Isolation Of An Iron Reducing Bacterium Sphingomonas Sp. DJ And Characterization Of Its Ability In Degradation Of Refractory Substances

Anaerobic technology is one of the most highly efficient methods for the biological treatment of organic wastewater. Dissimilatory iron reducing bacteria (DIRB), as the most typical representative of anaerobic microorganism, can conserve energy to support growth by coupling the oxidation of multiple organic substrates to the reduction of ferric iron. With the constantly in-depth study of iron reducing mechanism, it has been recognized that DIRB has a great application potential in the treatment of environmental pollution. However, current research mainly focuses on several type strains, which confines the application and extension of DIRB. More effort is still needed to employ more strain with iron-reducing ability to treat refractory organic s in wastewater.To investigate the characteristics of microbial anaerobic degradation of refractory organics, one strain with high efficiency of reducing Fe (III) and degrading AO7was isolated from the MEC-UASB reactor with Fe(OH)3by selective enrichment method. The strain was identified as Sphingomonas sp. according to its morphological, physicochemical characteristics and16S rDNA gene sequences analysis.AO7was selected as the target compound in the following experiments after investigating the degradation of different dyes by the strain. The characteristics of microbial anaerobic degradation of AO7were investigated in different conditions, i.e. temperature, pH, biomass, salinity, initial dye concentration and metal ion. The strain could decolorize as much as96.7%of150mg/L AO7. The optimal decolorization conditions were as follows,30-35℃, pH7-8, inocula higher than6%. The azoreductase activity of cells could maintain as high as65%within the range of NaC1(0to3%), which shows cells have strong tolerance to salt stress Some metal ions would inhibit the activity of azo reductase and the order of inhibition was as follows:Ca2+>Mg2+>Co2+>Pb2+>Zn2+>Cu2+,but the ions of Mn2+and Fe2+have little influence on this process. The result also shows Fe (III) as an energy source could enrich the biomass to promote decolorization. The cyclic voltammetry experiment and LC-MS measurement demonstrated that some intermediates produced during decolonization might play a role similar to redox mediators, participating in the electron transfers with regard to the reduction of azo bonds, and the possible degradation pathway was proposed. The strain could also degrade phenol, aniline and nitrobenzene, and the addition of Fe (III) may improve the efficiency of these aromatic compounds degradation. A microbial fuel cell (MFC) was operated with a pure culture of Sphingomonas sp. cells growing in the anode compartment in a defined medium containing acetate or nitrobenzene. The peak voltage output could reach at about295mV when85%of nitrobenzene was depleted.