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Homoacetogens

Decent Essays

1.4.1 Discovery and abundance of homoacetogens
Homoacetogens are strict anaerobic bacteria that produce acetate from CO2 as a diagnostic end-product of metabolism (Drake 1994, Muller 2003). They can grow on different substrates such as hydrogen, hexoses, formate, carbon monoxide, methoxylated compounds, and alcohols. Depending on what energy sources they are growing with, products in addition to acetate can be formed, and some can produce butyrate from CO2 using the same basic pathway as used for acetate formation. They are known as “homoacetogens” (organisms generating only acetate), “reductive acetogens”, “CO2-reducing acetogens”, or simply as “acetogens”. These different terminologies are confusing, and misleading, since they do not only produce acetate, and acetogens could form acetate by any pathway. In this thesis, the term “homoacetogen” will be used, because it is a simple one word descriptor for this taxonomically-diverse group of bacteria unified by using the Wood-Ljundahl pathway to form acetate from CO2. The term “homoacetogenesis” will be used for this metabolism, and “homobutyrogenesis” for the process in which butyrate is formed from CO2.

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2008). The formation of butyrate using CO2 and H2 by homoacetogens is referred to as “homobutyrogenesis” (equation (3)). In addition to the use of eight H2 to generate two moles of acetate, and additional two moles of H2 are used to reduce two acetate to butyrate via acetoacetate, 3-hydroxybutyrate, and crotonate, all as CoA derivatives (Kerby et al. 1983). Members of genera Acetonema and Eubacterium are some of the known homoacetogens that produce butyrate as well as acetate from H2 and CO2 (Schiel-Bengelsdorf & Dürre

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