EXPRESSION OF VIRULENCE FACTORS SECRETED BY ERWINIA AMYLOVORA.

Virulence of Erwinia amylovora depends on several factors which include (i) secretion of the capsular exopolysaccharide (EPS) amylovoran to protect the bacteria against recognition by host plant defense reactions, (ii) secretion of levansucrase, which polymerizes fructose residues of sucrose in the environment to levan, (iii) secretion of a protease, affecting colonization of host plant tissue by the pathogen.
The complex exopolysaccharide amylovoran forms a loose capsule around the bacterial cells.
The chromosomal region for amylovoran synthesis was characterized and gene functions assigned for the synthesis of the repeating units by using a subcellular system from ams-mutants.
Proteins with transport functions were tagged by fusions with -lactamase.
Expression of levansucrase is influenced by rlsA, located in the dsp/hrp-region.
No signal peptide could be detected in the amino acid sequence of levansucrase, but its fusion with -lactamase produced antibiotic-resistant cells confirming its transport in E. amylovora also for the truncated protein.
A protease is secreted by cultured cells and tryptic peptide fragments from the purified protein were sequenced and placed into the amino acid sequence deduced from the encoding gene.
The whole DNA region around the transposon insertion was sequenced.
The protease encoding chromosomal region starts with the structural gene for the secreted protease, and is followed by genes with features for protein transporters.
An E. amylovora strain deficient in this protease was retarded in colonization of host plants.

VIII International Workshop on Fire Blight

K. Geider, Y. Zhang, H. Ullrich, C. Langlotz

amylovoran, levan, protease, tissue colonization

https://doi.org/10.17660/ActaHortic.1999.489.61