AgricultureMicrobiology: Rhizobium Trichoderma Biodegradation of Xenobiotics Biodegradation of Plastics Biodegradation of pesticides

1. Agriculture Microbiology
Rhizobium:
Trichoderma
Biodegradation of Xenobiotics:
Biodegradation of Plastics:
Biodegradation of pesticides:
Dr. Aswartha Harinath Reddy M.Sc, Ph.D
Department of Life Sciences
Srikrishnadevaraya University
Anantapur –A.P. India

2.  Agricultural microbiology is a branch of microbiology dealing
with plant-associated microbes and microbiology of soil
fertility, such as microbial degradation of organic matter and
soil nutrient transformations.

3. Types of Soil Microorganisms:
 Bacteria: More dominant group of microorganisms in the soil and
equal to one half of the microbial biomass in soil.
Common soil bacteria:
 Agrobacterium, Arthrobacter, Bacillus, Alcaligens, Clostridium,
Corynebacterium, Erwinia, Nitrosomonas, Nitrobacter,
Pseudomonas, Rhizobium, Thiobacillus, etc.

4.  Actinomyces colonies form fungus-like branched networks of
hyphae. are known to produce antibiotics.
 Intermediate group between bacteria and fungi.
 They are Gram-positive and release antibiotic substances.
 Actinomyces, Actinoplanes, Micromonospora, Microbispora,
Nocardia, Streptomyces, Thermoactinomyces, etc.

5. Fungi:
 Decomposer or Saprophytes
 Example: Aspergillus, Rhizopus, Penicillium, Mucor,
Tricoderma, Alternaria, Cladosporium,, Fusarium etc.
Protozoa:
 Protozoa are single-celled animals.
 Protozoa believed to be responsible for mineralizing (releasing
nutrients from organic molecules) much of the nitrogen in
agricultural soils.

6. Algae: are present in most of the soils where moisture and
sunlight are available.
 Nostoc, Anabaena, Azolla, Blue green algae, Yellow green
algae.
 Plays important role in the maintenance of soil fertility
especially in tropical soils.

7. Rhizobium:
 Rhizobium is a genus of Gram-negative, Non spore forming,
motile, Microaerophilic soil bacteria that fix nitrogen.
 Rhizobium species form an endosymbiotic nitrogen-fixing
association with roots of legumes where they convert atmospheric
nitrogen into ammonia.

8.  Rhizobia infects the roots of the bacteria. They are usually found
in the soil and after the infection nodules are produced in the
legume.
 As a result, nitrogen gas is fixed from the atmosphere. After this
process, the nitrogen is used for the growth in the legume.
 Once legume dies there will be a breakdown of the nodule. as a
result, rhizobia is released back to the cell where they can affect
a new host.

9.  For nitrogen fixation, the specific strains of rhizobia are
required to make the functional nodules on the root to carry out
the process. This is beneficial to legume as it results in the
increase in crop yield. Legume inoculation has been an
agricultural practice for several years and has constantly
improved over time.

10.  Beside nitrogen fixation, many rhizobial strains exert plant-
growth-promoting traits such as the production of
phytohormones, siderophores and 1-aminocyclopropane-1-
carboxylic acid (ACC) deaminase as well as the solubilization
of inorganic phosphate.
 These make rhizobia become valuable for both legumes and
non-legumes. Effective rhizobial strains have been screened
and used as inoculants for improving plant growth. The
application of rhizobia as biofertilizer ensures success in crop
productivity and reduces the need for artificial fertilizers

11. Trichoderma viride

12.  Trichoderma is a genus of fungi that is present in all soils, where
they are the most prevalent culturable fungi.
 Many species in this genus can be characterized as opportunistic
avirulent plant symbiont.
 This refers to the ability of several Trichoderma species to form
mutualistic endophytic relationships with several plant species

13.  T. viride produces spores asexually, by mitosis, the sexual
reproductive stage of the fungus and produces a typical fungal
fruiting body.
 The mycelium of T. viride can produce a variety of enzymes,
including cellulases and chitinases which can degrade
cellulose and chitin respectively.

