Ambient nitrogen reduction cycle using a hybrid inorganic-biological system

We demonstrate the synthesis of NH3 from N-2 and H2O at ambient conditions in a single reactor by coupling hydrogen generation from catalytic water splitting to a H-2-oxidizing bacterium Xanthobacter autotrophicus, which performs N-2 and CO2 reduction to solid biomass. Living cells of X. autotrophicus may be directly applied as a biofertilizer to improve growth of radishes, a model crop plant, by up to similar to 1,440% in terms of storage root mass. The NH3 generated from nitrogenase (N(2)ase) in X. autotrophicus can be diverted from biomass formation to an extracellular ammonia production with the addition of a glutamate synthetase inhibitor. The N-2 reduction reaction proceeds at a low driving force with a turnover number of 9 x 10(9) cell(-1) and turnover frequency of 1.9 x 10(4) s(-1).cell(-1) without the use of sacrificial chemical reagents or carbon feedstocks other than CO2. This approach can be powered by renewable electricity, enabling the sustainable and selective production of ammonia and biofertilizers in a distributed manner.