110
P. Ghosh and U. Ghosh
mono-, di- and polyphenols, methoxyphenols, aromatic amine and aminophenols.
In the recent decades, it has been reported that a number of fungal laccases could
decolorize and degrade industrial dyes which are widely used in the dyeing fabric,
printing paper, leather, food process industries, colour photography and as additives
in petroleum-based products. Synthetic dyes are different types like azo, triarylmethane, indigoid and anthra-quinonic, used in dyeing process. The textile industry
stands out, as it produces a large amount of effluents which can cause serious environmental problems like affect photosynthetic activity in aquatic life by reducing
light penetration intensity and may also be toxic to some aquatic fauna and flora
due to the presence of aromatics, metals, chlorides, etc. (Chacko and Subramaniam
2011). It is estimated that about 10–15% of dyes are released into processing water
during dyeing and subsequent washing steps of procedure (Selvam et al. 2003).
Traditional processes are usually costly, complex and produced a large number of
slush but enzymatic process give an eco-friendly and capable substitute for decolorizing of dyes and also detoxify before discharging into the environment (Blanquez
et al. 2004). The enzymatic approach deals mainly with ligninolytic enzymes, of
which laccases are the most preferred enzymes for this purpose since they act oxidatively and less particularly on aromatic rings, thus having prospective to degrade a
various range of compound. The use of mediator compounds permits an expansion
of the reactivity of laccase to include such unnatural laccase substrates by generating
high redox potential species. Using mediator, laccase can indirectly oxidize large
molecules and even nonphenolic substrates also. 1-hydroxybenzotriazole (HBT) is
one of the most important laccase mediators (Moldes and Sanroman 2006), but
the prime issue of HBT using is its limited biodegradability and possible toxicity
(Murugesan et al. 2007). Hence, HBT concentration optimization is much more
important for efficient decolourization. In this present work, we have investigated
degradation/decolourization of textile dyes, Bromophenol blue, phenol red, malachite green, methyl orange and Congo red by laccase enzyme which is produced
from an isolated and identified fungus Aspergillus flavus PUF5. The aim of this
study is to optimize the HBT, pH, enzyme and dyes concentrations in order to obtain
the best possible results in dye decolourization by laccase.
2 Materials and Methods
2.1 Fungal Strain
The laccase producing fungi A. flavus PUF5 (GenBank accession number
KX181714.1) was maintained on potato dextrose agar slants. A suspension
containing about 5 × 10
9 spores/ml was used as an inoculum.
P. Ghosh and U. Ghosh
mono-, di- and polyphenols, methoxyphenols, aromatic amine and aminophenols.
In the recent decades, it has been reported that a number of fungal laccases could
decolorize and degrade industrial dyes which are widely used in the dyeing fabric,
printing paper, leather, food process industries, colour photography and as additives
in petroleum-based products. Synthetic dyes are different types like azo, triarylmethane, indigoid and anthra-quinonic, used in dyeing process. The textile industry
stands out, as it produces a large amount of effluents which can cause serious environmental problems like affect photosynthetic activity in aquatic life by reducing
light penetration intensity and may also be toxic to some aquatic fauna and flora
due to the presence of aromatics, metals, chlorides, etc. (Chacko and Subramaniam
2011). It is estimated that about 10–15% of dyes are released into processing water
during dyeing and subsequent washing steps of procedure (Selvam et al. 2003).
Traditional processes are usually costly, complex and produced a large number of
slush but enzymatic process give an eco-friendly and capable substitute for decolorizing of dyes and also detoxify before discharging into the environment (Blanquez
et al. 2004). The enzymatic approach deals mainly with ligninolytic enzymes, of
which laccases are the most preferred enzymes for this purpose since they act oxidatively and less particularly on aromatic rings, thus having prospective to degrade a
various range of compound. The use of mediator compounds permits an expansion
of the reactivity of laccase to include such unnatural laccase substrates by generating
high redox potential species. Using mediator, laccase can indirectly oxidize large
molecules and even nonphenolic substrates also. 1-hydroxybenzotriazole (HBT) is
one of the most important laccase mediators (Moldes and Sanroman 2006), but
the prime issue of HBT using is its limited biodegradability and possible toxicity
(Murugesan et al. 2007). Hence, HBT concentration optimization is much more
important for efficient decolourization. In this present work, we have investigated
degradation/decolourization of textile dyes, Bromophenol blue, phenol red, malachite green, methyl orange and Congo red by laccase enzyme which is produced
from an isolated and identified fungus Aspergillus flavus PUF5. The aim of this
study is to optimize the HBT, pH, enzyme and dyes concentrations in order to obtain
the best possible results in dye decolourization by laccase.
2 Materials and Methods
2.1 Fungal Strain
The laccase producing fungi A. flavus PUF5 (GenBank accession number
KX181714.1) was maintained on potato dextrose agar slants. A suspension
containing about 5 × 10
9 spores/ml was used as an inoculum.