The Characteristics And Mechanism Of Dye Decolorization By Bacillus Sp. UN2and Micrococcus Sp.BD15

Azo dyes are extensively used in textile, food and paper industries. Generally, they are toxic and recalcitrant to degradation and thus constitute a significant menace to the environment. The traditional physicochemical treatments are liable to produce secondary pollution while the biological methods are quite eco-compatible and low cost. Therefore, increasingly emphasis has been given to biological methods recently.The Bacillus sp. strain UN2was isolated from the bacteria library of Lab238at the College of Life Sciences, Zhejiang University. The present study is focused on exploring the capability of Bacillus sp. strain UN2for application in methyl red (MR) decolorization and degradation. Effects of physicochemical parameters (pH of medium, temperature, concentration of dye, composition of the medium) were studied in detail. The suitable pH and temperature range for decolorization by strain UN2were7.0-9.0and30℃-40℃, respectively. Especially, the optimal pH and temperature are8.0and35℃-40℃. Mg2+and Mn2+(1mM) were found to significantly accelerate the color removal rate. Meanwhile, we found the same phenomenon for both Fe2+and Fe3+. However, in most cases, Fe2+and Fe3+serve as inhibitors of micrbial decolorization. Thus, our strain is quite suitable for dye-containing wastewater in presence of Fe2+and Fe3+. Under optimal degradation conditions, the UN2strain exhibited greater than98%decolorization of the toxic azo dye MR (100ppm) within30min and it can decolorize up to400ppm MR within2h. The decolorization ability was significantly reduced when dye concentration reaches up to500ppm. We also discovered that for all experiments concerning dye concentraion influence, no subsequent decolorization occurred after2h incubation, which implied the strong to xicity of dye MR.Analysis of samples from decolorized culture flasks confirms biodegradation of MR into two prime metabolites:N, N’dimethyl-p-phenyle-nediamine (DMPD) and2-aminobenzoic acid (2-ABA). NAPH1was isolated to further degrade DMPD and it can degrade50%DMPD within48h. A study of the enzymes responsible for the biodegradation of MR, in the control and cells obtained during (10min) and after (30min) decolorization, showed a significant increase in the activities of azoreductase, laccase and NADH-DCIP reductase. Furthermore, a phytotoxicity analysis demonstrated that the germination inhibition was almost eliminated for both the plants Triticum aestivum and Sorghum bicolor by MR metabolites at100mg/L concentration, yet the germination inhibition for parent dye molecule was significant. We can also infer that bateria UN2could still be able to further degrade Methyl Red metabolites with a relatively low rate.The high efficient Micrococcus sp. strain BD15was also isolated from the bacteria library of Lab238at the College of Life Sciences, Zhejiang University. In this present study, the detailed Malachite Green degradation pathway by Micrococcus sp. Strain BD15was reported based on the intermediates tested. In general the intermiates of MG degradation include4-(Dimethylamino)benzophenone, Michler’s ketone,4-(methylamino)benzophenone, N,N-dimethylaniline,4-methylaminobenzoic acid,4-hydroxyl-N,N-dimethylaniline,4-aminobenzophenone,4-hydroxyl-aniline, hydro4-(dimethylamino)benzophenone.Consequently, Bacillus sp. Strain UN2and Micrococcus sp. Strain BD15are potential advantageous bacteria for bioremediation of wastewater containing MR and MG respectively.