Surfactin-like lipopeptides contribute to interference competition of Bacillus velezensis against the marine Flavobacteriaceae in phycosphere.

Background

The phycosphere is a nutrient-rich microenvironment surrounding phytoplankton cells and serves as a hotspot for microbial interactions by releasing phytoplankton-derived organic molecules to dynamically attract and support the colonization of heterotrophic bacteria. Although the taxonomic composition, metabolic profiles, and host-microbe interactions of phycosphere bacterial communities have been extensively characterized, the underlying mechanisms driving competition among these co-existing bacterial taxa remain poorly understood.

Results

In this study, we demonstrate that Bacillus velezensis SPE2, a low-abundance isolate from the phycosphere of dinoflagellate, exhibits a wide degree of antagonistic activity against multiple marine Flavobacteriaceae strains, a dominant taxonomic group across the phycosphere of diverse phytoplankton species. Through an integrative approach combining genetics and metabolomics, we show that the antagonistic behavior of strain SPE2 is primarily mediated by the production of bioactive secondary metabolites. Activity-guided purification further leads to the identification of two antibacterial surfactin-like lipopeptides as key exometabolites responsible for these inhibitory effects. Mechanistically, these lipopeptides exert their antibacterial activity against Flavobacteriaceae species by disrupting the integrity of bacterial cell membranes.

Conclusions

Our findings reveal surfactin-like lipopeptides as key molecular mediators of bacterial interference competition, conferring a competitive strategy for Bacillus species to secure persistence in the phycosphere. Moreover, this work underscores phycosphere as a largely untapped ecological niche for discovering novel bioactive compounds with potential applications in pharmaceutical and biotechnological fields.