1

Microorganism Removal of Xenobiotic CompoundsSahana VM.Tech, Biosciences and Engineering,DIAT

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2 Xenobiotic- What?

Xenos= Foreigner Bios= Life

Eg: Antibiotics- Human body Environmental Pollutants-

Accumulate in the environment

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3 Properties

High Molecular Mass

Low solubility in water

Condensed benzene and

pyridine rings: Polycyclic Structures

3- fold substituted N atoms

Quaternary C atoms

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4

Xenobiotics- A few examples

compoundsPesticides

Pollutants

Polyaromatic, chlorinated and nitro aromatic

Synthetic Azo Dyes

Polycyclic Hydrocarbons

More than 20,000 compounds are found to be toxic to human beings

Naphthalene

Methyl red

Dioxins

Endosulfan

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5 Effect of Xenobiotics

Health Effects• Mutagenicity• Teratogenicity• Carcinogenicity• Allergenicity

Soil Effects• Assimilated by

plants• Transported

with soli eroding particles to water

• Accumulation in the animal food chain

Water Effects• Sedimentation

of the hydrophobic pollutants

• Change in Physicochemical characteristics

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6 Biodegradation- Role of Microbes Great versatility of microbes

Simpler, economical more environmental friendly strategy

Bacterial - efficient in biotransformation processes

Strategies for obtaining energy from virtually every compound under oxic or anoxic conditions By using ultimate electron acceptors

such as nitrate, sulfate and ferric ions. Benzene ring next to glucosyl- to break

resonance structure10/20/2014

7

Criteria for BiodegradationBiodegradabilit

y

Mineralization potential

Availability of carbon and

energy

Availability of nutrients - N,

P

Extent and distribution

of contaminant

s

Electron acceptor

availability and redox condition

Sufficient number of degraders

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8

Some ExamplesTarget Compounds Bacteria degrading the

compoundsReferences

Endosulfan Compounds Mycobacterium sp. Sutherland et al., 2002

DDT Dehalospirilum multivorans Chaudhry and Chapalamadugu, 1991

Benzene Dechloromonas sp. Coates et al., 2001

Dioxins Dehalococcoides sp. Bunge et al., 2003

RDX Desulfovibrio sp. Boopathy and Kulpa, 1998

Petroleum products Achromobacter sp.Acinetobacter sp.Micrococcus sp.Nocardia sp.Bacillus sp.Flavobacterium sp.

Austin et al., 1977

Azo dyes Bacillus sp.Pseudomonas sp.Sphingomonas sp.Xanthomonas sp.

Dykes et al., 1994Stolz, 2001Stolz, 2001Reife and Freeman, 2000

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9 Biochemical Pathway

Path

way Aerobic

Anaerobic

Co-metabolism

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10Aerobic Pathway

Polycyclic Compounds

• Oxygenation

Dihydroxy aromatic

compounds• Ortho/ Meta

Cleavage

Tircarboxylic acid cycle

intermediates

Eg: The reductive decolourization of sulfonated azodyes are efficiently accomplished by miscellaneous strains such as Pseudomonas, Sphingomonas, Xanthomonas, Aeromonas and Bacillus (Stolz, 2001)

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11 Aerobic Biodegradation of Benzene

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12 Catechol to Acetyl-CoA

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13 Anaerobic Pathway

DealkyaltionNitro reductionHydrolysisDechlorinatio

nHalorespiration

Eg: Phthalate compound degradation is mainly carried out by anaerobic methanogens (Methanospirillum hungatei, Methanosaeta concilii, Syntrophobacter fumaroxidens), producing acetate and methane as end products by decarboxylation initially, then reduction followed by ring cleave and ultimately pave to the β-oxidation pathway (Qiu et al., 2004; Zhang and Bennet, 2005).

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14 Chlorinated Aliphatic Hydrocarbons Biodegradation

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15 Co-metabolic pathway

Cometabolism

Aerobicmicrobial metabolism of another compound

with oxygen

Anaerobicmicrobial metabolism of another compound

in an environment devoid of oxygen

• Cometabolism - transformation of an organic compound by a microorganism that is unable to use the substrate as a source of energy

• Metabolites or transformation products from cometabolism by one organism can typically be used as an energy source by another

• Ensign et al. (1992) reported that pure cultures of Xanthobacter sp. cometabilized TCE with the utilization of propylene as a substrate using the enzyme alkene monooxygenase

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16Cometabolic bioremediation substrates, enzymes, contaminants

Hazen (2009)10/20/2014

17 Fate of Biodegradation

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18 Bioremediation- For Large Scale

Types

Biotransformation Biodegradation Mineralization

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19 ex- situ Techniques

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20 Steps of in situ Bioremediation

Madsen, 1991 10/20/2014

21 Future Perspective

Organo sulphide compounds -to be explored. The efficiency - significantly improved by addressing key issues as

tolerance to various xenobiotics, constitutive expression of the catabolic genes and the substrate-specificity, kinetics The stability of the encoded enzyme.

The utility of constructed organisms in dealing with problems related to environmental pollution in nature is yet to be tested.

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22 Take- Home Message Xenobiotics are everywhere and that has to be removed

Reference: Shelly Sinha et al. Microbial transformation of xenobiotics for environmental bioremediation. African Journal of Biotechnology Vol. 8 (22), pp. 6016-6027, 16 November, 2009

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