Application of Extremophilic Microorganisms in Decolorization and Biodegradation of Textile Wastewater - Microbial Degradation of Synthetic Dyes in Wastewaters - page 280

Alkaline-adapted microorganisms can be divided into two main groups which
include; alkaliphiles and alkalitolerants. The term alkaliphiles is restricted to
microorganisms that require alkaline media for growth and their optimum growth
rate could be observed in at least two pH units above neutrality. Alkalitolerants are
able to grow at pH values more than 9 or 10, but their optimum growth rates occur
around neutrality or less (Grant and Tindall 1986 ; Jones et al. 1994 ). One of the
most important characteristic of textile wastewater ef uents is their alkalinity. Using

alkaliphiles is inevitable for bioremediation process, because they are adapted to
sustain in the harsh conditions of dyeing process. An obligate alkaliphilic bacterium
Bacillus cohnii MTCC 3616 was used for textile azo dye Direct Red-22 aerobic
decolorization, showing 95 % ef

C and pH 9 in 4 h
incubation under static conditions. The decolorization occurred in a broad pH range
(7

ciency for decolorization at 37 °

7 %) (Prasad and Rao 2013 ).
Alkaliphilic bacterial strain, Bacillus badius, isolated from a lake in India, showed
high potential towards the degradation of azo dyes up to 100 mg l − 1 in 24 h under
aerobic condition. Azoreductase enzyme, which is able to cleave azo and nitro
groups of various compounds, has also been puri

11), temperature (10 45 ° C) and salinity (1

- - -

ed from this strain (Misal et al.
2011 ). Clostridium bifermentans strain SL186 was isolated from a contaminated
site and investigated for Reactive Red 3B-A, Reactive black 5 and Reactive Yellow
3G-P dyes decolorization. The bacterium retained decolorizing activity over a wide
range of pH values (6 - 12) with optimum activity at pH 10 (Joe et al. 2008 ).

7 Polyextremophilic Microorganisms and Textile Dyes

Extremophilic microorganisms are able to live under different types of stressful
conditions which provide them an opportunity to extend habitable space on earth
which can support essential biological processes like cell growth and main
metabolism. It is important to note that there are some kinds of extremophiles that
are adopted to grow optimally under multiple stress factors, known as polyex-
tremophiles. The term polyextremophiles was rst coined by Rothschild and

Mancinelli ( 2001 ) to describe this group of micro-organisms. In comparison to
other types of microorganisms that will die or become dormant in harsh conditions,
extremophiles and polyextremophiles are able to grow with active metabolism in
the environmental harsh conditions, as they have application in such environments.
Different types of polyextremophiles are adopted to different combinations of
environmental extremes i.e. high temperature and low pH, high temperature and
high pH, high temperature and high pressure, low temperature and low pressure and
high salt concentration and high pH. The chemolithotrophic archaum Sulfolobus
acidocaldarius can easily

°

3, thus showing adaptation to
grow in high temperature and low pH (Reysenbach et al. 2006 ). The archaum
Thermococcus alcaliphilus, which is able to grow at 90

ourish at 75 CatpH2 -

rst
isolated from shallow marine hydrothermal springs (Keller et al., 1995 ). Thermo-
coccus barophilus, which

° C and at pH 10.5, was

ourishes at 100 ° C and needs 15 17.5 MPa at the

-