B. subtilis colony growth. To explore the specificity of the antagonism, we cocultured B. subtilis with a collection of fluorescent Pseudomonas spp. and found that the Bacillus-Pseudomonas interaction is conserved, expanding our understanding of the interplay between two of the most well-studied genera of soil bacteria.

Predicting Personalized Diets Based on Microbial Characteristics between Patients with Superficial Gastritis and Atrophic Gastritis

BACKGROUND

gastritis is a common stomach disease with a high global incidence and can potentially develop into gastric cancer. The treatment of gastritis focuses on medication or diets based on national guidelines. However, the specific diet that can alleviate gastritis remains largely unknown.

METHODS

we propose a microbiota-directed dietary strategy that investigates potential food factors using microbial exogenous metabolites. Given the current lack of understanding of the repeatable characteristics of gastric microbiota, we conducted a meta-analysis to identify the features of gastric bacteria. Local samples were collected as validation cohorts. Furthermore, RevEcoR was employed to identify bacteria's exogenous metabolites, and FooDB was used to retrieve foods that can target specific bacteria.

RESULTS

Bacteroides, Weissella, Actinomyces, Atopobium, Oribacterium, Peptostreptococcus, and Rothia were biomarkers between superficial gastritis (SG) and atrophic gastritis (AG) (AG_N) without H. pylori infection, whereas Bacillus, Actinomyces, Cutibacterium, Helicobacter, Novosphingobium, Pseudomonas, and Streptococcus were signatures between SG and AG (AG_P) with H. pylori infection. According to the exogenous metabolites, adenosyloobalamin, soybean, common wheat, dates, and barley were regarded as potential candidates for AG_N treatment, while gallate was regarded as a candidate for AG_P treatment.

CONCLUSIONS

this study firstly profiled the gastric microbiota of AG and SG with or without H. pylori and provided a recommended diet for global AG according to exogenous metabolites.

Selective inhibition of the amyloid matrix of Escherichia coli biofilms by a bifunctional microbial metabolite

The propensity of bacteria to grow collectively in communities known as biofilms and their ability to overcome clinical treatments in this condition has become a major medical problem, emphasizing the need for anti-biofilm strategies. Antagonistic microbial interactions have extensively served as searching platforms for antibiotics, but their potential as sources for anti-biofilm compounds has barely been exploited. By screening for microorganisms that in agar-set pairwise interactions could antagonize Escherichia coli's ability to form macrocolony biofilms, we found that the soil bacterium Bacillus subtilis strongly inhibits the synthesis of amyloid fibers -known as curli-, which are the primary extracellular matrix (ECM) components of E. coli biofilms. We identified bacillaene, a B. subtilis hybrid non-ribosomal peptide/polyketide metabolite, previously described as a bacteriostatic antibiotic, as the effector molecule. We found that bacillaene combines both antibiotic and anti-curli functions in a concentration-dependent order that potentiates the ecological competitiveness of B. subtilis, highlighting bacillaene as a metabolite naturally optimized for microbial inhibition. Our studies revealed that bacillaene inhibits curli by directly impeding the assembly of the CsgB and CsgA curli subunits into amyloid fibers. Moreover, we found that curli inhibition occurs despite E. coli attempts to reinforce its protective ECM by inducing curli genes via a RpoS-mediated competition sensing response trigged by the threatening presence of B. subtilis. Overall, our findings illustrate the relevance of exploring microbial interactions not only for finding compounds with unknown and unique activities, but for uncovering additional functions of compounds previously categorized as antibiotics.

Evaluation of Data-Dependent MS/MS Acquisition Parameters for Non-Targeted Metabolomics and Molecular Networking of Environmental Samples: Focus on the Q Exactive Platform

Non-targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a widely used tool for metabolomics analysis, enabling the detection and annotation of small molecules in complex environmental samples. Data-dependent acquisition (DDA) of product ion spectra is thereby currently one of the most frequently applied data acquisition strategies. The optimization of DDA parameters is central to ensuring high spectral quality, coverage, and number of compound annotations. Here, we evaluated the influence of 10 central DDA settings of the Q Exactive mass spectrometer on natural organic matter samples from ocean, river, and soil environments. After data analysis with classical and feature-based molecular networking using MZmine and GNPS, we compared the total number of network nodes, multivariate clustering, and spectrum quality-related metrics such as annotation and singleton rates, MS/MS placement, and coverage. Our results show that automatic gain control, microscans, mass resolving power, and dynamic exclusion are the most critical parameters, whereas collision energy, TopN, and isolation width had moderate and apex trigger, monoisotopic selection, and isotopic exclusion minor effects. The insights into the data acquisition ergonomics of the Q Exactive platform presented here can guide new users and provide them with initial method parameters, some of which may also be transferable to other sample types and MS platforms.

