BackgroundThe gram-negative Xanthomonas campestris pv. campestris is the pathogenic bacterium that causes black rot disease in crucifers. The virulence determinants of this bacterium include extracellular enzymes, exopolysaccharides, and biofilm formation. Here, one transposon mutant of X. campestris pv. campestris strain 17 that affects biofilm formation was isolated, and subsequent analyses led to the identification of the lolA gene, which encodes an outer membrane lipoprotein chaperone.ResultsThe lolA mutant exhibited significant reductions in bacterial attachment, extracellular enzyme production, virulence, and tolerance in the presence of myriad membrane-perturbing agents. These phenotypic changes of the mutant could be complemented to the wild-type level through the intact lolA gene. Proteomic analysis revealed that 109 proteins were differentially expressed after lolA mutation. These differentially expressed proteins were categorized in various functional groups and were mainly associated with the membrane component, were involved in transport, and contained receptor activity. Through reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) analysis, deletion of lolA was determined to have caused significantly reduced expression of genes that encode the major extracellular enzymes, the biofilm-related proteins, and the virulence-related proteins. The RT-qPCR analysis also indicated that the expression of several genes that encode putative outer membrane lipoproteins and TonB-dependent receptors was reduced after lolA mutation.ConclusionsThis is the first report to define the lolA gene as a virulence factor and to contribute to the functional understanding of, and provide new information concerning, the role of lolA in Xanthomonas. Furthermore, the results of this study provide and extend new insights into the function of lolA in bacteria.Electronic supplementary materialThe online version of this article (10.1186/s12866-019-1387-9) contains supplementary material, which is available to authorized users.
Isocitrate dehydrogenase (IDH) catalyzes the oxidative decarboxylation of isocitrate to alpha-ketoglutarate. In the genome of Xanthomonas campestris pv. campestris, the phytopathogen that causes black rot in cruciferous plants, two putative IDH genes, icd1 and icd2, have been annotated. Their physiological roles in X. campestris pv. campestris are unclear. In this study, the icd2 gene from X. campestris pv. campestris was characterized in detail. We demonstrated genetically that icd2 gene encodes a functional IDH, and is involved in virulence as well as bacterial attachment. Furthermore, the icd2 transcription initiation site was mapped at nucleotide G, 127 nucleotide upstream of the icd2 translation start codon. In addition, promoter analysis revealed that icd2 expression exhibits a distinct expression profile under different culture conditions, is subjected to catabolite repression, and is affected by acetate. This is the first time that the function and transcription of icd2 have been characterized in the crucifer pathogen X. campestris pv. campestris.
Xanthomonas campestris pv. campestris (Xcc) is the causative agent of black rot in crucifers. Here, one EZ-Tn5 transposon mutant of Xcc, altered in bacterial attachment, was isolated. Further analysis revealed that the transposon was inserted in the wxcX gene (encodes a hypothetical protein) of the transposon mutant. Sequence analysis revealed that WxcX is highly conserved in Xanthomonas, but none has been characterized. In this study, it was indicated that mutation of wxcX resulted in enhanced bacterial attachment, reduced virulence on the host cabbage, and increased sensitivity to sodium dodecyl sulfate. The affected phenotypes of the wxcX mutant could be complemented to wild-type levels by the intact wxcX gene. Site-directed mutagenesis revealed that E408 and E411 are critical amino acid residues for WxcX function in bacterial attachment. Taken together, our results demonstrate the roles of wxcX in attachment, virulence, and tolerance to sodium dodecyl sulfate in Xanthomonas for the first time.
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