Screening and characterization of bacteria that can utilize ammonium and nitrate ions simultaneously under controlled cultural conditions

Eighteen bacterial stock cultures were examined for their ability to utilize NH4+ and NO3− simultaneously in a medium containing NH4NO3 with shaking using a test tube capped with a cotton stopper. Pseudomonas aeruginosa NBRC 12689 utilized 1 mg/ml of NH4NO3 most rapidly of the cultures tested. The bacterium could completely utilize 5 mg/ml of NH4NO3 within 3 d, 6 mg/ml of NH4Cl within 3 d, and 20 mg/ml of NaNO3 within 2 d under optimum conditions. The addition of Fe2+ to the NH4NO3 medium markedly promoted the utilization of the two ions. When the Pseudomonas strain utilized 5 mg/ml of NH4NO3 completely, the total nitrogen in the culture including its cells decreased to 41% of that of the NH4NO3 originally provided. GC-MS analysis showed that the removed nitrogen was probably denitrified. When the bacterium was incubated in the NH4NO3 medium with shaking in a vial sealed with a rubber stopper, N2 accumulated, but not N2O at the final phase of cultivation. On the other hand, both N2 and N2O were detected in the NaNO3 medium. We concluded that the bacterium removed NH4+ from NH4NO3 as a nitrogen source for its cell components, together with the denitrification of NO3− under controlled shaking conditions. In addition, NH4+ promoted the cell growth of the bacterium and denitrification to N2, preventing the accumulation of N2O.