Project description:In the marine environment, surface-associated bacteria often produce an array of antimicrobial secondary metabolites (MSMs), which have predominantly been perceived as competition molecules. However, they may also affect other hallmarks of surface-associated living, such as motility and biofilm formation. Here, we investigate the ecological significance of an antibiotic secondary metabolite, tropodithietic acid (TDA), in the producing bacterium, Phaeobacter piscinae S26. We constructed a markerless in-frame deletion mutant deficient in TDA biosynthesis wherein TDA production was abolished. Molecular networking demonstrated that other chemical sulphur-containing features, likely related to TDA, were also altered in the secondary metabolome. We found dramatic changes in the physiology of the TDA-deficient mutant, S26�tdaB, compared to the wild type S26. Growth of the two strains were similar; however, S26�tdaB cells were shorter and more motile. Transcriptome and proteome profiling revealed an increase in expression of genes and relative abundance of proteins related to a type IV secretion system, a prophage, and a gene transfer agent (GTA) in S26�tdaB. All these systems may contribute to horizontal gene transfer (HGT), which may facilitate fast adaptation to novel niches. We speculate that, once a TDA-producing population has been established in a new niche, the accumulation of TDA acts as a signal of successful colonization, prompting a switch to a sessile lifestyle. This would lead to a decrease in motility and the rate of HGT, whilst filamentous cells could form the base of a biofilm. In addition, the antibiotic properties of TDA may inhibit invading competing microorganisms.
