Biodegradation of diazo dye Direct brown MR by Acinetobacter calcoaceticus NCIM 2890

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Abstract

Acinetobacter calcoaceticus was employed for the degradation of Direct brown MR (DBMR), commercially used azo dye in the textile industry in order to analyze mechanism of the degradation and role of inhibitors, redox mediators and stabilizers of lignin peroxidase during decolorization. Induction of intracellular and extracellular lignin peroxidase, intracellular laccase and DCIP reductase represented their involvement in the biodegradation of DBMR. Decolorization and biodegradation of azo dye DBMR in broth were monitored by UV–visible spectrophotometer and TLC. The products obtained from A. calcoaceticus degradation were characterized by FTIR and identified by GC/MS as biphenyl amine, biphenyl, 3-amino 6-hydroxybenzoic acid and naphthalene diazonium. Germination (%) and growth efficiency of Sorghum vulgare and Phaseolus mungo seeds revealed the degradation of DBMR into less toxic products than original dye. A. calcoaceticus also has a potential to degrade diverse dyes present in the textile effluent, into nontoxic metabolites, hence A. calcoaceticus can be applied for the commercial application.

Introduction

Global villages are facing many issues regarding industrial pollution such as textile, leather, food and agro industries have brought enormous atmospheric changes. The textile industry is one of the greatest generators of liquid effluent, due to the high quantities of water used in the dyeing processes (Jin et al., 2007). The effluents from these industries are complex, containing a wide variety of dyes and other products, such as dispersants, acids, bases, salts, detergents, humectants, oxidants, and high TDS, sodium, chloride, sulphate, hardness and carcinogenic dye ingredients (Tchobanoglous and Burton, 1995). The two major sources of dye release into the environment are the dyestuff manufacturing and textile industries (Nigam et al., 1996). Synthetic dyes such as azo, xanthene and anthraquinone dyes are very toxic to living organisms (Rafii et al., 1990). Azo dyes are reported to contribute mutagenic activity of ground and surface waters polluted by textile effluents (Rajaguru et al., 2002, Umbuzeiro et al., 2005). Azo dyes are aromatic compounds with one or more azo bond (–Ndouble bondN–) and constitute the largest class of synthetic dyes used (60–70%) of total consumption of dyes in commercial applications (Zollinger, 1987). All dyes do not bind to the fabric, depending on the class of the dye, its loss in wastewaters could vary from 2% for basic dyes to as high as 50% for reactive dyes, leading to severe contamination of surface and ground waters in the vicinity of dyeing industries (Ganesh et al., 1994) which implies their wide occurrence of dye in wastewaters. Furthermore, their discharge into surface water leads to aesthetic problems and obstructs light penetration and oxygen transfer into water bodies and there by affecting aquatic life. Azo dyes are poorly biodegradable because of their structure (Kim and Shoda, 1999) and they represent a potentially important class of organic pollutants, little is known about their fate (Chivukula and Renganathan, 1995). Thus the removal of color from textile effluents has been a major concern with these environmental pollutants that have prompted the need to develop novel treatment methods for converting organic contaminants, such as dye-containing effluents to harmless compounds (Stylidi et al., 2003).

Treatment of dye wastewater involves physical/chemical methods (coagulation, precipitation, adsorption by activated charcoal, oxidation by ozone, ionizing radiation and ultrafiltration). These methods are not only expensive but also commercially unattractive and generate wastes (secondary pollution), which are difficult to dispose off and are less efficient and of limited application (Chen et al., 1999, Golab et al., 2005). Biological processes provide an alternative to existing technologies because they are more cost-effective, environmentally friendly and do not produce large quantities of sludge (Azmi et al., 1998, Verma and Madamwar, 2003). It is now known that several microorganisms, including fungi, bacteria, yeasts and algae, can decolorize and even completely mineralize many azo dyes under certain environmental conditions (Pandey et al., 2007). The effectiveness of decolorization depends on the structure and complexity of each dye even though relatively small structural differences can markedly affect decolorization (Knapp et al., 1995). Complex enzymatic systems and the conditions, under which they are expressed, are responsible for organopollutant degradation.

The aim of this work was to find out the potential of Acinetobacter calcoaceticus for the decolorization of the mixture of synthetic dyes and original textile effluent. Direct brown MR (DBMR) was used as a model dye, in order to analyze the role of lignin peroxidase. Effect of various inhibitors, redox mediators and stabilizers of lignin peroxidase was studied during decolorization to establish the role of lignin peroxidase. This study also includes characterization and identification of DBMR products using analytical tools viz. FTIR and GC/MS, involvement of intra and extracellular enzymes responsible for degradation, and toxic effect on germination of agricultural important crops.

Section snippets

Dyes and chemicals

Textile dyes such as Direct brown MR were generous gift from Manpasand Textile Processors, Ichalkaranji, Kolhapur, Maharashtra, India. ABTS [2,2′Azino-bis 3-ethylbenzothiazoline 6-sulfonic acid] and butanol were obtained from Sigma Aldrich, USA. Tartaric acid, n-propanol and catechol were purchased from Sisco Research Laboratories, India. Peptone and beef extract were purchased from Hi-media, India.

Microorganism and culture conditions

A. calcoaceticus NCIM 2890 (A. calcoaceticus) used for the decolorization study was obtained from

Bacterial growth and decolorization of DBMR

The batch cultures turned light yellow from initial dark brown, which further became colorless indicates adsorption of the dye before degradation. The DBMR absorbance was measured at 410 nm with UV–visible spectrophotometer and observed that it was greatly decreased after incubation with A. calcoaceticus (Oranusi and Ogugbue, 2001) (data not shown). Decolorization of DBMR was observed effectively (91.3%) in static anoxic condition even though lower growth rate, whereas, agitated cultures grew

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