Physiological characterization of chlorate‐resistant mutants of the cyanobacterium Spirulina major

Chlorate‐resistant (Chl R )mutants SM 11 and SM 25 of the cyanobacterium Spirulina major were produced by N‐methyl‐N'‐nitro‐N‐nitrosoguanidine (NTG) 1 ) mutagenesis. Strain SM 11 showed nitrate reductase (NR) and glutamine synthetase (GS) activities equal to the SM P (parent) whereas SM 25 had about 45% NR and 78% GS as compared to SM P . However, the uptake of nitrate or ammonia was almost equal in SM P , SM 11 and SM 25 . Chl R strains differed physiologically between themselves, SM 11 being blocked in uptake system of chlorate (Chl up − ) and was not defective in NR or GS, while SM 25 showed chlorate uptake (Chl up − ) and was defective in NR (NR def ) and GS (GS def ). Thus strain SM 11 resembles SM P except that the latter is chlorate sensitive. This is the first report of defective NR in any filamentous, non‐heterocystous, non‐nitrogen fixing cyanobacterium. Defective chlorate uptake not accompanied by defective NO   3 −uptake has also been observed in strain SM 11 .