14. Uses:
 T. viride useful as a biological control against plant pathogenic
fungi.
 It has been shown to provide protection against such pathogens
as Rhizoctonia, Pythium and even Armillaria.
 It is found naturally in soil and is effective as a seed dressing
in the control of seed and soil-borne diseases including
Rhizoctonia solani, and Fusarium species.

15.  When it is applied at the same time as the seed, it colonizes the
seed surface and kills not only the pathogens present on the
cuticle, but also provides protection against soil-borne
pathogens.
Compatibility:
 Trichoderma is compatible with Organic manure
 Trichoderma is compatible with biofertilizers like Rhizobium,
Azospirillum, Bacillus Subtilis and Phosphobacteria.
 It can be mixed with chemical fungicides as tank mix.

16. Benefits:
 Enhances yield along with quality of produce
 Boost germination rate
 Increase in shoot & Root length Solubilizing various insoluble
forms of Phosphates Augment Nitrogen fixing.
 Promote healthy growth in early stages of crop
 Provides natural long term immunity to crops and soil
 Eliminates the use of costly and harmful chemicals

17. Biodegradation of Xenobiotics

18. Xenobiotics:
 A xenobiotic is a foreign chemical substance found within an
organism that is not produced naturally.
 Specifically, drugs such as antibiotics are xenobiotics in
humans because the human body does not produce them itself.
 Pesticides and plastics also xenobiotics.

19. Biodegradation of hydrocarbons:
 Hydrocarbons are organic compounds that are made of only
hydrogen and carbon atoms.
 They are found in many places, including crude oil, Petroleum
Hydrocarbons and natural gas (e.g. methane and propane), liquids
(e.g. hexane and benzene),

20.  The microorganisms, namely bacterial strains, namely,
 Pseudomonas fluorescens,
 P. putida
 P. aeruginosa,
 Bacillus subtilis,
 Alcaligenes sp.,
 Flavobacterium sp.,
 Corynebacterium sp. were isolated from the polluted stream which
could degrade crude oil.
 Acinetobacter sp. was found to be capable of utilizing n-alkanes of
chain length C10–C40 as a sole source of carbon.

21. 
Algae:
• Botryococcus braunii (Green algae) grows on C30-C36 long
chain petroleum hydrocarbons.
• It contain 30% of petrol in the dry weight of the cell.

22. Fungi in the biodegradation of Hydrocarbons:
 Fungal genera, namely, Aspergillus, Candida, Cephalosporium,
and Pencillium isolated from petroleum-contaminated soil and
proved to be the potential degrader of crude oil hydrocarbons.
 The yeast species, namely, Candida lipolytica, Geotrichum sp,
and Trichosporon mucoides isolated from contaminated water
were noted to degrade petroleum compound.

23. Enzymes Participating in Degradation of Hydrocarbons:
 Cytochrome P450 oxidases (CYP450) are super family of
Monooxygenases which play an important role in the
microbial degradation of petroleum hydrocarbons, chlorinated
hydrocarbons and many other compounds.
 Depending on the chain length, enzyme systems are required
to introduce oxygen in the substrate to initiate biodegradation.

24. There are two types of oxygenases:
• Monooxygenases: or mixed function oxidase, transfer one
oxygen atom to the substrate, and reduce the other oxygen
atom to water.
• Dioxygenases, or oxygen transferases, incorporate both
atoms of molecular oxygen (O2) into the substrates of the
reaction.
• Among the most important monooxygenases are the
cytochrome P450 oxidases, responsible for breaking down
numerous chemicals in the body.

25. Enzymes Substrates Microorganisms
Methane
Monooxygenase
s
C6–C8 alkanes alkenes
and cycloalkanes
Methylococcus,
Methylomonas
Eukaryotic
P450
C10–C16 alkanes, fatty
acids Candida maltosa,
Candida tropicalis
Bacterial P450
oxygenase
system
C5–C16 alkanes,
cycloalkanes
Acinetobacter,
Mycobacterium
Dioxygenases C10–C30 alkanes Acinetobacter sp.

