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

Summary

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 MA ^R strains were isolated with a frequency of 2.5(±2.4)×10⁶. A MA ^R strains of the Het ⁺ Nif ⁺ and a MA ^R 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 ⁺ MA ^R 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 ^- MA ^R strain shows good growth in MA-containing N₂ medium but no growth in MA-free N₂ medium. Furthermore, both the Het ⁺ Nif ⁺ MA ^R and Het ^- Nif ^- MA ^R strains show better growth in the presence than in the absence of MA in NO ^-₃ and NH ⁺₄ media. These results appear to suggest that the MA ^R phenotype in N. muscorum is due to the metabolic utilization of the ammonium analog as a nitrogen source.