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Lookup NU author(s): Dr Rebeca Gonzalez-Cabaleiro
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The on-going research towards sustainable fuel production entails the improvement of the microbialcatalysts involved. The possible reversibility of specific anaerobic catabolic reactions opens up a range ofpossibilities for the development of novel reductive bioprocesses. These reductive biohydrogenationpathways enable production of high energy density chemicals of interest as biofuels such as alcoholsand long chain fatty acids. Anaerobic bioprocesses take place under energy scarcity conditions due tothe absence of strong electron acceptors such as oxygen, and provide metabolic pathways towardsthese energy dense (reduced) chemicals. Metabolic reactions take place very close to thermodynamicequilibrium with minimum energy dissipation and consequently, environmental changes in product andsubstrate concentrations can easily reverse the driving force of the chemical reaction catalysed. Theobjective of this work is to investigate the potential reversibility of specific anaerobic pathways ofinterest. The thermodynamics of the different steps in biochemical pathways are analysed andcombined with assumptions concerning kinetic and physiological constraints to evaluate if pathways arepotentially reversible by imposing changes in process conditions. The results suggest that (i) inhomoacetogenesis they may operate in both reductive and oxidative directions depending on thehydrogen partial pressure in the system, (ii) acetate reduction to butyrate with hydrogen is not feasible,but no biochemical bottlenecks are apparent in butyrate production from acetate with ethanol orlactate as electron donors, (iii) the reduction of short chain to longer chain fatty acids with ethanol asthe electron donor appears thermodynamically and kinetically feasible, and (iv) alcohol production fromthe corresponding fatty acids (e.g. ethanol from acetate) was found to require proton translocations atspecific sites in the biochemical pathways in order to compensate for the ATP required forphosphatation of acetate and to enable energy harvesting. Overall, the methodology proposed hereallows for analysing the potential reversibility of catabolic pathways and therewith contributes to thedevelopment of efficient and reliable anaerobic bioprocesses for the production of biofuels and chemicals.
Author(s): Gonzalez-Cabaleiro R, Lema JM, Rodriguez R, Kleerebezem R
Publication type: Article
Publication status: Published
Journal: Energy and environmental science
Print publication date: 01/12/2013
Online publication date: 08/10/2013
Acceptance date: 08/10/2013
ISSN (print): 1754-5692
ISSN (electronic): 1754-5706
Publisher: Royal Society of Chemistry
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