This document summarizes microbial degradation of various xenobiotics and pollutants. It discusses how microbes like bacteria, fungi and actinomycetes are able to degrade compounds like hydrocarbons, PAHs, pesticides, dyes and other xenobiotics. The microbes produce enzymes that allow them to use these compounds as carbon and energy sources and breakdown the compounds into simpler molecules like carbon dioxide and water.

1. MICROBIAL DEGRADATION OF
XENOBIOTICS
DONE BY:
SHRUTHI K
II M.SC MICROBIOLOGY

2. • In Bioremediation, sites contaminated with xenobiotics are cleaned up in
situ using microorganisms.
• Petroleum products, aliphatic and aromatic hydrocarbons, solvents,
pesticides and metals are reduced.
• In recent years, a number of compounds previously considered non-
biodegradable are being degraded by microbes.
• Engineered microbes are being used to degrade xenobiotics by metabolic
engineering.
• Microbes can reduce various classes of hydrocarbons.

3. • PAHs are composed of fused, aromatic rings whose biochemical
persistence arises from dense clouds of π-electrons on both sides of the
ring structures making them resistant to nucleophilic attack.
• Pseudomonas spp., Burkholderia cepacia, Sphingomonas spp.,
Flavobacterium spp., Cycloclasticus spp., and Stenotrophomonas spp.,
have been proven to metabolize a large number of PAHs.
• Fungi : Phanerochaete chrysosporium (lignin), Pleurotus spp., Trametes
spp., and Bjerkandera spp.,
• Actinomycetes: Gordonia spp., and Rhodococcus spp.,(fluoranthene,
pyrene)

4. • They possess key enzymes, such as PAH dioxygenase and catechol
oxygenase.
• The effective lignin- and PAH degradation by Phanerochaete
chrysosporium is attributed to the nonspecific oxidoreductases secreted
by the fungi, among which lignin peroxidase (Lip) and manganese
peroxidase (MnP)
Napthalene:
• Fused ring bicyclic aromatic hydrocarbon.
• The aerobic and anaerobic degradation pathways of naphthalene occurs.
After the aldolase and hydroxylase reactions, trans-o-
hydroxybenzylidenepyruvate (tHBPA) is degraded to produce
gentisate or catechol. which is further mineralized to carbon dioxide and
water.

5. X.X. Zhang, S.P. Cheng, C.J. Zhu, S
.L. Sun Microbial PAH-
degradation in soil: degradation
pathways and contributing
factors,

6. Fluorene:
• Tricyclic aromatic hydrocarbon.
• Major component of fossil fuels and their derivatives and is also a
byproduct of coal-conversion and energy related industries.
dioxygenation at C-1, C-2 or at C-3, C-4
extradiol dioxygenase.
cis-dihydrodiols undergo dehydrogenation and then meta-cleavage
Aldolase and decarboxylation
• 1-indanone appears to be a substrate for aromatic hydroxylation yielding
3-hydroxy-l-indanone, which is easily mineralized to carbon dioxide and
water.

7. ENDOSULFAN COMPOUNDS:
• A endosulfan - degrading bacterium (strain ESD) was isolated from soil
inoculum after repeated culture with the insecticide as the sole source of
sulfur.
• Mycobacterium species from the mixed culture demonstrates both the
oxidative and hydrolytic and sulfur-separation endosulfan-degrading
activities.
• Mycobacterium strain is a Gram-positive rod that forms mostly rough,
convoluted and some smoother, cream coloured colonies after 3 d at 28˚C
on either tryptic soy agar, or sulfur-free medium with endosulfan.

8. • Mycobacterium strain ESD did not degrade endosulfan when sulphate,
sulfite or methionine were included in the growth medium in addition to
the insecticide.
• Conversely, endosulfan metabolism was observed in medium when the
insecticide was included in the presence of glutathione, 3-(N-mopholino)
propane sulphonic acid (MOPS), dimethyl sulfoxide (DMSO), cysteine
and sulfolane.
• Presumably the sulfite released by this chemical degradation was being
utilized for growth.
• The hydrophobic cell surfaces of Mycobacteria have been proposed to
increase contact with the organic matter and therefore with the
hydrophobic contaminant.

9. • Sulphate-starvation-induced stimulon (SSIS) proteins are thought to
play a role in scavenging alternative sulfur sources
• The absence of endosulfan-degrading activity in the presence of
sulphate and the biphasic utilization of sulphate then endosulfan as
sulfur sources suggest that the endosulfan degradative activities
observed in Mycobacterium strain ESD are part of the SSIS response in
this strain.

10. ATRAZINE:
• Pseudomonas sp. strain ADP is able to degrade atrazine as a sole
nitrogen source and therefore needs an additional carbon and energy
source for growth.
• Besides the typical C source for Pseudomonas, Na2-succinate, the strain
can also grow with phenol as a carbon source
• With atrazine as an N source, the strain was able to degrade phenol in
amounts of up to 1,000 mg/liter. At higher concentrations, even
completely adapted cells were no longer able to grow.

