Degradation of Azo Dyes by White-Rot Fungi - Microbial Degradation of Synthetic Dyes in Wastewaters - page 316

ability of white-rot fungi to degrade coloured ef uents in alkaline-saline conditions

(Ottoni et al. 2013 ). Recently, Ottoni et al. ( 2014 ) reported that the white-rot fungus
T. versicolor was able to completely decolourise the diazo dye Reactive Black 5
(0.1 g l − 1 ) in a liquid medium containing 15 g l − 1 NaCl at pH 9.5 in batch culture.
Also, they found that T. versicolor, immobilised on either polyurethane foam or
nylon sponge, was able to operate in continuous mode for 40 days in a xed-bed

bioreactor with decolouration range of 85 100 %.

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3.7 Aeration and Shaking

White-rot fungi are aerobic in nature; hence they need oxygen for growth and
maintenance. Also, ligninolytic enzymes need oxygen to bring about their catalytic
action. This oxygen requirement depends on the fungus and its ligninolytic system.
Shaking favours oxygen transfer, but it affects fungal morphology and can diminish
the rate of the enzyme synthesis ( Ž nidar š i č and Pavko 2001 ).

4 Involvement of Oxidoreductive Enzymes
in the Degradation Process

The ability of white-rot fungi to degrade lignin is due to the secretion of several
extracellular non-speci

c LMEs (Table 2 ). LMEs production by white-rot fungi
occurs usually at the onset of secondary metabolism (Hatakka 1994 ; Camarero et al.
1999 ). The main LMEs are two glycosylated hemo-containing peroxidases, lignin

Table 2 Ligninolytic enzymes and their main reactions
Enzyme and
abbreviation

Cofactor Substrate, mediator Reaction

Lignin
peroxidase (LiP)

H 2 O 2 Veratryl alcohol Aromatic ring oxidised

to cation radical

Manganese-dependent
peroxidase (MnP)

H 2 O 2 Mn, organic acids

as chelators, thiols,
unsaturated fatty acids

Mn(II) oxidised to Mn(III);
chelated Mn(III) oxidises
phenolic compounds to
phenoxyl radicals; other
reactions in the presence
of additional compounds

Phenols are oxidised
to phenoxyl radicals;
other reactions in the
presence of mediators
Hatakka ( 2001 ); Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission

Laccase O 2 Phenols, mediators,

e.g. hydroxybenzotriazole
or ABTS