Abstract
Chlorate-resistant (ChlR)mutants SM11 and SM25 of the cyanobacterium Spirulina major were produced by N-methyl-N'-nitro-N-nitrosoguanidine (NTG)1) mutagenesis. Strain SM11 showed nitrate reductase (NR) and glutamine synthetase (GS) activities equal to the SMP (parent) whereas SM25 had about 45% NR and 78% GS as compared to SMP. However, the uptake of nitrate or ammonia was almost equal in SMP, SM11 and SM25. ChlR strains differed physiologically between themselves, SM11 being blocked in uptake system of chlorate (Chl up−) and was not defective in NR or GS, while SM25 showed chlorate uptake (Chl up−) and was defective in NR (NRdef) and GS (GSdef). Thus strain SM11 resembles SMP 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 uptake has also been observed in strain SM11.
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