Assembly of an active microbial consortium by engineering compatible combinations containing foreign and native biocontrol bacteria of kiwifruit

Assembling functional bacterial biocontrol consortia is expected to expand the scope and efficiency of biocontrol agents. Generally, bacterial interspecies interactions lead to incompatibility events, as bacteria can produce antibacterial compounds and/or assemble contact-dependent killing (CDK) devices. Here, we aimed to assemble a bacterial consortium comprising Lysobacter enzymogenes OH11 and Bacillus safensis ZK-1 for the synergistic control of bacterial and fungal diseases of kiwifruit. ZK-1, a native kiwifruit biocontrol bacterium, is effective against Pseudomonas syringae pv. actinidiae (Psa) that causes bacterial kiwifruit canker, but has weak antifungal activity. OH11 is a foreign kiwifruit biocontrol agent with strong antifungal activity. While OH11 was unable to produce anti-Gram-negative metabolites, this strain could utilize type IV secretion system as an antibacterial CDK weapon. We first observed that OH11 could inhibit growth of ZK-1 by generating diffusible anti-Gram-positive antibiotic WAP-8294A2, whereas ZK-1 failed to generate diffusible antibacterial compound to inhibit growth of OH11. To disrupt this interspecies incompatibility, we generated a transgenic OH11-derived strain, OH11W, by deleting the WAP-8294A2 biosynthetic gene and found that OH11W did not kill ZK-1. We further observed that when OH11W and ZK-1 were co-inoculated on agar plates, no CDK effect was observed between them, whereas co-culture of OH11W or ZK-1 with Psa on agar plates resulted in Psa killing, suggesting L. enzymogenes and B. safensis assemble antibacterial CDK weapons against bacterial pathogens, and these CDK weapons did not affect the compatibility between OH11W and ZK-1. Based on these findings, we assembled an OH11W/ZK-1 dependent consortium that was shown to be functional in controlling bacterial canker and several representative fungal diseases of kiwifruit.

Pyochelin biotransformation by Staphylococcus aureus shapes bacterial competition with Pseudomonas aeruginosa in polymicrobial infections

Pseudomonas aeruginosa and Staphylococcus aureus are among the most frequently isolated bacterial species from polymicrobial infections of patients with cystic fibrosis and chronic wounds. We apply mass spectrometry guided interaction studies to determine how chemical interaction shapes the fitness and community structure during co-infection of these two pathogens. We demonstrate that S. aureus is equipped with an elegant mechanism to inactivate pyochelin via the yet uncharacterized methyltransferase Spm (staphylococcal pyochelin methyltransferase). Methylation of pyochelin abolishes the siderophore activity of pyochelin and significantly lowers pyochelin-mediated intracellular reactive oxygen species (ROS) production in S. aureus. In a murine wound co-infection model, an S. aureus mutant unable to methylate pyochelin shows significantly lower fitness compared with its parental strain. Thus, Spm-mediated pyochelin methylation is a mechanism to increase S. aureus survival during in vivo competition with P. aeruginosa.

Transcriptomic response of Sinorhizobium meliloti to the predatory attack of Myxococcus xanthus

