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

Abstract

Eighteen bacterial stock cultures were examined for their ability to utilize NH4+and NO3-simultaneously in a medium containing NH4NO3with shaking using a test tube capped with a cotton stopper. Pseudomonas aeruginosa NBRC 12689 utilized 1 mg/ml of NH4NO3most rapidly of the cultures tested. The bacterium could completely utilize 5 mg/ml of NH4NO3within 3 d, 6 mg/ml of NH4Cl within 3 d, and 20 mg/ml of NaNO3within 2 d under optimum conditions. The addition of Fe2+to the NH4NO3medium markedly promoted the utilization of the two ions. When the Pseudomonas strain utilized 5 mg/ml of NH4NO3completely, the total nitrogen in the culture including its cells decreased to 41% of that of the NH4NO3originally provided. GC-MS analysis showed that the removed nitrogen was probably denitrified. When the bacterium was incubated in the NH4NO3medium with shaking in a vial sealed with a rubber stopper, N2accumulated, but not N2O at the final phase of cultivation. On the other hand, both N2and N2O were detected in the NaNO3medium. We concluded that the bacterium removed NH4+from NH4NO3as 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. © 2007 The Society for Biotechnology, Japan.