Biology subjects

Romero, D.

Publications and source records attributed to Romero, D..

18 recordsLinked to original sources

bioRxiv2026

Cooperative siderophore use stabilizes a protective leaf microbiome

Plant-associated microbial communities provide crucial protection against pathogens. Specialized metabolites play key roles in plant-microbe and microbe-microbe interactions and, ultimately, in plant health; however, the molecular mechanisms underlying their plant-protecting properties remain largely unknown. Nutrient deficiency (e.g., iron) on leaf surfaces creates intense competition among microbes, driving both antagonism and cooperation. Using a gnotobiotic Arabidopsis thaliana model and a synthetic leaf microbial community, we show that community stability and plant protection depend on cooperative siderophore exchange between the basidiomycete yeast Rhodotorula kratochvilovae and commensal Pseudomonas species. Removal of Pseudomonas caused a strong shift in the community metabolome and accumulation of the yeast siderophore rhodotorulic acid (RA). RA selectively promoted the growth of commensal Pseudomonas via TonB-dependent transporters, which are absent in pathogenic Pseudomonas strains. Inactivation of these transporter genes abolished RA uptake, destabilized the synthetic community, and eliminated protection against Pseudomonas syringae infection. RA and Rhodotorula also induced host iron-deficiency and jasmonate-related defense metabolites, linking microbial cooperation to plant stress responses. These findings reveal that microbial siderophore exchange acts as a key mechanism that maintains stability in the phyllosphere microbiome. Rather than solely promoting competition, iron-binding compounds can serve as cooperative currencies that align microbial fitness with host protection.

microbiology↗

bioRxiv2025

Early seed priming with closely related Bacillus strains induces divergent physiological and defense responses in melon

Early microbial seed priming is a promising strategy to improve crop resilience, yet it remains unclear whether plants can discriminate among closely related beneficial strains and integrate dose-dependent microbial cues. We primed melon (Cucumis melo) seeds with two phylogenetically similar Bacillus strains (B. subtilis NCIB3610 and B. velezensis FZB42) and combined transcriptomic, metabolomic and physiological analyses across development. Despite comparable colonization, the strains provoked contrasting host programs and distinct dose responses. B. subtilis promoted radicle elongation, chloroplastic starch storage and drought tolerance irrespective of inoculum level, together with L-tryptophan and palatinose accumulation. By contrast, B. velezensis displayed a clear dose effect: low inoculum sustained normal radicle growth, whereas high inoculum transiently repressed it, coinciding with retrotransposon activation, suppression of AOS and proteasome genes, and enrichment of flavonoids and glutathione in leaves. Chemical assays showed that radicle inhibition requires the combination of surfactin, produced by both strains, with bacillomycin D, an iturin-type lipopeptide unique to FZB42; neither molecule alone reproduced the effect. This synergy links the strain-specific lipopeptide repertoire to the dose-dependent growth response. Although their early trajectories diverged, both primings converged on improved above-ground performance. 3610-primed plants restricted Botrytis cinerea via caffeic- and rosmarinic-acid accumulation, whereas FZB42-primed plants curtailed jasmonate-sensitive Tetranychus urticae mites through early JA-pathway activation. Our results demonstrate that melon perceives inoculum dose and microbial identity, translating them into distinct metabolic and defense programs that converge on stress resilience. These mechanistic insights-linking lipopeptide fingerprints, sentinel metabolites and defense transcripts-provide a framework for precision seed treatments in horticultural crops.

plant biology↗

bioRxiv2025

The offensive role of the Bacillus extracellular matrix in driving metabolite-mediated dialogue and adaptive strategies with pathogenic fungi

Bacterial{square}fungal interactions have traditionally been attributed to secondary metabolites, but the role of the bacterial extracellular matrix (ECM) in shaping these relationships has remained unclear. Here, we demonstrate that the ECM protein TasA is a key mediator in the antagonistic interaction between Bacillus subtilis and Botrytis cinerea. TasA enables Bacillus to tightly adhere to fungal hyphae, disrupts the {beta}-glucan layer, and compromises fungal cytoskeletal integrity synergistically with fengycin, which causes cytological damage. Additionally, TasA acts as a carrier for bacillaene, amplifying its fungistatic activity. In response, B. cinerea mounts a multifaceted defense, enzymatically degrading fengycin, producing antibacterial oxylipins, and activating adaptive programs such as hyphal branching and chlamydospore formation. Our findings reveal the previously unrecognized role of ECM components in fungal suppression and the modulation of fungal adaptive responses. This study reveals the complex interplay between microbial aggression and defense, providing new insights into the ecological dynamics of microbial competition and coexistence.

