Microbial Decolorization of Triphenylmethane Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 170

Bacillus sp., Sphingomonas paucimobilis and A. hydrophila strains was found more
ef cient for faster decolorization of Malachite green and Crystal violet in com-

parison to individual cultures. Similarly, Acid violet 17 was decolorized more
effectively by a consortium including the cells of Bacillus sp., Alcaligenes sp. and
Aeromonas sp. than by the single bacterium (Sharma et al. 2004 ). It has been
suggested that a microbial consortium may increase the rate of dyes decolorization
due to synergistic actions among microorganisms.

3 Factors Affecting Bioelimination of TPM Dyes

TPM dyes bioelimination is strongly in uenced by numerous operational param-

eters. Due to an enormous effect on organism growth and metabolism, media
composition (especially compounds used as carbon and nitrogen sources) strongly
affects synthetic dyes decolorization. Glucose and sucrose appeared to be the most
suitable carbon sources for microbial removal of such TPM dyes as Basic violet 3
and Malachite green (Jadhav and Govindwar 2006 ; Deivasigamani and Das 2011 ).
Acceleration of dye removal in culture media containing glucose, often results from
the promotion of biomass production. However, due to the high cost of glucose,
various cheaper compounds have been used as carbon sources in decolorization
processes (Kaushik and Malik 2009 ). Among four different carbon sources (glu-
cose, sucrose, starch and sodium citrate), starch was proved to be the best for
Crystal violet decolorization by a strain of F. solani (Abedin 2008 ). Also Parshetti
et al. ( 2006 ) successfully applied molasses (instead of glucose or sucrose) for
Malachite green decolorization by K. rosea MTCC 1532.
Compounds, utilized as nitrogen sources, may also affect dyes biodegradation
due to their in uence on the synthesis of ligninolytic enzymes such as laccases and

peroxidases. Generally, production of fungal ligninolytic enzymes is often stimu-
lated by nitrogen de ciency depletion. For example, Ghasemzadeh et al. ( 2011 )

reported high production of LiP and MnP by P. chrysosporium in nitrogen-limited
conditions and was correlated with effective elimination of Crystal violet. Dyes
decolorization may be affected not only by the concentration, but also by the type of
nitrogen source. It is postulated that in comparison to inorganic sources, organic
compounds, such as peptone or yeast extract, frequently accelerate decolorization
processes. Indeed, yeast extract was reported as the best nitrogen source for ef

cient
decolorization of various TPM dyes (Cheriaa and Bakhrouf 2009 ; Parshetti et al.
2011 ). Recognition of yeast extract as an essential culture media supplement is
probably related to its suitability for the regeneration of NADH acting as an electron
donor for the enzymatic reduction of TPM dyes (Jang et al. 2005 ; Ogugbue and
Sawidis 2011 ).
pH value of the decolorization environment in uences the transport of dye

molecules across cell membranes as well as extracellular biotransformation of TPM
dyes by ligninolytic enzymes. Nozaki et al. ( 2008 ), while studying the decolor-
ization of TPM dyes by 21 fungi of Basidiomycota, found that the optimum pH for