Characterization of Pathogenicity Genes of Erwinia Carotovora

Abstract

The plant pathogenic bacterium, Erwinia carotovora subsp. carotovora (Ecc), causes soft rot on a number of plant species. The most striking characteristic of soft-rot Erwinias is the production of large amounts of extracellular pectolytic enzymes (2). Ecc produces several pectate lyases and polygalacturonases (7,8,10). In addition to pectic enzymes, several environmental components, especially anaerobic conditions, have been implicated in the development of severity of soft rot disease (3). During the last five years, several laboratories have cloned DNA sequences encoding pectolytic enzymes in order to clarify their role in the disease development (7,8,10, Handa et al. unpublished results). Isolated PL and PG can cause soft rot symptoms on potato tuber (7,8,10). However, an E. coli strain expressing both PL and PG from cloned genes caused only a limited tissue maceration of potato tuber (8), thus suggesting the involvement of other gene product(s) in the development of disease. At present, little is known about the nature of these gene products. To investigate the genetic factors responsible for the virulence of Ecc we have isolated and characterized a large number of nonpathogenic mutants by transposon mutagenesis. Partial characterization of some of these mutants is presented in this paper.