Mixed acid fermentation

[3] The mixture of end products produced by mixed acid fermentation includes lactate, acetate, succinate, formate, ethanol and the gases H2 and CO2.

The end products of mixed acid fermentation can have many useful applications in biotechnology and industry.

[5] Therefore, multiple bacterial strains have been metabolically engineered in the laboratory to increase the individual yields of certain end products.

After the variable amounts of different end products are formed by these pathways, they are secreted from the cell.

This acetyl-CoA is then converted into acetate in E. coli, whilst producing ATP by substrate-level phosphorylation.

This reaction is catalysed by the enzyme pyruvate-formate lyase (PFL), which plays an important role in regulating anaerobic fermentation in E.

This is the only case in the mixed acid fermentation pathway where ATP is not produced via substrate-level phosphorylation.

[1] formate → H2 and CO2 The methyl red (MR) test can detect whether the mixed acid fermentation pathway occurs in microbes when given glucose.

Multiple bacterial strains have been metabolically engineered to increase the individual yields of end products formed by mixed acid fermentation.

[2] The major limiting factor for this engineering is the need to maintain a redox balance in the mixture of acids produced by the fermentation pathway.

[14][15] A plasmid that carried the pyruvate decarboxylase and alcohol dehydrogenase genes from the bacteria Z. mobilis was used by scientists.

[18] Early experiments engineered the E. coli strain RR1 to produce either one of the two optical isomers of lactate.

[20] Increasing the yield of succinate from mixed acid fermentation was first done by overexpressing the enzyme PEP carboxylase.

Alternative approaches have altered the redox and ATP balance to optimize the succinate yield.

[4] All these pathways begin by converting pyruvate, but their end products and the key enzymes they require are different.