Efficient biodegradation and detoxification of Congo red via newly isolated Bacillus strains

Pollution with xenobiotic compounds such as congo red (CR) is a serious problem in the environment. In the present study, an attempt has been made to screen and isolate a potential local bacterial strains from dye contaminated area for decolorization of CR dye as an example of (azo-dye). Out of 52 bacterial isolates demonstrated the ability to grow on CR dye as a sole carbon source, three bacterial isolates showed high dye decolorization percentage ranged from 65.8 to 81.5% after 4 days of incubation (lambda max of CR 498 nm). The selected bacterial strains were identified as Bacillus licheniformis S2, Bacillus amyloliquefaciens S12 and Bacillus subtilis S50 based on morphological, molecular and biochemical characteristics. A set of experiments were carried out to optimize the degradation ability of the selected isolates under different physicochemical conditions such as different concentrations of CR, pH range, temperatures and static and shaking incubation. The results revealed that the three Bacillus species were able to degrade CR more efficiently at static conditions compared to shaking conditions and the optimum CR dye concentration for the three isolates was 100 mu M at 37 oC and pH 7.0. Spectroscopic techniques were performed to evaluate the isolates degradation abilities and to identify the degradation by-products by UVVis and GC-MS, indicated the complete degradation of congo red to other less-toxic compounds after 6 days of incubation. The phytotoxicity test on Vicia faba and Triticum aestivum seeds revealed that all bacterial degraded dye metabolites had almost negligible effect on both plant germinations compared to untreated dye, which indicating the successful detoxification of CR dye. Therefore, the selected Bacillus strains from this study might be useful in the treatment of industrial effluent contaminated with synthetic dyes.