Microbial decolorization and degradation of crystal violet dye by Aspergillus niger

Two fungi were isolated and examined to decolorize crystal violet dye, frequently used as textile dye and in microorganism staining, using basal salt medium under static condition at 30 °C. The more effective fungus gave less dry weight and lower pH indicating that the process was directed toward the decolorization process giving acidic products rather than microbial growth. The effective fungus was identified as Aspergillus niger and was used in the rest of experiments. Increasing the incubation period more than 10 days did not improve the decolorization process, while the best pH was 5.5. The decolorization process was effective (up to 84.6 %) with the examined range of dye concentrations (10–40 ppm). Sucrose content, as a carbon source, more than 1 % did not improve the decolorization process (80.9 %). Using ammonium sulfate as a nitrogen source, instead of sodium nitrate in the original basal medium, lowered the decolorization process, while using corn steep liquor enhanced the biodegradation up to 96.1 %. Although the dye violet color vanishes in acid medium because of decreasing the possibility of extending the benzene chromophore as a result of binding the nitrogen lone pair in the ammonium ion, the UV–Vis spectra and LC–MS–ESI analysis of the bioassay products proved that the decolorization is due to the biodegradation of the dye rather than the resonance factor in acidic medium or biosorption by fungus mycelia.