Microbial Decolorization of Triphenylmethane Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 171

dyes removal ranged from 3 to 5. Similarly, according to Sarnthima et al. ( 2009 ),
the highest percentage of Bromophenol blue removal by a strain of Lentinus
polychrous occurred at pH 4. Generally fungi and yeast prefer acidic pH; however,
Malachite green was effectively decolorized at pH 7 by the mycelium of P.
ochrochloron (Shedbalkar and Jadhav 2011 ). Similarly, Deivasigamani and Das
( 2011 ) reported complete Basic Violet 3 elimination by a C. krusei strain cultured at
pH 7. Yang et al. ( 2011a ) estimated that growth medium at pH 6 accelerated
Malachite green decolorization by the strain Penicillium sp. YW01. Bacteria more
often decolorize dyes at neutral and alkaline pH. Du et al. ( 2011 ) observed that the
proper pH for Malachite green decolorization by Pseudomonas sp. DY1 was
between 5.5 and 8, and the highest decolorization was recorded at 6.6. Decolor-
ization of Victoria blue R by A. calcoaceticus YC210 was found to be the most
effective within a range of pH 5

7 (Chen et al. 2011 ). P. aeruginosa BCH
decolorized Acid violet 19 up to 98 % within 30 min with optimum of pH 7 (Jadhav
et al. 2012 ).
In most cases, the rate of TPM dyes bioremoval increases up to the temperature
which is optimal for the growth of organisms and also the rate of dyes removal
often rises with an increase in the temperature due to respiration and substrate
metabolism acceleration. It is worth mentioning that some TPM dyes degrading
enzymes are active and stable even at high temperatures. For example, Malachite
green was decolorized by Trametes trogii Berk S0301 effectively in the range of
30

-

C (Yan et al. 2014 ). According
to Zhang et al. ( 2012 ), spore laccase from Bacillus vallismortis fmb-103 was quite
stable at a temperature range between 25 and 90

80 ° C with an optimum decolorization at 50 70 °

- -

C. TPM reductase from Citro-
bacter sp. KCTC catalyzing the NADH-dependent reduction of Crystal violet to its
leuco dyes, exhibited maximum activity at 60

°

C (Jang et al. 2005 ).
Biodegradation of TPM dyes may occur under aerobic as well as anaerobic
conditions depending on metabolic features of particular microorganisms. Most
fungi are obligate aerobes and they need oxygen for their growth and maintenance
of viability. In order to meet their oxygen requirements and to enhance the oxygen
gas-liquid mass transfer, the agitation is necessary. Most literature data indicate that
fungi eliminate TPM dyes faster under shaking conditions (Saratale et al. 2006 ;
Przysta

°

et al. 2013 ). Usually TPM dyes elimination by bacterial strains is also
improved in the shaking conditions (Ali 2010 ; Du et al. 2011 ). In contrast, Mala-
chite green decolorization by B. cereus DC11 required anaerobic or microaerophilic
conditions and was strongly inhibited in an aerobic culture (Deng et al. 2008 ). It is
suggested that the lack of decolorization in shaking conditions could result from the
fact that dissolved oxygen often inhibits reductase-driven decolorization. Under
aerobic conditions, oxygen can compete with the dye for the reduced electron
carriers (Moosvi et al. 2005 ).
Generally, the decolorization ef

ś

ciency decreases with an increase in the con-
centration of TPM dyes, which mainly results from the rising toxicity of dyes.
When the microbial growth is reduced, secretion of enzymes can be also limited,
especially in solid media (Eichlerov et al. 2006a ; Parshetti et al. 2006 ). However,

the initial concentration of the dye can possess a strong driving force to overcome

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