Temperature and oxygen level determine N 2 O respiration activities of heterotrophic N 2 O‐reducing bacteria: Biokinetic study

Nitrous oxide (N 2 O), a potent greenhouse gas, is reduced to N 2 gas by N 2 O‐reducing bacteria (N 2 ORB), a process which represents an N 2 O sink in natural and engineered ecosystems. The N 2 O sink activity by N 2 ORB 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 N 2 ORB. Four N 2 ORB, representing either clade I type nos Z ( Pseudomonas stutzeri JCM5965 and Paracoccus denitrificans NBRC102528) or clade II type nos Z ( Azospira sp. strains I09 and I13), were individually tested. The higher activation energy for N 2 O by Azospira sp. strain I13 (114.0 ± 22.6 kJ mol −1 ) compared with the other tested N 2 ORB (38.3–60.1 kJ mol −1 ) indicates that N 2 ORB 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 μmol L −1 to 0.92 ± 0.24 and 0.84 ± 0.31 μmol L −1 , respectively, as the temperature increased from 15°C to 35°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 N 2 ORB as N 2 O sinks. This knowledge can help develop a suitable N 2 O mitigation strategy according to the physiologies of the predominant N 2 ORB.