L-Glutamate production from nitrogen gas by co-culturing Corynebacterium glutamicum with Azotobacter vinelandii

Biological nitrogen fixation has attracted considerable attention as an alternative to Haber–Bosch-dependent fermentation processes and agricultural systems. Azotobacter vinelandii, a well-established model organism for aerobic nitrogen fixation, has been engineered to produce ammonium; however, studies on its utilization as a nitrogen source are limited. In this study, we constructed A. vinelandii strains by integrating a nifA overexpression cassette driven by the tac promoter into the algU locus. The engineered strain stably produced ammonium at a concentration of 1 g L−1 in flask culture. Ammonium production was further enhanced to 1.5 g L−1 in a jar fermenter by combining fed-batch cultivation with antifoam treatment and lactic acid addition. Furthermore, co-cultivation of the ammonium-producing A. vinelandii strain with Corynebacterium glutamicum enabled the production of 2 g L−1 l-glutamate from nitrogen gas. The proposed strategy contributes to the development of environment-friendly fermentation processes for producing various nitrogen-containing compounds from nitrogen gas. Key points • An A. vinelandii strain stably overexpressing nifA was constructed. • Engineered strain achieved enhanced ammonium production in a jar fermenter. • Co-cultivation of A. vinelandii with C. glutamicum enabled L-glutamate production.