Abstract
The abundance of methane in shale gas and of other gases such as carbon monoxide, hydrogen, and carbon dioxide as chemical process byproducts has motivated the use of gas fermentation for bioproduction. Recent advances in metabolic engineering and synthetic biology allow for engineering of microbes metabolizing a variety of chemicals including gaseous feeds into a number of biorenewables and transportation liquid fuels. New computational tools enable the systematic exploration of all feasible conversion alternatives. Here we computationally assessed all thermodynamically feasible ways of co-utilizing CH4, CO, and CO2 using ferric as terminal electron acceptor for the production of all key precursor metabolites. We identified the thermodynamically feasible co-utilization ratio ranges of CH4, CO, and CO2 toward production of the target metabolite(s) as a function of ferric uptake. A revised version of the iMAC868 genome-scale metabolic model of Methanosarcina acetivorans was chosen to assess co-utilization of CH4, CO, and CO2 and their conversion into selected target products using the optStoic pathway design tool. This revised version contains the latest information on electron flow mechanisms by the methanogen while supplied with methane as the sole carbon source. The interplay between different gas co-utilization ratios and the energetics of reverse methanogenesis were also analyzed using the same metabolic model.
Highlights
The global increase in oil production, fossil fuel combustion, biomass burning, and hydraulic fracturing of shale gas and climate change concerns has motivated the reduction of emissions from anthropogenic sources
In this work, we have demonstrated the utility of deploying computational tools such as optStoic along with “genome-scale” metabolic modeling to inform optimal metabolic engineering designs and strategies satisfying an overall desired bioconversion
The combined use of optStoic and metabolic modeling presented in this work puts forth an efficient platform for quickly exploring in silico the feasibility and limits of various gaseous substrate utilization options
Summary
The global increase in oil production, fossil fuel combustion, biomass burning, and hydraulic fracturing of shale gas and climate change concerns has motivated the reduction of emissions from anthropogenic sources. Mitigation of gaseous emissions (such as methane, carbon dioxide, and carbon monoxide) from the environment and their microbial conversion into useful products provides a sustainable and transformative solution that avoids the “food vs fuel” dilemma. The biological routes of methane utilization, have received renewed interest because of process simplicity (Lopez et al, 2013), selectivity toward targeted pathways (Haynes and Gonzalez, 2014; Mueller et al, 2015), and recent advancements in the characterization and genetic tools of methanotrophic microbes enabling direct transformation of methane into valuable chemicals and fuel molecules (Coleman et al, 2014; Fei et al, 2014; Strong et al, 2015; Henard et al, 2016). A recent study on the co-utilization of carbon dioxide and carbon monoxide or hydrogen to produce acetate using Moorella thermoacetica (Hu et al, 2016) further demonstrates the need for systematic study of co-utilization of various C1 gases in other potential microbial hosts
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