An Extracellular Pectate Lyase is the Pathogenicity Factor of the Soft-Rotting Bacterium Pseudomonas viridiflava. Ching-Hsing Liao. U.S. Department of Agriculture, Agriculture Research Service, Eastern Regional Research Center, Philadelphia, PA 19118. Hsueh-Yun Hung(1), and Arun K. Chatterjee(2). (1) U.S. Department of Agriculture, Agriculture Research Service, Eastern Regional Research Center, Philadelphia, PA 19118, and (2) Department of Plant Pathology, University of Missouri, Columbia 65211 U.S.A.. MPMI 1:199-206. Accepted 15 August 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988.

Pseudomonas viridiflava is a soft-rotting pathogen of harvested vegetables. The genetic and biochemical evidence presented here demonstrates that an extracellular pectate lyase (PL) of P. viridiflava is responsible for the maceration of plant tissues. The PL from culture supernatant was purified to apparent homogeneity by ammonium-sulfate precipitation and ion-exchange chromatography. The purified PL was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and thin-layer polyacrylamide gel isoelectric focusing, and was shown to contain a single polypeptide with M_r 42 kD and pI 9.7. This PL preparation was devoid of pectin lyase, polygalacturonase and protease activities, and readily macerated plant tissues. P. viridiflava was mutagenized with Tn5 by using pSUP1011 as a mobilizing vector. Two classes of mutants were altered in pectolytic ability. The Pel^- mutants were apparently defective in the synthesis of PL, whereas the Out^- mutants were pleiotropically altered in the export of PL and protease. Both Pel^- and Out^- mutants failed to induce soft rot in five unrelated plants. Southern blot analyses of the restriction enzyme-generated genomic DNA revealed that the Pel^- (M1-4) and the Out^- (M1-2) mutants carried single copies of Tn5. IS50, in addition to Tn5, was also detected in several mutants. Our observations indicate that PL, but not protease, is responsible for the pathogenicity of P. viridiflava. In addition, the data show that PL and protease share a common export system in this bacterium.