Research On Nitrite Utilization And Regulation By Shewanella Oneidensis Under Aerobic Condition

As one of the facultative anaerobic γ-proteobacteria, Shewanella oneidensis has drawn high attention in recent years because of its diverse respiratory capacities. As nitrite utilization by the microorganism under aerobic conditions is seldom concerned and its high significance in environmental remediation, its nitrite respiration and regulation in the presence of oxygen is studied. The main results are summarized below.Nitrite utilization under aerobic conditions by S. oneidensis MR-1S. oneidensis MR-1is more resistant to nitrite stress under aerobic conditions compared to anaerobic conditions. The strain is able to grow and utilize nitrite when the chemical is supplemented less than30mM. With the increase of nitrite concentration, growth is much more impaired. Interestingly, S. oneidensis utilizes nitrite under aerobic conditions only when growth enters stationary phase. As the only nitrite reductase, the expression of NrfA is an induced process depending on growth phase and nitrite existence. Overexpression of NrfA is insufficient to induce nitrite utilization in young cells. During exponential phase, electron flux has a preference towards terminal reductases and pathways for electron acceptors with more positive redox potential. Additionally, a substitutive pathway must exist because cymA and menA in frame deletion mutants retain nitrite reduction ability.Regulation of nitrite utilization under aerobic conditionsWe carried out experiments to explore the regulatory function of Crp and NarP on nitrite utilization. Crp and NarQP system regulate nrfA expression at the transcriptional level directly. The expression of crp also exhibits a hysteretic inducing phenomenon in the existence of O2and NO2-in response to growth phase. Besides, the Acrp mutant exhibits an extremely low nitrite tolerance compared to other related deletion mutants.