Effect of amino acids and its analogues on Gloeotrichia ghosei and its non-nitrogen fixing mutants.

Mutants of Gloeotrichia ghosei fil1 het++ and pol- het- failed to grow on molecular nitrogen and required combined nitrogen sources. NO3- and NH4+ supported maximum growth of parent and mutant strains under aerobic conditions but not under reducing anaerobic or heterotrophic conditions. Glutamine and tryptophan were superior for the parent strain compared to inorganic nitrogen sources. By mutants only glutamine was used whereas tryptophan was inhibitory to them. Development of heterocyst and polarity in the parent and in fil1 het++ was inhibited in the presence of all combined nitrogen sources compared to molecular nitrogen which supported their formation. MSX and AZT (analogues of glutamine and tryptophan, respectively) completely inhibited the growth of all strains in the nitrogen-fixing and NH4(+)-medium. When glutamine and tryptophan were added to MSX- and AZT-containing medium, growth of parent strain was similar to that of the respective amino acids. The mutants grew only with glutamine + MSX, and tryptophan + AZT complex medium inhibited growth.