Characteristics and comparisons of the aerobic and anaerobic denitrification of a Klebsiella oxytoca strain: Performance, electron transfer pathway, and mechanism.

The performance and electron (e) transfer mechanisms of anaerobic and aerobic denitrification by strain Klebsiella were investigated in this study. The RT-PCR results demonstrated that the membrane bound nitrate reductase gene (narG) and Cu-nitrite reductase gene (nirK) were responsible for both aerobic and anerobic denitrification. The extreme low gene relative abundance of nirK might be responsible for the severe accumulation of NO-N (nitrogen in the form of NO ion) under anaerobic condition. Moreover, the nitrite reductase (Nir) activity was 0.31 μg NO-N min mg protein under anaerobic conditions, which was lower than that under aerobic conditions (0.38 μg NO-N min mg protein). By using respiration chain inhibitors, the e transfer pathways of anaerobic and aerobic denitrification of Klebsiella strain were constructed. Fe-S protein and Complex III were the core components under anaerobic conditions, while Coenzyme Q (CoQ), Complexes I and III played a key role in aerobic denitrification. Nitrogen assimilation was found to be the main way to generate NH-N (nitrogen in the form of NH ion) during anaerobic denitrification, and also served as the primary nitrogen removal way under aerobic condition. The results of this study may help to improve the understanding of the core components of strain Klebsiella during aerobic and anaerobic denitrifications, and may suggest potential applications of the strain for nitrogen-containing wastewater.