Degradation of Azo Dyes by White-Rot Fungi - Microbial Degradation of Synthetic Dyes in Wastewaters - page 314

Table 1 Anatomical and chemical features of different types of wood decaying by white-rot-fungi
(Mart í nez et al. 2005 )
Simultaneous rot Selective deligni cation

Decay
aspect and
consistency

Bleached appearance, lighter in colour than sound wood, moist, soft, spongy,
strength loss after advanced decay

Host
(wood-type)

Hardwood, rarely softwood Hardwood and softwood

Cell-wall
constituents
degraded

Cellulose, lignin and hemicelluloses Initial attack selective for

hemicelluloses and lignin,
later cellulose also

Brittle fracture Fibrous feature

Anatomical
features

Cell wall attacked progressively
from lumen. Erosion furrows
associated with hyphae

Lignin degradation in middle lamella
and secondary wall. Middle lamella
dissolved by diffusion mechanism (not
in contact with hyphae), radial cavities
in cell wall

Fungi Basidiomycetes (e.g. T. versicolor,

Irpex lacteus, P. chrysosporium and
Heterobasidium annosum) and
some Ascomycetes (e.g. Xylaria
hypoxylon)

Basidiomycetes (e.g. Ganoderma
austral, Phlebiatremellosa,
C. subvermispora, Pleurotus spp.
and Phellinus pini)

such as NH-triazine. In addition, it was observed that if the electro-withdrawing

groups were in the para or ortho positions to the azo bond, degradation was faster
than, if they were in the meta position. This is due to the fact that they make azo dyes
highly electrophilic (Pricelius et al. 2007 ; Tauber et al. 2008 ; Hsueh et al. 2009 ) and
with less steric hindrance near the azo bond (Chen et al. 2011 ).

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3.2 In uence of Carbon and Nitrogen Sources

Carbon and nitrogen sources considerably affect azo dye decolouration by micro-
organisms. Carbon sources function as sources of carbon and energy for growth and
survival of the fungus and as electron donors to break the azo bond (Yang et al.
2009 ; Yemendzhiev et al. 2009 ). Carbon sources are accepted differently by dif-
ferent micro-organisms and have an important effect on the extent of decolouration.
Thus, in several cases, the microbial decolouration of azo dyes is increased in the
presence of glucose, whereas in other cases, the presence of several carbon sources
is required and in others, the presence of a carbon source inhibits azo dye decol-
ouration (Solis et al. 2012 ). Besides the type of carbon source, its concentration is
also an important parameter affecting dye decolouration, as high carbon concen-
trations can diminish decolouration (Solis et al. 2012 ).