Glucose/Citrate Cometabolism in Lactococcus lactis subsp. lactis biovar diacetylactis with Impaired α-Acetolactate Decarboxylase

• Published in: Metabolic engineering 1999-10, Vol.1 (4), p.291-298
• Main Authors: Curic, Mirjana, de Richelieu, Marianne, Henriksen, Claus Maxel, Jochumsen, Kirsten Væver, Villadsen, John, Nilsson, Dan
• Format: Article
• Language: English
• Subjects: Biotechnology; Carboxy-Lyases - genetics; Carboxy-Lyases - metabolism; Citric Acid - metabolism; Diacetyl - metabolism; Fermentation; Glucose - metabolism; Lactococcus lactis - genetics; Lactococcus lactis - growth & development; Lactococcus lactis - metabolism; Mutation; Oxidation-Reduction; Pyruvic Acid - metabolism; Thioctic Acid - pharmacology
• ISSN: 1096-7176; 1096-7184
• DOI: 10.1006/mben.1999.0123

The pyruvate metabolism of a Lactococcus lactis subsp. lactis biovar diacetylactis mutant deficient in α-acetolactate decarboxylase and its wild-type strain was studied during batch cultivations. A chemically defined medium was used containing glucose as carbon- and energy-source. The α-acetolactate decarboxylase deficiency had no effect on the specific growth rate. Addition of citrate was found to increase the specific growth rate of both strains under aerobic and anaerobic conditions. The product formation was monitored throughout the cultivations. The carbon- and redox-balances were within the accuracy of the experimental data. When citrate was added, α-acetolactate, diacetyl, and acetoin were formed, and aeration was shown to have a positive effect on the formation of these metabolites. By omitting lipoic acid (required for a functional pyruvate dehydrogenase complex) from the growth medium, a similar stimulatory effect on α-acetolactate, diacetyl, and acetoin formation was observed under aerobic conditions. The strain with impaired α-acetolactate decarboxylase activity accumulated α-acetolactate which resulted in an increased diacetyl formation compared to the wild-type strain, under aerobic and anaerobic conditions.