Biotransformation of Direct Blue 1 by a moderately halophilic bacterium Marinobacter sp. strain HBRA and toxicity assessment of degraded metabolites

doi:10.1016/j.jhazmat.2013.09.011

Journal of Hazardous Materials

Volume 262, 15 November 2013, Pages 674-684

https://doi.org/10.1016/j.jhazmat.2013.09.011 Get rights and content

Highlights

•
A moderately halophilic bacterial strain was isolated that effectively degraded DB-1.
•
HBRA was identified to be Marinobacter sp.
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Deduction of possible biotransformation pathway for DB-1.
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Toxicity evaluation of DB-1 and its degraded metabolites.

Abstract

The ability of halophiles to survive in the extreme salt concentrations has gained them the importance of being used in the treatment of industrial waste waters. A moderately halophilic bacterial strain with the ability to degrade the complex azo dye Direct Blue-1 (DB-1) was isolated from sea water and identified as Marinobacter sp. strain HBRA. Complete decolorization of DB-1 (100 mg L⁻¹) was achieved in 6 h at 37 °C, pH 8 and with 70 g L⁻¹ NaCl. Decolorization was analyzed by UV–vis spectrophotometer. The FT-IR spectrum revealed that Marinobacter sp. strain HBRA specifically targeted azo bond (N double bond N) at 1631 cm⁻¹ to break down Direct Blue-1. Formation of metabolites at different retention times in HPLC indicated degradation. Biotransformation pathway for DB-1 was proposed based on LC–MS. Phytotoxicity study revealed the less toxic nature of the metabolites compared to the dye. Genotoxicity with Allium cepa confirmed the cytotoxic nature of DB-1 by inducing several chromosomal abnormalities compared to the negligible effects of degraded metabolites. The current study is the first report on the detoxification of DB-1 by Marinobacter sp. strain HBRA.

Introduction

Among the various colourants used in textile industry, azo dyes constitute 70% by weight the most common compounds used for this purpose. Azo dyes are represented by substituted aromatic rings that are joined by one or more azo groups (R₁ single bond N double bond NR₂). The azo groups are generally connected to benzene and naphthalene rings and to aromatic heterocycles, which intensify the colour of the azo compounds and provide bonding affinity groups [1]. The largest amount of azo dyes is used for the dyeing of textiles, of which nearly 10–15% dyestuff remains unbound to the fibre and is therefore released into the environment leading to severe contamination of surface and ground waters [2]. Therefore the treatment of dye wastewaters is necessary before their safe disposal to the environment [3]. Different physicochemical methods such as adsorption, chemical oxidation, coagulation and precipitation are available for the treatment of dye containing effluents [4], [5]. High cost, limited versatility, low efficiency and formation of secondary sludge which requires additional treatment are the major disadvantages of physicochemical methods. These constraints have led to the consideration of biological methods as attractive options as they are cost effective, environmental friendly, produce less sludge and are efficient in completely mineralizing organic pollutants [6]. Microorganisms play a remarkable role in decomposition and ultimate mineralization of various azo dyes [7], [8], [9]. Bacterial decolorization of azo dyes has gained importance in recent times [10] as they are easy to culture and grow quickly. Many microorganisms from various taxonomic groups have been found to decolorize different kinds of azo dyes [11], [12], [13], [14], [15]. These conventional non extremophilic microorganisms are inefficient in completely degrading the azo dyes at high salt levels present in the textile dyeing effluents. Biodegradation of azo dyes in salty environments inevitably requires the application of halophilic and halotolerant microorganisms as they are metabolically diverse in nature and are acquainted with the harsh and high saline conditions of the textile effluent. Hence, these halophiles are good candidates for the bioremediation of saline environments and in the treatment of textile dyeing effluents.

