EFFECTS OF FIMBRIAL (FIMA, FIMF) AND AFIMBRIAL (XADA, HXFB) ADHESINS ON THE ADHESION OF XYLELLA FASTIDIOSA TO SURFACES

• Author(s): Lindow, Steven; Feil, Helene;
• Abstract: We investigated the role of fimbrial and afimbrial adhesions in the attachment of Xylella fastidiosa (Xf) to grape. We have individually disrupted FimA, FimF, XadA, and HxfB to assess their role in adhesion to plants and in the disease process. We performed adhesion assays using each mutant and wild-type separately as well as a combination of two mutants at one time to observe the phenotypes of these mutants using fluorescence or confocal microscopy. The fimbrial mutants FimA- or FimF- did not aggregate nor did they attach to the glass surface whereas the adhesion mutants XadA- or HxfB- did not attach to glass but did form aggregates and attached to cells that had adhered to a surface. All mutants had fewer single cells or aggregates that remained attached to glass than wild-type cells did after washing steps. We observed that afimbrial mutant cells (i.e. XadA- or HxfB-) were clumped on top of fimbrial mutant cells (i.e. FimA- or FimF-). Both afimbrial and fimbrial proteins thus apparently play a role in attachment of cells to glass in the early phases of adhesion while fimbrial proteins appear more important in cell-to-cell aggregations than afimbrial proteins. To determine if these adhesions are important in virulence, rooted grapevine cuttings were inoculated with FimA-, FimF-, XadA-, HxfB-, and wild-type Xf Temecula or STL. A higher incidence and severity of disease was observed in vines inoculated with the wild-type Xf strain compared with FimA-, FimF-, XadA- or HxfB- mutant strains. Similarly, wild-type strain Xf STL resulted in more vines with symptoms than FimA-, FimF- or XadA- mutants of this strain indicating that the process of attachment appears to involve similar genes in both the Temecula and STL strains. It thus appears that successful colonization of plants by Xf requires both cell-to-cell and cell-to-surface attachment.
• Publication Date: Dec 2005
• Journal: 2005 Pierce's Disease Research Symposium