Discussion
The purification and characterization of insecticidal protein/s produced by Bacillus thuringiensis during the exponential phase of growth was carried out. Protein fractions were purified both from cell pellet (P) as well as from culture supernatant (S). The purified toxin proteins were heated at indicated temperatures and then used in bioassays against first instar larvae of black cut worm. Percent mortality of the larvae when feeded with toxin proteins were as follows :
| Temperature °C | Mortality % Toxin Protein (P) | Mortality % Toxin Protein (S) |
|---|---|---|
| 28 | 100 | 50 |
| 37 | 75 | 50 |
| 50 | 68 | 50 |
| 65 | 40 | 50 |
| 85 | 10 | 50 |
| Boiled | 0 | 30 |
Which of the following is not true for the given data ?
Answer: A
The statement that is not true is Toxin [S] is thermolabile.
Toxin (S) gives the same 50% mortality from 28 °C right up to 85 °C, and still kills 30% after boiling. Its activity is hardly affected by heat, so it is thermostable, the opposite of thermolabile.
The other statements fit the data. Toxin (P) falls from 100% mortality at 28 °C to 10% at 85 °C and 0 after boiling, so heat clearly harms it. Both proteins kill larvae, with different stability. And at the moderate temperatures where larvae feed, toxin (P) is the more potent, with 100% against 50% mortality at 28 °C.
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