ROLE OF MICROBES IN DEGRADATION K R.ppt.

1. K R MICRO NOTES 1

2.  According to the definition by the International Union of Pure and
Applied Chemistry, the term biodegradation is “Breakdown of a
substance catalyzed by enzymes in vitro or in vivo”.
 Biodegradation is the process by which organic substances are
decomposed by microorganisms into simpler substances such as
carbondioxide, water, ammonia.
 In other words , defined as the ability of microorganisms to convert
toxic chemicals (Xenobiotics) to simpler non-toxic compounds by
synthesis of certain enzymes.
 Biodegradation of xenobiotics can be affected by substrate
specificity , nutrition source, temperature, pH, etc.
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3.  It is derived from a Greek word “XENOS”means ‘foreign’
 A xenobiotic is a chemical substance found with in an organism that is not
naturally produced.
 Actual meaning xenobiotic are the compounds that are foreign to an
organism for its actual nature.
 Xenobiotics are those chemicals which are man made and do not occur
naturally in nature.
 They are usually synthesized for industrial or agriculture purpose
 E.g. Pesticides, Hydrocarbons, Plastics, Ligin etc.
 They are also called RECALCITRANTS as they can resist degradation to
maximum level.
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4. 1. Petrochemical industry:
-oil/gas industry, refineries
-produce basic chemicals
-e.g. vinyl chloride and benzene
2. Plastic industry:
-closely related to the petrochemical industry
-uses a number of complex organic compounds
-such as anti oxidants, plasticizers, cross-linking agents
3. Others:
-pesticide industry, electronic industry, textile industry, pulp
and paper industry, cosmetics and pharmaceutical industry,
wood preservation
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5.  Pesticides are substances meant for destroying any pest.
 They are a class of biocide
 The most common use of pesticides is as plant protection products(also
known as crop protection products)
 It includes: herbicide, insecticide, nematicide, rodenticide, insect repellent,
animal repellent, fungicide, disinfectant and sanitizer
 DIFFERENT METHODS
a) Detoxification:
 Conversion of the pesticide molecule to a non toxic compound
 A single moiety in the side chain of a complex molecule is
disturbed(removed)
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6. b) DEGRADATION:
 Break down or transformation of a complex substrate into simpler
products leading to mineralization.
 Ex: Thirum (fungicide) is degraded by a strain of pseudomonas and the
degradation products are dimethylamine, proteins , sulpholipids , etc…
c) CONJUGATION:
 An organism makes the substrate more complex or combines the
pesticide with cell metabolites.
 Conjugation or the formation of addition product is accomplished by those
organism catalyzing the reaction of addition of an amino acid , organic
acid, to the substrate thereby inactivating the pesticides.
d) Changing the spectrum of toxicity:
 Some pesticides are designed to control one particular group of pests, but
are metabolized to yield products inhibitory to entirely dissimilar groups of
organisms.
 Ex : Fungicide PCNB is converted in soil to chlorinated benzoic acid that
kill plants
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7.  Plastic is a broad name given to different polymers with high molecular
weight , which can be degraded by various processes.
 It consist of two steps –fragmentation and mineralization but at the core ,
reaction occurring at molecular level are –oxidation and hydrolysis.
 The decomposition of major condensation polymers (polyesters and
polyamides) takes place through hydrolysis.
 The decomposition of polymer in which the main chain contains only
carbon atoms (polyvinyl alcohol, lignin) includes oxidation which can be
followed by hydrolysis of the products of oxidation.
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8.  HYDROLYSIS:
 The process of breaking these chains and dissolving the polymers into
smaller fragments is called hydrolysis. Ex:Pseudomonas sps
 Polymeric chains are broken down into constituent parts for the energy
potential by microorganisms. Monomers are readily available to other
bacteria and is used.
 Acetate and hydrogen produced is used directly by methanogens.
 Other molecules such as volatile fatty acids(VFAs) with a chain length
greater than that of acetate is first catabolized into compounds that can be
directly used by methanogens .
 ACIDOGENESIS:
 This results in further breakdown of the remaining components by
acidogenic (fermentative) bacteria into ammonia, ethanol, carbon dioxide,
and hydrogen sulphide.
 Ex: Streptococcus acidophillus
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9.  Simple molecules created through the acidogenesis phase are further
digested by acetogens to produce largely acetic acid , as well as carbon
dioxide and hydrogen.
METHANOGENISIS:
 Here methanogens use the intermediate products of the preceding stages
and convert them into methane , carbon dioxide and water.
 These components make up the majority of the biogas emitted.
 Methanogenesis is sensitive to both high and low pH and occurs between
pH6.5and pH 8. The remaining , indigestible material the microbes cannot
use and any dead bacterial remains constitute the digestate.
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10.  Aliphatic polyesters
 Polyethylene adipate (PEA): Lipases from R. arrizus , R. delemar,
Achromobacter sps. And Candida cylindracea
 Poly (β-Proplolactone) PPL: estereases from Acidovarax sps,
Variovarax paradoxous, Sphingomonas paucimobills
 Aromatic polyesters:
 Poly-3-Hydroxybutyrate (PHB): estereases from Pseudomonas
lemoigne , Aspergillus fumigatus
 Poly lactic acid (PLA): proteinase K from Tritirachium album,
Amycolatopsis sps.
 Strains of Actinomycetes has been reported to degrade Polyamide
, Polystyrene, Polyethylene.
K R MICRO NOTES 10

