The role of the epipeptide EpeX in defining competitive fitness in intra-species mixed isolate colony biofilms ofBacillus subtilis

Abstract

AbstractBacteria engage in competitive interactions with neighbours that can either be of the same or different species. Multiple mechanisms are deployed to ensure the desired outcome and one tactic commonly implemented is the production of specialised metabolites. The Gram-positive bacteriumBacillus subtilisuses specialised metabolites as part of its intraspecies competition determinants to differentiate between kin and non-kin isolates. It is, however, unknown if the collection of specialised metabolites defines competitive fitness when the two isolates start as a close, interwoven community that grows into a densely packed colony biofilm. Moreover, the identity of the most effective specialised metabolites has not been revealed. Here, we determine the competition outcomes that manifest when 21 environmental isolates ofB. subtilisare individually co-incubated with the model isolate NCIB 3610 in a colony biofilm. We correlated these data with the suite of specialised metabolite biosynthesis clusters encoded by each isolate. We found that theepeXEPABgene cluster correlated with a strong competitive phenotype. This cluster is responsible for producing the epipeptide EpeX. We demonstrated that EpeX is a competition determinant ofB. subtilisin an otherwise isogenic context. When we competed the NCIB 3610 EpeX deficient strain against our suite of environmental isolates we found that the impact of EpeX in competition is isolate-specific, as only one of the 21 isolates showed increased survival when EpeX was lacking. Taken together, we have shown that EpeX is a competition determinant used byB. subtilisthat impacts intra-species interactions in an isolate-specific manner.