Isolation and Characterization of an rcsA-like Gene of Erwinia amylovora that Activates Extracellular Polysaccharide Production in Erwinia species, Escherichia coli, and Salmonella typhimurium. Asita Chatterjee. Department of Plant Pathology, University of Missouri, Columbia 65211 U.S.A. Wesley Chun, and Arun K. Chatterjee. Department of Plant Pathology, University of Missouri, Columbia 65211 U.S.A. MPMI 3:144-148. Accepted 14 November 1989. Copyright 1990 The American Phytopathological Society.

Extracellular (= capsular) polysaccharide (EPS) production by Erwinia amylovora is required in the elicitation of the fire blight disease in apples and pears. To examine the regulation of EPS biosynthesis, we isolated from an E. amylovora cosmid library, Escherichia coli (HB101) clones that had a mucoid phenotype. The subcloning of a 2.2-kb DNA fragment of one the cosmid clones resulted in the construct pAKC111, which conferred a mucoid phenotype in strains of E. amylovora, E. stewartii, E. coli, and Salmonella typhimurium. By analyzing a series of nested deletions, we localized the gene controlling EPS production within a 1-kb DNA segment. In E. coli and S. typhimurium, the E. amylovora gene activated the biosynthesis of structurally different polysaccharides as indicated by their differential susceptibility to a depolymerase specific for the E. amylovora EPS. The presence of an rcsA-like gene on pAKC111 was determined by its ability to complement E. coli rcsA mutations. However, with Southern hybridizations under high stringency conditions, homology between the cloned E. amylovora DNA and the rcsA genes of E. coli, E. stewartii, and Klebsiella aerogenes was not detected.