1. Microorganism Removal of
Xenobiotic Compounds
Sahana V
M.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
compounds
Pesticides
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 structure
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7. Criteria for Biodegradation
Biodegradability
Mineralization
potential
Availability of
carbon and
energy
Availability of
nutrients - N, P
Extent and
distribution of
contaminants
Electron
acceptor
availability and
redox condition
Sufficient
number of
degraders
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8. Some Examples
Target Compounds Bacteria degrading the
compounds
References
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., 1994
Stolz, 2001
Stolz, 2001
Reife and Freeman, 2000
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9. Biochemical Pathway
Pathway
Aerobic
Anaerobic
Co-metabolism
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10. Aerobic Pathway
Polycyclic
Compounds
• Oxygenation Dihydroxy
aromatic
compounds
• Ortho/ Meta Cleavage Tircarboxylic
acid cycle
intermediatesEg: The reductive decolourization of sulfonated azo
dyes 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 reductionHydrolysisDechlorination
Halorespiration
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
Aerobic
microbial metabolism
of another compound
with oxygen
Anaerobic
microbial 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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16. Cometabolic bioremediation substrates,
enzymes, contaminants
Hazen (2009)
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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
Bio- augmentation
Bio-stimulation
Bio-attenuation
Madsen, 1991 10/20/2014
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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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