Enzymatic Degradation of Azo Bonds and Other Functional Groups on Commercial Silk Dyes by Streptomyces coelicoflavus CS-29

Abstract

Azo dyes are used for silk textile manufacture, where their decolorization and detoxication are necessary after initial dying in the craft industry. The bio-decolorization efficiency of Streptomyces coelicoflavus CS-29 toward commercial azo blue and red dyes was investigated, analyzing the degradation and adsorption of dye molecules. S. coelicoflavus CS-29 showed reductions of 70% and 51% in red and blue dyes, respectively, after seven days. Morphological observation by light microscopy showed that dye molecules were adsorbed onto S. coelicoflavus CS-29 cell surface to form a dense cell pellet. Moreover, peroxidase and laccase activity were detected as extracellular enzymes, but no azo-reductase was detected. From the enzymatic activity, changes of dye profiles in HPLC showed differences between control dyes (untreated dyes) and metabolized products of dyes treated with S. coelicoflavus CS-29. The presence of main functional azo groups (-N=N-) in both blue and red silk dyes was indicated by FTIR analysis, in the untreated azo dyes. The azo bonds seemed to disappear in metabolites after S. coelicoflavus CS-29 treatment and other functional groups were changed compared to the control dyes. The treated dyes showed no significant effect on seed germination, root length, and shoot length of mung beans during phytotoxicity analysis. The red dyes showed a more negative effect on shoot lengths than the blue dyes. The overall results showed that S. coelicoflavus CS-29 is an effective and promising tool for the treatment of dye contaminated wastewater and the permanent elimination of recalcitrant commercial azo dye pollutants.