Assessing methanotrophic capabilities of Methanosarcina acetivorans for bioproduction

Mitigation of methane, the second most important greenhouse gas, and transforming it into liquid fuels via biological routes has received renewed interest following advancements in characterization of microbial consortia in anoxic/oxic habitats controlling the global methane cycle. On the other hand, the abundance of methane, major component of natural gas, in shale gas has strengthened the idea of converting methane into liquid fuels for easier and safer transportation. New computational tools such as optStoic enable the systematic exploration of all feasible conversion stoichiometries. In this effort we aimed at exploring thermodynamically feasible biofuels and/or bio-renewables production pathways via inorganic electron acceptor-coupled anaerobic oxidation of methane (AOM). Maximum product yields, indispensability of an external electron acceptor, and the prospect of co-utilization of methane and other C1 gas substrates such as carbon monoxide (CO) and CO₂ for yield improvement have also been assessed. Optimal overall conversions and pathways are designed using optStoic. An up-to-date metabolic model was developed for M. acetivorans based on two previously published reconstructions (i.e., iVS941 and iMB745). The model was augmented with proteomics-based regulatory switches and a thermodynamic constraint (ΔG≤0) to enable accurate prediction of thermodynamically feasible paths for methanotrophic biofuel production using various terminal electron acceptors (i.e., Fe³⁺, NO₃⁻, SO₄²⁻, and MnO₂). optStoic was developed as a constraint-based optimization formulation enabling identification of optimal overall stoichiometry designs for given substrates subject to mass/charge balances and thermodynamic feasibility.