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Presented by-
Panchali das
M.ScBiotechnolgy
3rd sem, BBAU
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Biopesticides –Bacillus thuringiensis
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Introduction
As defined by the United States Environmental
Protection Agency (EPA), biopesticides are
pesticides derived from such natural materials as
animals, plants, bacteria and certain minerals.
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Types Divided into three main groups:
Microbial Pesticides: Their active ingredient is a
microorganism that occurs naturally. The microorganisms
used in microbial biopesticides are bacteria, fungi,
nematodes, protozoa, yeast and viruses.
Biochemical Pesticides: Naturally occurring substances
that control pests by non-toxic mechanisms.
Include substances, such as insect sex pheromones, that
interfere with mating, as well as various scented plant
extracts that attract insect pests to traps.
Plant Pesticides: Pesticidal substances that plants
produce from genetic material that has been added to
the plant.
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Microbes used as Biopesticides
Bacteria- Bacillus thuringiensis, commonly referred to as “Bt.”
Certain strains of Bacillus subtilis, Bacillus pumilus, Pseudomonas spp. and Streptomyces spp. increase yield and prevent plant diseases by outcompeting plant pathogens in the rhizosphere, producing anti-fungal compounds, and by promoting plant and root growth.
Viruses- Cydia pomonella granulosis virus (CpGV), cytoplasmic polyhedrosis virus {Cypovirus (CPV)}
Protozoan- Nosema ceranae
Fungi- Aschersonia aleyrodis , Metarhizium anisophliae
Require a wide host range , can cause allergies in man , in few cases they can infect man.
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Table:11 Summary of desirable characteristics required
by microbial pesticidesCharacteristic Bacteria Fungi Viruses Protozoa
Time to kill Good Poor Poor Poor
Easy to apply Yes Yes Yes Yes
Storage
Characteristics
Good Poor Good Poor
Environmental
stability
Poor Poor Poor Poor
Safe to non target
organisms
Yes Yes Yes Yes
Easy to produce Yes Yes Poor Poor
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Biopesticide
Microbial Pesticides Bacteria
Biochemical Pesticides
Biological Control Agents
Bacillus
thuringiensis
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Bacillus thuringiensis
Bt is an aerobic or anaerobic facultative and
sporulating bacterium.
It can remain latent in the environment even in
adverse conditions for its development.
Bt can be found in soil, insects and their habitats,
stored products, plants, forest, and aquatic
environments.
B. thuringiensis can also serve as a source of toxic
genes that can be expressed in plants and thus
confer toxic property against different species of
insect pests.
They have no toxicity to human & there is no
withholding period on produce sprayed with Bt.
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Contd..
Bt is used mainly to control larvae of insects in the Lepidoptera order (butterflies and moths).
It should be applied to the underside of leaves because:
most larvae feed on the underside of the leaves.
Bt breaks down faster in sunlight which will reduce its effectiveness.
This bacterium differs from other species belonging to this genus by the presence of a parasporal inclusion body (crystal) of protein origin, formed during sporulation.
These crystals are predominantly comprised of one or more proteins (Cry and Cyt toxins), also called δ-endotoxins.
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What are Cry proteins? Cry proteins are a large family of crystalline toxins
produced by Bacillus thuringiensis.
Each Bt species/ strain produces a unique set of
CRY proteins.
Genes that express the delta- endotoxins are called
“cry genes” due to their crystalline phenotype.
Located on plasmids of large molecular weight.
Similarly, Cyt proteins are parasporal inclusion
proteins from Bacillus thuringiensis that exhibits
hemolytic (Cytolitic) activity.
Bt Cry and Cyt toxins belong to a class of bacterial
toxins known as pore-forming toxins (PFT) or δ-
endotoxins.
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Contd..
There are two main groups of PFT:
(i) the α-helical toxins,(includes Cry proteins) to this
the α-helix region of the protein form a pore in the
membrane and
(ii) the β-barrel toxins,(includes Cyt proteins) these
insert into the membrane by forming a β-barrel
composed of βsheet hairpins from each monomer.
In general, PFT producing-bacteria secrete their toxins
and these toxins interact with specific receptors
located on the host cell surface.
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Diversity and Structure of Cry toxins
Cry proteins are specifically toxic to the insect
orders:
Lepidoptera (butterflies and moths)
Diptera (flies and mosquitoes)
Orthoptera (grasshoppers and crickets)
Homoptera (aphids)
Coleoptera (beetles).
Cyt toxins are mostly found in Bt strains active
against Diptera.
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Contd..
Primary sequence identity among different gene sequences is the bases of the nomenclature of Cry and Cyt proteins and within each family there may be further levels or ranks of subfamily.
The cry genes were classified into four major classes based on their protein toxicity.
Cry I : Lepidopteran specific.
Cry II : Lepidopteran and Dipteran specific.
Cry III : Coleopteran specific.
Cry IV : Dipteran specific.
Cry v & vi : Nematodes
The members of the three-domain family, the larger group of Cry proteins, are globular molecules containing three structural domains connected by single linkers.
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Contd..
1 2 3
Activated Toxin...
.
.
.
.
..
.
.
.
.
.
Cry 1A
Cry 1B
Cry 3A
Truncated forms in transgenic plants
0 600 1200
Amino acid residues
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Comparison of the structures of different classes of Cry protein
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Structure of activated toxin demonstrating three distinct domains.
Contd..
Mode of action16
Anticarsia gemmatalis
Application of Bt technologies Bt products-
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Monterey Bt (Bacillus thuringiensis) is a
naturally occurring soil bacteria ideal
for controlling cabbageworm, tent
caterpillars, gypsy moth, tomato
hornworm and other leaf eating
caterpillars.
Safer Garden Dust is a highly selective
biological pesticide containing Bacillus
thuringiensis to control leaf-eating
caterpillars and worms. After ingesting
a treated portion of the leaf,
caterpillars stop feeding within a few
hours. Death occurs in a few days.
Contd.. Bt Plants-
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Advantages Difficult for insects to develop resistance to these
pesticides.
Ability to multiply in the target cells.
No problem of toxic residue.
Permanent control of pest or long persisting effect.
No fear of environment pollution and hence
ecofriendly.
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Unprotected Cabbage Bt-protected Cabbage
Disadvantages
Rapidly degraded by UV light so residual action is
slow.
Difficulty of culturing in large quantities.
All products applied followed by growers have not
been scientifically verified.
Biopesticide is more costly and less readily available
than conventional pesticide. Farmers with large
crops may find it difficult to consistently use
Biopesticide.
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References
www.ncbi.com
Plant Biotechnology - The genetic manipulation of plants ,
Second Edition-Adrian Slater, Nigel Scott, and Mark Fowler
http://www.biology.50webs.com/bt.htm
en.wikipedia.org/wiki/Bacillus_thuringiensis
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