Growth energetics of Lactococcus lactis subsp lactis biovar diacetylactis in cometabolism of citrate and glucose

Certain strains of lactic acid bacteria present in commercial cheese starters, characterized by faint transparent colonies on an agar plate containing 1 mg kg(-1) crystal violet (CVT), were identified as Lactococcus lactis subsp. (ssp) lactis biovar diacetylactis. The effect of citrate on the growth of these strains (CVT strains) in the presence of glucose was studied, in comparison with L. lactis strains. Molar growth yield from glucose (Y-G, g dry weight/mole of glucose consumed) for CVT strains grown on glucose plus citrate was significantly higher than the control (i.e. without citrate), but not for other L. lactis strains tested. Enhanced Y-G was also observed at a pH-controlled experiment, indicating that enhanced Y-G did not result from a buffering effect of citrate. CVT strains, in contrast to other strains of the same species, were shown to obtain enough energy to enhance Y-G on glucose-citrate mixtures. (C) 2000 Elsevier Science Ltd. All rights reserved.