New approach to improve degradation of recalcitrant azo dyes by Streptomyces spp. and Phanerochaete chrysosporium

Abstract

Three azo dyes, the commercially available acid yellow 9(4-amino-1,1′-azobenzene-3,4′-disulfonic acid), and two synthesized dyes, azo dye 1 [4-(3-methoxy-4-hydroxyphenylazo)-azobenzene-3,4′-disulfonic acid] and azo dye 2 (3-methoxy-4-hydroxy-azobenzene-4′-sulfonic acid), plus sulfanilic acid and vanillic acid, were tested as substrates for degradation by 12 Streptomyces spp. and the white-rot fungus Phanerochaete chrysosporium. None of the Streptomyces spp. degraded acid yellow 9 or sulfanilic acid. The linkage of a guaiacol molecule onto acid yellow 9 or sulfanilic acid via azo-linkages resulted in dyes that were decolorized by 5 of the 12 Streptomyces strains. These Streptomyces were those that could also attack vanillic acid, which has the same ring substitution pattern (4-hydroxy-3-methoxy) as guaiacol. While P. chrysosporium transformed both acid yellow 9 and sulfanilic acid, the two guaiacol-substituted azo dyes were decolorized more readily by P. chrysosporium than the corresponding unsubstituted molecules. Ligninase and manganese peroxidase preparations from the P. chrysosporium culture were involved in the degradation. The discovery that one may enhance the degradability of azo dyes by linking selected, readily degradable substituents into the dyes' chemical structure, is a novel observation. This approach should be considered for use in commercial production of azo dyes or other recalcitrant compounds as a way of producing compounds that are more easily degraded in the environment.