Glutamate production from aerial nitrogen using nitrogen-fixing bacterium Klebsiella oxytoca

Abstract Glutamate is an essential biological compound produced for various practical uses. However, the current glutamate production process requires a large amount of ammonium produced through the most energy-consuming and CO2-emitting Haber–Bosch process; hence, the development of bioeconomical glutamate-producing processes has long been awaited. This study demonstrates a novel strategy for glutamate production from aerial nitrogen using the nitrogen-fixing bacterium Klebsiella oxytoca. Carbon sources were first investigated to enhance the nitrogenase activity of K. oxytoca, and it was found that the simultaneous supply of glucose and citrate was effective. K. oxytoca was genetically engineered to increase citrate uptake under glucose-citrate-coexisting conditions and the supply of 2-oxoglutarate, a direct precursor of glutamate synthesis. As a result, extracellular production of glutamate over 1 g L-1 of culture from aerial nitrogen was achieved. This strategy offers a sustainable and eco-friendly manufacturing process to produce various nitrogen-containing compounds using aerial nitrogen.