Degradation of Malachite Green by Enterobacter asburiae Strain XJUHX-4TM

Malachite green is a highly toxic and recalcitrant dye used worldwide in various industries. The dye has been found to induce carcinogenesis andmutagenesis againstmany organisms. In this study, the degradation capacity of a bacterium, Enterobacter asburiae strain XJUHX-4TM has been evaluated against malachite green. The organism showed very good consistency in decolorizing the dye till a concentration of 1000 mg/L from semi-synthetic media, after which it starts falling down. It prefers sucrose and beef extract as carbon and nitrogen sources, respectively, in a ratio of 5: 1 for maximum decolorization (>98%) in semi-synthetic media. The organism demonstrated good efficiency (>95% decolorizaton) to be utilized in repeated batch decolorization studies in three consecutive cycles after which its efficiency decreased. It showed efficacy in decolorizing other industrial dyes as well. The decolorized products of malachite green were investigated with UV-Vis spectroscopy, thin layer chromatography and gas chromatography-mass spectroscopy, which indicated its transformation into other compounds. The analyzed products were found to be a mixture of leucomalachite green, desmethyl leucomalachite green, didesmethyl leucomalachite green, (dimethyl amino phenyl)-phenyl methanone, (methyl amino phenyl)-phenyl methanone, (amino phenyl)-phenyl methanone and aniline. A significant increase in the activities of enzymes - laccase, dichlorophenolindopnenol reductase and malachite green reductase were observed during MG degradation process, indicating their involvement in degradation. The Ames Salmonella mutagenicity assay, microbial toxicity study and chemical oxygen demand analyses conducted on the degraded products revealed their non-mutagenic and less toxic nature - an indication of microbial bioremediation in true sense.