pfs-Dependent Regulation of Autoinducer 2 Production inSalmonella entericaSerovar Typhimurium
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ABSTRACTBacterial intercellular communication provides a mechanism for signal-dependent regulation of gene expression to promote coordinated population behavior.Salmonella entericaserovar Typhimurium produces a non-homoserine lactone autoinducer in exponential phase as detected by aVibrio harveyireporter assay for autoinducer 2 (AI-2) (M. G. Surette and B. L. Bassler, Proc. Natl. Acad. Sci. USA 95:7046-7050, 1998). TheluxSgene 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, thepfsgene product (Pfs) is required for AI-2 production, as well asS-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 inSalmonella, we constructedpfsandluxSpromoter fusions to aluxCDABEreporter in a low-copy-number vector, allowing an examination of transcription of the genes in the pathway for signal synthesis. Here we report thatluxSexpression is constitutive but that the transcription ofpfsis tightly correlated to AI-2 production inSalmonellaserovar Typhimurium 14028. NeitherluxSnorpfsexpression 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 ofluxSexpression. Our results indicate that AI-2-dependent signaling is a reflection of metabolic state of the cell and not cell density.
