Thermostable DNA polymerase used in PCR was isolated from :

Option (3) is the answer, because Thermostable DNA polymerase (Taq polymerase) used in PCR was isolated from a bacterium Thermus aquaticus. Option (1) is not the answer as Agrobacterium tumifaciens is a pathogen of several dicot plants. Option (2) is not the answer as, specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into the several crop plants for the development of pest resistant crops. E. Coli was used as a host by Eli lily to produce human insulin.