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Characterization of sliding motility driven by exopolysaccharides amylovoran and levan in the fire blight pathogen Erwinia amylovora
Lauren Eldred, 4th-year |
Abstract:
Erwinia amylovora is a gram-negative plant pathogen that causes fire blight in rosaceous plants. This bacterium colonizes the flower stigma and utilizes a flagellum-dependent swimming motility to migrate from the stigma tip to the hypanthium, in which it enters the xylem through natural openings.
Once inside the xylem, E. amylovora produces a biofilm consisting of three exopolysaccharides (EPSs), amylovoran, levan, and cellulose. Interestingly, a loss of flagella once inside xylem has been reported, suggesting that a flagellum-independent motility is required for migration of E. amylovora in planta. In this study, we constructed mutants lacking flagella in E. amylovora strain Ea1189 and found that these cells are unable to swim, but can still slide on sliding media the same as the wild-type bacteria. We demonstrated that the ability to produce amylovoran and levan, but not cellulose, is required for sliding when sucrose is the carbon source whereas amylovoran production alone is required for sliding when sorbitol serves as the carbon source. Comparison of Ea1189 to a more virulent strain of E. amylovora, Ea110, showed that Ea110 had increased sliding motility compared to Ea1189, suggesting that sliding motility is a virulence factor. We also showed that gravity has an impact on sliding: increased angles assist sliding motility on a decline surface, however, no sliding was observed on an incline. Finally, we observed different sliding behaviors between amylovoran and levan mutants when cells were co-sliding with the wild-type bacteria. Future studies focusing on the significance of sliding motility in planta will be conducted.