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Acetogenesis is a process through which acetyl-CoA [1] or acetic acid is produced by anaerobic bacteria through the reduction of CO 2 via the Wood–Ljungdahl pathway.Other microbial processes that produce acetic acid (like certain types of fermentation or the oxidative breakdown of carbohydrates or ethanol by acetic acid bacteria) are not considered acetogenesis.
Acetic acid bacteria (AAB) are a group of Gram-negative bacteria which oxidize sugars or ethanol and produce acetic acid during fermentation. [1] The acetic acid bacteria consist of 10 genera in the family Acetobacteraceae. [1] Several species of acetic acid bacteria are used in industry for production of certain foods and chemicals. [1]
The worldwide production of acetic anhydride is a major application, and uses approximately 25% to 30% of the global production of acetic acid. The main process involves dehydration of acetic acid to give ketene at 700–750 °C. Ketene is thereafter reacted with acetic acid to obtain the anhydride: [50] CH 3 CO 2 H → CH 2 =C=O + H 2 O
The Monsanto process is an industrial method for the manufacture of acetic acid by catalytic carbonylation of methanol. [1] The Monsanto process has largely been supplanted by the Cativa process, a similar iridium-based process developed by BP Chemicals Ltd, which is more economical and environmentally friendly.
Industrial fermentation is the intentional use of fermentation in manufacturing processes. In addition to the mass production of fermented foods and drinks, industrial fermentation has widespread applications in chemical industry. Commodity chemicals, such as acetic acid, citric acid, and ethanol are made by fermentation. [1]
Fermentation of feedstocks, including sugarcane, maize, and sugar beets, produces ethanol that is added to gasoline. [16] In some species of fish, including goldfish and carp, it provides energy when oxygen is scarce (along with lactic acid fermentation). [17] Before fermentation, a glucose molecule breaks down into two pyruvate molecules .
Louis Pasteur made the decisive discovery that a special type of bacteria, later known as acetic acid bacteria, was the agent of fermentation for vinegar production. [10] In the 20th century, vinegar production was again revolutionized by the invention of the submerged fermentation process that cut production times down to 1–2 days. [11]
Fermentation only allows the breakdown of larger organic compounds, and produces small organic compounds. Methanogenesis effectively removes the semi-final products of decay: hydrogen, small organics, and carbon dioxide. Without methanogenesis, a great deal of carbon (in the form of fermentation products) would accumulate in anaerobic environments.