Bifidobacterium Lactic Acid Fermentation

This type of lactic acid fermentation is exclusive to Grampositive bacteria belonging to the genus Bifidobacterium. These bacteria are found mainly in the intestinal tracts of warmblooded animals and they are recognized as pro-biotic. In fact, they help in the maintenance of the balanced composition of the intestinal microflora and they exert positive effects on the health and well-being of the host. Bifidobacteria do not have aldolase and glu-cose-6-phosphate dehydrogenase; they thus ferment hexose via a phosphoketolase pathway that is known as the 'bifid shunt', where the final products are acetic and lactic acids in a molar ratio of 3:2. The key enzyme in the bifid shunt is fructose-6-phosphate phosphoketolase (F6PPK), which converts frutose 6-phosphate into acetyl 1-phosphate and eritrose 4-phosphate (Figure 5). The ATP yield is 5 mol per 2 mol of glucose, and it is therefore higher than that of homolactic fermentation.

2 Glucose

2 ATP

2 ADP 2 Fructose-6P

Acetate

Acetyl-P + Eritrose-4P

Heptose-P + Triose-P

2 Acetyl-P

2 ADP

2 ATP

Acetyl-P + Eritrose-4P

Fructose-6P

Heptose-P + Triose-P

2 Glyceraldehyde-3P 4 ADP 4 ATP

2 Pyruvate

2 NADH

2 Acetyl-P

2 Acetate

Figure 5 Schematic representation of bifid shunt

2 NAD+ 2 Lactate

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