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pfs-Dependent Regulation of Autoinducer 2 Production in Salmonella enterica Serovar Typhimurium. Anne L. Beeston, 2002.Bacterial intercellular communication provides a mechanism for signal-dependent regulation of gene expression to promote coordinated population behavior . Salmonella enterica serovar Typhimurium produces a non-homoserine lactone autoinducer in exponential phase as detected by a Vibrio harveyi reporter assay for autoinducer 2 (AI-2) (M . G . Surette and B . L . Bassler, Proc . Natl . Acad . Sci . USA 95:7046-7050, 1998) . The luxS gene product mediates the production of AI-2 (M . G . Surette, M . B . Miller, and B . L . Bassler, Proc . Natl . Acad . Sci . USA 96:1639-1644, 1999) . Environmental cues such as rapid growth, the presence of preferred carbon sources, low pH, and/or high osmolarity were found to influence the production of AI-2 (M . G . Surette and B . L . Bassler, Mol . Microbiol . 31:585-595, 1999) . In addition to LuxS, the pfs gene product (Pfs) is required for AI-2 production, as well as S-adenosylhomocysteine (SAH) (S . Schauder, K . Shokat, M . G . Surette, and B . L . Bassler, Mol . Microbiol . 41:463-476, 2001) . In bacterial cells, Pfs exhibits both 5'-methylthioadenosine (MTA) and SAH nucleosidase functions . Pfs is involved in methionine metabolism, regulating intracellular MTA and SAH levels (elevated levels of MTA and SAH are potent inhibitors of polyamine synthetases and S-adenosylmethionine dependent methyltransferase reactions, respectively) . To further investigate regulation of AI-2 production in Salmonella, we constructed pfs and luxS promoter fusions to a luxCDABE reporter in a low-copy-number vector, allowing an examination of transcription of the genes in the pathway for signal synthesis . Here we report that luxS expression is constitutive but that the transcription of pfs is tightly correlated to AI-2 production in Salmonella serovar Typhimurium 14028 . Neither luxS nor pfs expression appears to be regulated by AI-2 . These results suggest that AI-2 production is regulated at the level of LuxS substrate availability and not at the level of luxS expression . Our results indicate that AI-2-dependent signaling is a reflection of metabolic state of the cell and not cell density . Escherichia coli Gene Expression Responsive to Levels of the Response Regulator EvgA. Nobuhisa Masuda, 2002.To investigate the function of the EvgA response regulator, we compared the genome-wide transcription profile of EvgA-overexpressing and EvgA-lacking Escherichia coli strains by oligonucleotide microarrays . The microarray measurements allowed the identification of at least 37 EvgA-activated genes, including acid resistance-related genes gadABC and hdeAB, efflux pump genes yhiUV and emrK, and 21 genes with unknown function . EvgA overexpression conferred acid resistance to exponentially growing cells . This acid resistance was abolished by deletion of ydeP, ydeO, or yhiE, which was induced by EvgA overexpression . These results suggest that ydeP, ydeO, and yhiE are novel genes related to acid resistance and that EvgA regulates several acid resistance genes . Furthermore, the deletion of yhiE completely abolished acid resistance in stationary-phase cells, suggesting that YhiE plays a critical role in stationary-phase acid resistance . The multidrug resistance in an acrB deletion mutant caused by EvgA overexpression was completely abolished by deletion of yhiUV, while the emrKY deletion had no effect on the increase in resistance by EvgA overexpression . In addition, EvgA overexpression did not confer resistance in a tolC-deficient strain . These results suggest that YhiUV induced by EvgA overexpression is functionally associated with TolC and contributes to multidrug resistance . Extremophiles 2002. Mosè Rossi, 2003.
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