Understanding Bt (Bacillus thuringiensis) Strain

The question asks about what is true regarding Bt (Bacillus thuringiensis) strain. Let's examine each option based on the known properties of Bacillus thuringiensis and its use in biotechnology.

Analysis of Options for Bt Strain Properties

Here is a breakdown of each statement:

• Option 1: The concerned Bacillus has antitoxins.

  This statement is incorrect. Bacillus thuringiensis produces crystal proteins (often referred to as Bt toxins) which are toxic to certain insects. Antitoxins neutralize toxins, they are not produced by the bacteria in this context. The bacteria produces the toxin itself.

• Option 2: The Bt-strains have been used for designing novel Bioinsecticidal plants.

  This statement is correct. Genes from Bt strains that produce insecticidal toxins (Bt toxins) have been isolated and introduced into various crop plants, such as cotton, corn, and brinjal. These genetically modified plants produce the Bt toxin protein, which makes them resistant to specific insect pests. These are known as bioinsecticidal plants because they produce a biological agent (the Bt toxin) that kills insects.

• Option 3: Bt-toxins exists as active toxins in the Bacillus.

  This statement is incorrect. The Bt toxins produced by Bacillus thuringiensis exist in an inactive form called protoxins within the bacterial cells, often as crystalline structures. These protoxins become active only when ingested by susceptible insects and processed in the alkaline environment of the insect's gut. The alkaline pH solubilizes the crystals, and specific proteases in the gut cleave the protoxin to release the active toxin.

• Option 4: The activated toxins enters the ovaries of the pest to sterilize it and thus prevent its multiplication.

  This statement is incorrect. The primary mode of action of activated Bt toxins is in the midgut of susceptible insects. The activated toxin binds to specific receptors on the gut epithelial cells, causing pore formation. This disrupts the cell membrane integrity, leading to cell swelling and lysis. This damage to the gut lining disrupts digestion and ultimately leads to the death of the insect. The toxin does not primarily target the ovaries for sterilization.

Conclusion on Bt Strain Characteristics

Based on the analysis, the only true statement about Bt (Bacillus thuringiensis) strain among the given options is that Bt-strains have been utilized in the development of novel bioinsecticidal plants through genetic engineering.