CONSTITUTIVE NITRATE AND NITRITE REDUCTASE ACTIVITIES OF RHIZOBIUM IN RELATION TO DENITRIFICATION

Nitrate reductase (NR) activity of R. meliloti SU 47 grown in yeast extract mannitol (YM) medium not containing any nitrate was highest during early stationary phase of growth. The strain did not express nitrite reductase (NiR) activity under this condition. In this medium stationary phase cells of some strains of rhizobia expressed nitrite reductase activity and produced gas from nitrate or nitrite in Durham tubes under anaerobic condition in 72 hrs. The strain SU 47, although, did not produce any gas in 72 hrs, did so and expressed NiR activity when grown far 8 days under anaerobic condition. The data indicated a positive correlation between gas production and NiR activity.