Salmonella enterica Typhimurium grown with and without glucose

Cell to cell communication in bacteria to regulate various cellular processes with respect to their population density is termed quorum sensing and is achieved using signaling molecules called autoinducers. LuxS, which is involved in the synthesis of the autoinducer molecule-2 (AI-2), is conserved in several Gram-positive and Gram-negative bacteria including the enteric pathogen Salmonella Typhimurium. Genes that are regulated by luxS in S. Typhimurium were identified using microarrays and RNA samples from wild type S. Typhimurium and its isogenic luxS mutant, in two growth conditions (presence and absence of glucose), and at two different time points (mid-log and early-stationary phases). Minimal differential gene expression was observed in the presence of glucose. In the absence of both luxS and glucose, a total of 1560 genes were differentially expressed and 1361 genes were identified as luxS/AI-2-regulated at the mid-log phase and 199 genes at the early-stationary phase. Quantitative real-time PCR was performed on selected genes to validate the microarray results. These results suggest that although the expression of the luxS gene in S. Typhimurium is independent of the growth condition, its role in the production of AI-2 depends on the growth condition. It was found that luxS/AI-2 plays a vital role in a variety of processes such as metabolism, virulence gene expression, motility, transcription and translation. Keywords: Salmonella Typhimurium, quorum sensing, luxS mutant, autoinducer-2 Purified cDNAs from the wild type and mutant were each labeled with Cy-3 mono-Reactive Dye and Cy-5 mono-Reactive Dye (GE Health Care) and were processed using a dye-swapping design.