PNNL

Abstract

Bioconversion processes require nitrogen for growth and production of intracellular enzymes to produce biofuels and bioproducts. Typically, this is supplied as reduced nitrogen in the form of ammonia produced offsite from N2 and H2 using the industrial Haber-Bosch process. While this has revolutionized processes dependent on fixed nitrogen (primarily modern agriculture) its current reliance on natural gas combustion for energy is responsible for substantial global CO2 emissions. Here we investigated the feasibility of in situ biological nitrogen fixation from N2 gas as an approach to reduce greenhouse gas impacts of aerobic bioconversion processes. We developed an efficient and inexpensive approach to screening fungal bioconversion hosts for compatibility with the free-living diazotrophic bacterium Azotobacter vinelandii in nitrogen fixing conditions and found that the genus Yarrowia is specifically enriched during co-culture screening. Follow-up experiments identified four Y. lipolytica strains (NRRL Y-11853, NRRL Y-7208, NRRL Y-7317, and NRRL YB-618) that are able to grow in co-culture with A. vinelandii by using ammonium secreted during diazotrophic fixation of N2 provided as a component of the air input stream during aerobic fermentation. This demonstrates the feasibly of in situ biological nitrogen fixation to support heterotrophic fermentation processes for the production of fuels and chemicals.