11. • In the presence of cyanuric acid, the strain degraded phenol much
faster. At higher concentrations, the toxic effects of phenol seem to
reduce the growth rate of the cells.
• These data showed that it was possible to cultivate Pseudomonas sp.
strain ADP with phenol as a sole C and energy source and
simultaneously with atrazine or cyanuric acid as an N source.
• Phenol is usually degraded via the catechol degradation pathway. There
are two pathways for catechol ring fission,
the meta and ortho pathways
• This is the first description of the simultaneous degradation of two
hazardous compounds used by a single bacterium as the C and N
source, respectively.

12. • Divided into four classes: the saturates, the aromatics, the asphaltenes
and the resins.
• The susceptibility of hydrocarbons to microbial degradation can be
generally ranked as follows: linear alkanes > branched alkanes > small
aromatics > cyclic alkanes.
• Bacteria: Arthrobacter, Burkholderia, Mycobacterium, Pseudomonas,
Sphingomonas, and Rhodococcus and 25 other genera.
• Fungi: Talaromyces, and Graphium and yeast genera,
namely, Candida, Yarrowia, and Pichia
• Algae: Prototheca zopf

13. • initial intracellular attack of
organic pollutants is an oxidative
process and the activation as
well as incorporation of oxygen
is the enzymatic key reaction
catalyzed by oxygenases and
peroxidases.
• Peripheral degradation pathways
convert organic pollutants step
by step into intermediates of the
central intermediary metabolism,
for example, the tricarboxylic
acid cycle.

14. • Mechanisms involved are (1) attachment of microbial cells to the
substrates and (2) production of biosurfactants .
Microbial Degradation of Petroleum Hydrocarbon Contaminants:
An Overview by Nilanjana das and Preethy Chandran.

15. • Cytochrome P450 alkane hydroxylases play an important role in
the microbial degradation of oil, chlorinated hydrocarbons, fuel
additives.
• Yeast: Candida maltosa, Candida tropicalis, and Candida
apicola
• Alkaneoxygenase systems in prokaryotes and eukaryotes are
involved in degradation of alkanes under aerobic conditions.
Cytochrome P450 enzymes and membrane-bound copper
containing methane monooxygenases

17. • The excessive discharge of the effluents from the textile industries
contains toxic chemicals such as azo dyes affect the natural resources.
• It increases the biochemical oxygen demand (BOD) and chemical
oxygen demand (COD).
• Azo dyes are the largest class of synthetic aromatic dyes composed with
one or more ( N=N ) groups and sulfonic (-SO3 groups.
• Generally, azo dyes contain one, two or three azo linkages, linking
phenyl, naphthyl rings that are usually substituted with some functional
groups including triazine amine, chloro, hydroxyl, methyl, nitro, and
sulphonate

18. •10% of the dyes used in dyeing process do not bind to the fiber and are
released into the environment.
•They possess toxicity like lethal effect, genotoxicity, mutagenicity, and
carcinogenicity to plants and animals.
•Microorganism can be used to completely degrade the azo dyes, because
microorganisms reduce the azo dyes by secreting enzymes such as laccase,
azo reductase, peroxidase, and hydrogenase.

19. • Non-specific degradation
• Bacteria: Bacilus subtilis,
Pseudomonas sp, Escherichia
coli, Rhabdobacter sp,
Enterococcus sp, Staphylococcus
• Used as sole source of carbon
and nitrogen and others reduce
azo dyes by oxygen tolerant azo
reductases.
• Azo dyes are not readily
metabolized under aerobic
condition and are degraded into
intermediate compounds but not
mineralized. Aerobic- anaerobic
coupled reaction.
M.Sudha, A.Saranya, G. Selvakumar
and N. Sivakumar Microbial
degradation of Azo Dyes: A review

20. Azo undergoes to generate
aromatic amines under
anaerobic condition
Mineralized by non-specific
enzymes cleaving ring by
aerobic method
Color removal was obtained
with a high efficiency in
anoxic or anaerobic culture

21. • Fungi : Phanerochaete chrysosporium, Rhizopus oryzar, Pleurotus
ostreatus, Rigidoporus lignosus, Pycnoporus sanguineus,
Aspergillus flavus, and Aspergillus niger.
• White-rot fungi produces lignin peroxidase, manganese peroxidase
and laccase that degrades many aromatic compounds.
• Lignin peroxidase plays a major role in the degradation of azo dyes
using P. chrysosporium

24. • X.X. Zhang, S.P. Cheng, C.J. Zhu, S.L. Sun Microbial PAH-
degradation in soil: degradation pathways and contributing factors,
Pedosphere, 16 (2006), pp. 555-565
• Sutherland TD, Home I, Harcourt RL, Russel RJ and Oakeshott JG
(2002) Isolation and characterization of a Mycobacterium strain that
metabolizes the insecticide endosulfan. J Appl Microbiol 93:380–389
• Microbial Degradation of Petroleum Hydrocarbon Contaminants: An
Overview by Nilanjana das and Preethy Chandran.
• M.Sudha, A.Saranya, G. Selvakumar and N. Sivakumar Microbial
degradation of Azo Dyes: A review, Int.J.Curr.Microbiol.App.Sci
(2014) 3(2): 670-690