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MICROBES: "A TRIBUTE" TO CLEAN ENVIRONMENT Prof.
D. Lalithakumari Director, Centre for Advanced Studies
in Botany, University of Madras, Chennai 600 025. |
The paramount of pollution in
our environment is a dire consequence of continually
expanding population along with an exponential development
in the industrial field. Microbes are ubiquitous in
nature and are being exposed to the continuous release
of more and more recalcitrant xenobiotic compounds into
the environment. No wonder, these microbes, inhabiting
polluted environments, are armed with various resistance
and catabolic potentials. The catalytic potential of
microbes in nature is enormous and this is advantageous
to mankind for a cleaner and healthier environment through
bioremediation. |
In general, potential microbes with broad spectrum of
activities from their native habitat have been screened,
characterized, genetically modified and released back
to their native habitat for better performance. By such
studies, the core problem of pollution is tactfully
attacked and benefits of decontamination add healthy
atmosphere to mankind. The purified degrading enzymes,
Nitrilase, Azoreductases and Oragnophosphate hydrolases
could be effectively used in industry for the treatment
of effluents. The systems developed are eco-friendly
and economical and hence could effectively be integrated
with physico-chemical methods for pollution control. |
The index
of xenobiotic compounds released into the environment
increases due to industrialization and combating pollution
by the release of these compounds is essential for the
sustenance of the future generation. In this context,
microbes such as algae, fungi and bacteria, play an
important role by giving us a helping hand in bioremediation
of these xenobiotic compounds. |
Degradation
of pesticides by different bacterial population proves
to be the best example for citing the role of microbes
in bioremediation of xenobiotic compounds. A large number
of pesticides and insecticides like morpholine, methyl
parathion, organophosphorous compounds and benzimidazoles
are widely used to increase the agricultural output
and has also contributed to the pollution load, as many
of these man-made chemicals are non-biodegradable. The
pollution control strategies involving physico-chemical
methods many a time aggravate the problem, rather than
eliminating it. Microbes play a very important role
in the mineralization of pollutants either by natural
selection or through recombinant DNA technology making
bioremediation process an extension of normal microbial
metabolism. Xenobiotic compounds are also widely employed
in our day to day life. Microbes also mediate degradation
of xenobiotic compounds like dyes and plastics. |
Our Center,
CAS in Botany, University of Madras, Chennai, has done
extensive work in degradation of xenobiotic compounds.
Different, pure isolates of Pseudomonas sp.
have been well characterized for complete and partial
mineralization of morpholine, methyl parathion and other
organophosphorous pesticides and fungicides. Pseudomonas
sp. has also been used for oil hydration by means of
both aromatic and aliphatic hydrocarbon degradation.
Other isolates of bacteria, Serratia sp. and
Bacillus sp. have also been characterized and
documented for their ability to degrade benzimidazole
compounds and to effectively decolorize distillery and
textile mill effluents respectively. |
Understanding
the molecular biology of the microorganisms, and the
ability to genetically manipulate the microorganisms
and infuse engineering principles into biology have
led to novel strategies for combating environmental
problems. |
Construction
of strains with broad spectrum of catabolic potential
with heavy metal resistant traits makes them ideal for
bioremediation of polluted environments in both aquatic
and terrestrial ecosystems. The transfer of genetic
traits from one organism to another paves way in creating
Genetically Engineered Organisms (GEM's) for combating
pollution in extreme environments making it a boon to
mankind to cleanup the mess that has created in nature.
Therefore, bioremediation protocols for treatment of
industrial wastewaters like distillery effluent, textile
mill effluent, tannery effluent and pharmaceutical effluent
have been devised and managed by the author for commercial
applications. |
Degradation
of broad spectrum of pesticides |
Degradation
of pesticides in situ (in soil) has been studied extensively
and the results indicated complete mineralization of
pesticides and fungicides in soil by microbes. Pseudomonas
A3, Pseudomonas putida, P. aeruginosa,
Serratia marinorubra either singly or as a consortia
have been used for complete mineralization of broad-spectrum
fungicides in soil. These microbial strains have also
been used for the industrial effluents containing pesticides
and fungicides residues. |
Decolorization
and degradation of textile mill dyes & effluents
|
Rich
collection of bacteria capable of degradation of commercial
textile mill azo reactive dyes like Black B, Turq Blue
GN, Yellow HEM, Red HEFB and Navy HER along with a number
of mono, bi, poly azo dyes and triphenylmethane dyes
like Methyl red, Acid black 53, Acid black 76, Acid
black 210, Acid green, Acid brown, Sudan black, Sudan
IV and Crystal violet are available in the CAS in Botany,
University of Madras. The organisms employed are
Serratia marinorubra, Bacillus sp.
