THE HETEROLACTIC FERMENTATION

Abstract

A new route of ethanol formation has recently been shown to exist in Leuconostoc mesenteroides (I).The evidence thus far available indicates that (a) glucose fermentation always yields 1 mole each of lactate, ethanol, and COZ, (b) aldolase and isomerase do not function in glucose fermentation by this organism, (c) the enzymes for the formation of D(-)-lactic acid from n-glyceraldehyde phosphate via DPN-linked dehydrogenases and intervening enzymes are present, (d) acetate stimulates the rate of CO, evolution during glucose fermentation by cell suspensions.Acetaldehyde and acetoin, for which DPN-linked dehydrogenases are present in cell extracts of the organism, also stimulate the fermentation rate.A brief review of the fermentation characteristics of the heterofermentative lactic cocci is given by DeMoss et al. (1) ; for more detailed data and biological characteristics see Hucker and Pederson (2).A preliminary report of the labeling of the products from the fermentation of C14-labeled glucose (3), in addition to the fermentation balances and enzyme experiments (I), indicates that lactate and ethanol plus CO2 may arise from different ends of the glucose molecule.The occurrence of a glucose-&phosphate dehydrogenase in L. mesenteroides and its possible rBle in the anaerobic dissimilation of glucose to the products of the heterolactic fermentation have been reported (4).The present experiments were designed to test the possibility of a lack of mixing of the two halves of glucose in the heterolactic fermentation and to find whether acetate can serve as a precursor of ethanol.In fermentations by cell suspensions of L. mesenteroides, glucose-l-U4 yielded CY402 at approximately 6 times the specific activity of the glucose fermented.Glucose-3, 4-U4 yielded carbinollabeled ethanol and carboxyl-labeled lactate.Fermentation of unlabeled glucose, with acetate-2-C" added, yielded methyl-labeled ethanol.The implications of these data are discussed.Methods Bacteriological-L.mesenteroides, strain 39, was employed throughout these experiments.The growth medium and fermentation conditions em-