26. 26
Biodegradation of Petroleum compounds
Petroleum compounds are categorized into 2 groups
 Aliphatic hydrocarbon e.g. alkane, alcohol,
aldehyde.
 Aromatic hydrocarbon e.g. benzene, phenol,
toluene, catechol
 H.C. (substrate) + O2 H.C.-OH + H2O
 H.C. (substrate) + O2 H.C.
O
H
O
H
monooxyge
nase
dioxygenase

27. 27
Straight
chain
of
Aliphatic
hydrocarbon
compounds
Bio degradation of
n-alkanes
Monooxygenases:
Monooxygenases
Monooxygenases

28. 28
Bio degradation of
Cyclic aromatic
hydrocarbon
compounds
by
monooxygenases
Monooxygenases
Monooxygenases

29. 29
Aerobic degradation
of aromatic compounds

32. Effects of pesticides:
 Alterations in the soil microbial flora.
 Adverse effect on soil fertility and crop productivity.
 Inhibition of N2 fixing soil microorganisms such
as Rhizobium, Azotobacter, Azospirillum,
Nitrosomonas and Nitrobacter.
 Adverse effect on mycorrhizal symbioses in plants and
nodulation in legumes.

33. Persistence of pesticides in soil:
 The chlorinated hydrocarbon insecticides (eg, Dichloro-
diphenyl-trichloroethane (DDT), aldrin, chlordane etc) are
known to persist at least for 4-5 years and some times more than
15 years.
 Toxic effects of organophosphate and carbamate pesticides
disrupt the enzyme that regulates acetyl-cholinesterase, a
neurotransmitter in the nervous system.

34. Degradation:
 Degradation is often considered to breaking down / transformation
of a complex substrate into simpler products leading finally to
mineralization.
 E.g: Thirum (C6H12N2S4: fungicide) is degraded by a strain
of Pseudomonas and the degradation products are dimethlamine,
proteins, sulpholipids, etc.

35. Table 1: Major groups of pesticides, their target organisms and
common examples
Group of
Pesticide
Target
organisms
Common examples
Insecticides Insects Carbamyl,
Hexachlorohexane (HCH),
DDT, aldrin, endosulfan,
malathione.
Fungicides Fungi Bordeaux mixture,
Pentachlorophenol (PCP)
Herbicides Weeds Atrazine, 2,4D,

36. Microbial potential for degradation of pesticides
 The microbes having the potential for pesticide degradation are
mainly bacteria, especially actinomycetes and cyanobacteria,
the species of Pseudomonas, Alcaligenes, Bacillus,
Arthrobacter, Brevibacterium, Flavobacterium, Klebsiella,
Methylococcus, etc.
 Several fungi having pesticide degrading potential have also
been identified, such as the species of Aspergillus, Candida,
Fusarium, Penicillium, Trichoderma, Rhodotorula, Pleurotus,
Phaenerochaete, etc.

37. Table 2: Bacteria capable of degrading pesticides or their
metabolites
Bacteria Organic compound or
pesticide
Alcaligenes denitrificans Fluoranthene (PAH)
Arthrobacter sp. Carbofuran, Parathion
Desulfovibrio sp. Nitroaromatic compounds
Methylococcus capsulatus Trichloroethylene
Nocardia sp. Quinoline

38. Table 3: Fungi capable of degrading pesticides or their
metabolites
Fungi Organic compound or pesticide
Aspergillus flavus DDT
Aspergillus paraceticus DDT
Aspergillus niger 2,4-D (2,4-Dichlorophenoxyacetic
acid) Herbicide.
Candida tropicalis Phenol
Fusarium oxysporum DDT

39. Biochemical mechanisms involved in microbial degradation of
pesticides.
Oxidative transformations by cytochrome p450
 Oxygenation is the most frequent first step in the
biotransformation of pesticides and other organic xenobiotics.
 Cytochrome P450 oxidases are the most extensively studied
oxidative enzymes and are the most important enzymes in
Phase I pesticide metabolism.

