Extracellular Polysaccharide Genes in Erwinia stewartii: Directed Mutagenesis and Complementation Analysis. D. L. Coplin. Department of Plant Pathology, The Ohio State University, Columbus 43210-1087 U.S.A. D. R. Majerczak. Department of Plant Pathology, The Ohio State University, Columbus 43210-1087 U.S.A. . MPMI 3:286-292. Accepted 20 March 1990. Copyright 1990 The American Phytopathological Society.

A cosmid containing a cluster of cps genes required for extracellular polysaccharide synthesis in Erwinia stewartii was subjected to transposon mutagenesis, and the resulting cps mutations were crossed into the chromosome of E. stewartii SS104. Trans complementation tests between chromosomal mutants and mutant cosmids revealed that this cluster contains at least five complementation groups; these have been designated cpsA through cpsE and represent separate transcriptional units. The region from cpsA to cpsD is 10 kilobases long and appears to be contiguous. Strains of E. stewartii with mutations in cpsA, cpsB, and in some cases cpsD formed restricted, necrotic lesions on corn seedlings, whereas cpsC and cpsE mutants were completely avirulent. Strains with mutations in cpsA through cpsD grew normally in planta during the first 24 hr after infiltration into corn leaves, but a cpsE mutant failed to multiply.