VIEW ARTICLE

Physiology and Biochemistry

Cellular Localization and Characterization of Pectic Enzymes of Erwinia carotovora subsp. atroseptica. Helga L. George, Graduate research assistant, Department of Plant Pathology, University of Massachusetts, Amherst 01003, Present address: Department of Plant Pathology, University of Arizona, Tucson 85721; M. S. Mount(2), and Phyllis M. Berman(3). (2)(3)Professor, and research associate, respectively, Department of Plant Pathology, University of Massachusetts, Amherst 01003. Phytopathology 81:134-139. Accepted for publication 25 September 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-134.

Pectate lyase (PL) and polygalacturonase (PG) enzymes were isolated from the extracellular, periplasmic, and cytoplasmic fractions of Erwinia carotovora subsp. atroseptica strain SR-8 grown on a sodium polypectate minimal salts broth. The enzymes were purified and characterized for mode of action, ion requirements, and isoelectric point (pI). Six endoPLs with pIs of 10.2, 9.6, 9.5, 9.4, 9.2, and 8.9 were found in the extracellular fraction, along with endoPGs with approximate pIs of 10.7 and 3.9. The endoPLs produced unsaturated dimers as their final product, while the endoPGs produced saturated trimers. The periplasm contained the PLs with pIs of 9.5 and 9.4, and a small amount of the PG with a pI of 3.9. It also contained an exoPL (pI7.1) that generated unsaturated dimers as its sole reaction product. The cytoplasm contained the PLs with pIs of 9.5 and 9.4, small amounts of the other PLs, and a large quantity of the PG with pI 3.9. Cation preferences differed among the enzymes isolated. The PL profile of Erwinia carotovora subsp. atroseptica is much more complex than previously realized, and unlike Erwinia carotovora subsp. carotovora and Erwinia chrysanthemi, this strain produces two endoPGs. The cellular location and physiological characteristics of the various enzymes may give clues to their role in pathogenicity.