Acetogenesis

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Acetogenesis is a process through which acetate is produced from CO2 and an electron source (e.g., H2, CO, formate, etc.) by anaerobic bacteria via the reductive acetyl-CoA or Wood-Ljungdahl pathway. The different bacterial species that are capable of acetogenesis are collectively termed acetogens. Some acetogens can synthesize acetate autotrophically from carbon dioxide and hydrogen gas.[1]

Discovery[edit]

In 1932, organisms were discovered that could convert hydrogen gas and carbon dioxide into acetic acid. The first acetogenic bacterium species, Clostridium aceticum, was discovered in 1936 by Klaas Tammo Wieringa. A second species, Moorella thermoacetica, attracted wide interest when it was first isolated because of its ability to convert glucose into three moles of acetic acid.[2]

Biochemistry[edit]

The precursor to acetic acid is the thioester acetyl CoA. The key aspects of the acetogenic pathway are several reactions that include the reduction of carbon dioxide to carbon monoxide and the attachment of the carbon monoxide to a methyl group. The first process is catalyzed by enzymes called carbon monoxide dehydrogenase. The coupling of the methyl group (provided by methylcobalamin) and the CO is catalyzed by acetyl CoA synthetase.[3]

2 CO2 + 4 H2 → CH3COOH + 2H2O

Applications[edit]

The unique metabolism of acetogens has significance in biotechnological uses. In carbohydrate fermentations, the decarboxylation reactions involved result in the loss of carbon into carbon dioxide. This loss is an issue with an increased requirement of minimization of CO2 emissions, as well as successful competition for fossil fuels with biofuel production being limited by monetary value. Acetogens can ferment glucose without any CO 2 emissions and convert it to 3 acetates, which can theoretically increase product yield by 50%. Acetogeneis does not replace glycolysis with a different pathway, but is rather used by capturing CO2 from glycolysis and placing it through acetogenesis.[4]

References[edit]

  1. ^ Singleton P (2006). "Acetogenesis". Dictionary of microbiology and molecular biology (3rd ed.). Chichester: John Wiley. ISBN 978-0-470-03545-0.
  2. ^ Ragsdale SW, Pierce E (December 2008). "Acetogenesis and the Wood-Ljungdahl pathway of CO(2) fixation". Biochimica et Biophysica Acta. 1784 (12): 1873–98. doi:10.1016/j.bbapap.2008.08.012. PMC 2646786. PMID 18801467.
  3. ^ Ragsdale SW (August 2006). "Metals and their scaffolds to promote difficult enzymatic reactions". Chemical Reviews. 106 (8): 3317–37. doi:10.1021/cr0503153. PMID 16895330.
  4. ^ Schuchmann K, Müller V (July 2016). "Energetics and Application of Heterotrophy in Acetogenic Bacteria". Applied and Environmental Microbiology. 82 (14): 4056–69. doi:10.1128/AEM.00882-16. PMC 4959221. PMID 27208103.