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The phytopathogenic enterobacteriumErwinia chrysanthemi strain EC16 produces four isozymes of pectate lyase (PL), an extracellular enzyme that macerates parenchymatous plant tissues and kills plant cells. A 1.8-kilobaseEco RI DNA fragment containing the entirepelE gene was deleted from theE. chrysanthemi chromosome by marker exchange of a cloned fragment that had been modified in vitro. The resulting mutant, UM1001, produced the isozymes PLa, PLb, and PLc, but not PLe. Mutant UM1001 was compared with wild-typeE. chrysanthemi , withEscherichia coli JA221, and with JA221 containing expression vectors with clonedpel genes producing high levels of PLe (pPEL748) or PLb (pPEL343) for the ability to multiply and cause symptoms in intact potato tubers. Tubers were injected with less than 100 bacteria per inoculation site and incubated aerobically or anaerobically. While maceration occurred only in anaerobically incubated tubers, all of the bacteria, including nonpectolyticE. coli controls, multiplied substantially under all conditions.E. coli JA221(pPEL748) caused significantly more maceration thanE. coli JA221(pPEL343) or wild-typeE. chrysanthemi. Mutant UM1001 caused significantly less maceration than the wild-typeE. chrysanthemi. The results establish the importance of PLe in the pectolytic arsenal ofE. chrysanthemi by demonstrating that production of PLe can enableE. coli to aggressively macerate tuber tissue and that deletion ofpelE significantly diminishes the virulence ofE. chrysanthemi.

applied and environmental microbiology

Multiplication and Virulence in Plant Tissues of <i>Escherichia coli</i> Clones Producing Pectate Lyase Isozymes PLb and PLe at High Levels and of an <i>Erwinia chrysanthemi</i> Mutant Deficient in PLe

Multiplication and Virulence in Plant Tissues of Escherichia coli Clones Producing Pectate Lyase Isozymes PLb and PLe at High Levels and of an Erwinia chrysanthemi Mutant Deficient in PLe