microbiology↗

bioRxiv2025

Characterization of BvlzGluc, a Novel Antifungal beta-Glucanase from Bacillus velezensis, with Potential Agricultural and Industrial Applications

{beta}-glucanases play a critical role in degrading {beta}-glucans, which are essential components of fungal cell walls that maintain fungal structure and physiology. This study characterizes BvlzGluc, a novel {beta}-glucanase produced by Bacillus velezensis CECT 8237, which has potent antifungal properties. BvlzGluc specifically targets the {beta}-glucan layer of Botrytis cinerea, causing significant structural malformations, impaired fungal development, and reduced virulence. These effects weaken the fungal cell wall, increasing its susceptibility to environmental stress and reducing its capacity to infect host plants. Notably, BvlzGluc is a noncanonical {beta}-glucanase belonging to glycoside hydrolase family 16 (GH16) but presents unique structural features that distinguish it from typical members of this family, suggesting potential reclassification. Its physicochemical stability and simple structural design increase its suitability for scalable production, positioning it as a promising candidate for agricultural and industrial applications requiring efficient {beta}-glucan degradation. This work builds on previous studies of microbial antifungal mechanisms, providing new insights into bacterial-fungal interactions and reinforcing the potential of bacterial enzymes in sustainable pathogen management and advancing biotechnological innovations.

microbiology↗

bioRxiv2024

Strengthening Phage Resistance of Streptococcus thermophilus by Leveraging Complementary Defense Systems

CRISPR-Cas and restriction-modification systems represent the core defense arsenal in Streptococcus thermophilus to block lytic phages, but their effectiveness is compromised by phages encoding anti-CRISPR proteins (ACRs) and other counter-defense strategies. Here, we explored the resistome of 263 S. thermophilus strains to uncover other anti-phage systems. The defense landscape of S. thermophilus was enriched by 21 accessory defense systems, 13 of which had not been previously investigated in this species. Experimental validation of 17 systems with 14 phages showed varying anti-phage levels, uncovering intra-genus specificities among the five viral genera infecting S. thermophilus. Interestingly, the resistance levels were even higher when some defense systems (Dodola and PD-Lambda-1) were expressed from a low-copy plasmid or when integrated into the chromosome. We also observed a synergistic effect when combining Gabija with CRISPR-Cas, underscoring the potential of these additional defense systems for developing more robust industrial S. thermophilus strains, particularly against ACR-encoding phages.

microbiology↗

bioRxiv2024

CapP mediates the structural formation of biofilm-specific pili in the opportunistic human pathogen Bacillus cereus

Polymeric proteinaceous filaments are structural scaffolds that diversify the functionality of the bacterial extracellular matrix. Here, we report a previously uncharacterized bacterial factor called bc1280 that is exclusive to B. cereus group and indispensable for the establishment of a biofilm lifestyle. We propose that BC1280 is an essential chaperone for the assembly of the filamentous platform that tightly controls the polymerization of heteropili containing CalY and TasA as major subunits in a concentration-dependent manner. Additionally, BC1280 modulates the expression of EPS via an uncharacterized pathway that is activated by a protease and an ECF-type sigma factor. The pilus biogenesis system described in this work highlights the complexity of extracellular matrix assembly in B. cereus and introduces a singular three-part structuration mechanism during biofilm formation and maturation. Graphical abstractDuring the process of biofilm formation in B. cereus, TasA, CapP, and CalY serve as the main components, in addition to other factors, ensuring that the extracellular matrix correctly assembles. The three proteins are produced and processed by the signal peptidase SipW and subsequently secreted through the Sec pathway in an unfolded conformation. At early biofilm formation stages, CapP is initially present at low levels, associates with the cell wall and is secreted into the ECM where it interacts with unfolded subunits of CalY, facilitating CalY folding and initiating fibril growth. CalY serves as a nucleator for incorporating TasA subunits into the pilus, forming TasA-CalY heteropolymers. Once the ECM scaffold is established, CapP levels increase, forming stable complexes with CalY that prevent its folding and arrest filament growth. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=142 SRC="FIGDIR/small/582368v2_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@df9d9dorg.highwire.dtl.DTLVardef@e4b712org.highwire.dtl.DTLVardef@1af2421org.highwire.dtl.DTLVardef@16d02c7_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2024

