Lactic acid production and carbon catabolite repression from single and mixed sugars using Enterococcus faecalis RKY1

Enterococcus faecalis RKY1, a newly isolated lactic acid bacterium, efficiently metabolized glucose, fructose, and maltose to lactic acid by the homolactic fermentation pathway through Embden-Meyerhof glycolysis. During lactic acid fermentation with glucose, fructose, or maltose as a sole carbon source, the average volumetric productivities. were 3.56, 4.12, and 3.54 g/litre/h with final lactic acid concentrations of 139, 144, and 138 g/litre, respectively. Furthermore, for the lactic acid fermentations with glucose/fructose, glucose/maltose, and fructose/maltose mixtures as carbon sources, Enterococcus faecalis RKY1 grown on a mixture of glucose/fructose simultaneously consumed these sugars, and the cell growth and average volumetric productivity were higher than when grown on the individual sugars. However, it preferentially metabolized the glucose and fructose in the glucose/maltose and fructose/maltose mixtures. Therefore, carbon catabolite repression on its maltose metabolism was triggered by these preferentially metabolized sugars. (C) 2001 Elsevier Science Ltd. All rights reserved.