Mechanisms For Anaerobic Reduction Of Nitarsone And Cr(?) By Dissimilatory Metal-reducing Bacteria

The dissimilatory metal-reducing bacteria,represented by Shewcanella and Aeromonas,could transfer electrons from intracellular to extracellular through a series of extracellular cytochrome C proteins under anaerobic conditions.Their reducing power generated by anaerobic respiration could reduce various metals or degrade organic compounds in the environment.Therefore,these bacteria are widely used for bioremediation.As a model strain of dissimilatory metal-reducing bacteria,Shewanella has respiratory diversity and extensive environmental adaptability,endowing it value and impact in both geochemical cycling of elements and environmental remediation.Shewanella can reduce a variety of extracellular electron receptors mainly through direct electron transport and indirect electron transport.Its main electron transport pathway is the Metal-Reducing pathway.However,the function of the Mtr pathway is not the same when Shewanella reduces different types of electron acceptors.Which role does the Mtr pathway play when Shewanella reduces new environmental pollutants?Are there any other unproven electron transfer routes in Shewanella?These problems have not answered yet.Moreover,a large number of genes encoding homologous Mtr pathway proteins also exist in the genomes of many metal-reducing bacteria,such as Aeromonas hydrophila.It is not clear whether this pathway could function in Aeromonas hydrophila.To answer the above two questions,this thesis intends to explore the anaerobic reduction process of different pollutants by two different metalo-reducing bacteria,examine the specific reduction pathways,and finally elucidate the reduction mechanism at the molecular level.The main contents are as follows:1.Shewanella oncidensis MR-1 was used to anacrobically degrade the organoarsenical pollutantnitarsone,which is widely used in aquaculture.The related mutant strains were obtained by gene knock-out.Shewanella oneidensis MR-1 was able to degrade nitarsone through the Mtr and the DMS pathway.Its main reduction products were arsanilic acid,aniline and inorganic arsenic.The toxicity test showed that the reduction of nitarsone by Shewanella oneidensis MR-1 decreased the toxicity of nitarsone.This study provides new ideas for the treatment of organoarsenical pollutants in the environment.2.Under anaerobic conditions Aeromonas hydrophila ATCC7966 could reduce Cr(?)through anaerobic respiration.Aeromonas hydrophila ATCC7966 mainly reduced Cr(?)through the Mtr pathway,and also could partially reduce Cr(?)intracellularly.The extracellularly and intracellularly reduced Cr(?)had different molecular conformations.The intracellular Cr(?)was in the form of solid particles,while the extracellular Cr(?)showed different states under different cultivation conditions.Aeromonas hydrophila is able to utilize various types of carbon sources in the environment and widely present in the environment as compared to Shewanella,which requires strict carbon sources,and Geobacter,which requires strict anaerobic conditions.Aeromonas hydrophila might have a wide potential application in the ecological restoration of heavy metal-polluted environment.