Regulation of Pectobacterium virulence by membrane transporters
Pectobacterium carotovorum is a plant pathogenic bacterium that causes soft rot disease of fruits and vegetables. The disease is characterized by water-soaked soft decay resulting from the action of cell wall-degrading exoenzymes that the pathogen secretes. Using mini-Tn5 transposon mutagenesis, two mutants of P. carotovorum strain Ecc71 were isolated each with transposon insertions in a gene for small molecule membrane transporters. The first mutant was reduced in the production of extracellular pectate lyase, polygalacturonase, cellulase, and protease and exhibited decreased virulence in celery and carrot. The gene responsible for this altered phenotype was identified as corA, which codes for the Mg2+, Ni2+, Co2+ membrane transporter CorA. A functional copy of the corA+ gene complemented the CorA - mutant and restored both exoenzyme production and virulence to parental levels. The CorA- mutant was resistant to cobalt toxicity but its total intracellular Mg2+ concentration was not reduced. The transcripts for the positive exoenzyme regulator rsmB and flagellin subunit fliC were decreased in the CorA - mutant, whereas transcripts of siderophore receptor fepA were increased. The corA locus of P. carotovorum Ecc71 is constitutively expressed and negatively auto-regulated. The locus is also regulated by the sigma factor, HrpL and increases in expression in a dose dependent manner in response to a CorA inhibitor. The second mutant had increased production of pectate lyase, polygalacturonase, cellulase, protease, and their corresponding transcripts levels of pel-1, peh-1, celV, and prtW. The Tn-5 transposon was inserted in an upstream intergenic region of putative sodium/sulfate symporter gene nssA (PC1_0037). This mutant had increased tissue maceration in celery petioles but neither exoenzyme activity nor virulence was complemented by wild type nssA+ copy. The levels of mRNA transcript of nssA in this mutant were 3.5 fold higher than parental levels. NssA has high homology to ECA3984, a member of divalent anion sodium symporters family that is involved in the pathogenesis of P. atrosepticum, another soft rot bacterium. In conclusion, I used a transposon mutagenesis approach to identify pathogenicity genes in P. carotovorum. The results of these studies lend support that membrane transporters influence virulence and exoenzyme production in soft rot bacteria.
Caleb M Kersey,
"Regulation of Pectobacterium virulence by membrane transporters"
ETD Collection for Tennessee State University.