Question

Which one of the following converts sulfate to hydrogen sulfide?

• A. Beggiatoa
• B. Desulfovibrio
• C. Thiobacillus
• D. Thiothrix

Hint:

Remember: Sulfate-reducing bacteria (e.g., Desulfovibrio) reduce SO$_4^{2-}$ → H$_2$S, while sulfur-oxidizers (e.g., Beggiatoa, Thiobacillus, Thiothrix) carry out the reverse reaction.

Answer 1

The Correct Option is B

Step 1: Sulfate reduction
The process of converting sulfate (SO$_4^{2-}$) into hydrogen sulfide (H$_2$S) is known as dissimilatory sulfate reduction. This is carried out by sulfate-reducing bacteria (SRB) under anaerobic conditions. Step 2: Role of Desulfovibrio
Desulfovibrio species are classical sulfate-reducing bacteria. They use sulfate as a terminal electron acceptor during anaerobic respiration, reducing it stepwise via APS (adenosine phosphosulfate) and sulfite intermediates to H$_2$S. Step 3: Elimination of wrong options
(A) Beggiatoa – oxidizes H$_2$S to sulfate (reverse direction).
(C) Thiobacillus – also sulfur-oxidizing bacteria, not reducers.
(D) Thiothrix – filamentous sulfur-oxidizers.
Thus, the correct organism is Desulfovibrio.