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Microbial Degradation of Organic
Pollutants
Biodegradation: Process in which highly complex substances are broken down into simpler
products by the action of microbes
Mineralization: The breakdown of organic compounds into inorganic forms by microbes
Xenobiotics: Man-made synthetic organic compounds which are partially or completely
non-degradable and create pollution problems
- Ex
...
Bioconcentration
2
...
Crude oil, refined oil, phosphates, heavy metals
Xenobiotics: chemically synthesized compounds that have never occurred in nature
Ex
...
Oxidation of TCA (Trichloroacetic acid) by methanotrophic bacteria which grow on
methane (CH4)
- TCA is the most frequent pollutant and is resistant to biodegradation

Factors which Affect Biodegradation
These include:
- Environmental factors
- Microbial characteristics
- Physio-chemical properties of pollutants
Environmental Factors
These include
- Oxygen
- Nitrogen level
- Temperature
- Water activity (Humidity)
- Organic matter
- pH level
- Salinity
Microbial Characteristics
-

Genetic potential
Presence of degrading genes

Physio-Chemical Properties of Organic Pollutants
-

Bioavailability
Toxicity
Structure

Biodegradation of Natural Organic Compounds

The ability of the microorganisms that degrade the natural organic compound benefit human
beings in 3 ways:
1
...
CO2 evolved is used for photosynthesis
3
...
Proteins: most often proteins are associated with polysaccharides and tannins and are
resistant to decay
- Attacked by:
- Streptomyces, penicillium
B
...
Chitin: it is an important source of carbon
- Easily degraded by actinomycetes (streptomyces) under aerobic conditions and
other bacteria such as pseudomonas, bacillus, clostridium
D
...
Cellulose and Hemicellulose: cellulose is a polymer of D-glucopyranose
- Under aerobic conditions a number of fungi can degrade: chaetomium,
trichoderma, penicillium, clostridium, aspergillus, alternaria, fusarium

Degradation of Organic Pollutants
Sources of Chemical pollutants:
- Textile industries
- Transport
- Electronics
- Defense

-

Agriculture (fertilizers & pesticides)

Various Categories of Environmental Pollutants
Pollutant (Hydrocarbon type)

Names

Aliphatics

Propane(gas), Hexane (liquid/solid),
Hexatiacontane (solid)

Substituted aliphatics

Chloroform, TCE

Alicyclics

Cyclohexane (liquid), Cyclopentane (liquid)

Aromatics

Benzene (liquid), Naphthalene(solid)
Phenanthrene (solid)

Heterocyclic

Pyridine(liquid), Thiophene (liquid)

Pesticides

A large group: insecticides, herbicides,
nematicides, fungicides

Aliphatic Group
Common sources:
- Petroleum
- Detergents
- Solvents
- Alkanes
- Alkenes
- Chlorinated aliphatic
Aliphatic are readily biodegradable
Monooxygenases as well as dioxygenases are involved in their breakdown
TCE (Trichloroethylene) is extensively used as industrial solvent
All have been detected in groundwater near industries

How Biodegradation of Aliphatics Occurs

It occurs in 3 steps:
1
...
Oxidation
3
...
g
...
White rotting fungus
Phanerochaete chrysosporium degrade pesticide like DDT and 2,4-D herbicide

Substituted Aromatics

These are chlorinated aromatics and have been extensively used as solvents, fumigants, and
wood preservatives
These are also basic compounds in many pesticides
Degraded with difficulty by the microbes
These compounds are attacked on the methyl group
Bacteria and fungi e
...
Phanerochaete chrysosporium (fungus) is able to degrade at minimal
level

Pesticides
It is the biggest source of chemical pollutants in the environment
The organic pesticides are easily degradable
The synthetic pesticides are difficult to biodegrade
One of the major problem of pesticides is biomagnification
Biomagnification: when a pesticide leaves its residual effect in an organism to a level of
concentration higher than its environmental and becomes toxic to the organism

Some Pesticides and Their Persistence
Pesticide

Persistence

Aldrine

More than 15 years

Chlordane

More than 15 years

DDT

More than 15 years

Endrine

More than 14 years

Heptachlor

More than 14 years

Lindane

More than 14 years

Parathion

More than 16 years

Microbial Biodegradation of Pesticides
3 Types of mechanisms are involved for their breakdown:
1
...
Degradation by sunlight
3
...
Plastics

Metabolic Processes which take Place in Microbes for
Biodegradation
1
...

3
...


Fermentation
Anaerobic metabolism
Metabolism through exoenzymes
Adaptation to adverse environment through mutation

Metabolic Processes
The microbes biodegrade these pesticides by enzymatic or non-enzymatic processes
These compounds are biotransformed through:
- Oxidation
- Reduction
- Hydrolysis
- Condensation
Synthetic pesticides mostly contain hydrocarbons skeletons with a variety of substitutes e
...

- Halogens
- Amino group
- Nitro group
- Hydroxy group
Aliphatic hydrocarbons are oxidized to fatty acids

-

Fatty acids are then degraded to beta-oxidation

Some Examples of Microbes which Degrade Pesticides
Pesticides

Name of Microbes

DDT, Lindane

Aerobacter aerogenes, E
...
textiles, leather, pesticides and paints
Microbes are also involved in deterioration of agriculture produce
- Ex

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