Bacterial predation impacts microbial community structures, which can have both positive and negative effects on plant and animal health and on environmental sustainability. Myxococcus xanthus is an epibiotic soil predator with a broad range of prey, including Sinorhizobium meliloti, which establishes nitrogen-fixing symbiosis with legumes. During the M. xanthus-S. meliloti interaction, the predator must adapt its transcriptome to kill and lyse the target (predatosome), and the prey must orchestrate a transcriptional response (defensome) to protect itself against the biotic stress caused by the predatory attack. Here, we describe the transcriptional changes taking place in S. meliloti in response to myxobacterial predation. The results indicate that the predator induces massive changes in the prey transcriptome with up-regulation of protein synthesis and secretion, energy generation, and fatty acid (FA) synthesis, while down-regulating genes required for FA degradation and carbohydrate transport and metabolism. The reconstruction of up-regulated pathways suggests that S. meliloti modifies the cell envelop by increasing the production of different surface polysaccharides (SPSs) and membrane lipids. Besides the barrier role of SPSs, additional mechanisms involving the activity of efflux pumps and the peptide uptake transporter BacA, together with the production of H₂O₂ and formaldehyde have been unveiled. Also, the induction of the iron-uptake machinery in both predator and prey reflects a strong competition for this metal. With this research we complete the characterization of the complex transcriptional changes that occur during the M. xanthus-S. meliloti interaction, which can impact the establishment of beneficial symbiosis with legumes.

Perenniality, more than genotypes, shapes biological and chemical rhizosphere composition of perennial wheat lines

Perennial grains provide various ecosystem services compared to the annual counterparts thanks to their extensive root system and permanent soil cover. However, little is known about the evolution and diversification of perennial grains rhizosphere and its ecological functions over time. In this study, a suite of -OMICSs - metagenomics, enzymomics, metabolomics and lipidomics - was used to compare the rhizosphere environment of four perennial wheat lines at the first and fourth year of growth in comparison with an annual durum wheat cultivar and the parental species Thinopyrum intermedium. We hypothesized that wheat perenniality has a greater role in shaping the rhizobiome composition, biomass, diversity, and activity than plant genotypes because perenniality affects the quality and quantity of C input - mainly root exudates - hence modulating the plant-microbes crosstalk. In support of this hypothesis, the continuous supply of sugars in the rhizosphere along the years created a favorable environment for microbial growth which is reflected in a higher microbial biomass and enzymatic activity. Moreover, modification in the rhizosphere metabolome and lipidome over the years led to changes in the microbial community composition favoring the coexistence of more diverse microbial taxa, increasing plant tolerance to biotic and abiotic stresses. Despite the dominance of the perenniality effect, our data underlined that the OK72 line rhizobiome distinguished from the others by the increase in abundance of Pseudomonas spp., most of which are known as potential beneficial microorganisms, identifying this line as a suitable candidate for the study and selection of new perennial wheat lines.

Sporulation Activated via σW Protects Bacillus from a Tse1 Peptidoglycan Hydrolase Type VI Secretion System Effector

Within bacterial communities, community members engage in interactions employing diverse offensive and defensive tools to reach coexistence. Extracellular-matrix production and sporulation are defensive mechanisms used by Bacillus subtilis cells when they interact with Pseudomonas chlororaphis strains expressing a type VI secretion system (T6SS). Here, we define Tse1 as the main toxin mobilized by the Pseudomonas chlororaphis T6SS that triggers sporulation in Bacillus subtilis. We characterize Tse1 as a peptidoglycan hydrolase that indirectly alters the dynamics and functionality of the Bacillus cell membrane. We also delineate the response of Bacillus cells to Tse1, which through the coordinated actions of the extracellular sigma factor σW and the cytoplasmic histidine kinases KinA and KinB, culminates in activation of the sporulation cascade. We propose that this cellular developmental response permits bacilli to defend against the toxicity of T6SS-mobilized Tse1 effector. IMPORTANCE The study of bacterial interactions is helping to define species-specific strategies used to modulate the competition dynamics underlying the development of community compositions. In this study, we deciphered the role of Pseudomonas T6SS when competing with Bacillus and the mechanism by which a T6SS-toxin modifies Bacillus physiology. We found that Pseudomonas triggers Bacillus sporulation by injecting through T6SS a toxin that we called Tse1. We found that Tse1 is a hydrolase that degrades Bacillus peptidoglycan and indirectly damages Bacillus membrane functionality. In addition, we demonstrated the mechanism by which Bacillus cells increase the sporulation rate upon recognition of the presence of Tse1. Interestingly, asporogenic Bacillus cells are more sensitive to T6SS activity, which led us to propose sporulation as a last resort of bacilli to overcome this family of toxins.

