Decolorization of Orange G and Remazol Brilliant Blue R by the white rot fungus Dichomitus squalens: Toxicological evaluation and morphological study

Dichomitus squalens efficiently decolorized both Orange G and Remazol Brilliant Blue R (RBBR) at concentrations of 0.5 g l −1 and 3 g l −1 in static and shaken culture and also on solid medium within 14 d. The presence of the dyes in the culture medium mostly caused a decrease in biomass production and in growth rate, which was more significant in the case of RBBR. After 14 d of cultivation, electron microscopy showed substantial morphological changes in mycelia of D. squalens growing in media containing dyes. The hyphae deformations were more intensively manifested in solid media than in liquid culture. In all the cases, the morphological changes were more prominent in the presence of RBBR. Higher concentrations of both dyes brought about more intensive changes. The toxicity of synthetic dyes Orange G and RBBR was tested using a bioassay based on the growth inhibition of duckweed Lemna minor. Two endpoints such as the number of fronds and their weight were studied during the bioassay. The results showed higher toxicity of RBBR than that of Orange G. The toxicity of both dyes decreased after the decolorization process.