CITRATE AND SUGAR COFERMENTATION IN LEUCONOSTOC-OENOS, A C-13 NUCLEAR-MAGNETIC-RESONANCE STUDY

C-13 nuclear magnetic resonance spectroscopy was used to investigate c itrate-glucose cometabolism in nongrowing cell suspensions of the wine lactic acid bacterium Leuconostoc oenos. The use of isotopically enri ched substrates allowed us to identify and quantify in the end product s the carbon atoms derived from each of the substrates supplied; furth ermore, it was possible to differentiate between products derived from the metabolism of endogenous carbon reserves and those derived from e xternal substrates. Citrate-sugar cometabolism was also monitored in d ilute cell suspensions for comparison with the nuclear magnetic resona nce results. A clear metabolic shift of the end products from glucose metabolism was observed when citrate was provided along with glucose: ethanol was replaced by acetate, and 2,3-butanediol was produced. Reci procally, the production of lactate and 2,3-butanediol from citrate wa s increased in the presence of glucose. When citrate was cometabolized with glucose, a 10-fold reduction in the intracellular concentration of glucose-6-phosphate was observed, a result in line with the observe d citrate-induced stimulation of glucose consumption. The presence of citrate provided additional pathways for NADP(+) regeneration and allo wed the diversion of sugar carbon to reactions in which ATP was synthe sized. The increased growth rates and maximal biomass yields of L. oen os growing on citrate-glucose mixtures resulted from increased ATP syn thesis both by substrate-level phosphorylation and by a chemiosmotic m echanism.