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Regulation of gene expression by putative aspartate racemases, YgeA and AspR, in Salmonella Typhimurium

ABSTRACT: Amino acid racemases are enzymes that catalyze the conversion between L and D- forms of amino acids. While the role of alanine and glutamate raemases in bacteria (specifically Salmonella) are well-studied, relatively less is known about the function of other non-canonical racemases. This study focuses on delineating the role of two such putative aspartate raceases viz. YgeA and AspR in Salmonella Typhimurium. For this purpose, Salmonella strains engineered to lack either one or both of these genes were compared to the wild type strain under planktonic and biofilm-inducing conditions to identify the global changes in gene expression orchestrated by these genes.

ORGANISM(S): Salmonella enterica subsp. enterica serovar Typhimurium

PROVIDER: GSE62658 | GEO | 2015/08/31

SECONDARY ACCESSION(S): PRJNA264729

REPOSITORIES: GEO

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Project description:Background: Biofilm formation by Salmonella species enhances the capacity of these pathogenic bacteria to survive stresses that are commonly encountered within food processing and during host infection. The persistence of Salmonella within the food chain has become a major health concern, as biofilms can serve as a reservoir to contaminate food products. While the molecular mechanisms required for the survival of bacteria on surfaces are not fully understood, transcriptional studies of other bacteria have demonstrated that biofilm growth triggers the expression of specific sets of genes, compared with planktonic cells. Until now, most transcriptomic studies of Salmonella have focused on the effect of infection-relevant stressors on virulence and on comparing mutant and wild-type (WT). However little is known about the physiological responses taking place inside a Salmonella biofilm. Results: We have determined the transcriptomic and proteomic profiles of biofilms of Salmonella enterica serovar Typhimurium. We discovered that 124 of detectable proteins were differentially expressed in the biofilm compared with planktonic cells, and that 10% (433 genes) of S. Typhimurium genes showed a biofilm-specific pattern of transcription (i.e. a 2-fold or more change in the biofilm compared with planktonic cells). The genes that were significantly up-regulated implicated specific cellular processes in biofilm development including amino acid metabolism, cell motility, global regulation and tolerance to stress. We found that the most highly down-regulated genes in the biofilm were located on Salmonella Pathogenicity Island 2 (SPI2), but that a functional SPI2 secretion system regulator (ssrA) was required for WT biofilm formation. We identified STM0341 as a gene of unknown function that was needed for WT biofilm growth. Genes involved in tryptophan (trp) biosynthesis and transport were up-regulated in the biofilm. Deletion of trpE led to a decrease in bacterial attachment and we show that this biofilm defect is restored by exogenous tryptophan or indole. Conclusion: Biofilm growth of S. Typhimurium causes distinct changes in gene and protein expression. Our results show that aromatic amino acids make an important contribution to biofilm formation, and reveal that SPI2 genes, required for virulence in host cells, show opposing patterns of expression to biofilm-specific genes in S. Typhimurium.

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Regulation of gene expression by putative aspartate racemases, YgeA and AspR, in Salmonella Typhimurium

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