A New Alkali-Thermostable Azoreductase from Bacillus sp. Strain SF

Abstract

A screening for dye-decolorizing alkali-thermophilic microorganisms resulted in a Bacillus sp. strain isolated out of the wastewater drain of a textile finishing company. An NADH-dependent azoreductase of this strain, Bacillus sp. strain SF, was found to be responsible for the decolorization of azo dyes. This enzyme was purified by a combination of ammonium sulfate precipitation and anion-exchange and affinity chromatography and had a molecular mass of 61.6 kDa and an isoelectric point at pH 5.3. The pH optimum of the azoreductase depended on the substrate and was within the range of pHs 8 to 9, while the temperature maximum was reached at 80°C. Decolorization only took place in the absence of oxygen and was enhanced by FAD, which was not consumed during the reaction. A 26% similarity of this azoreductase to chaperonin Cpn60 from a Bacillus sp. was found by peptide mass mapping experiments. Substrate specificities of the azoreductase were studied by using synthesized model substrates based on di-sodium-(R)-benzyl-azo-2,7-dihydroxy-3,6-disulfonyl-naphthaline. Those dyes with NO 2 substituents, especially in the ortho position, were degraded fastest, while analogues with a methyl substitution showed the lowest degradation rates.In the last few years, environmental legislation, e.g., about the appearance of color in discharges, combined with the increasing cost of water for the industrial sector, has made the treatment and reuse of dyeing effluents increasingly attractive to the industry. The common method for the treatment of wastewater in the textile finishing industry is physicochemical flocculation in combination with biological treatment (17). The conventional treatment of colored effluents produces a lot of sludge, but does not remove all dyes, thus preventing recycling of the treated wastewater. In activated sludge treatments, dyeing effluents, e.g., reactive azo dyes and naphthaline-sulfonic acids as well as aromatic amino derivatives, represent an extensive nonbiodegradable class of compounds (18) and can even inhibit activated sludge organisms. Thus, the development of more effective biological systems for the treatment of these types of wastewater has resulted in considerable interest by the industry.Wood-rotting fungi (e.g., Phanerochaete chrysosporium, Trametes sp., and Aspergillus sp.) have been found to effectively degrade a variety of azo dyes under aerobic conditions (16). Dye-degrading fungi have been used frequently in bioreactors for the decolorization and degradation of azo dyes (37). While fungal treatment of effluents is usually very time-consuming (3), immobilized enzymes could have potential for dye decolorization and recycling of effluents (1) without the need for the addition of growth substrates. The enzymes involved in the degradation of azo dyes are mainly peroxidases (12) and laccases (1). However, a significant cost reduction for these enzymes would be required in order to make this process economically more attractive. Aerobic bacteria have been described to oxidatively decolorize m...

Bacterial diversity and composition in major fresh produce growing soils affected by physiochemical properties and geographic locations

“…Two broad types of azoreductases including flavin-dependent and non-flavin reductases have been reported (Blumel & Stolz, 2003;Maier et al, 2004;Suzuki et al, 2001). Flavin-dependent azoreductases usually reduce azo dyes through a Ping-Pong Bi-Bi mechanism (Nakanishi et al, 2001;Ryan et al, 2010;Wang et al, 2010).…”

“…The azoreductases are classified into two groups on the basis of their electron donor requirements. The first includes flavin containing azoreductases, which show preference for NADH, while the second performs better with NADPH as a reductant for azo dye decolorization (Chen et al, 2005;Maier et al, 2004;Punj & John, 2008). Burger & Stolz (2010) isolated a flavin free azoreductase enzyme from Xenophilus azovorans KF46F strain.…”

“…Azoreductases exhibiting dye-degradation activities have been shown to function over a wide range from as low as pH 4.0) and as high as pH 9 (Johansson et al, 2011;Maier et al, 2004;Misal et al, 2011;Sharma et al, 2013;Yang et al, 2013). In contrast, bacterial laccases are reported to have their highest activities under neutral to alkaline conditions (Reiss et al, 2011).…”

Evaluation of Microbial Systems for Biotreatment of Textile Waste Effluents in Nigeria: Biodecolourization and Biodegradation of textile Dye

“…However, it has been reported that very few strains can withstand the conditions of dyeing effluents (Maier, 2004). Thus, as a preliminary step in the development of textile waste effluents biotreatment process involving indigenous microbial species, the present study have shown that Aspergillus niger, Pseudomonas fluorescence, Proteus morganii, Fusarium compacticum, Pseudomonas nigificans and Pseudomonas gellucidium, respectively, has a significant potential for dye decolourization and degradation.…”

“…The treatment of textile waste effluents is still a major environmental concern because of synthetic dyes which are difficult to be removed by conventional physical and chemical technologies (Zhang et al, 2004) such as membrane filtration, coagulation, precipitation, flotation, adsorption, ion exchange, chemical reduction, ultrasonic mineralization, electrolysis and advanced chemical oxidation (Gogate and Pandit, 2004;Kang et al, 2010). Some of these methods are effective but have inherent drawbacks such as high cost, intensive energy requirements, formation of hazardous by-products and generation of sludge which causes secondary pollution (Do et al, 2002;Verma et al, 2003;Maier et al, 2004;Ramya et al, 2007;Dayaram and Dasgupta, 2008). Current available treatment technologies have been reviewed by Robinson ) and specific attention is given to biological treatment processes because they are cost-effective and environmentally friendly.…”