Evaluation of in vitro efficacy for decolorization and degradation of commercial azo dye RB-B by Morganella sp. HK-1 isolated from dye contaminated industrial landfill

• Morganella sp. HK-1 degraded Reactive Black B dye (20 g L−1) within 24 h.
• This is the first report that describes the pathway for degradation of RB-B dye.
• Degraded dye metabolites demonstrated non-phytotoxic and non-genotoxic behavior.

Reactive Black-B (RB-B) – one of the multi-sulphonated reactive azo dye – is being used extensively in textile as well as paper industries. Reactive azo dyes comprise of a significant group of synthetic compounds categorized as xenobiotics and its abatement from the environment still remains a challenge. In the present study, a newly isolated indigenous bacterial strain Morganella sp. HK-1 was exploited for its ability to decolorize and degrade RB-B dye. The isolate completely degraded RB-B (20 g L−1) within 24 h under static conditions. Furthermore, the visible and FTIR spectral analysis established the bio-degradation of RB-B. The degraded metabolites of RB-B by Morganella sp. HK-1 were identified by GC–MS analysis as disodium 3,4,6-triamino-5-hydroxynaphthalene-2,7-disulfonate, 4-aminophenylsulfonylethyl hydrogen sulfate, naphthalene-1-ol, aniline and benzene. Based on this information, a putative pathway of degradation of RB-B by Morganella sp. HK-1 has been proposed. This study is the first report on elucidation of mechanism of bacterial degradation of RB-B dye. Furthermore, phytotoxicity, genotoxicity and aquatic acute toxicity studies of the parent dye and the bio-degraded dye products revealed drastic reduction in the toxicity of metabolites as compared to the parent dye. This implies that the biotreatment of the dye is of non-toxic nature. This study thus indicates the effectiveness of Morganella sp. HK-1 for the treatment of textile effluents containing sulphonated azo dyes.