Abstract:Alcaligenes faecalis predominantly utilizes NH4+-N as nitrogen source,when it grows in the culture medium contained both N HI and NO3-Ammonia inhibits the assimilation of nitrate by bacterium under aerobic condition.Nitrate serves as a terminal election acceptor in Alcaligenes faecalis,when it grows anaerobically with lactate and ammonia as the carbon and nitrogen sources,respectively.Under anaerobic condition nitrate accepts the terminal electron transfered from respiratory chain,and then reduces N2 via nitrite in the bacterium.Nitrite inhibits the growth rate of the bacterium even in low concentrations.The utilization of nitrite is not restricted by ammonia in the bacterium under both aerobic and anaerobic conditions.Nitrate-dependent nitrogenase activity has been shown in A.faecalis under severe oxygen-limited condition,but nitrite inhibits nitrogenase activity even in low concentrations under the same condition.In the presence of O2(air).nitrogenase activity dramatically decreased with increasing concentration of nitrate in the bacterium.A.faecalis could fix 15N2 which was converted from 15NO3-by denitrification.