Ammonia assimilation and glutamate formation in Caulobacter crescentus

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Abstract
In the dimorphic bacterium C. crescentus, net NH3 assimilation occurs only via the combined action of the enzymes glutamine synthetase and glutamate synthase. Mutants auxotrophic for glutamate lacked glutamate synthase activity, and the mutations leading to the glutamate auxotrophy appeared to lie at 2 distinct genetic loci. Both glutamate synthase and glutamine synthetase activities were subject to regulation by repression. Glutamate synthase activity was highest in cultures grown in minimal medium with NH3 as sole N source and was about 5 fold lower in rich broth. Glutamine synthetase activity was highest in cells grown with growth-rate-limiting amounts of NH3 as N source and was about 4 fold lower in rich broth. Glutamine synthetase activity appeared to be regulated by an adenylylation system like that described for Escherichia coli.