The aim of the present study is to evaluate the potential of a moderately halophilic bacterium Marinobacter sp. strain HBRA isolated from sea water to decolorize and degrade the complex azo dye Colour Index Direct Blue-1. The strain HBRA was evaluated for its ability to decolorize DB-1 at different pH, temperature, salinity and increasing dye concentration under static conditions. The degradation products of DB-1 were analyzed by FTIR, HPLC and LC–MS. Biotransformation pathway for DB-1 was proposed based on degradation pattern. Phytotoxicity study upon three common plant seeds Vigna radiata, Sorghum bicolor and Vigna mungo indicated the less-toxic nature of degraded metabolites. Cytogenotoxicity assay with meristematic root tip cells of Allium cepa revealed the non-toxic nature of degraded metabolites compared to the toxic azo dye inducing chromosomal aberrations and reduction in the mitotic index (MI). Currently available studies on Direct Blue-1 decolorization were limited to cyanobacterial [16] (Gloeocapsa pleurocapsoides and Phormidium ceylanicum) and fungal strains [17] (Cerrena unicolor and Trametes versicolor) but with moderate decolorization efficiency and lacking details of degradation and detoxification of DB-1. Hence, the present study is the first report on the degradation and detoxification of Direct Blue-1 by a Marinobacter sp. strain HBRA.

Section snippets

Chemicals

Azo dye C.I. Direct Blue-1 (DB-1) was a generous gift from C.P.S Textile Mill in Tirupur, Tamil Nadu, India. The CAS number of Direct Blue-1 is 2610-05-1 with purity of 99%. Nearly 25–40% of Direct Blue-1 is used for dyeing various fabrics in textile industries. HPLC grade methanol was purchased from Merck, Indian Ltd. All other chemicals used were of analytical grade. The stock solution of dye was prepared by dissolving 1000 mg L⁻¹ of DB-1 in double distilled water and purified by membrane

Isolation, screening and identification of bacteria

Among the 25 distinct bacterial strains isolated from the sea water sample and screened for decolorization of DB-1 in Luria-Bertani broth, a moderately halophilic bacterium was selected based on its decolorizing potential. The strain HBRA was able to decolorize 100 mg L⁻¹ of DB-1 with 100% efficiency at 37 °C, pH 8 and in the presence of 70 g L⁻¹ NaCl under static conditions in 6 h. Different Marinobacter strains with the ability to decolorize various azo dyes were reported earlier. Marinobacter

Conclusion

In the present study, a moderately halophilic bacterial strain HBRA was isolated that effectively degraded the structurally complex azo dye DB-1. Based on 16S rRNA gene sequence analysis, HBRA was identified to be a member of the Marinobacter genus. Complete decolorization of DB-1 was achieved in a short time under static conditions. Biotransformation pathway for DB-1 was proposed tentatively. The non-toxic metabolites generated by the degradation of DB-1 prove the detoxifying potential of the

Acknowledgement

The authors gratefully acknowledge the facilities provided by VIT University, Tamil Nadu, India.

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Biotransformation of Direct Blue 1 by a moderately halophilic bacterium Marinobacter sp. strain HBRA and toxicity assessment of degraded metabolites

Highlights

Abstract

Introduction

Section snippets

Chemicals

Isolation, screening and identification of bacteria

Conclusion

Acknowledgement

Int. Biodeterior. Biodegrad.

Mutat. Res.

Chemosphere

Bioresour. Technol.

J. Hazard. Mater.

J. Taiwan Inst. Chem. Eng.

Bioresour. Technol.

J. Biosci. Bioeng.

Int. Biodeterior. Biodegrad.

Int. Biodeterior. Biodegrad.

Int. Biodeterior. Biodegrad.

Enzyme Microbiol. Technol.

Int. Biodeterior. Biodegrad.

Enzyme Microbiol. Technol.

J. Hazard. Mater.

Dyes Pigments

Efficiency of the coagulation/flocculation method for the treatment of dye bath effluent

Dyes Pigments

Decolorization of azo dyes by Shewanella sp. under saline conditions

Appl. Microbiol. Biotechnol.

Degradation of azo dye acid orange 7 in a membrane bioreactor by pellets and attached growth of Coriolus versicolour

Bioresour. Technol.