Molecular response to multiple trace-element contamination of the European sardine

In marine ecosystems, the presence of trace elements resulting from anthropogenic activities has raised concerns regarding their potential effects on marine organisms. This study delves into the intricate relationship between trace element contamination and the physiological responses of a key marine species in the Mediterranean Sea: the European sardine. Since 2008, this species has been experiencing a significant crisis in the region, prompting numerous studies to investigate the potential factors behind the dramatic decline in sardines size, age, and body condition. However, thorough information on chemical contamination by trace elements and its physiological impact on this species was lacking. We found evidence for the accumulation of multiple elements in sardines, with a light East-West contamination gradient within the Gulf of Lions. While macro-physiological parameters (i.e. body condition) were not affected by contamination, pathways involved in cellular organization and response to stress were clearly upregulated, particularly in the liver, but also in muscle. In addition, a global upregulation in processes linked to the immune system, lipid homeostasis and oxidative stress was recorded in the liver. The associated energetic cost may add a substantial burden to sardines that already face multi-factorial constraints. This study also allows to pinpoint biomarkers of exposure and effects that may be important for monitoring Mediterranean sardines health. The results of this study and particularly the complex changes in protein expression demonstrate the need for future studies to test the concomitant effects of multiple stressors acting simultaneously, including large scale contamination.

physiology↗

bioRxiv2023

Cyclo(Pro-Tyr) elicits conserved cellular damage in fungi by targeting the ATPase Pma1 in plasma membrane domains

Bioactive metabolites play a crucial role in shaping interactions among diverse organisms. In this study, we identified cyclo(Pro-Tyr), a metabolite produced by Bacillus velezensis, as a potent inhibitor of Botrytis cinerea and Caenorhabditis elegans, two potential cohabitant eukaryotic organisms. Based on our investigation, cyclo(Pro-Tyr) disrupts plasma membrane polarization, induces oxidative stress and increases membrane fluidity, which compromises fungal membrane integrity. These cytological and physiological changes induced by cyclo(Pro-Tyr) may be triggered by the destabilization of membrane microdomains containing the [H+]ATPase Pma1. In response to cyclo(Pro-Tyr) stress, fungal cells activate a transcriptomic and metabolomic response, which primarily involves lipid metabolism and Reactive Oxygen Species (ROS) detoxification, to mitigate membrane damage. This similar response occurs in the nematode C. elegans, suggesting that cyclo(Pro-Tyr) universally targets eukaryotic cellular membranes.

microbiology↗

bioRxiv2023

Potential climate change effects on the distribution of urban and sylvatic dengue and yellow fever vectors

Climate change may increase the risk of dengue and yellow fever transmission by urban and sylvatic mosquito vectors. Previous research primarily focused on Aedes aegypti and Aedes albopictus. However, these diseases involve a complex transmission cycle in which sylvatic vectors are also involved. Our aim was to analyse which mosquito species could contribute to the increased risk of transmission of these diseases due to climate change, and to identify where the risk increase could most likely occur. Using a biogeographical approach, we mapped areas where mosquito favourability could increase, decrease or remain stable in the near (2041-2060) and distant (2061-2080) future. Models predict dengue vectors expanding in West and Central Africa and in South-East Asia, reaching Borneo. Yellow fever vectors could spread in West and Central Africa and in the Amazon. In Europe, the models suggest a re-establishment of Ae. aegypti, while Ae. albopictus will continue to find new favourable areas. The results underline the need to focus more on vectors Ae. vittatus, Ae. luteocephalus and Ae. africanus in West and Central sub-Saharan Africa, especially Cameroon, Central Africa Republic, and northern Democratic Republic of Congo; and suggest the need for a protocol to prevent dengue and yellow fever that include surveillance of neglected sylvatic vectors.

ecology↗

bioRxiv2023

Molecular characterization of the N-terminal half of TasA during functional amyloid assembly and its contribution to Bacillus subtilis biofilm formation

