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

Abstract

Chlorate-resistant (Chl^R)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 SM^P (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 SM^P, SM¹¹ and SM²⁵. Chl^R strains differed physiologically between themselves, SM¹¹ being blocked in uptake system of chlorate (Ch^l up^-) and was not defective in NR or GS, while SM²⁵ showed chlorate uptake (Ch^l up^-) and was defective in NR (NRdef) and GS (GS^def). Thus strain SM¹¹ 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 SM¹¹.