Mutants of the cyanobacterium Anabaena sp PCC 7120 altered in nitrate transport and reduction

Nitrate assimilation-defective mutants SP7, SP9, and SP17 of the cyanobacte rium Anabaena sp. PCC 7120 were isolated by use of transposon mutagenesis a nd screened on medium containing chlorate. SP7 and SP17 represented nitrate reductase-defective nature, while mutant SP9 appeared to be a regulatory m utant exhibiting pleiotropic behavior. Kinetics of nitrate uptake system ex hibited K-s values of 31-38 mu M for parent, SP7, and SP17 strains; however . mutant SP9 exhibited a high K-s value of 109.5 mu M. Defective nitrate re ductase was apparent in mutant SP7 and SP9, while mutant SP17 exhibited par tial defective nature. Methyl viologen-dependent NR activity in parent stra in presented a biphasic nature with K-m values of 0.13 and 2.47 mM, whereas a single K-m value (2.96 mM) was observed for mutant SP17. Mutant SP9 was also defective in nitrite uptake and reduction. Mutant strains exhibited de repressed nitrogenase activity in the presence of nitrate, while glutamine synthetase activity remained unaltered.