CITRATE METABOLISM BY ENTEROCOCCUS FAECIUM AND ENTEROCOCCUS DURANS

CABRAL MARÍA E.; MUKDSI, MARÍA C. ABEIJÓN; MEDINA DE FIGUEROA ROXANA B.; GONZÁLEZ SILVIA N.

CANADIAN JOURNAL OF MICROBIOLOGY

Año: 2007 vol. 53 p. 607 - 615

0008-4166

Citrate metabolism by Enterococcus faecium ETC9 and Enterococcus durans Ov421 was studied as sole energy source and in presence of glucose or lactose. Both strains utilized citrate as the sole energy source. Enterococcus faecium ETC9 showed diauxic growth in the presence of a limiting concentration of glucose. Neither strain used citrate until glucose was fully metabolized. The strains showed co-metabolism of citrate and lactose. Lactate, acetate, formate, and flavour compounds (diacetyl, acetoin, and 2,3-butanediol) were detected in both strains. The highest production of flavour compounds was detected during growth of E.durans Ov421 in media supplemented with citrate-glucose and citrate-lactose. Citrate lyase was inducible in both strains. Acetate kinase activities presented the highest values in LAPTc medium, with E.faecium ETC9 displaying a specific activity 2.4-fold higher than E.durans. The highest levels of á-acetolactate synthase specific activity were detected in E.durans grown in LAPTc+g, in accordance with the maximum production of flavour compounds detected in this medium. Diacetyl and acetoinreductases displayed lower specific activity values in the presence of citrate. Enterococcus faecium and E.durans displayed citrate lyase, acetate kinase, á-acetolactate synthase, and diacetyl and acetoin reductase activities. These enzymes are necessary for conversion of citrate to flavour compounds that are important in fermented dairy products.