11.  A Hydrocarbon is an organic compound consisting entirely of hydrogen and
carbon
 The majority of hydrocarbons found on earth naturally occur in crude oil.
 Aromatic hydrocarbons , alkenes, alkanes, cycloalkanes, alkyne based
compounds are different types of hydrocarbons.
K R MICRO NOTES 11

12.  Chemicals derived from petroleum or natural gas
Petroleum compounds are categorized into 2 groups
1. Aliphatic Hydrocarbon:Eg- Alkane, alcohol, aldehyde
2. Aromatic Hydrocarbon:Eg- benzene, phenol, toluene, catechol
 A huge variety of products are made with petrochemicals
 Including plastics, soaps, pharmaceuticals, fertilizers, pesticides, and
detergents.
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13.  Organic pollutants
 Phenolic compound
 Benzoate compound
 Surfactants
 Organisms
 Achromobacter, Candida,
Alcaligenes, Acinetobacter,
Arthrobacter, Flavobacterium,
Trichosporon, Aspergillus,
Pencillium
Arthrobacter, Bacillus sps,
Micrococcus,
P. putida
Achromobacter, bacillus,
Flavobacterium, Candida,
Pseudomonas
K R MICRO NOTES 13

14.  Bacteria, fungi, yeast, and algae have the ability to metabolize both lower
and higher molecular weight PAHs found in the natural environment.
 Most bacteria have been found to oxygenate the PAH initially to form
dihydrodial with a cis-configuiration which can be further oxidized to
catechols.
 Most fungi oxidize PAHs via a cytochrome P catalyzed mono – oxygenase
reaction to form reactive arene oxides that can isomerizes to phenols.
 White – rot fungi oxidizes PAHs via ligninases (lignin peroxidases and
laccase )to form highly reactive quinones.
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15. K R MICRO NOTES 15

16.  COMPOUND
 Naphthalene
Acenaphthene
Pyrene
 Chrysene
 ORGANISMS
Mycobacterium sp..,
Pseudomonas Sp.., P. putida
Alcaligenes denitrificans,
Pseudomonas putida, pseudomonas
flurorescens, pseudomonas
cepacia
Alcaligenes denitrificans,
Mycobacterium Sp..,
Rhodococcus Sp..
Rhodococcus Sp..
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17.  Synthesized chemicals from petrochemical industry used as lubricants and
insulators in heavy industry.
 First manufactured in 1929 by Monsanto
 Used because of
• Low reactivity
• Non – flammable
• High electrical resistance
• Stable when exposed to heat and pressure
 Used as Hydraulic fluid , Casting wax, Compressors, Heat transfer system,
Pigments, Liquid cooled electric motors, Fluorescent lights.
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18. K R MICRO NOTES 18

19.  Causes reproductive disabilities in animals humans and birds.
 Carcinogenic
 Bio accumulation
 Soluble in almost all the solvents, fats, oils.
 Nervous system damage
 Endocrine gland malfunction
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20. 1) http://www.intechopen.com
2) http://www.sciencedirect.com
3) http://www.researchgate.com
4) Microbial Biodegradation by Jarvo M. David
5) Microbial metabolism of Xenobiotic compounds by P .
K. Arora
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