Abstract
BackgroundThe Yersinia enterocolitica flagellar master regulator FlhD/FlhC affects the expression levels of non-flagellar genes, including 21 genes that are involved in central metabolism. The sigma factor of the flagellar system, FliA, has a negative effect on the expression levels of seven plasmid-encoded virulence genes in addition to its positive effect on the expression levels of eight of the flagellar operons. This study investigates the phenotypes of flhD and fliA mutants that result from the complex gene regulation.ResultsPhenotypes relating to central metabolism were investigated with Phenotype MicroArrays. Compared to the wild-type strain, isogenic flhD and fliA mutants exhibited increased growth on purines and reduced growth on N-acetyl-D-glucosamine and D-mannose, when used as a sole carbon source. Both mutants grew more poorly on pyrimidines and L-histidine as sole nitrogen source. Several intermediates of the tricarboxylic acid and the urea cycle, as well as several dipeptides, provided differential growth conditions for the two mutants. Gene expression was determined for selected genes and correlated with the observed phenotypes. Phenotypes relating to virulence were determined with the chicken embryo lethality assay. The assay that was previously established for Escherichia coli strains was modified for Y. enterocolitica. The flhD mutant caused reduced chicken embryo lethality when compared to wild-type bacteria. In contrast, the fliA mutant caused wild-type lethality. This indicates that the virulence phenotype of the flhD mutant might be due to genes that are regulated by FlhD/FlhC but not FliA, such as those that encode the flagellar type III secretion system.ConclusionPhenotypes of flhD and fliA mutants are related to central metabolism and virulence and correlate with gene regulation.
Highlights
The Yersinia enterocolitica flagellar master regulator FlhD/FlhC affects the expression levels of non-flagellar genes, including 21 genes that are involved in central metabolism
The flagellar hierarchy in Yersinia enterocolitica is believed to be similar to E. coli with FlhD/FlhC constituting the master regulator [1] and FliA the sigma factor [2]
We extend our phenotypic analysis of Y. enterocolitica flhD and fliA mutants
Summary
The Yersinia enterocolitica flagellar master regulator FlhD/FlhC affects the expression levels of non-flagellar genes, including 21 genes that are involved in central metabolism. The flagellar hierarchy in Yersinia enterocolitica is believed to be similar to E. coli with FlhD/FlhC constituting the master regulator [1] and FliA the sigma factor [2]. The FlhD/FlhC complex binds to upstream sequences of class II genes, including the fliA gene [9]. FliA is the sigma factor of the flagellar system [10] and is required for the expression of the class III flagellar genes [11]. A more detailed investigation of the flagellar hierarchy of Y. enterocolitica demonstrated FliA regulation of eight of the 15 flagellar operons [12]. The expression levels of the remaining seven operons were affected by FlhD/FlhC in a FliA independent manner. Regulation of the three Y. enterocolitica flagellin genes, fleA, fleB, and fleC, by FliA had been previously shown [13,14]
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