Microbial Decolorization of Triphenylmethane Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 176

several enzymes decolorizing TPM dyes were identi ed, cloned and expressed in

diverse host organisms (Jang et al. 2005 ; Ren et al. 2006 ; Lu et al. 2009 ; Moturi and
Singara Charya 2009 ). Recently, Chengalroyen and Dabbs ( 2013 ) identi

ed in a
strain of Amycolatopsis sp. four TPM dyes biodegradation genes encoding 3-deoxy-
7-phosphoheptulonate synthase, N5,N10-methylenetetrahydro methanopterin
reductase, polycystic kidney domain I and glucose/sorbose dehydrogenase. The
synergistic action of these genes expressed in Streptomyces lividans TK23 led to
complete decolorization of Crystal violet. Their activity was also tested in Myco-
bacterium sp. mc 2 155 and three strains of Rhodococcus sp. The range of decolorized
dyes was extended in both species, showing that cloned genes had adopted novel
functional potentials within the hosts. Also, a system of phytoremediation by Ara-
bidopsis plants based on overexpression of TPM reductase from Citrobacter sp. was
presented by Fu et al. ( 2013 ). The morphology and growth of transgenic Arabidopsis
plants showed signi cantly enhanced tolerance to Crystal violet and Malachite green

and ability to decolorize these dyes.

8 Conclusion

Due to the large-scale production and wide application, TPM dyes are serious
health-risk factors and can cause considerable environmental damage. So far, a
number of strategies for the treatment of dye containing wastewaters have been
developed. However, the most promising method of the dyes removal seems to be
bioremediation which is cost effective, ecologically suitable and involves the usage
of various organisms especially bacteria, microscopic algae and fungi. The litera-
ture reviewed in this paper indicates that a large number of TPM dyes can be
ef ciently decolorized by bacterial (pure or mixed) and fungal cultures mainly due

to the action of extra- and/or intracellular enzymes (e.g. laccases, peroxidases and
reductases). Strains isolated from dye polluted environments (such as contaminated
soil, dye ef

uents and sludges) are often well adapted to live in the presence of high
concentrations of dyes and metabolize them to non-toxic intermediates. Some
bacterial strains can even completely mineralize dyes, converting them into CO 2 ,
H 2 O, and/or any other inorganic end products. The biodegradation ef ciency can be

enhanced by exposing microorganisms to higher concentrations of synthetic dyes
and using some molecular biology techniques. Biodegradation of TPM dyes is
strongly in

uenced by various environmental factors (e.g. availability of nutrient
compounds and oxygen, pH, temperature, initial dye concentration). Therefore,
optimal operation parameters and toxicity of formed intermediates should be
determined before practical utilization of biodegradation processes. Efforts should
also be made to scale-up these processes before applying them for in real industrial
ef uents treatment.