Heterolactic fermentation

Figure 9.10 Pathways of heterolactic fermentation of lactose. Fd, oxidized ferredoxin, Fd gj, reduced ferredoxin.

A variation of the heterolactic fermentation is used by Bifidobacterium (Eq. 17-34).149 Phosphoketolase and a phosphohexoketolase, which cleaves fructose 6-P to erythrose 4-P and acetyl-P, are required, as are the enzymes of the sugar rearrangement system (Section E,3). The net yield of ATP is 2 V2 molecules per molecule of glucose. 

Some lactic acid bacteria of the genus Lactobacillus, as well as Leuconostoc mesenteroides and Zymomonas mobilis, carry out the heterolactic fermentation (Eq. 17-33) which is based on the reactions of the pentose phosphate pathway. These organisms lack aldolase, the key enzyme necessary for cleavage of fructose 1,6-bisphosphate to the triose phosphates. Glucose is converted to ribulose 5-P using the oxidative reactions of the pentose phosphate pathway. The ribulose-phosphate is cleaved by phosphoketolase (Eq. 14-23) to acetyl-phosphate and glyceraldehyde 3-phosphate, which are converted to ethanol and lactate, respectively. The overall yield is only one ATP per glucose fermented. 

Some bacteria that lack the usual aldolase produce ethanol and lactic acid in a 1 1 molar ratio via the "heterolactic fermentation." Glucose is converted to ribulose 5-phosphate via the pentose phosphate pathway enzymes. A thiamin diphosphate-dependent "phosphoketolase" cleaves xylulose 5-phosphate in the presence of inorganic phosphate to acetyl phosphate and glyceraldehyde 3-phosphate. 

Busse, M., Kindel, P. K., and Gibbs, M. 1961. The heterolactic fermentation. 3 Positions of 13C in the products of fructose dissimilation by Leuconostoc mesenteroides. J. Biol. Chem.,236, 2850-2853. 

During heterolactic fermentation, the fermentation of one mole of glucose yields one mole each of lactic acid, ethanol, and carbon dioxide ... 

However, heterolactic fermentation produces only 50% lactic acid and considerable amounts of ethanol, acetic acid, and carbon dioxide (Figure 4.2). 

Thomas, T. D., Ellwood, D. C., and Longyear, M. C. (1979), Change from homo- to heterolactic fermentation by Streptococcus lactis resulting from glucose limitation in anaerobic chemos-tat cultures. J. Bacteriol. 138,109-117. 

Reduction of fructose to mannitol brings about reoxidation of reduced NADH formed during heterolactic fermentation of glucose ... 

Fig. 5.2. Metabolic pathway of glucose fermentation by heterolactic bacteria (pentose phosphate pathway)...

Heterolactic fermentation pathway of glucose (6-phosphogluconate/phosphoketolase pathway]... 

Large-scale production is based on fermentation processes (homolactic or heterolactic), starting from glucose-containing or delivering materials, such as -+starch, - molasses, - whey, sulfite liquors (- paper and pulp) and - sucrose, with various strains of Lactobacillus (L. leichmannii, L. casei, L. delbriickii, L. brevis, L. bulgaricus). 

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