Abstract
The present investigation focused on screening of a new potent strain for laccase production and optimizing the process parameters to achieve the maximum enzymatic decolourization of textile azo dye Congo red. Seven hydrocarbonoclastic bacterial strains were selected as positive in laccase production in solid medium using 2,6 dimethoxyphenol as an enzyme activity indicator. The best enzyme producer Pseudomonas extremorientalis BU118 showed a maximum laccase activity of about 7000 U/L of wheat bran under solid-state conditions. The influence of different concentrations of dye, enzyme, salt and various incubation times on Congo red decolourization was studied using response surface methodology to find the optimum conditions required for maximum decolourization by P. extremorientalis laccase. The enzyme exhibited a remarkable colour removal capability over a wide range of dye and salt concentrations. The above results show the potential use of this bacterial laccase in the biological treatment of the textile effluent.
Highlights
Laccase is one of the best-known multicopper enzymes and catalyzes the oxidation of a variety of aromatic compounds, in particular phenolic substrates, coupled to the reduction of molecular oxygen to water
The influence of different concentrations of dye, enzyme, salt and various incubation times on Congo red decolourization was studied using response surface methodology to find the optimum conditions required for maximum decolourization by P. extremorientalis laccase
Laccases have been discovered in a small number of bacteria including Bacillus subtilis, Bordetella campestris, Caulobacter crescentus, Escherichia coli, Mycobacterium tuberculosis, Pseudomonas syringae, P. aeruginosa, P. putida, P. fluorescens, Yersinia pestis and Stenotrophomonas maltophilia (Claus 2003; Sharma et al 2007; Imran et al 2012; Kuddus et al 2013; Vandana and Peter 2014; Verma et al 2016)
Summary
Laccase (benzenediol:oxygen oxidoreductase, EC 1.10.3.2) is one of the best-known multicopper enzymes and catalyzes the oxidation of a variety of aromatic compounds, in particular phenolic substrates, coupled to the reduction of molecular oxygen to water These enzymes are of low substrate specificity and oxidize a broad group of monophenols, diphenols, polyphenols and methoxy-substituted phenols as well as aromatic amines and metallic ions (Claus 2003; Canas and Camarero 2010; Neifar et al 2011). Laccases have been discovered in a small number of bacteria including Bacillus subtilis, Bordetella campestris, Caulobacter crescentus, Escherichia coli, Mycobacterium tuberculosis, Pseudomonas syringae, P. aeruginosa, P. putida, P. fluorescens, Yersinia pestis and Stenotrophomonas maltophilia (Claus 2003; Sharma et al 2007; Imran et al 2012; Kuddus et al 2013; Vandana and Peter 2014; Verma et al 2016). Some bacterial laccases have been well characterized, little information is available concerning their substrate specificities towards colour removal (Hadibarata and Tachibana 2009)
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