Cell Surface Attachment Structures Contribute to Biofilm Formation and Xylem Colonization by Erwinia amylovora

Abstract

ABSTRACTBiofilm formation plays a critical role in the pathogenesis ofErwinia amylovoraand the systemic invasion of plant hosts. The functional role of the exopolysaccharides amylovoran and levan in pathogenesis and biofilm formation has been evaluated. However, the role of biofilm formation, independent of exopolysaccharide production, in pathogenesis and movement within plants has not been studied previously. Evaluation of the role of attachment inE. amylovorabiofilm formation and virulence was examined through the analysis of deletion mutants lacking genes encoding structures postulated to function in attachment to surfaces or in cellular aggregation. The genes and gene clusters studied were selected based onin silicoanalyses. Microscopic analyses and quantitative assays demonstrated that attachment structures such as fimbriae and pili are involved in the attachment ofE. amylovorato surfaces and are necessary for the production of mature biofilms. A time course assay indicated that type I fimbriae function earlier in attachment, while type IV pilus structures appear to function later in attachment. Our results indicate that multiple attachment structures are needed for mature biofilm formation and full virulence and that biofilm formation facilitates entry and is necessary for the buildup of large populations ofE. amylovoracells in xylem tissue.