Identification of New Flagellar Genes ofSalmonella entericaSerovar Typhimurium

Abstract

RNA levels of flagellar genes in eight different genetic backgrounds were compared to that of the wild type by DNA microarray analysis. Cluster analysis identified new, potential flagellar genes, three putative methyl-accepting chemotaxis proteins, STM3138 (McpA), STM3152 (McpB), and STM3216(McpC), and a CheV homolog, STM2314, in Salmonella, that are not found in Escherichia coli. Isolation and characterization of Mud-lac insertions in cheV, mcpB, mcpC, and the previously uncharacterized aer locus of S. enterica serovar Typhimurium revealed them to be controlled by σ²⁸-dependent flagellar class 3 promoters. In addition, the srfABC operon previously isolated as an SsrB-regulated operon clustered with the flagellar class 2 operon and was determined to be under FlhDC control. The previously unclassified fliB gene, encoding flagellin methylase, clustered as a class 2 gene, which was verified using reporter fusions, and the fliB transcriptional start site was identified by primer extension analysis. RNA levels of all flagellar genes were elevated in flgM or fliT null strains. RNA levels of class 3 flagellar genes were elevated in a fliS null strain, while deletion of the fliY, fliZ, or flk gene did not affect flagellar RNA levels relative to those of the wild type. The cafA (RNase G) and yhjH genes clustered with flagellar class 3 transcribed genes. Null alleles in cheV, mcpA, mcpB, mcpC, and srfB did not affect motility, while deletion of yhjH did result in reduced motility compared to that of the wild type.