Control of ammonium assimilation in Rhizobium 32H1

R A Ludwig
1978 Journal of Bacteriology  
The symbiotic, nitrogen-fixing bacterium Rhizobium sp. 32H1 is a specialized ammonium producer during symbiosis. However, during free-living growth, Rhizobium 32H1 assimilates ammonium very poorly. Two pathways of ammonium assimilation exist in enteric bacteria. One is mediated by glutamate dehydrogenase, and the other is mediated by glutamine synthetase-glutamate synthase. The former pathway is altogether inoperative in Rhizobium 32H1; the latter pathway operates at a slow rate and is under
more » ... ate and is under strict negative control by ammonium itself. Rhizobium 32H1 glutamine synthetase activity is modulated by both repressionderepression and reversible adenylylation. For a biochemical process lacking an alternative pathway, such a regulatory pattern exacerbates the very process. This suggests that Rhizobium 32H1 restricts its own ammonium assimilation to maximize the contribution of fixed nitrogen to the host plant during symbiosis.
doi:10.1128/jb.135.1.114-123.1978 fatcat:etbx7azdzrdofgwlyoddcxysfm