Frenemies of the soil: Bacillus and Pseudomonas interspecies interactions

Bacillus and Pseudomonas ubiquitously occur in natural environments and are two of the most intensively studied bacterial genera in the soil. They are often coisolated from environmental samples, and as a result, several studies have experimentally cocultured bacilli and pseudomonads to obtain emergent properties. Even so, the general interaction between members of these genera is virtually unknown. In the past decade, data on interspecies interactions between natural isolates of Bacillus and Pseudomonas has become more detailed, and now, molecular studies permit mapping of the mechanisms behind their pairwise ecology. This review addresses the current knowledge about microbe-microbe interactions between strains of Bacillus and Pseudomonas and discusses how we can attempt to generalize the interaction on a taxonomic and molecular level.

Microbes to support plant health: understanding bioinoculant success in complex conditions

A promising, sustainable way to enhance plant health and productivity is by leveraging beneficial microbes. Beneficial microbes are natural soil residents with proven benefits for plant performance and health. When applied in agriculture to improve crop yield and performance, these microbes are commonly referred to as bioinoculants. Yet, despite their promising properties, bioinoculant efficacy can vary dramatically in the field, hampering their applicability. Invasion of the rhizosphere microbiome is a critical determinant for bioinoculant success. Invasion is a complex phenomenon that is shaped by interactions with the local, resident microbiome and the host plant. Here, we explore all of these dimensions by cross-cutting ecological theory and molecular biology of microbial invasion in the rhizosphere. We refer to the famous Chinese philosopher and strategist Sun Tzu, who believed that solutions for problems require deep understanding of the problems themselves, to review the major biotic factors determining bioinoculant effectiveness.

Bacillaene, sharp objects consist in the arsenal of antibiotics produced by Bacillus

Bacillus species act as plant growth-promoting rhizobacteria (PGPR) that can produce a large number of bioactive metabolites. Bacillaene, a linear polyketide/nonribosomal peptide produced by Bacillus strains, is synthesized by the trans-acyltransferase polyketide synthetase. The complexity of the chemical structure, particularity of biosynthesis, potent bioactivity, and the important role of competition make Bacillus an ideal antibiotic weapon to resist other microbes and maintain the optimal rhizosphere environment. This review provides an updated view of the structural features, biological activity, biosynthetic regulators of biosynthetic pathways, and the important competitive role of bacillaene during Bacillus survival.

Plant-associated Bacillus mobilizes its secondary metabolites upon perception of the siderophore pyochelin produced by a Pseudomonas competitor

Bacillus velezensis is considered as model species for plant-associated bacilli providing benefits to its host such as protection against phytopathogens. This is mainly due to the potential to secrete a wide range of secondary metabolites with specific and complementary bioactivities. This metabolite arsenal has been quite well defined genetically and chemically but much remains to be explored regarding how it is expressed under natural conditions and notably how it can be modulated upon interspecies interactions in the competitive rhizosphere niche. Here, we show that B. velezensis can mobilize a substantial part of its metabolome upon the perception of Pseudomonas, as a soil-dwelling competitor. This metabolite response reflects a multimodal defensive strategy as it includes polyketides and the bacteriocin amylocyclicin, with broad antibiotic activity, as well as surfactin lipopeptides, contributing to biofilm formation and enhanced motility. Furthermore, we identified the secondary Pseudomonas siderophore pyochelin as an info-chemical, which triggers this response via a mechanism independent of iron stress. We hypothesize that B. velezensis relies on such chelator sensing to accurately identify competitors, illustrating a new facet of siderophore-mediated interactions beyond the concept of competition for iron and siderophore piracy. This phenomenon may thus represent a new component of the microbial conversations driving the behavior of members of the rhizosphere community.

A Noninvasive Method for Time-Lapse Imaging of Microbial Interactions and Colony Dynamics

Complex interactions between microbial populations can greatly affect the overall properties of a microbial community, sometimes leading to cooperation and mutually beneficial coexistence, or competition and the death or displacement of organisms or subpopulations. Interactions between different biofilm populations are highly relevant in diverse scientific areas, from antimicrobial resistance to microbial ecology. The utilization of modern microscopic techniques has provided a new and interesting insight into how bacteria interact at the cellular level to form and maintain microbial biofilms. However, our ability to follow complex intraspecies and interspecies interactions in vivo at the microscopic level has remained somewhat limited. Here, we detailed BacLive, a novel noninvasive method for tracking bacterial growth and biofilm dynamics using high-resolution fluorescence microscopy and an associated ImageJ processing macro (https://github.com/BacLive) for easier data handling and image analysis. Finally, we provided examples of how BacLive can be used in the analysis of complex bacterial communities.

