Bacterial Degradation of Azo Dye Containing Wastes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 70

5.3 Lignin Peroxidases

Lignin peroxidase (EC 1.11.1.14; LiP) was rst discovered from Phanerochaete

chrysosporium and shown to attack lignin type compounds (Tien and Kirk 1984 ).
This enzyme belongs to the family of oxidoreductases, speci

cally those acting on
peroxide as an acceptor (peroxidases) and can be included in the broad category of
ligninases. The systematic name of this enzyme class is 1, 2-bis (3, 4-dimethoxy-
phenyl) propane-1, 3-diol: hydrogen-peroxide oxidoreductase. LiP is glycoprotein
having molecular weight between 38 and 46 kDa. LiP is haem containing peroxidase
with high redox potential. The optimum pH of this enzyme is below 3.0. The
mechanism of sulphonated azo dye degradation by LiP involves two successive one-
electron oxidations in the phenolic ring by the H 2 O 2 -oxidised forms of LiP and
produces a radical at the carbon bearing the azo linkages. Now, nucleophilic attacks
by water on phenolic carbon produce phenyldiazene. This product is then oxidized by
O 2 to a phenyl radical, and the azo linkage is eliminated as N 2 . The most widely
accepted assay for detecting lignin peroxidase is based on the oxidation of veratryl
alcohol to veratraldehyde. Moreover, from the crystal structure of Lip, it can be
inferred that only veratryl alcohol can enter the active site. It is not possible for the
lignin polymer to interact directly with the haem-group of the enzyme. The lignolytic
enzymes have been widely studied in fungi, but very few reports are available for
activity of lignolytic enzymes in bacteria for azo dye degradation. However, puri ed

LiP from Bacillus sp. strain UVS, Brevibacillus laterosporous MTCC 2298 and
Acinetobacter calcoaceticus NCIM 2890 ef

ciently decolorized the various synthetic

azo dyes. Invariables, the puri ciency for decolorization of

dyes than intact cells. Lignocellulosic substrates inmedium induce the production and
activity of LiP for degradation of azo dyes (Saratale et al. 2011 ).

ed LiP shows better ef

5.4 NADH-DCIP Reductases

The NADH-DCIP reductase (EC 1.6.99.3) reduces the DCIP (2,6-dichloroindo-
phenol) using NADH as an electron donor. The enzyme acts as a monomer with a
molecular mass of 43 kDa. DCIP is blue in its oxidized form and becomes colorless
after reduction by a reductase enzyme. NADH-DCIP reductase from Bacillus ste-
arothermophilus was reported in 1980. Several researchers reported NADH-DCIP
reductase as marker enzyme for the reduction of azo dyes. A signi cant induction of

DCIP reductase activity during the decolorization of various dyes has been reported
from Bacillus sp. ADR, Pseudomonas aeruginosa BCH, Alcaligenes faecalis PMS-
1, Brevibacilus laterospores, Acinetobacter calcoaceticus, Pseudomonas sp. SUK1.
Consortium GB, consisting of Galactomycesgeotrichum MTCC 1360 and Bacillus
sp. VUS, also showed NADH-DCIP reductase activity for azo dye Brilliant Blue G
degradation (Saratale et al. 2011 ; Shah et al. 2012 ; Solis et al. 2012 ).