Biochemical conversion of six-carbon sugars into acids in bacteria
The mixed acid fermentation pathway in E. coli.[1][2] End products are highlighted in blue.
In biochemistry, mixed acid fermentation is the metabolic process by which a six-carbon sugar (e.g. glucose, C6H12O6) is converted into a complex and variable mixture of acids. It is an anaerobic (non-oxygen-requiring) fermentation reaction that is common in bacteria. It is characteristic for members of the Enterobacteriaceae, a large family of Gram-negative bacteria that includes E. coli.[3]
The mixture of end products produced by mixed acid fermentation includes lactate, acetate, succinate, formate, ethanol and the gases H2 and CO2. The formation of these end products depends on the presence of certain key enzymes in the bacterium. The proportion in which they are formed varies between different bacterial species.[4] The mixed acid fermentation pathway differs from other fermentation pathways, which produce fewer end products in fixed amounts. The end products of mixed acid fermentation can have many useful applications in biotechnology and industry. For instance, ethanol is widely used as a biofuel.[5] Therefore, multiple bacterial strains have been metabolically engineered in the laboratory to increase the individual yields of certain end products.[2] This research has been carried out primarily in E. coli and is ongoing. Variations of mixed acid fermentation occur in a number of bacterial species, including bacterial pathogens such as Haemophilus influenzae where mostly acetate and succinate are produced and lactate can serve as a growth substrate.[6]
^Cite error: The named reference Keseler2011 was invoked but never defined (see the help page).
^ abFörster, Andreas H. & Johannes Gescher (2014). "Metabolic engineering of Escherichia coli for production of mixed-acid fermentation end products". Frontiers in Bioengineering and Biotechnology. 2: 506–508. doi:10.3389/fbioe.2014.00016. PMC 4126452. PMID 25152889.
^Farrell, Alexander E.; et al. (2006). "Ethanol can contribute to energy and environmental goals". Science. 311 (5760): 506–508. Bibcode:2006Sci...311..506F. doi:10.1126/science.1121416. PMID 16439656. S2CID 16061891.
^Hosmer, Jennifer; Nasreen, Marufa; Dhouib, Rabeb; Essilfie, Ama-Tawiah; Schirra, Horst Joachim; Henningham, Anna; Fantino, Emmanuelle; Sly, Peter; McEwan, Alastair G.; Kappler, Ulrike (2022-01-27). "Access to highly specialized growth substrates and production of epithelial immunomodulatory metabolites determine survival of Haemophilus influenzae in human airway epithelial cells". PLOS Pathogens. 18 (1): e1010209. doi:10.1371/journal.ppat.1010209. ISSN 1553-7374. PMC 8794153. PMID 35085362.
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