Genetical studies on the heterocyst and nitrogen fixation of the blue-green alga Nostoc muscorum

Abstract

The short-trichome-forming, non-heterocystous and non-nitrogen-fixing (het− nif−) mutant of the nitrogen-fixing blue-green alga Nostoc muscorum was isolated by N-methyl-N′-nitro-N-nitrosoguanidine (NTG)-mutagenesis after penicillin enrichment technique and characterized. The mutant did not grow and fix nitrogen in combined-nitrogen-free medium while in nitrate-containing medium it grew well (‘K’=0.112/day, ‘G’=64.27 h), although its growth was comparatively poor than the parent alga (K=0.128/day; G=56.14 h). The mutant was stable and both the het− and nif− characters reverted to wild type (het+ nif+) with the reversion frequency of 2.62×10-7.