Simultaneous Assimilation and Denitrification of Nitrate by Bradyrhizobium japonicum

Bradyrhizobium japonicum strain CB 1809 assimilated and denitrified 15NO− 3 simultaneously to 15NH+ 4 and 15N2, respectively, when incubated under anaerobiosis. Washed cells from cultures grown in air in the presence of 5 mM-nitrate, assimilated 70% of the 15NO− 3 into cell-nitrogen but only after a lag of 10 h during which time NO− 2 accumulated. In washed cells grown at 2% (v/v) O2 with 5 mm-nitrate, 15NO− 3 was denitrified to 15N2 (95%) in 1–2 h. The low O2 tension in the culture medium resulted in increased activity of nitrate and nitrite reductases in the cells. When 10 mm-glutamate was included with 5 mm-nitrate at 2% (v/v) O2, washed cells from these cultures had less nitrate and nitrite reductase activities and when 15NO− 3 was supplied to these cells there was a transient accumulation of NO− 2 (1 h) prior to maximum denitrification. Washed cells prepared from cultures grown at 2% (v/v) O2 with glutamate alone utilized 15NO− 3, only after a lag period of 20-40 h, assimilation by (60%) and denitrification (40%).