INCOMPLETE OPERATION OF BIOSYNTHETIC AND BIOENERGETIC FUNCTIONS OF THE CITRIC-ACID CYCLE IN MULTIPLE AUXOTROPHIC LACTOBACILLI

Many of the putative enzymes mediating oxidative reactions of the citr ic acid cycle were measured in cell-free extracts of Lactobacillus pla ntarum ATCC 8014, L. casei ATCC 7469, L. helveticus ATCC 15009, and L. acidophilus ATCC 11506. The activities of citrate synthase and aconit ase were demonstrated in all the strains investigated. None of isocitr ate dehydrogenase, 2-oxoglutarate dehydrogenase, and succinate dehydro genase activities were detected in any of the strains tested. Fumarase and malate dehydrogenase activities could be detected in some but not all of the strains. On the other hand, all the strains had the activi ties of fumarase and malate dehydrogenase when measured in the directi on of reductive reactions of the cycle. In addition, the activities of fumarate reductase and citrate lyase were found in all the strains an d in most strains, respectively. All these results suggest that the ox idative pathway in the citric acid cycle serving both bioenergetic and 2-oxoglutarate biosynthetic functions is completely inoperative in la ctobacilli, while a set of reversed reactions leading to succinate syn thesis functions in these bacteria. These findings also suggest that t he lack of 2-oxoglutarate dehydrogenase activities is closely related to the inability to synthesize glutamate in lactobacilli.