BIOCHEMICAL AND GENETIC-ANALYSIS OF A PECTATE LYASE GENE FROM XANTHOMONAS-CAMPESTRIS PV-VESICATORIA

Twenty-two percent of 522 strains of Xanthomonas campestris pv. vesicatoria were pectolytic on a sodium polypectate medium. Biochemical and genetic aspects of the pectolytic activity were further analyzed in strain XV56. The pectolytic activity was due to the secretion of a single pectate lyase with a pI of 8.8. From a genomic library of DNA of XV56, recombinant cosmids conferring pectolytic activity to nonpectolytic strains of X. c. pv. vesicatoria were identified. By subcloning, the pectate lyase gene was located within a PstI restriction fragment of 1.4 kb. The pectate lyase gene of XV56 shared no homology to DNA of the soft-rotting bacterium, Erwinia chrysanthemi, but hybridized to the DNA of all xanthomonads tested, irrespective of their ability to degrade pectic compounds. Mutants deficient in synthesis of the pectate lyase were selected after treatment of cells with nitrosoguanidine. The mutants were not altered in their ability to evoke disease symptoms, their growth in plants, or the ability to induce the hypersensitive reaction in nonhost plants. Thus, the pectate lyase gene appeared to play no essential role in pathogenicity.