1Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China, 2Graduate Institute of Environmental Engineering, National Taiwan University, 10617, Taiwan
A facultative anaerobic bacterium, designated as strain SCS5, is isolated from anodic biofilm of a mediator-less microbial fuel cell. The isolate is a Gram-negative, motile and rod in shape (0.9 _ 1.3 _m in length and 0.4 _ 0.5 _m in width) as well as identified as a novel subsp. of Aeromonas jandaei on the basis of phylogenetic analysis of 16S rRNA, gyrB and rpoD genes, phenotypic, cellular fatty acid profile and DNA G+C content analysis. The strain SCS5 showed highest 16S rRNA sequence similarity (99.45 %) with Aeromonas jandaei ATCC 49568 and contains 59.18 % DNA G+C content. The optimum growth temperature, pH and NaCl (%) for strain SCS5 are 35 °C, 7.0 and 0.5 % respectively. The isolate SCS5 is capable of reducing insoluble iron oxide (α-FeOOH) and transferring electrons to extracellular material (carbon electrode). The electrochemical activity of strain SCS5 is corroborated by cyclic voltammetry and two pairs of oxidation-reduction peaks were appeared under both anaerobic and aerobic conditions. Thus the strain SCS5 is an exoelectrogenic bacterium that should be considered as a novel sub species and is named as Aeromonas jandaei subsp. electrodiphilus subsp. nov. Due to electron transferring ability, strain SCS5 can decolorize azo dye methyl red (MR). The degradation of MR was evaluated by UV-visible (200 _ 800 nm) and GC-mass spectral analysis. The complete decolorization of MR was obtained at 6 h in both anaerobic and aerobic cultures where the decolorization rate was much faster in acidic pH than basic condition with the optimum temperature 35 °C. The decolorization efficiency increases with increasing cell mass of inoculation and decreases with increasing initial dye concentration. The MR degradation products showed less toxic than MR. The immobilized cell of strain SCS5 can also decolorize MR, but the decolorization rate was enhanced several folds by the immobilization of redox mediators such as anthraquinone-2, 6-disulphonate (AQDS) and magnetic Fe3O4 compare to immobilized cell only. However AQDS was more effective than Fe3O4 to accelerate the decolorization of MR.