ISHS Acta Horticulturae 704: X International Workshop on Fireblight
EXOPOLYSACCHARIDES OF ERWINIA AMYLOVORA AND RELATED PATHOGENS |
| Authors: | K. Geider, Z. Du, M. Hildebrand, W.S. Kim, V. Jakovljevic, S. Jock |
| Keywords: | amylovoran, pyrifolan, levan, regulation of EPS synthesis, H-NS protein |
| Abstract:
Exopolysaccharides (EPS) are synthesized by many bacteria to modulate the interactions between the bacteria and the environment. Erwinia amylovora produces amylovoran and the homopolymer levan, similar to a glucose side chain in the complex capsular EPS. Levan is not synthesized by the Asian pear pathogens. Genes coding for capsular EPS synthesis in the cps operon of E. pyrifoliae are highly homologous to the ams genes of E. amylovora. Ams mutants were not virulent in plant assays, and the bacteria were exposed to plant defense reactions inactivating the pathogen. EPS synthesis of these three pathogens is regulated by several genes including rcsA, rcsB and hns. With RcsC as sensor, RcsB is the activator protein in a two-component system enhanced by RcsA. As for E. amylovora, E. pyrifoliae mutants in rcsB completely lacked EPS. Mutations in rcsC in E. pyrifoliae decreased EPS synthesis. The hns genes affected amylovoran synthesis and expression of levansucrase. Levan production in E. amylovora is activated by rlsC, rlsB upstream of lsc and rlsA adjacent to the hrp region. Cells can survive in necrotic plant lesions, but without EPS capsules they decay rapidly in dry environments. | |
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