Short-term regulation of nitrogenase activity by NH4+ in Rhodobacter capsulatus: Multiple in vivo nitrogenase responses to NH4+ addition

Abstract

The photosynthetic bacterium Rhodobacter capsulatus has been shown to carry out nitrogenase 'switch-off,' a rapid, reversible inhibition of in vivo activity. Here, we demonstrate that highly nitrogen-limited cultures of both the wild-type strain and a draT draG mutant are capable of nitrogenase switch-off while moderately nitrogen-limited cultures show instead a 'magnitude' response, with a decrease in in vivo nitrogenase activity that is proportional to the amount of added NH4+.