title: Identification of gene loci controlling pectate lyase production and soft-rot pathogenicity in Pseudomonas marginalis.
abstract: Pseudomonas marginalis is an important postharvest pathogen capable of causing soft rot in a wide variety of harvested fruits and vegetables. Following transposon mutagenesis, we isolated two groups of P. marginalis CY091 mutants deficient in production of pectate lyase (Pel) and soft-rot pathogenicity in plants. The first group, designated Pel-, was caused by the insertion of Tn5 into a pel structural gene, and the second group, designated LemA-, was caused by the insertion of Tn5 into a regulatory locus corresponding to the lemA gene previously identified in other Gram-negative bacteria. The LemA- mutants also exhibited alteration in colony morphology and showed deficiency in production of protease (Prt). A cosmid clone pCIC carrying the P. marginalis lemA gene was isolated and characterized. pCIC was capable of restoring Pel production and soft-rot pathogenicity in LemA- mutants of P. marginalis and Pseudomonas viridiflava, indicating that the function of lemA gene in these two pseudomonads was similar and interchangeable. Using MudI-mediated mutagenesis, we isolated a third group of P. marginalis mutants deficient in production of Pel, Prt, and soft-rot pathogenicity. Mutants in this group (designated GacA-1) contained an insertion of MudI in a locus corresponding to the gacA gene of P. viridiflava. Like LemA- mutants, GacA- mutants also exhibited alteration in colony morphology and showed deficiency in production of Pel and Prt. However, GacA- mutants produced much lower levels of levan and fluorescent pyoverdine siderophore than the wild type and LemA- mutants. These results provide the first genetic evidence that P. marginalis produces a single alkaline Pel for maceration of plant tissue and demonstrate that production of Pel, Prt, levan, and pyoverdin by this bacterium is mediated by the two-component lemA/gacA gene system.
authors.affiliation: Eastern Regional Research Center, U.S. Department of Agriculture, Wyndmoor, PA 19038, USA. cliao@arserrc.gov
authors.forename: C H
authors.initials: CH
authors.lastname: Liao
authors.forename: D E
authors.initials: DE
authors.lastname: McCallus
authors.forename: W F
authors.initials: WF
authors.lastname: Fett
authors.forename: Y
authors.initials: Y
authors.lastname: Kang
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D005516:Food Microbiology; D005630:Fructans / Q000096:biosynthesis; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D016254:Mutagenesis, Insertional; D010935:Plant Diseases / Q000382:microbiology; D011133:Polysaccharide-Lyases / Q000096:biosynthesis*; D011549:Pseudomonas / Q000235:genetics*; D015183:Restriction Mapping; D017262:Siderophores / Q000096:biosynthesis; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D005630:Fructans; C091100:GacA protein, Bacteria; D017262:Siderophores; D014157:Transcription Factors; C074165:lemA protein, bacterial; D011133:Polysaccharide-Lyases; C023911:pectate lyase