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

Abstract

Amino acid uptake and utilization of various nitrogen sources (amino acids, nitrite, nitrate and ammonia) were studied in <i>Nostoc </i>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 <i>Nostoc </i>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 <i>de</i> <i>novo</i><i> </i>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.