A synthetic co-culture for bioproduction of ammonia from methane and air.

Abstract

Fixed nitrogen fertilizers feed fifty percent of the global population, but most fixed nitrogen production occurs using energy-intensive Haber-Bosch-based chemistry combining nitrogen (N2) from air with gaseous hydrogen (H2) from methane (CH4) at high temperatures and pressures in large-scale facilities sensitive to supply chain disruptions. This work demonstrates the biological transformation of atmospheric nitrogen (N2) into ammonia (NH3) using methane (CH4) as the sole carbon and energy source in a single vessel at ambient pressure and temperature, representing a biological 'room-pressure and room-temperature' route to ammonia (NH3) that could ultimately be developed to support compact, remote, ammonia (NH3) production facilities amenable to distributed biomanufacturing. The synthetic microbial co-culture of engineered methanotroph Methylomicrobium buryatense (now Methylotuvimicrobium buryatense) and diazotroph Azotobacter vinelandii converted three methane (CH4) molecules to L-lactate (C3H6O3) and powered gaseous nitrogen (N2) conversion to ammonia (NH3). The design used division of labor and mutualistic metabolism strategies to address the oxygen sensitivity of nitrogenase and maximize methane oxidation efficiency. Media pH and salinity were central variables supporting co-cultivation. Carbon concentration heavily influenced ammonia production. Smaller scale ammonia (NH3) production near dispersed, abundant, and renewable methane (CH4) sources could reduce disruption risks and capitalize on untapped energy resources.