Heterolactic Fermentation

Heterolactic fermentation is carried out mainly by bacteria of the genera Leuconostoc, Oenococcus, and Weissella, and by heterofermentative lactobacilli. Obligate hetero-fermentative bacteria do not perform glycolysis due to the lack of aldolase, the enzyme that breaks down fructose 1,6-bisphosphate into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. Glucose 6-phosphate is oxidized to 6-phosphogluconate and fermentation is carried out through the phosphoketolase pathway

ATP Glucose

Glucose-6P

Fructose-6P ADP

Fructose-1,6PP

2 Glyceraldehyde-3P 4ADP

ADP Glucose-6P 1

6P-gluconate i

Ribulose-5P + CO2

Xylulose-5P ATP

4ATP

2 ADP

Glyceraldehyde-3P + Acetyl-P ADP

Pyruvate

2 NADH

Lactate (a)

2 ATP

Piruvate NADH

NAD+

Lactate

ATP NADH

NAD+ Ethanol

Figure 4 Schematic representation of homolactic (a) and heterolactic (b) fermentations. Pyruvate reduction leads to the regeneration of NAD+.

(Figure 4). The final products of this fermentation are lactate, ethanol, and CO2 but acetate may also be produced. The ATP yield is 1 mol per mole of glucose; thus, heterolactic metabolism yields less energy than homolac-tic fermentation. Heterolactic fermentation can also be carried out by facultative homofermentative bacteria.

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