The pathways of glucose dissimilation by Microbacterium lacticum.

Glucose fermentation by lactic acid bacteria occurs by at least two different routes. Homolactic species, the streptococci and homolactobacilli, convert hexoses to lactate by the EmbdenMeyerhof pathway. Although the demonstration of glycolytic enzymes and the formation and degradation of glycolytic intermediates by cellfree preparations is incomplete, the conversion of glucose-3,4-C'4 to carboxyl-labeled lactate by Lactobacillus casei (Gibbs et al., 1950) and by Streptococcus faecalis (Gibbs et al., 1955) strongly supports this premise. In contrast, the heterolactic organisms (Leuconostoc and Lactobacillus) ferment glucose via an anaerobic hexose monophosphate pathway. Fermentation of glucose-iC14 and glucose-3 ,4-C04 by Leuconostoc mesenteroides (Gunsalus and Gibbs, 1952) and by Leuconostoc dextranicum and heterolactobacilli (Gibbs et al., 1955) revealed that carbon 1 of glucose appears as carbon dioxide and carbon 2 as methyl group of ethanol. In addition, enzyme preparations of L. mesenteroides were devoid of fructose-1,6-diphosphate aldolase but contained glucose-6-phosphate (G-6-P) dehydrogenase and 6-phosphogluconate (6-PG) dehydrogenase (DeMoss et al., 1951). Although fermentation of labeled glucose by other Lactobacteriaceae such as Propionibacterium pentosaceum (Leaver and Wood, 1953) and Butyribacterium rettgeri (Pine et al., 1954) leads to labeling of products, which indicates that the Embden-Meyerhof pathway plays a major role in these fermentations, details of the mechanism of hexose fermentation in many of the Lactobacteriaceae are almost entirely lacking. While fermentation appears to be the dominant