Microbial Decolorization of Triphenylmethane Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 173

performs one-electron oxidation of phenolic compounds, but also reactions not
normally associated with other peroxidases, i.e. oxidation of non-phenolic aromatic
substrates (Husain 2006 ). LiP decolorization activity can be enhanced in the
presence of some compounds, such as veratryl alcohol, which acts as a redox
mediator between an oxidized LiP and a dye (Alam et al. 2009 ). According to the
data obtained by Gomaa et al. ( 2008 ), laccase, oxygenase/oxidase and/or a heat-
stable non-enzymatic factor were suggested as the most probable agents involved in
Victoria blue elimination by P. chrysosporium ATCC 34541. High laccase and
MnP activities were also correlated with Ethyl violet decolorization by Pleurotus
pulmonarius (FR) (dos Santos Bazanella et al. 2013 ). A white-rot fungus Ischno-
derma resinosum was reported to be capable of almost complete decolorization of
Malachite green and Crystal violet mainly by laccase and MnP action within
20 days of culturing in liquid medium (Eichlerov

et al. 2006b ). Degradation of the
Malachite green-loaded rapeseed press cake in a laccase containing culture of the
M. roridum IM 6482 was also described by Jasi

á

ska et al. ( 2013 ). Crude laccase of
Coprinus comatus was able to decolorize over 90 % of Malachite Green, and higher
decolorization was obtained in the presence of redox mediators (especially in the
presence of 1-hydroxybenzotriazol) (Jiang et al. 2013 ). The strain Lentinula edodes
CCB-42 was able to eliminate Methyl violet, Ethyl violet and Methyl green (Boer
et al. 2004 ). Because the process was strongly in

ń

uenced by the Mn ions and H 2 O 2
presence, Mn peroxidase action was suggested as the main mechanism of dyes
elimination. Transformation of Cotton blue, as a result of Penicillium ochrochloron
MTCC517 LiP induction, was reported by Shedbalkar et al. ( 2008 ). The same strain
was also found to detoxify Malachite green via peroxidase-mediated reactions.
TPM dyes can be also decolorized via NADH/NADPH-dependent reduction
under the control of TPM reductase (TMR). The

ed and characterized
biochemically TMR was isolated from Citrobacter sp. KCTC 18061P (Jang et al.
2005 ). However, TMR was also identi

rst puri

ed in Pseudomonas aeruginosa NCIM
2074, Exiguobacterium sp. MG2 and Mucor mucedo cells (Moturi and Singara
Charya 2009 ; Kalyani et al. 2012 ; Wang et al. 2012 ). It shows that TMR decol-
orization activity is dependent on the chemical structure of the dyes. The most
ef

cient TMR substrate appeared to be Malachite green, while Crystal violet was
less favorable, perhaps because of the additional dimethyl amino group (Jang et al.
2005 ). Kim et al. ( 2008 ) suggested that the structures of other TPM dyes, such as
Brilliant green, Bromophenol blue, Methyl red, and Congo red, made them
incompatible with the size and hydrophobic restrictions of the TMR substrate
binding pocket. Based on structural inspection, the modeled ternary protein/
cofactor/substrate complex structure and mechanism of Malachite green decolor-
ization by TMR were also proposed (Fig. 2 ).
TPM dyes removal by microorganisms may also occur as a result of action of
membrane associated oxidoreductive enzymes. For example, the membrane fraction
of Mycobacterium avium A5 had an about 5-fold higher Malachite green speci c

decolorization rate than the crude extract which suggested the involvement of
membrane associated proteins e.g. cytochrome P-450 (Jones and Falkinham 2003 ).