Derepression of nitrogenase by addition of malate to cultures of Rhodospirillum rubrum grown with glutamate as the carbon and nitrogen source.

Rhodospirillum rubrum grown in continuous culture with glutamate as the sole fixed C and N source produced no nitrogenase, and the cultures were characterized by high extracellular ammonium concentrations. Addition of organic acids derepressed nitrogenase. Glutamate dehydrogenase, glutamine synthetase, glutamate synthase, malate dehydrogenase, nitrogenase, and ammonium were assayed before and after malate addition.