Study On The Extracellular Reduction Mechanism Of Nitroaromatic Compounds By Electrochemically Active Microorganisms

In recent years,electrochemically active microorganisms have attracted extensive attentions from researchers due to their unique respiratory metabolic capabilities.As a model electrochemical active microorganism,Shewanella oneidensis MR-1 is widely applied for environmental remediation,biological energy and nanomaterial synthesis.With the development of society and economy,nitroaromatic compounds(NACs),which are difficult to degrade than other compounds,are released into the environment.The method of microbial remediation has gradually become a hot topic of environment remediation.However,studies about the remediation of NACs by microorganisms are mostly focused on low-polarity molecules.Moreover,there are still many deficiencies in its anaerobic remediation process and molecular regulation mechanism.Therefore,this study aimed to investigate the extracellular reduction mechanism of NACs by S.oneidensis MR-1.For this purpose,the anaerobic degradation of 3-nitrobenzene sulfonic sodium(3-NBS),a kind of NACs with high polarity,was investigated using S.oneidensis MR-1.The main conclusions of this paper are as follows:(1)Under anaerobic conditions,S.oneidensis MR-1 had significant biodegradability on3-NBS.Based on experimental results,the optimum conditions were 100 mg/L of 3-NBS and6×10~7 CFU/mL of S.oneidensis MR-1 inoculum.When lactate was used as the optimum carbon source,63.91%of 3-NBS could be degraded by S.oneidensis MR-1 after 5-d incubation.Under this condition,the HPLC method for the determination of 3-NBS and its reduction products was established by chemical analysis.Experimental results showed that the nitro group of 3-NBS can be reduced to an amino group by S.oneidensis MR-1.(2)The extracellular reduction of 3-NBS by S.oneidensis MR-1 via the Mtr pathway.Results of the Mtr pathway-associated mutants and different electron acceptors experiments indicate that S.oneidensis MR-1 transports electrons from CymA to the outer cell membrane surface through the Mtr transmembrane electron pathway,and further transfers electrons directly to the terminal electron acceptor 3-NBS through the c-type cytochrome protein which in outer cell membrane surface.Thus,the extracellular reductive degradation of 3-NBS can be achieved by S.oneidensis MR-1.(3)The permeability of the cell membrane affects the electron transport process and the exoelectrogenic ability of S.oneidensis MR-1,which conduct the reduction efficiency of3-NBS.Riboflavin,AQS,and AQDS all could enhance the extracellular reduction of 3-NBS by S.oneidensis MR-1,but obviously different effect exhibited among the anaerobic reduction process of 3-NBS conducted by(35)cymA mutant.The stronger the polarity,the weaker the promotion effects.The permeability of the cell membrane gradually increased during the reaction process.A weak polar electron mediator could compensate the bottleneck in transmembrane electron transport caused by the block of CymA,thereby promoting the extracellular reduction of pollutants by S.oneidensis MR-1.