Temperature and oxygen level determine N2O respiration activities of heterotrophic N2O-reducing bacteria: Biokinetic study

Nitrous oxide (N2O), a potent greenhouse gas, is reduced to N-2 gas by N2O-reducing bacteria (N2ORB), a process which represents an N2O sink in natural and engineered ecosystems. The N2O sink activity by N2ORB depends on temperature and O-2 exposure, yet the specifics are not yet understood. This study explores the effects of temperature and oxygen exposure on biokinetics of pure culture N2ORB. Four N2ORB, representing either clade I type nosZ (Pseudomonas stutzeri JCM5965 and Paracoccus denitrificans NBRC102528) or clade II type nosZ (Azospira sp. strains I09 and I13), were individually tested. The higher activation energy for N2O by Azospira sp. strain I13 (114.0 +/- 22.6 kJ mol(-1)) compared with the other tested N2ORB (38.3-60.1 kJ mol(-1)) indicates that N2ORB can adapt to different temperatures. The O-2 inhibition constants (K-I) of Azospira sp. strain I09 and Ps. stutzeri JCM5965 increased from 0.06 +/- 0.05 and 0.05 +/- 0.02 mu mol L-1 to 0.92 +/- 0.24 and 0.84 +/- 0.31 mu mol L-1, respectively, as the temperature increased from 15 degrees C to 35 degrees C, while that of Azospira sp. strain I13 was temperature-independent (p = 0.106). Within the range of temperatures examined, Azospira sp. strain I13 had a faster recovery after O-2 exposure compared with Azospira sp. strain I09 and Ps. stutzeri JCM5965 (p < 0.05). These results suggest that temperature and O-2 exposure result in the growth of ecophysiologically distinct N2ORB as N2O sinks. This knowledge can help develop a suitable N2O mitigation strategy according to the physiologies of the predominant N2ORB.