YW and YDLK consortia for decolorization of textile
mill effluents. They are capable of effective decolorization
of a wide range of dyes. The biomass concentration of
20g wet weight/L (w/v) and 5 h of treatment time at
room temperature with 250 rpm of agitation rate was
able to decolorize the textile mill effluents up to
a depth of 160cm in static conditions within 5 h with
external supplement and nutrition. Bacterial Extracellular
polysaccharides (EPS) as biomatrix (bio-reactor) for
the decolorization of textile mill effluents and dyes
was standardized by the author using pesticides as energy
source for enhanced EPS production. |
Decolorization
and degradation of industrial effluents |
Effluents
of textile mill, distillery, pharmaceutical and tannery
decolorization was done using both pure culture of bacteria
and microbial consortium. Significant reduction in the
Biological Oxygen Demand (BOD) and Chemical Oxygen Demand
(COD) values of the textile mill effluent by 96% and
94% respectively, was achieved along with 100% decolorization
of textile mill effluents. The treatment studies revealed
that the organism grew effectively in the raw effluent
and further dilution of the effluent resulted in faster
decolorization and degradation of dyes.
Bacillus
sp. YW, YDLK consortia and Trichoderma viride
are able to bring about 90% color reduction in distillery
effluent with an aeration rate of 2kg oxygen / L along
with the addition of 1 % DAP as nitrogen source. The
colorants and the COD components of the effluent after
biological treatment was reduced up to 95% and BOD values
reduced up to 96%. Both batch and continuous treatment
systems in laboratory and pilot scale experiments were
standardized for obtaining the most suitable treatment
system for decolorization of the distillery effluent.
This system is ready for its usage in sick unit treatment
program. |
Heavy
metal detoxification and biosorption
|
Work
on heavy metal detoxification and biosorption was initially
started by employing the bacterium Bacillus
sp. YW, which was found to be effective in reducing
hexavalent Cr to its non toxic trivalent form and the
chromate resistance and reduction was found to be plasmid
mediated process. Further work was carried out to remove
the less toxic trivalent Cr through biosorption using
the EPS of Azotobacter sp. as the biomatrix.
The Cr bound EPS-Azotransformant was flocculated from
the tannery effluent using copper, which flocculates
the culture of Azotobacter sp; Leuconostoc
sp., an EPS producer (Plate 1) has been characterized
and cloned for its EPS production for biosorption of
many heavy metals like Cadmium, Zinc, Arsenate, Chromium
etc. from polluted samples. EPS is also used as matrix
to entrap bacteria for column reactor. EPS also induces
rapid and more root nodulations of symbiotic nitrogen
fixers. |
Degradation
of hydrocarbons |
Aliphatic
and aromatic hydrocarbons, crude oil, nitroaromatic
compounds and BTEX are successfully degraded by a wide
range of Pseudomonas sp. isolated and characterized
in our laboratory. Most of the strains harboured a catabolic
plasmid, which encodes the genes for hydrocarbon degradation.
The biotransformation of this plasmid to various terrestrial
and natural marine bacteria has been carried out, indicating
the horizontal transfer of catabolic genes from one
bacteria to another, paving way to create "Super
Bugs" for bioremediation program in differing and
metamorphosing ecosystems. Besides Pseudomonas
sp. HC1 and Raulstonia sp. also have been successfully
used for oil degradation. |
Decolorization
and deodourization of highly polluted Coovum river water |
Potential
bacteria and fungi capable of deodourising and decolourising
Coovum river water have been isolated, characterized
and used for treatment. Our observations are repeatable
and recommended for Coovum water treatment and thereby
the treated water can be used for agriculture, industry,
aquarium and also for household purposes after proper
bioremediation. A series of experiments performed using
the isolates of various microbial strains further confirm
their innovative application in the management of various
pollutants. |
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| Microbes
- For Ecofriendly Environment |
| As on
date the most reliable strategy is biodegradation by
eco-friendly microbes, which is generally accepted as
an environmentally sound and economically feasible protocol
for the treatment of hazardous waste and effluents.
Hence microbes are the tribute for clean environment. |
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