Demonstration of natural gas bioconversion to liquid fuels using Methylomicrobium buryatense 5GB1S

Use of methane as transportation fuel is limited by its low energy density. Transformation of methane, the main component of natural gas, into higher energy liquid fuels (GTL) is achieved through the Fischer-Tropsch process, which requires high capital expenses and operating cost. However, many natural gas resources are geographically scattered, thus making it economically infeasible to deploy such a GTL process. Alternatively, biological GTL (Bio-GTL) using methanotrophic bacteria for methane conversion is a potentially attractive way since it can operate at small scale facilities at lower capital and operational cost. In this work, we demonstrated the direct bioconversion of in-house natural gas (through laboratory bench gas) into a liquid fuel ethanol using a haloalkaliphilic methanotrophic bacteria, M. buryatense 5GB1S. By genome integration of pyruvate decarboxylase and alcohol dehydrogenase genes from Zymomonas mobilis, the ethanol titers using batch culture conditions with bench gas and methanol as substrates were 50 mg/L and 80 mg/L, respectively. The subsequent endeavor extending natural gas conversion into the longer chain alcohol, n-butanol, was done by the implementation of a modified clostridial n-butanol pathway. While n-butanol production remains to be achieved, all the required enzymes were heterologously expressed and the activities were measured in the crude extract. This work represents the first ethanol production from natural gas using laboratory bench gas and demonstrates the possibility of natural gas bioconversion to liquid fuel for transportation usage.