Question

Cholera toxin is due to -

• A. Chromosome
• B. Plasmid
• C. Phage
• D. Transposons

Hint:

Toxin genes are introduced by lysogenic conversion via a filamentous CTX element.

Answer 1

The Correct Option is C

Step 1: Cholera is caused by Vibrio cholerae, and its severe watery diarrhoea is driven by cholera toxin (CT). The question asks about the genetic element that determines toxin production.

Step 2: The genes for cholera toxin (ctxA and ctxB) are carried by a filamentous bacteriophage called CTX phage, which becomes integrated into the bacterial chromosome. So the toxin is phage-determined.

Step 3: The other options are wrong: although the phage integrates into the chromosome, the toxin genes themselves are introduced by the phage, so plain chromosomal origin is not the best answer. The toxin is not coded by a plasmid or by transposons.

Step 4: Hence cholera toxin production is determined by a phage (CTX phage).