Biofilms are bacterial communities that result from a cell differentiation process that leads to the secretion of an extracellular matrix (ECM) by part of the bacterial population. In Bacillus subtilis, the main protein component of the ECM is the functional amyloid TasA, which forms a fiber-based scaffold that confers structure to the ECM. The N-terminal half of TasA is strongly conserved among Bacillus species and contains a protein domain, the amyloid core (AcTasA), which is critical for the formation of the amyloid architecture. In this study, we demonstrate that recombinantly purified AcTasA in vitro retains biochemical properties previously observed for the entire protein. Further analysis of the AcTasA amino acid sequence revealed two amyloidogenic stretches and a region of imperfect amino acid repeats, which are known to contribute to functional amyloid assembly. Biochemical characterization of these amyloidogenic stretches found in AcTasA revealed their amyloid capacity in vitro, contributing to the amyloid nature of AcTasA. Moreover, the study of the imperfect amino acid repeats revealed the critical role of residues D64, K68 and D69 in the structural function of TasA. In vivo and in vitro experiments with versions of TasA carrying the substitutions D64A, K68A, and D69A demonstrated a partial loss of function of the protein either in the assembly of the ECM or in the stability of the core and amyloid polymerization. Taken together, our findings allow us to better understand the polymerization process of TasA during biofilm formation and provide knowledge into the sequence determinants that promote the molecular behavior of functional amyloids.

microbiology↗

bioRxiv2023

BundleWarp, streamline-based nonlinear registration of white matter tracts

Tractometry analysis represents a significant advancement in neuroimaging, offering a detailed examination of the brains white matter at a micro level. Unlike traditional ROI or voxel-based methods, tractometry precisely reconstructs and characterizes white matter tracts. Using advanced diffusion MRI and tractography algorithms, it maps the trajectory, shape, and connectivity patterns of individual white matter bundles. Accurate alignment of these tracts across different groups is crucial for reliable and reproducible results. Nonlinear registration techniques are essential for achieving this alignment, harmonizing bundle shapes, and improving sensitivity to disease-related changes. However, nonlinear registration is complex, especially with tractography data, which digitally represents the brains white matter anatomy. Potential structural changes in the bundles shape during registration can lead to artifacts that obscure critical anatomical details needed for disease identification. We introduce BundleWarp, a streamline-based nonlinear deformable registration method designed specifically for white matter tracts. BundleWarp employs a sophisticated approach to align two white matter bundles while preserving their topological and anatomical features. It is formulated as a probability density estimation problem with motion coherence penalties, ensuring coherent movement of points along streamlines and maintaining the anatomical integrity of tracts through displacement field regularization. Additionally, we introduce a tract morphometry framework utilizing the displacement field generated by BundleWarp to analyze white matter tract shape differences. Our results show that BundleWarp effectively quantifies bundle shape differences and enhances structural harmonization in tractometry analysis for diverse subjects, including those with Alzheimers and Parkinsons disease. Test-retest experiments further demonstrate that BundleWarp substantially improves subject finger-printing by increasing within-subject reproducibility of both bundle shape and microstructural profiles (FA, MD, RD, AD). It precisely maps the brains neuronal pathways, offering a robust tractometry framework with enhanced sensitivity for detecting disease-related structural and microstructural changes in white matter tracts associated with Mild Cognitive Impairment (MCI), dementia, and early-stage Alzheimers biomarkers, including amyloid-beta plaques and tau neurofibrillary tangles.

neuroscience↗

bioRxiv2022

A non-invasive method for time-lapse imaging of microbial interactions and biofilm 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 to competition and the death or displacement of particular organisms or sub-populations. 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 new and interesting insight into how bacteria interact at the cellular level to form and maintain microbial biofilms. However, our ability to follow complex intra- and inter-species interactions in vivo at the microscopic level has remained somewhat limited. Here, we detail BacLive, a novel non-invasive 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 provide examples of how BacLive can be used in the analysis of complex bacterial communities. ImportanceCommunication and interactions between single cells are continuously defining the structure and composition of microbial communities timely and spatially. Methods routinely used to the study of these communities at cellular level rely on sample manipulation what deprives from microscopic time lapse experiments on a given sample. BacLive is conceived as a method for the non-invasive study of the formation and development of bacterial communities, such as biofilms, and the dynamics of formation of specialized subpopulations in time-lapse experiments. In addition we prove that BacLive largely simplifies the analysis of the data generated.

