Structure, Biosynthesis, and Regulation of Capsular Exopolysaccharide of Erwinia amylovora and Other Erwinia Species and Role in Pathogenicity
from: Bacterial Polysaccharides: Current Innovations and Future Trends (Edited by: Matthias Ullrich). Caister Academic Press, U.K. (2009)
The fire blight pathogen E. amylovora and related bacteria synthesize complex EPS with galactose, glucuronic acid and eventually glucose residues. For E. amylovora, the capsules of amylovoran have been investigated by staining techniques and visualized by light and electron microscopy. They protect the pathogen against plant defense recognition, provide a moist environment against desiccation and bind ions and nutrients to support the cell metabolism. Amylovoran consists of repeating units forming chains up to 5 MDa and can be detached from the cells by mild treatments. EPS deficient mutants of E. amylovora and E. pyrifoliae are non-pathogenic. Synthesis requires at least twelve genes for assembly of the repeating units, transport and polymerization. Similar genes were found for other Erwinia species that produce EPS related to amylovoran. Expression of the EPS encoding gene clusters depends on specific or global regulators including siRNAs, such as RcsA, B, C or Hns and RsmA/rsmB, which may adjust the EPS level to actual needs of the bacteria. Degradation or absence of EPS capsules results in pathogen recognition by plant defense mechanisms and provides a strategy to control fire blight read more ...