Altered Strategies to Inhibit Surface Colonies.

and infections frequently co-localize in lungs of immunocompromised patients and individuals with cystic fibrosis (CF). The antifungal activity of has been described for its filtrates. Pyoverdine and pyocyanin are the principal antifungal molecules active against biofilm metabolism present in iron-limited or iron-replete planktonic culture filtrates, respectively. Using various laboratory wild-type strains (PA14, PAO1, PAK), we found antifungal activity against colonies on agar. Comparing 36 PA14 and 7 PAO1 mutants, we found that mutants lacking both major siderophores, pyoverdine and pyochelin, display higher antifungal activity on agar than their wild types, while quorum sensing mutants lost antifungal activity. Addition of ferric iron, but not calcium or magnesium, reduced the antifungal effects of on agar, whereas iron-poor agar enhanced antifungal effects. Antifungal activity on agar was mediated by PQS and HHQ, MvfR. Among the MvfR downstream factors, rhamnolipids and elastase were produced in larger quantities by pyoverdine-pyochelin double mutants and showed antifungal activity on agar. In summary, antifungal factors produced by on agar differ from those produced by bacteria grown in liquid cultures, are dependent on quorum sensing, and are downregulated by the availability of ferric iron. Rhamnolipids and elastase seem to be major mediators of ' antifungal activity on a solid surface.