Decolorization of azo dyes by a salt-tolerant Staphylococcus cohnii strain isolated from textile wastewater

The salt-tolerant Staphylococcus cohnii strain, isolated from textile wastewater, has been found effective on decolorizing several kinds of azo dyes with different structures. The optimal conditions for azo dye acid red B （ARB） decolorization by S. cohnii were determined to be pH= 7.0 and 30℃. The decolorization efficiency increased with the increase of the salinity concentration, and around 90% of ARB （100mg.L-1） could be decolorized in 24 h when the salinity concentration was up to 50 g-L 1. Moreover, the strain could still decolorize 19% of ARB in 24 h even when the NaC1 concentration was increased to 150 g. L1. Meanwhile, the dependence of the specific decolorization rate by S. cohnii on the ARB concentration could be described with Michaelis-Menten kinetics （Kin = 585.7mg·L-1, Vmax = t09.8mg-g cell ·h ^-1）. The addition of quinone redox mediator, named 2-hydroxy-l,4-naphthoquinone and anthraqui- none-2,6-disulfonate, significantly accelerated the deco- lorization performance ofS. cohnii. Furtherly, the activities of azoreductase （0.55 μmol.mg protein^-1.min-1） and Nicotineamide adenine dinucleotide-dichlorophenol indophenol （NADH-DCIP） reductase （8.9μmol.mg proteinl.min-1） have been observed in the crude cell extracts of S. cohnii. The decolorization products of ARB were analyzed by HPLC-MS, and the results indicated the reductive pathway was responsible for azo dye decoloriza- tion by S. cohnii.