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

Abstract

Some bacterial species are important members of the rhizosphere microbiome and confer protection to the host plant against pathogens. However, our knowledge is still limited about the multitrophic interactions determining the ecological fitness of these biocontrol bacteria in their highly competitive natural niche. In this work, we have 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 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 capability but, unexpectedly, this lipopeptide also acts as a chemical trap that reduce the toxicity of other lipopeptides released by Pseudomonas challengers. This 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.

Bacillus Cyclic Lipopeptides Iturin and Fengycin Control Rice Blast Caused by Pyricularia oryzae in Potting and Acid Sulfate Soils by Direct Antagonism and Induced Systemic Resistance

“…Bacillus velezensis GA1 mutants deficient in the production of a single CLiP were constructed by marker gene replacement, as previously described [ 37 ]. To construct CLiP double mutants, a recombinant fragment containing a phleomycin cassette flanked by 1000 bp of the upstream region and 1000 bp of the downstream region of the targeted gene was generated by overlap PCR with specific primers ( Table A1 ) (see Appendix A ) [ 37 ]. The recombinant fragment was introduced into B. velezensis GA1 derivative mutants (GA1∆ srfaA , GA1∆ ituA , GA1∆ fenA ) by inducing natural competence, as previously described [ 37 ].…”

“…Subsequently, supernatants were filter sterilized through a Millipore filter (Millex-GV, 0.22 µm) to exclude bacterial cells. Cell free supernatants were collected for UPLC–MS analysis to detect and quantify CLiPs, as previous described [ 37 ], and utilized for direct antagonism assays in this study.…”