Abstract
Carboxydothermus hydrogenoformans is a carboxydotrophic hydrogenogenic bacterium species that produces hydrogen molecule by utilizing carbon monoxide (CO) or pyruvate as a carbon source. To investigate the underlying biochemical mechanism of hydrogen production, an elementary mode analysis of acetyl-CoA pathway was performed to determine the intermediate fluxes by combining linear programming (LP) method available in CellNetAnalyzer software. We hypothesized that addition of enzymes necessary for carbon monoxide fixation and pyruvate dissimilation would enhance the theoretical yield of hydrogen. An in silico gene knockout of pyk, pykC, and mdh genes of modeled acetyl-CoA pathway allows the maximum theoretical hydrogen yield of 47.62 mmol/gCDW/h for 1 mole of carbon monoxide (CO) uptake. The obtained hydrogen yield is comparatively two times greater than the previous experimental data. Therefore, it could be concluded that this elementary flux mode analysis is a crucial way to achieve efficient hydrogen production through acetyl-CoA pathway and act as a model for strain improvement.
Highlights
Use of fossil fuels causes adverse effect on environment through pollution
Our strategy for improving hydrogen production involved the modification of energy metabolism to direct the flow of major metabolites pyruvate and acetyl-CoA through elementary flux mode analysis
A previous metabolic engineering study by gene deletion on model microorganism Escherichia coli described that one mole of glucose has maximum hydrogen yields of approximately 14.9 mmols/mg dry cell mass [47]
Summary
Use of fossil fuels causes adverse effect on environment through pollution. the availability of fuels such as oils and natural gases is limited and are likely to be depleted soon [1]. It is indispensable to search for alternate fuel source and hydrogen is one of the efficient sources of energy that could effectively replace the available fossil fuels. It is considered as fuel of the future, since it is ecofriendly and emits zero carbon. Hydrogen is conventionally produced from fossil fuels by steam reforming other industrial methods such as coal gasification and electrolysis [3] These methods uses nonrenewable energy source to produce hydrogen. The autotrophic fixation of CO and pyruvate dissimilation have been achieved through acetyl-CoA or Wood-Ljungdahl pathway and hydrogen molecule has been produced as one of the end product. The CooX cluster of genes is the major component of this pathway that fixes CO and pyruvate dissimilation catalyzed by pdh gene during acetyl-CoA pathway, a key biochemical feature that supports hydrogen production [13, 14]
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