Regulation Of Citrate Metabolism In Enterococcus faecalis ATCC29212

BLANCATO, VS; REPIZO, GD; MAGNI, C

Pinamar (Buenos Aires)

Congreso; XLI Reunión Anual de SAIB; 2005

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Citrate fermentation is an important industrial feature of Lactic Acid Bacteria. In addition, citrate metabolization has been described in pathogenic and opportunistic bacteria such Klebsiella pneumoniae and Enterococcus faecalis. The latter is involved in traditional raw milk cheese manufacture, contributing in the ripening process and in aroma development. Volatile compounds such as acetaldehyde, diacetyl, and acetoin, produced during cheese ripening as a consequence of metabolization of citrate, contribute to flavor. In this report we characterized the expression profile of the cit locus and protein-DNA interactions involved in the locus regulation. Transcriptional analysis of the cit locus revealed two divergent operons, citHO and oadDBcitCDEFXoadAcitMG. The transcriptional initiation start sites of these two operons were mapped by primer extension. The transcriptional patterns show activation of both operons by citrate and strong catabolite repression in response to glucose addition to the growth medium. In vitro transcription and band shift experiments show that CitO, a member of the GntR family, is a new positive regulator involved in the regulation of the citrate fermentation in bacteria. In addition, we identified a cre site (catabolite response element) located in the promoter region of citHO, our results suggest that CcpA binds to the cre site diminishing the expression of the citrate transporter CitH and the transcriptional factor CitO.