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Journal of Bacteriology, July 2002, p. 3450-3456, Vol. 184, No. 13
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.13.3450-3456.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

pfs-Dependent Regulation of Autoinducer 2 Production in Salmonella enterica Serovar Typhimurium

Anne L. Beeston and Michael G. Surette*

Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alberta T2N 4N1, Canada

Received 4 October 2001/ Accepted 19 March 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.


* Corresponding author. Mailing address: Department of Microbiology and Infectious Diseases, University of Calgary, 3330 Hospital Dr., NW, Calgary, Alberta T2N 4N1, Canada. Phone: (403) 220-2774. Fax: (403) 270-2772. E-mail: surette{at}ucalgary.ca.


Journal of Bacteriology, July 2002, p. 3450-3456, Vol. 184, No. 13
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.13.3450-3456.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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