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Journal of Bacteriology, August 1999, p. 5042-5050, Vol. 181, No. 16
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Sensing of Nitrogen Limitation by Bacillus subtilis: Comparison to Enteric Bacteria

Ping Hu,1,dagger Terrance Leighton,2 Galina Ishkhanova,1 and Sydney Kustu1,*

Department of Plant and Microbial Biology1 and Department of Molecular and Cell Biology,2 University of California, Berkeley, California 94720

Received 4 February 1999/Accepted 11 June 1999

Previous studies showed that Salmonella typhimurium apparently senses external nitrogen limitation as a decrease in the concentration of the internal glutamine pool. To determine whether the inverse relationship observed between doubling time and the glutamine pool size in enteric bacteria was also seen in phylogenetically distant organisms, we studied this correlation in Bacillus subtilis, a gram-positive, sporulating bacterium. We measured the sizes of the glutamine and glutamate pools for cells grown in batch culture on different nitrogen sources that yielded a range of doubling times, for cells grown in ammonia-limited continuous culture, and for mutant strains (glnA) in which the catalytic activity of glutamine synthetase was lowered. Although the glutamine pool size of B. subtilis clearly decreased under certain conditions of nitrogen limitation, particularly in continuous culture, the inverse relationship seen between glutamine pool size and doubling time in enteric bacteria was far less obvious in B. subtilis. To rule out the possibility that differences were due to the fact that B. subtilis has only a single pathway for ammonia assimilation, we disrupted the gene (gdh) that encodes the biosynthetic glutamate dehydrogenase in Salmonella. Studies of the S. typhimurium gdh strain in ammonia-limited continuous culture and of gdh glnA double-mutant strains indicated that decreases in the glutamine pool remained profound in strains with a single pathway for ammonia assimilation. Simple working hypotheses to account for the results with B. subtilis are that this organism refills an initially low glutamine pool by diminishing the utilization of glutamine for biosynthetic reactions and/or replenishes the pool by means of macromolecular degradation.

* Corresponding author. Mailing address: 111 Koshland Hall, UC Berkeley, Berkeley, CA 94720-3102. Phone: (510) 643-9308. Fax: (510) 642-4995. E-mail: kustu{at}nature.berkeley.edu.

dagger Present address: diaDexus, LLC, Santa Clara, CA 95054.

Journal of Bacteriology, August 1999, p. 5042-5050, Vol. 181, No. 16
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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