ABSTRACT
OBJECTIVES: To synthesize hydrazine (N2H4) from ammonium and hydroxylamine (NH2OH) using an anaerobic ammonium oxidation (anammox) bacterium, Candidatus Kuenenia stuttgartiensis. RESULTS: K. stuttgartiensis cells were anoxically cultivated with the addition of ammonium (2 mM) and NH2OH (1-100 mM) at pH 6-10.5, and 4-65 °C to examine the favorable cultivation conditions for N2H4 production. The influence of NH2OH concentration was more prominent than that of pH and temperature, and NH2OH concentration higher than 1 mM deteriorated N2H4 yields significantly. The following conditions were found to be favorable for N2H4 production using K. stuttgartiensis cells: pH 9, 38 °C, and < 1 mM NH2OH. In a continuous-feed system operated at these conditions, K. stuttgartiensis cells produced N2H4 with a maximum concentration of 0.65 mM, which is the highest N2H4 concentration previously reported in biological processes. CONCLUSIONS: Optimal cultivation conditions for K. stuttgartiensis for N2H4 production were successfully determined, and the present study is the first to document potential biological N2H4 production using anammox bacteria.