microbiology↗

bioRxiv2021

Denitrification in foraminifera has ancient origins and is complemented by associated bacteria

Benthic foraminifera are unicellular eukaryotes that inhabit sediments of aquatic environments. Several foraminifera of the order Rotaliida are known to store and use nitrate for denitrification, a unique energy metabolism among eukaryotes. The rotaliid Globobulimina spp. has been shown to encode an incomplete denitrification pathway of bacterial origin. However, the prevalence of denitrification genes in foraminifera remains unknown and the missing denitrification pathway components are elusive. Analysing transcriptomes and metagenomes of ten foraminiferal species from the Peruvian oxygen minimum zone, we show that denitrification genes are highly conserved in foraminifera. We infer of the last common ancestor of denitrifying foraminifera, which enables us to predict the ability to denitrify for additional foraminiferal species. Additionally, an examination of the foraminiferal microbiota reveals evidence for a stable interaction with Desulfobacteracea, which harbour genes that complement the foraminiferal denitrification pathway. Our results provide evidence that foraminiferal denitrification is complemented by the foraminifera-associated microbiome. The interaction of foraminifera with their resident bacteria is at the basis of foraminiferal adaptation to anaerobic environments that manifested in ecological success within oxygen depleted habitats. Significance StatementA substantial component of the global nitrogen cycle is the production of biologically inaccessible dinitrogen attributed to anaerobic denitrification by prokaryotes. Recent evidence identified a eukaryote - foraminifera - as new key players in this loss of bioavailable nitrogen. The evolution of denitrification in eukaryotes constitutes a rare event and the genetic mechanisms of the denitrification pathway in foraminifera are just starting to be elucidated. We present large-scale sequencing analyses of ten denitrifying foraminiferal species, which reveals the high conservation of the foraminiferal denitrification pathway. We further find evidence for a complementation of denitrification by the foraminiferal microbiome. Together, these findings provide novel insights on the early evolution of a previously overlooked component in the marine nitrogen cycle.

evolutionary biology↗

bioRxiv2021

Mutualistic interactions between B. subtilis and seeds dictate plant development

A tightly coordinated developmental program controls precise genetic and metabolic reprogramming that dictates efficient transition of the seeds from dormancy to metabolically active seedlings. Beneficial microbes are known to stimulate the germination of the seeds or adaptation of the seedlings; however, investigations of exact mechanisms mediating these interactions and the resulting physiological responses of the plants are only beginning. Bacillus subtilis is commonly detected in the plant holobiont and belongs to the group of microbes that provide multifaceted contribution to the health of the plants. The present study demonstrated that B. subtilis triggered genetic and physiological responses in the seeds that determined subsequent metabolic and developmental status of adult plants. Chemically diverse extracellular matrix of Bacillus was demonstrated to structurally cooperate in bacterial colonization of the seed storage tissues. Additionally, an amyloid protein and fengycin, which are two components of the extracellular matrix, targeted the oil bodies of the seed endosperm, provoking changes in lipid metabolism or accumulation of glutathione-related molecules that stimulated two different plant growth programs: the development of seed radicles or overgrowth and immunization of adult plants. We propose this mutualistic interaction is conserved in Bacilli and plant seeds containing storage oil bodies.

microbiology↗

bioRxiv2021

Sporulation is dispensable for the vegetable-associated life cycle of the human pathogen Bacillus cereus

Bacillus cereus is a common food-borne pathogen that is responsible for important outbreaks of food poisoning in humans. Diseases caused by B. cereus usually exhibit two major symptoms, emetic or diarrheic, depending on the toxins produced. It is assumed that after the ingestion of contaminated vegetables or processed food, spores of enterotoxigenic B. cereus reach the intestine, where they germinate and produce the enterotoxins that are responsible for food poisoning. In our study, we observed that sporulation is required for the survival of B. cereus in leaves but is dispensable in ready-to-eat vegetables, such as endives. We demonstrate that vegetative cells of B. cereus that are originally impaired in sporulation but not biofilm formation are able to reach the intestine and cause severe disorders in a murine model. We propose that loss of part of the sporulation programme and reinforcement of structural factors related to adhesion, biofilm formation and pathogenic interaction with the host are adaptive traits of B. cereus with a life cycle primarily related to human hosts. Furthermore, our findings emphasise that the number of food poisoning cases associated with B. cereus is underestimated and suggest the need to revise the detection protocols, which are based primarily on spores and toxins.

