Objective: Malachite green (MG), an N-methylated diaminotriphenylmethane dye, is widely used in aquaculture, textile industry, and various microbiological techniques including mycobacterial isolation, spore dying, and photodynamic therapy. The use of microbes for the removal of environmentally hazardous dyes is emerging as a promising alternative to the current treatments. In this study, MG-degradation activity of Exophiala species, which are regularly encountered in human-made, hydrocarbon-polluted environments, has been examined.

Material and Methods: In order to investigate the MG decolorization activities a total of 191 Exophiala strains consisting of 109 Exophiala dermatitidis strains isolated from 69 dishwashers, 33 railway sleepers, and 7 clinical samples, and 82 Exophiala phaeomuriformis strains isolated from 32 dishwashers and 50 railway sleepers were included in the study. MG sensitivities and decolorization activities of the strains were tested by agar dilution method. Decolorization activities of all Exophiala strains were investigated spectrophotometrically in broth medium containing 32 μg/mL MG.

Results: In both Exophiala species, the MG MIK90 values were found to be 128 μg/mL by the agar dilution method. On unaided visual evaluation, the best decolorization activity was seen in ≥32 μg/mL MG concentration. There was no difference in decolorization rates of MG between Exophiala species in agar based-medium tests (p>0.05). In comparison of the spectrophotometrically performed decolorization activities, no difference was found between Exophiala species and isolation regions (p>0.05). Among all strains, an E. dermatitidis strain isolated from a dishwasher showed the highest decolorization ratio as 62.6%.

Conclusion: The decolorization potential of black yeasts such as Exophiala species and its applicability in the biodegradation of toxic dyes in environments should be further investigated.