Activation of the diacetyl / acetoin pathway in L. lactis CRL264 by acidic growh

GARCÍA-QUINTÁNS, N, REPIZO, G, MARTÍN, MAURICIO, MAGNI, CHRISTIAN, LÓPEZ, PALOMA

APPLIED AND ENVIRONMENTAL MICROBIOLOGY

ASM

Año: 2008 vol. 74 p. 1988 - 1996

0099-2240

Lactococcus lactis subsp. lactis bv. diacetylactis strains are aroma-producing organisms used in startercultures for the elaboration of dairy products. This species is essentially a fermentative microorganism, whichcometabolizes glucose and citrate to yield aroma compounds through the diacetyl/acetoin biosynthetic pathway.Our previous results have shown that under acidic growth Lactococcus bv. diacetylactis CRL264 expressescoordinately the genes responsible for citrate transport and its conversion into pyruvate. In the present workthe impact of acidic growth on glucose, citrate, and pyruvate metabolism of Lactococcus bv. diacetylactisCRL264 has been investigated by proteomic analysis. The results indicated that acid growth triggers theconversion of citrate, but not glucose, into -acetolactate via pyruvate. Moreover, they showed that low pH hasno influence on levels of lactate dehydrogenase and pyruvate dehydrogenase. Therefore, the influence ofexternal pH on regulation of the diacetyl/acetoin biosynthetic pathway in Lactococcus bv. diacetylactis CRL264has been analyzed at the transcriptional level. Expression of the als, aldB, aldC, and butBA genes encoding theenzymes involved in conversion of pyruvate into aroma compounds has been investigated by primer extension,reverse transcription-PCR analysis, and transcriptional fusions. The results support that this biosyntheticpathway is induced at the transcriptional level by acidic growth conditions, presumably contributing tolactococcal pH homeostasis by synthesis of neutral compounds and by decreasing levels of pyruvate.