Abstract
Bet-hedging in denitrification is a survival strategy that allows denitrifying bacteria to rapidly switch electron acceptors during transient anoxia. This study investigated whether the bet-hedging strategy contributes to nitrous oxide (N2O) consumption in Azospira sp. strain I13, a model denitrifying bacterium with strong N2O-reducing capacity. To evaluate this under stable conditions, this study developed a chemostat cultivating system and determined the strain's growth parameters, including the maximum specific growth rate and half-saturation constant for organic carbon. Under optimized chemostat operation, the strain exhibited transcription of the N2O reductase gene (nosZ) even when oxygen was the sole electron acceptor, whereas transcription of the nitrite reductase gene (nirS) remained low. This indicates that the strain maintains nosZ expression as a preparatory mechanism for a rapid switch to anoxic respiration. Furthermore, the microrespirometric assay showed that N2O consumption activity quickly recovered after oxygen exposure. Collectively, these results demonstrate that Azospira sp. strain I13 employs a bet-hedging strategy that facilitates rapid adaptation from aerobic to anaerobic conditions, with potential implications for mitigating N2O emissions. Future work should clarify the mechanistic link between N2O consumption recovery and bet-hedging.
