What Is Bacillus thuringiensis Its Structure Mode of Action and Applications
It is also known as Bt, it is a gram-positive bacteria found in soil. It is commonly used as a pesticide. It is also found naturally in the guts of butterflies, several types of moths, and caterpillars. This paradise can also cause disease in some of the moths such as Cadra calidella. The B. thuringiensis was first discovered in 1902, in silkworms by a sericulture engineer of Japan and named it B. Sotto. Then later in 1911, Ernst Berliner a German microbiologist rediscovered the Bt in the diseased moths found in Thuringia, thus the species name. Bt is closely related to B. cereus and B. anthracis in which it is found in soil and can cause anthrax respectively. All these three organisms vary mainly depending on the plasmids present in them.
Bacteria Bacillus Thuringiensis
The scientific classification of Bt is as follows:
Domain: Bacteria
Phylum: Firmicutes
Class: Bacilli
Order: Bacillales
Family: Bacillaceae
Genus: Bacillus
Species: B. thuringiensis
Thus leading to the binomial nomenclature named Bacillus thuringiensis.
Structure:
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As the Bacillus thuringiensis is a gram-positive bacteria it has a thick cell wall. This cell wall is made up of peptidoglycan. In between the cell wall and a plasma membrane a periplasmic space is present. This space is a small section that is responsible for protection and biosynthesis. It has a circular-shaped chromosome. It has many plasmids. The Bt strains produce the crystal proteins during the process of sporulation called -endotoxins.
Use of Bacillus Thuringiensis
The environment protection agency approved a CRY 3A Bt toxin that was produced from potato plants in 1985. It is the first human-modified pesticide that produces crops.
The European corn borer was killed by Bt Cry protein produced from genetically modified maize in 1996. The Bt genes were introduced in the corn there and it killed the corn rootworm larvae.
By 2014 in India more than seven million farmers have adopted the Bt cotton by occupying the 2 million hectares
Bacillus Thuringiensis Products
Bt is a naturally occurring bacteria, that consists of spore where the protein inside it is toxic. This spore is persistence. Depending on the subspecies the toxic proteins differ. When the toxic protein gets inside the gut of the insect, the toxic crystal is released and it makes the gut highly alkaline. This makes the insect get favored from the digestive juices thus the insect dies due to poisoning. But in the case of mammals, birds, and fish due to their acidic gut, it makes it difficult to survive the bacteria.
Some of the Bacillus thuringiensis products are used as,
Bt Kurstaki (Bt-k) – Bacillus thuringiensis var kurstaki: Bt-k is a naturally occurring bacteria. It helps in the ideal control of tomato hornworm, cabbage looper, and other leaf-eating caterpillars found in trees, tomatoes, shrubs, and other vegetables. In the first and second instars if the caterpillars are given with the Bt-k it is more effective. It can degrade quickly in the sunlight, thus under heavy insect pressure, reapplication is required.
Bt Israelensis (Bt-i) – Bacillus thuringiensis var israelensis: It is a biological pesticide that is highly specific and used against mosquito, fungus gnut larvae, and black fly. Anyplace that has standing water Bt-i can be injected in order to kill the larvae, once it is injected it can kill up to 95% of the larvae within 24 hours.
Bt San Diego (Bt-sd) – Bacillus thuringiensis var san Diego and Bt tenebrionis (Bt-t) – Bacillus thuringiensis var tenebrionis: A Colorado potato beetle has very resistant to multiple applications of insecticides. These two can control the leaf-eating beetle species to a limited range. These can be applied only to the larvae as in adults the effect is found to be very small.
Bacillus Popilliae: Milky spore is a disease caused to Japanese beetle larvae succumb to the Bacillus popilliae bacteria. The bacteria spreads normally by killing each of the larvae.
Bacillus Thuringiensis Application
Used in biotechnology, through genetic engineering, it can be introduced into the crops. Bt crop varieties are invented to produce the protein toxic to certain specific insects and are used in the areas where the pests are targeted. Bt cotton, corn, rice, and potato commercial production was increased in many of the countries. Bacillus thuringiensis biopesticide has become a boon for the farmers to protect their crops.
Golden rice that is rich in vitamin A is produced.
