Physiological role at low pH of the C4 metabolic pathway in Enterococcus faecalis

REPIZO G. D.; MAGNI C.

Carlos Paz

Congreso; XLIV Reunión Anual de SAIB; 2008

SAIB

Lactic Acid Bacteria (LAB) are recognized as safe microorganisms that are capable to improve the quality of diary products. When the LAB Lactococcus lactis is employed as a starter strain for the production of fermented foods, high quantities of important aroma compounds such as diacetyl are generated by means of the C4 metabolic pathway. This route depends on the expression at low pH of the als, aldB, aldC and butBA genes encoding the enzymes involved in the conversion of pyruvate into aroma compounds. In the non-starter LAB Enterococcus faecalis, a bioinformatic search determined that only als and the L. lactis aldB orthologous gene alsD are present in its genome. Our studies showed that these genes compose a single operon which is maximally transcribed during the mid-exponential phase of growth from a promoter located 34 nucleotides upstream from the ATG of als gene. The trancriptional analysis indicated that this operon is induced in the presence of pyruvate. The disruption of the als gene, produced a C4 deficient strain sensible to low medium pH and high concentrations of pyruvate. Moreover, we found that the putative transcriptional regulator LytR, transcribed divergently to the als operon, is not involved in its induction. Finally, we determined that LytR is associated to cell wall maintenance since a lytR deficient strain showed a higher rate of autolysis.