40. Transformation by peroxidases, phenoloxidases, and related
oxidoreductases:
 In addition to P450s, microorganisms produce other oxidative
enzymes (e.g., peroxidase, polyphenol-oxidase, laccase, and
tyrosinase).
 These enzymes can degrade a wide range of pollutants such as
polychlorinated biphenyls (PCBs) and nitroaromatic
explosives.

41. Hydrolytic Transformations:
 Hydrolytic enzymes cleave the bonds of a substrate by adding
-H or -OH group from H2O to each product.
 Example for Hydrolytic enzymes: Esterases, nucleases,
phosphodiesterases, lipase and phosphatase.

42. Biodegradation of 2,4-D by Pseudomonas sp.

43. Biodegradation of Hexa-chlorobenzene by bacteria.

44. Biodegradation of Plastics

45. Plastic:
 Plastic is material consisting of any of a wide range of synthetic
or semi-synthetic organic compounds most commonly derived
from petrochemicals.
 The two most common petrochemical classes are alkenes
(including ethylene and propylene) and aromatics (including
benzene, toluene and xylene isomers).

46. Types of Common plastics:
 Polyethylene (C2H4)n – a wide range of inexpensive uses
including supermarket bags detergent bottles and plastic bottles.
 Polypropylene: bottle caps, drinking straws, and plastic pressure
pipe systems.
 Polycarbonate (PC) –eyeglasses, security windows, traffic lights
and lenses.

47. Effects of Plastic Pollution:
 It Upsets the Food Chain
 Groundwater Pollution
 Land Pollution
 Air Pollution
 It kills animals and humans
 Effect the synthesis of Thyroid hormone and sex hormone.

48. Different steps of plastic degradation by microorganisms:
 Bio-deterioration:
 Bio-fragmentation:
 Assimilation:
 Mineralisation:

49. Bio-deterioration:
 Deterioration is a process it modifies mechanical, physical and
chemical properties of the plastic.
 The bio-deterioration seems to be triggered by the formation of
a microbial biofilm growing on the surface and inside the plastic
material.
 The development of the biofilm is dependent on the composition
and the structure of the plastic, but also on the environmental
conditions.

50.  Biofilm may release acid compounds such as nitrous acid (e.g.
Nitrosomonas spp.), nitric acid (e.g. Nitrobacter spp.) or
sulphuric acid (e.g. Thiobacillus spp.) by chemolithotrophic
bacteria.
 The pH of the plastic is then modified, resulting in a
progressive degradation that changes the microstructure of
the plastic matrix.

51. Bio-fragmentation:
 Plastic polymers are molecules with high molecular weight that
cannot cross the cell wall.
 Bacteria that can break down plastics usually contain enzymes
called oxygenases, which can add oxygen to a long carbon
chain.
 For instance, mono-oxygenases and di-oxygenases incorporate,
respectively, one and two oxygen atoms, forming alcohol groups
that are easily biodegradable.

52.  Assimilation: characterizes to the integration of molecules
transported in to the cytoplasm in the microbial metabolism.
 Mineralisation: refers to the complete degradation of
molecules that resulted in the excretion of completely oxidized
metabolites (CO2, N2, CH4, H2O).

53. Table: The different microorganisms reported to degrade
different types of plastics.
Plastic Microorganism
Polyethylene Pseudomonas putida,
Rhodococcus rubber,
Polyurethane Fusarium solani,
Cladosporium sp.
Polyvinylchloride Pseudomonas putida,
Pseudomonas fluorescens,
Aspergillus niger (Fungi)
Polylactic acid Bacillus brevis
Pseudomonas putida super bug

54. Thank you……………………………..