Detoxification and Bioremediation of Sulfa Drugs and Synthetic Dyes by Streptomyces mutabilis A17 Laccase Produced in Solid State Fermentation

Abstract

Laccase enzyme has many important applications as bioremediation and removal of environmental wastes and also in industrial processes. Therefore, large-scale of novel producers of laccase is demanded to use cheap and low cost substrates. Hence, solid state fermentation is the best strategy to achieve this proposes. The present study is designed to optimize laccase production by Streptomyces mutabilis A17 using agro-wastes including rice bran, castor seed cake, wheat bran, wheat straw, soybeans cake, peanut cake, cotton seed cake and chicken feathers. Cotton seed cake significantly enhanced S. mutabilis A17 laccase production when it was incubated for 6 days at 37°C and 70% moisture content in presence of yeast extract and glucose as the best nitrogen and carbon sources, respectively. After purification steps, the purified laccase showed maximum activity at 40°C and pH 8.0 within stability pH range of 7.0 to 9.0. Laccase activity was highly increased to 195, 180 and 166% by the addition of Ba+2, Cu+2 and Mn+2, respectively. Sulfa drugs and synthetic dyes cause various pollutants due to their toxic effects in different environments. Therefore, a purified laccase was utilized for removal of sulfa drugs as sulfadiazine (SDZ) and sulfathiazole (STZ) and also synthetic dyes. The results showed that the maximal enzymatic removal of SDZ and STZ was attained at 50°C and pH 6.0 for 1 h at presence of 1mM HBT(1-hydroxybenzotriazole) as a laccase mediator by removal percentage of 73% and 90%, respectively. Detoxification effects of laccase-treated sulfa drugs and two synthetic dyes; congo red and malachite green solutions, were investigated using microbial toxicity test. Our results indicated that the toxicity of these laccase-treated samples against tested bacterial strains were significantly decreased. It was concluded from this study that SSF laccase is playing an important role for decreasing the toxic effects of pharmaceutical wastes and organic pollutants.

Keywords

• solid state fermentation
• laccase
• bioremediation
• sulfa drugs
• synthetic dyes.