Nitrogen Starvation and the Regulation of Glutamine Synthetase in Agmenellum quadruplicatum

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Abstract
The level of glutamine synthetase activity in A. quadruplicatum strain PR-6 was dependent on the N source used for growth and on the nutritional status of the cells. During exponential growth, glutamine synthetase activity was low in cells grown on ammonia, urea or nitrate. During the transition from N replete to N starved growth, glutamine synthetase activity began to rise. With ammonia as a N source, glutamine synthetase activity as determined in whole cells increased from 1 nmol/min per ml during exponential growth to 22 nmol/min per ml during severe N starvation. In cells grown on nitrate the increase was from 5-39 nmol/min per ml and in cells grown on urea the increase was from 4-31 nmol/min per ml. The rise in glutamine synthetase activity corresponded with the rapid decline in the N and c-phycocyanin content of the cells. Prior to N starvation, the N content of the cells was 140, 90 and 83 .mu.g N/mg dry weight for ammonia, urea and nitrate grown cells, respectively. During N starvation where glutamine synthetase activity was highest, the N content of the cells had declined to 35-40 .mu.g N/mg dry weight of cells. At the same time, the c-phycocyanin content of cells dropped by 95%.
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