Submitted to: Journal of Bacteriology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/18/2005
Publication Date: 3/1/2006
Citation: Frye,J.G., Karlinsey, J.E.,Felise, H.R., Marzolf,B., Dowidar,N., Mcclelland,M., Hughes,K.T. 2006. Identification of new flagellar genes of salmonella enterica serovar typhimurium. Journal of Bacteriology. 188(6):2233-2243. Interpretive Summary: Flagella are organelles produced by bacteria which enable them to move in their environment. Motility is a virulence factor for pathogens like Salmonella which they use to invade a host, seek food and avoid toxins. The flagella are complex and require the coordinated expression of over 60 genes in order to be correctly assembled. While this process has been well studied in Salmonella, some questions remain. To identify all genes expressed during flagella construction, we assayed the gene expression of several Salmonella strains lacking certain regulatory genes. This study allowed us to confirm the categorization of gene expression into three classes and to identify four new flagella genes. These genes are involved in chemotoaxis and allow the bacteria to sense their environment and swim towards food sources and away from toxins. This explains how flagella are constructed for host invasion and is a model for all flagellated pathogens. This information will be useful researchers who study the book biology of bacterial flagella.
Technical Abstract: RNA levels of flagellar genes in 8 different genetic backgrounds were compared to wild-type by DNA microarray analysis. Cluster analysis revealed that 3 putative methyl-accepting chemotaxis proteins, STM3138(McpA), STM3152(McpB) and STM 3216(McpC) and a CheV homolog, STM2314 are present in Salmonella, but not in E. coli. Isolation and characterization of Mud-lac insertions in cheV, mcpB, mcpC and previously uncharacterized aer locus of S. typhimurium revealed them to be controlled by sigma28-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 genes did not affect flagellar RNA levels relative to wild-type. The cafA (RNase G) and yhjH genes clustered with flagellar class 3 transcribed genes. Null alleles in cheV, mcpA, mcpB, mcpC, srfB and cafA did not affect motility, while deletion of yhjH did result in reduced motility compared to wild-type.