Removal Of Sudan Dyes By Shewanella Oneidensis MR-1

Although there have been many studies on bacterial removal of soluble azo dyes, much less information was available for biological treatment of water-insoluble azo dyes. Currently available studies on Sudan dye reduction were generally performed with human intestinal or skin bacteria, whereas little was known about the reduction capacity of other bacteria. The few bacterial species capable of removing Sudan dye generally require a long time to remove low concentrations of insoluble dye particles. In this study, the utilization of Sudan dyes was investigated with Shewanella oneidensis MR-1, which was shown to reduce water-insoluble Sudan I particles to corresponding aromatic amines. The effects of redox mediators on Sudan I removal by S. oneidensisMR-1were also examined.Decolorization of water-insoluble Sudan dyes was studied with S. oneidensis MR-1, which removed66.8%,43.4%,56.0%and33.7%Sudan1-IV in104h, respectively and reduced Sudan I to aniline and1-amino-2-naphthol. Lactate was identified as the most efficient electron donor for Sudan I reduction. Improved reduction performance was obtained in the presence of higher lactate or biomass concentration. The correlation between specific reduction rate and initial Sudan I concentration could be described with Michaelis-Menten kinetics (vmax=0.81mg g cell-1h-1and Km=18.0mg1-1). The main azoreductase activity was found with membrane-bound proteins of MR-1and no reduction occurred when Sudan I was incubated with cell extracts. These data indicated for the first time that Shewanella could reduce solid-phase azo dye particles.The addition of100umol1-1different quinone compounds led to4.3-54.7%increases in removal efficiencies in22h. The addition of10,50and100μmol1-1anthraquinone-2,6-disulfonate (AQDS) increased the removal efficiency in10h from26.4%to42.8%,54.9%and64.0%, respectively. The presence of300μmol1-1AQDS resulted in8-fold increase in initial removal rate to1.52mg h-1g cell-1. And linear relationship was observed between the initial removal rates and AQDS concentrations (0-100μmol1-1). Comparison of Michaelis-Menten kinetic constants (vmax=5.31mg g cell-1h-1,Km=60.8mg1-1) revealed the advantage of AQDS-mediated removal over direct reduction. Different species of humic acids could also stimulate the removal of Sudan1. Scanning electronic microscopy analysis confirmed the accelerated removal performance in the presence of AQDS.