New Horizons in Acetogenic Conversion of One-Carbon Substrates and Biological Hydrogen Storage

• Published in: Trends in biotechnology (Regular ed.) Vol. 37; no. 12; pp. 1344 - 1354
• Main Author: Muller, Volker Müller
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.12.2019; Elsevier Limited
• Subjects: Acetic acid; Biocatalysts; biofuels; Biohydrogen; carbon capture; Carbon dioxide; Carbon sources; Catalysts; Coenzyme A; Dehydrogenases; E coli; Energy conservation; Enzymes; Ethanol; Fatty acids; Formic acid; Hydrogen; Hydrogen storage; Hydrogen-based energy; Metabolism; Organic chemistry; single cell protein; Substrates; Synthesis gas; biofuels; biohydrogen; carbon capture; single cell protein; hydrogen storage
• ISSN: 0167-7799; 1879-3096
• DOI: 10.1016/j.tibtech.2019.05.008

Strictly anaerobic, acetogenic (acetate-forming) bacteria are characterized by a reductive pathway in which two mol of CO2 are reduced to one mol of acetyl coenzyme A (acetyl-CoA) and then further to acetate, ethanol, or butyrate. Therefore, they have come into focus for an alternative, CO2-based bioeconomy. Other one-carbon (C1) substrates, such as formic acid or methanol, are promising feedstocks for an alternative bioeconomy using acetogens as biocatalysts that have been somewhat overlooked. In addition, acetogens, such as Acetobacterium woodii and Thermoanaerobacter kivui, have a unique enzyme system capable of reducing CO2 to formate with H2 as reductant that is superior over any chemical catalyst for CO2-based hydrogen storage. Therefore, acetogens are also promising candidates in the hydrogen economy as potential catalysts for hydrogen storage or production. Acetogenic bacteria are strictly anaerobic bacteria that grow by conversion of C1 substrates to acetate and ethanol. This is the result of an ancient pathway, the Wood–Ljungdahl pathway, that combines CO2 fixation with the synthesis of ATP.Acetogens are industrial platform organisms that produce ethanol from synthesis gas (CO2, CO, H2). In addition, other C1 substrates, such as formate and methanol, can be used as feedstocks, and thus, these bacteria are an important part of a formate- or methanol-bioeconomy.Some acetogens have a novel enzyme to reduce CO2 directly with molecular hydrogen to formic acid, the hydrogen-dependent CO2 reductase (HDCR). This enzyme is superior over any chemical catalyst in hydrogenation of CO2 and offers new strategic possibilities in the hydrogen storage economy.The HDCR reaction is reversible and this enzyme has the highest biohydrogen production rates reported.