Abstract

In view of compliance with increasingly stringent environmental legislation imposed by regional, national and supranational (for example, European Union) authorities, innovative environmental technologies for the treatment of dye-contaminated effluents are necessary in the color industry. In this study, azo (methyl orange (MO) and methyl red (MR)) and triphenylmethanes (malachite green (MG), fushin (F) and crystal violet (CV)) dyes were subjected to distinct treatment strains following an initial qualitative characterization. The effectiveness of their biodegradation using Staphylococcus epidermidis strain was compared with respect to parameters such as residual color, and toxicity on human cells. The Hep-2 cells were exposed to three azo and two triphenylmethane dyes at various concentrations. After 72 h exposure, the protein contents of the samples compared to the protein contents of non-exposed cells were measured. The level of protein content indicates the viability of the cells. The IC20 values show the limiting value of toxicity. The IC50 values before biodegradation show whether samples are clearly toxic. The IC50 value for the azo dyes (MO, MR) were 65 and 10 μg/ml, the IC20 value were 10 and 5 μg/ml. The IC50 for the triphenylmethane dyes (MG, F and CV) were 35, 25 and 30 μg/ml, the IC20 value were 5, 5 and 10 μg/ml. The viability of the cells was good, the protein content of the samples being over 80% compared to the non-exposed cells. The Hep-2 cell test indicated the toxicity of pure dyes before biodegradation; the dyes after decolorization had no adverse effect. The human keratinocyte Hep-2 cells seem to be a useful tool for the study of the purity/toxicity of dyes and other substances applied to textiles. In addition, the initial cytotoxicity of dyes was still present after the biodegradation, while it was completely removed through the bacterial treatment. Our results show that S. epidermidis was a slime-producer developing almost black colonies on Congo red agar plate. A significant increase in azoreductase, lignin peroxidase and laccase activities in the cells were obtained after complete decolorization.

Key words: Azo dye, triphenylmethane dye, Staphylococcus epidermidis, cytotoxicity, slime production.

Abbreviation

MO, Methyl orange; MR, methyl red; MG, malachite green; F, fushin; CV, crystal violet; DMSO, dimethyl sulfoxide; FBS, fetal bovine serum; DMEM, Dulbecco's modified Eagle's medium; CRA, Congo red agar; Lip, lignin peroxidase; ABTS, 2, 2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid