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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