Nitrogen nutrition in the cyanobacterium <i>Nostoc </i>ANTH, a symbiotic isolate from <i>Anthoceros: </i>Uptake and assimilation of inorganic-N and amino acids
163-169Amino acid uptake and utilization of
various nitrogen sources (amino acids, nitrite, nitrate and ammonia) were studied
in Nostoc ANTH and its mutant (Het-Nif) isolate defective in
heterocyst formation and N2-fixation. Both parent and its mutant grew
at the expense of glutamine, asparagine and arginine as a source of
fixed-nitrogen. Growth was better in
glutamine-and asparagine-media as compared
to that in arginine media. Glutamine and asparagine repressed heterocyst formation,
N2-fixation and nitrate reduction in Nostoc ANTH, but arginine
did so only partially. The poor growth in arginine-medium was not due to poor uptake
rates, since the uptake rates were not significantly different from those for
glutamine or asparagine. The glutamine
synthetase activity remained unaffected during cultivation in media containing
any one of the three amino acids tested. The uptake of amino acids was
substrate-inducible, energy-dependent and required de novo protein synthesis. Nitrate and ammonium
repressed ammonium uptake, but did not repress uptake of amino acids. In N2-medium
(BG-110), the uptake of ammonium and amino acids in the mutant was
significantly higher than its parent strain. This was apparently due to
nitrogen limitation since the mutant was unable to fix N2 and the growth
medium lacked combined-N