IMPORTANCE Communication and interactions between single cells are continuously defining the structure and composition of microbial communities temporally and spatially. Methods routinely used to study these communities at the cellular level rely on sample manipulation which makes microscopic time-lapse experiments impossible. BacLive was conceived as a method for the noninvasive study of the formation and development of bacterial communities, such as biofilms, and the formation dynamics of specialized subpopulations in time-lapse experiments at a colony level. In addition, we developed a tool to simplify the processing and analysis of the data generated by this method.

Discrimination between the Two Closely Related Species of the Operational Group B. amyloliquefaciens Based on Whole-Cell Fatty Acid Profiling

(1) Background: Bacillus velezensis and Bacillus amyloliquefaciens are closely related members of the “operational group B. amyloliquefaciens”, a taxonomical unit above species level within the ”Bacillus subtilis species complex”. They have similar morphological, physiological, biochemical, phenotypic, and phylogenetic characteristics. Thus, separating these two taxa from each another has proven to be difficult to implement and could not be pushed easily into the line of routine analyses. (2) Methods: The aim of this study was to determine whether whole FAME profiling could be used to distinguish between these two species, using both type strains and environmental isolates. Initially, the classification was determined by partial sequences of the gyrA and rpoB genes and the classified isolates and type strains were considered as samples to develop the identification method, based on FAME profiles. (3) Results: The dissimilarities in 16:0, 17:0 iso, and 17:0 FA components have drawn a distinction between the two species and minor differences in FA 14:0, 15:0 iso, and 16:0 iso were also visible. The statistical analysis of the FA profiles confirmed that the two taxa can be distinguished into two separate groups, where the isolates are identified without misreading. (4) Conclusions: Our study proposes that the developed easy and fast-automated identification tool based on cellular FA profiles can be routinely applied to distinguish B. velezensis and B. amyloliquefaciens.

Lipopeptide Interplay Mediates Molecular Interactions between Soil Bacilli and Pseudomonads

Some Bacillus species, such as B. velezensis, are important members of the plant-associated microbiome, conferring protection against phytopathogens. However, our knowledge about multitrophic interactions determining the ecological fitness of these biocontrol bacteria in the competitive rhizosphere niche is still limited. Here, we investigated molecular mechanisms underlying interactions between B. velezensis and Pseudomonas as a soil-dwelling competitor. Upon their contact-independent in vitro confrontation, a multifaceted macroscopic outcome was observed and characterized by Bacillus growth inhibition, white line formation in the interaction zone, and enhanced motility. We correlated these phenotypes with the production of bioactive secondary metabolites and identified specific lipopeptides as key compounds involved in the interference interaction and motile response. Bacillus mobilizes its lipopeptide surfactin not only to enhance motility but also to act as a chemical trap to reduce the toxicity of lipopeptides formed by Pseudomonas. We demonstrated the relevance of these unsuspected roles of lipopeptides in the context of competitive tomato root colonization by the two bacterial genera.

IMPORTANCE Plant-associated Bacillus velezensis and Pseudomonas spp. represent excellent model species as strong producers of bioactive metabolites involved in phytopathogen inhibition and the elicitation of plant immunity. However, the ecological role of these metabolites during microbial interspecies interactions and the way their expression may be modulated under naturally competitive soil conditions has been poorly investigated. Through this work, we report various phenotypic outcomes from the interactions between B. velezensis and 10 Pseudomonas strains used as competitors and correlate them with the production of specific metabolites called lipopeptides from both species. More precisely, Bacillus overproduces surfactin to enhance motility, which also, by acting as a chemical trap, reduces the toxicity of other lipopeptides formed by Pseudomonas. Based on data from interspecies competition on plant roots, we assume this would allow Bacillus to gain fitness and persistence in its natural rhizosphere niche. The discovery of new ecological functions for Bacillus and Pseudomonas secondary metabolites is crucial to rationally design compatible consortia, more efficient than single-species inoculants, to promote plant health and growth by fighting economically important pathogens in sustainable agriculture.