Steels, S. | bioRxiv Science

bioRxiv2021

Chelator sensing and lipopeptide interplay mediates molecular interspecies interactions between soil bacilli and pseudomonads

AbstractSome bacterial species are important members of the rhizosphere microbiome and confer protection to the host plant against pathogens. However, our knowledge of the multitrophic interactions determining the ecological fitness of these biocontrol bacteria in their highly competitive natural niche is still limited. In this work, we investigated the molecular mechanisms underlying interactions between B. velezensis, considered as model plant-associated and beneficial species in the Bacillus genus, and Pseudomonas as a rhizosphere-dwelling competitor. Our data show that B. velezensis boosts its arsenal of specialized antibacterials upon the perception of the secondary siderophore enantio-pyochelin produced by phylogenetically distinct pseudomonads and some other genera. We postulate that B. velezensis has developed some chelator sensing systems to learn about the identity of its surrounding competitors. Illustrating the multifaceted molecular response of Bacillus, surfactin is another crucial component of the secondary metabolome mobilized in interbacteria competition. Its accumulation not only enhances motility but, unexpectedly, the lipopeptide also acts as a chemical trap that reduces the toxicity of other lipopeptides released by Pseudomonas challengers. This in turn favors the persistence of Bacillus populations upon competitive root colonization. Our work thus highlights new ecological roles for bacterial secondary metabolites acting as key drivers of social interactions.

microbiology↗

bioRxiv2021

Surfactin stimulated by pectin molecular patterns and root exudates acts as a key driver of Bacillus-plant mutualistic interaction

Bacillus velezensis is considered as model species belonging to the so-called B. subtilis complex that typically evolved to dwell in the soil rhizosphere niche and establish intimate association with plant roots. This bacterium provides protection to its natural host against diseases and represents one of the most promising biocontrol agents. However, the molecular basis of the cross-talk that this bacterium establishes with its natural host has been poorly investigated. We show here that these plant-associated bacteria have evolved some polymer-sensing system to perceive their host and that in response, they increase the production of the surfactin-type lipopeptide. Furthermore, we demonstrate that surfactin synthesis is favoured upon growth on root exudates and that this lipopeptide is a key component used by the bacterium to optimize biofilm formation, motility and early root colonization. In this specific nutritional context, the bacterium also modulates qualitatively the pattern of surfactin homologues co-produced in planta and mainly forms variants that are the most active at triggering plant immunity. Surfactin represents a shared good as it reinforces the defensive capacity of the host. ImportanceWithin the plant-associated microbiome, some bacterial species are of particular interest due to the disease protective effect they provide via direct pathogen suppression and/or stimulation of host immunity. While these biocontrol mechanisms are quite well characterized, we still poorly understand the molecular basis of the cross talk these beneficial bacteria initiate with their host. Here we show that the model species Bacillus velezensis stimulates production of the surfactin lipopeptide upon sensing pectin as cell surface molecular pattern and upon feeding on root exudates. Surfactin favors bacterial rhizosphere fitness on one hand and primes the plant immune system on the other hand. Our data therefore illustrate how both partners use this multifunctional compound as unique shared good to sustain mutualistic interaction.

microbiology↗