Abstract
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.
Highlights
The gram-negative Xanthomonas campestris pv. campestris is the pathogenic bacterium that causes black rot disease in crucifers
X. campestris pv. campestris employs myriad virulence factors to invade its host, such as extracellular enzymes secreted by the type II secretion system, effector proteins exported by the type III secretin system, and exopolysaccharides [5,6,7]
These findings indicated that the transposon insertion in H27 was most likely not a polar mutation; the insertion inactivation of the lolA gene affected the bacterial attachment exhibited in this mutant rather than the malfunction of other genes flanking lolA
Summary
The gram-negative Xanthomonas campestris pv. campestris is the pathogenic bacterium that causes black rot disease in crucifers. 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. Xanthomonas is a large genus comprised of 27 species of gram-negative bacteria that cause severe diseases in approximately 400 host plants that include crops of major economic value [1]. X. campestris pathovar campestris infects cruciferous plants and causes black rot disease, which may be the most problematic disease to affect crucifers worldwide [2]. Campestris employs myriad virulence factors to invade its host, such as extracellular enzymes (cellulase, mannanase, pectinase, and protease) secreted by the type II secretion system, effector proteins exported by the type III secretin system, and exopolysaccharides [5,6,7]. The extracellular enzymes can degrade plant cell components and induce plant tissue maceration, and the effector proteins injected into the plant cells can interfere with cell
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