ecology↗

bioRxiv2019

Biofilm formation displays intrinsic offensive and defensive features of Bacillus cereus

BackgroundBiofilm formation is a strategy of many bacterial species to adapt to a variety of stresses and has become a part of infections, contaminations or beneficial interactions. We previously observed that B. cereus ATCC 14579 (CECT148), formed a thick biomass of cells firmly adhered to abiotic surfaces.\n\nResultsIn this study, we combined two techniques, RNAseq and iTRAQ mass spectrometry, to demonstrate the profound physiological changes that permit Bacillus cereus to switch from a floating to a sessile lifestyle, to undergo further maturation of the biofilm, and to differentiate into offensive or defensive populations. The rearrangement of nucleotides, sugars, amino acids and energy metabolism lead to changes promoting reinforcement of the cell wall, activation of ROS detoxification strategies or secondary metabolite production, all oriented to defend biofilm cells from external aggressions. However, floating cells maintain a fermentative metabolic status along with a higher aggressiveness against hosts, evidenced by the production of toxins and other virulent factors.\n\nConclusionsWe show that biofilm-associated cells seem to direct the energy to the individual and global defense against external aggressions and competitors. By contrary, floating cells are more aggressive against hosts. The maintenance of the two distinct subpopulations is an effective strategy to face changeable environmental conditions found in the life cycle of B. cereus.

microbiology↗

bioRxiv2019

Dual functionality of the TasA amyloid protein in Bacillus physiology and fitness on the phylloplane

Bacteria can form biofilms that consist of multicellular communities embedded in an extracellular matrix (ECM). Previous studies have demonstrated that genetic pathways involved in biofilm formation are activated under a variety of environmental conditions to enhance bacterial fitness; however, the functions of the individual ECM components are still poorly understood. In Bacillus subtilis, the main protein component of the ECM is the functional amyloid TasA. In this study, we demonstrate that beyond their well-known defect in biofilm formation,{Delta} tasA cells also exhibit a range of cytological symptoms indicative of excessive cellular stress, including DNA damage accumulation, changes in membrane potential, higher susceptibility to oxidative stress, and alterations in membrane dynamics. Collectively, these events can lead to increased programmed cell death in the colony. We show that these major physiological changes in{Delta} tasA cells are likely independent of the structural role of TasA during amyloid fiber formation in the ECM. The presence of TasA in cellular membranes, which would place it in proximity to functional membrane microdomains, and mislocalization of the flotillin-like protein FloT in{Delta} tasA cells, led us to propose a role for TasA in the stabilization of membrane dynamics as cells enter stationary phase. We found that these alterations caused by the absence of TasA impair the survival, colonization and competition of Bacillus cells on the phylloplane. Taken together, our results allow the separation of two complementary roles of this functional amyloid protein: i) structural functions during ECM assembly and interactions with plants, and ii) a physiological function in which TasA, via its localization to the cell membrane, stabilizes membrane dynamics and supports more effective cellular adaptation to environmental cues.

microbiology↗

bioRxiv2018

Extracellular matrix components are required to protect Bacillus subtilis colonies from T6SS-dependent Pseudomonas invasion and modulate co-colonization of plant

Bacteria adapt to environmental changes and interact with other microorganisms using a wide array of molecules, metabolic plasticity, secretion systems and the formation of biofilms. Some research has looked at changes in the expression of biofilm related genes during interactions between different bacterial species, however no studies have directly demonstrated the functional significance of biofilms in modulating such interactions. In this study, we have explored this fundamental question by studying the interaction between Bacillus subtilis 3610 and Pseudomonas chlororaphis PCL1606. We demonstrate the important role of the extracellular matrix in protecting B. subtilis colonies from infiltration by Pseudomonas. Surprisingly, we find that the Pseudomonas type VI secretion system (T6SS) is required in the cell-to-cell contact with matrix-impaired B. subtilis cells, revealing a novel role for T6SS against Gram-positive bacteria. In response to P. chlororaphis infiltration, we find that B. subtilis activates sporulation and expresses motility-related genes. Experiments using plant organs demonstrate the functional importance of these different bacterial strategies in their coexistence as stable bacterial communities. The findings described here further our understanding of the functional role played by biofilms in mediating bacterial social interactions.

microbiology↗