Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves ,why ?

Toxin is inactive.

The reason that crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves is that the toxin is typically inactive within the bacterial cells.

Bacillus thuringiensis (Bt) is a bacterium that produces crystal-like proteins known as Bt toxins. These toxins are effective against certain insects and pests when ingested by them, causing damage to their digestive systems and leading to their death. However, the Bt bacteria themselves do not get harmed by these toxins.

The reason for this is that the Bt bacteria produce the inactive form of the toxin as an inclusion body or crystal. These crystals are stable and remain inactive within the bacterial cell until the bacteria are ingested by susceptible insect larvae. Inside the insect's gut, the alkaline pH activates the toxin, converting it into an active form. This activated form binds to specific receptors in the insect's digestive system, leading to pore formation and ultimately causing the death of the insect.

Therefore, the reason the crystals of Bt toxin produced by the bacteria do not kill the bacteria themselves is that the toxin remains inactive within the bacterial cells until it encounters the specific conditions present in the digestive system of susceptible insects.