ANALYSIS OF MECHANISMS OF BACTERIAL (SERRATIA MARCESCENS) ATTACHMENT, MIGRATION AND KILLING OF FUNGAL HYPHAE

We have found a remarkable capacity of the ubiquitous gram negative rod bacterium Serratia marcescens to migrate along and kill the mycelium of Zygomycete molds. This migration was restricted to Zygomycete molds, and several Basidiomycete spp. No migration was seen on any mold of the phylum Ascomycota. S. marcescens migration did not necessitate fungal viability or surrounding growth medium, as bacteria migrated along aerial hyphae as well. S. marcescens did not exhibit growth tropism towards Zygomycete mycelium. Bacterial migration along hyphae proceeded only when the hyphae grew into the bacterial colony. S. marcescens cells initially migrated along the hyphae, forming attached microcolonies that grew and coalesced to generate a biofilm covering and killing the mycelium. Flagellum-defective strains of S. marcescens were able to migrate along Zygomycete hyphae, although significantly slower than the wild-type strain and were delayed in fungal killing. Bacterial attachment to the mycelium does not necessitate type 1 fimbrial adhesion since mutants defective in this adhesin migrated equally well or faster than the wild type strain. Killing does not depend on the secretion of S. marcescens chitinases as mutants in which all three chitinase genes were deleted retained wild-type killing abilities. Better understanding of the mechanisms by which S. marcescens binds, spreads and kills fungal hyphae could serve as an excellent model system for such interactions in general; fungal killing could be employed in agricultural fungal biocontrol.