PHYSIOLOGY OF PYRUVATE METABOLISM IN LACTOCOCCUS-LACTIS

Lactococcus lactis, a homofermentative lactic acid bacterium, has been studied extensively over several decades to obtain sometimes conflict ing concepts relating to the growth behaviour. In this review some of the data will be examined with respect to pyruvate metabolism. It will be demonstrated that the metabolic transformation of pyruvate can be predicted if the growth-limiting constraints are adequately establishe d. In general lactate remains the major product under conditions in wh ich sugar metabolism via a homolactic fermentation can satisfy the ene rgy requirements necessary to assimilate anabolic substrates from the medium. In contrast, alternative pathways are involved when this energ y supply becomes limiting or when the normal pathways can no longer ma intain balanced carbon flux. Pyruvate occupies an important position w ithin the metabolic network. of L. lactis and the control of pyruvate distribution within the various pathways is subject to co-ordinated re gulation by both gene expression mechanisms and allosteric modulation of enzyme activity.