SHORT-TERM REGULATION OF NITROGENASE ACTIVITY BY NH4-CAPSULATUS - MULTIPLE IN-VIVO NITROGENASE RESPONSES TO NH4+ ADDITION( IN RHODOBACTER)

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