Conclusion:
The process of creating a new species with the selected traits is genetic engineering. Bt is a soil-dwelling bacterium that produces certain toxic proteins. These proteins are dangerous to herbivorous insects. To apply Bacillus thuringiensis spray some tips have to be followed, if the larvae are small and Bt is injected at that time then it is more effective. If the pH is more than 8 then this level activates the toxin in the insect’s gut thus this pH level is to be managed. If the spray is mixed then it should be applied within twelve hours for effective results and the spray is to be applied to both sides of the leaves. The bacteria can live in the ground for years but if it gets absorbed then the UV radiation from the sun can destroy it. Thus most people spray the Bt during the evenings to work on the insects overnight as during the daytime the bacterium can be inactivated by the radiations. These are sensitive to temperature and can be stored within 50 to 60 F. While storing the bacillus thuringiensis insecticide some of the precautions have to be followed.
FAQs on Bacillus thuringiensis and Its Role in Biological Pest Control
1. What is Bacillus thuringiensis?
Bacillus thuringiensis (Bt) is a Gram-positive, soil-dwelling bacterium that produces insecticidal proteins toxic to specific insect larvae. It is commonly used as a biological pesticide in agriculture. Bt forms spores and synthesizes crystalline proteins called Cry toxins during sporulation, which target insects such as caterpillars, mosquitoes, and beetles. Because of its specificity, Bt is considered environmentally friendly compared to chemical insecticides.
2. How does Bacillus thuringiensis kill insects?
Bacillus thuringiensis kills insects by producing Cry toxins that disrupt the insect’s gut lining. The process occurs in several steps:
- Insect larvae ingest Bt spores or Cry proteins.
- The alkaline gut environment activates the Cry toxin.
- The toxin binds to specific receptors in the midgut epithelial cells.
- Pores form in the gut wall, causing cell lysis and death.
3. What are Cry toxins in Bacillus thuringiensis?
Cry toxins are crystalline insecticidal proteins produced by Bacillus thuringiensis during sporulation. These proteins are encoded by cry genes and are toxic to specific insect groups. Different Cry proteins target different insect orders, such as:
- Lepidoptera (moths and butterflies)
- Diptera (flies and mosquitoes)
- Coleoptera (beetles)
4. Why is Bacillus thuringiensis considered safe for humans?
Bacillus thuringiensis is considered safe for humans because its Cry toxins are activated only in the alkaline gut of specific insects. Humans and other mammals have acidic stomach conditions and lack the specific gut receptors required for toxin binding. Additionally:
- Bt does not infect healthy human tissues.
- It has been used in agriculture for decades with a strong safety record.
5. What is Bt cotton?
Bt cotton is a genetically modified cotton plant that contains cry genes from Bacillus thuringiensis to resist insect pests. The inserted gene enables the plant to produce Cry toxin in its tissues. As a result:
- The plant becomes resistant to pests like the cotton bollworm.
- Farmers reduce the use of chemical insecticides.
6. What is the difference between Bt crops and Bt spray?
The main difference between Bt crops and Bt spray is that Bt crops produce Cry toxins internally, while Bt spray applies the bacteria externally.
- Bt spray: Contains spores and Cry proteins applied to plant surfaces; insects must ingest it.
- Bt crops: Genetically engineered to express cry genes within plant tissues.
7. Where is Bacillus thuringiensis found naturally?
Bacillus thuringiensis is naturally found in soil, water, plant surfaces, and insect cadavers. It is a common component of the soil microbiota. Bt survives in harsh conditions by forming resistant endospores. Its natural presence in the environment is one reason it is considered a sustainable biological control agent.
8. What insects does Bacillus thuringiensis target?
Bacillus thuringiensis targets specific insect larvae depending on the type of Cry toxin produced. Major target groups include:
- Lepidoptera – caterpillars such as armyworms and bollworms
- Diptera – mosquito and blackfly larvae
- Coleoptera – beetle larvae
9. What is the life cycle of Bacillus thuringiensis?
The life cycle of Bacillus thuringiensis includes vegetative growth followed by sporulation and crystal formation. The stages are:
- Vegetative phase – active bacterial growth and division.
- Sporulation – formation of resistant endospores under stress.
- Crystal protein formation – production of Cry toxin crystals alongside spores.
10. Can insects develop resistance to Bacillus thuringiensis?
Yes, insects can develop resistance to Bacillus thuringiensis through genetic changes affecting toxin binding or activation. Resistance may occur due to:
- Altered gut receptors that prevent Cry toxin binding.
- Increased toxin degradation in the gut.
- Selection pressure from continuous Bt exposure.
