Isolation and preliminary characterization of mutants of the cyanobacterium Nostoc muscorum resistant to growth inhibition by methylamine.

The wild-type heterocystous and nitrogen-fixing (Het+Nif+) N. muscorum and its non-heterocystous non-nitrogen-fixing (Het-Nif-) mutant strain both fail to grow in different inorganic nitrogen media containing 1 mM methylamine hydrochloride (MA). Mutants of the Het+Nif+ and Het-Nif- parents resistant to growth inhibition by 5 mM MA and thus designated as MAR strains were isolated with a frequency of 2.5(+/- 2.4) x 10(6). A MAR strain of the Het+Nif+ and a MAR strain of the Het-Nif- parent were characterized for growth, heterocyst formation and acetylene reducing activity in the presence and absence of methylamine in N2 medium. The Het+Nif+ MAR strain grows better in MA containing than in MA-free N2 medium, and all cultures grown with MA are found to lack both acetylene reducing activity and heterocyst. The Het-Nif-MAR strain shows good growth in MA-containing N2 medium but no growth in MA-free N2 medium. Furthermore, both the Het+Nif+MAR and Het-Nif-MAR strains show better growth in the presence than in the absence of MA in NO3- and HN4+ media. These results appear to suggest that the MAR phenotype in N. muscorum is due to the metabolic utilization of the ammonium analog as a nitrogen source.