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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.
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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