The marine epiphytic bacterium
Pseudoalteromonas tunicataproduces a range of extracellular secondary metabolites that inhibit an array of common fouling organisms, including fungi. In this study, we test the hypothesis that the ability to inhibit fungi provides P. tunicatawith an advantage during colonization of a surface. Studies on a transposon-generated antifungal-deficient mutant of P. tunicata, FM3, indicated that a long-chain fatty acid-coenzyme A ligase is involved in the production of a broad-range antifungal compound by P. tunicata. Flow cell experiments demonstrated that production of an antifungal compound provided P. tunicatawith a competitive advantage against a marine yeast isolate during surface colonization. This compound enabled P. tunicatato disrupt an already established fungal biofilm by decreasing the number of yeast cells attached to the surface by 66% ï¿½ 9%. For in vivo experiments, the wild-type and FM3 strains of P. tunicatawere used to inoculate the surface of the green alga Ulva australis. Double-gradient denaturing gradient gel electrophoresis analysis revealed that after 48 h, the wild-type P. tunicatahad outcompeted the surface-associated fungal community, whereas the antifungal-deficient mutant had no effect on the fungal community. Our data suggest that P. tunicatais an effective competitor against fungal surface communities in the marine environment.