What is the Difference Between Assimilatory and Dissimilatory Sulphate Reduction?

Assimilatory and dissimilatory sulfate reduction are two different anaerobic processes that occur in microorganisms, fungi, and photosynthetic organisms. Both processes involve the reduction of sulfate, but they differ in the final products and the reactions involved.

Assimilatory Sulfate Reduction:

• Results in the production of amino acids containing sulfur, such as cysteine or homocysteine.
• Adenosine 5'-phosphosulphate (APS) is further phosphorylated to phospho-adenosine phosphosulfate (PAPS) before reduction to the oxidation state of sulfite and sulfide.
• Commonly occurs in plants and bacteria.

Dissimilatory Sulfate Reduction:

• Produces sulfide as the end product.
• Involves the reduction of sulfate to sulfite by the enzyme APS reductase.
• Sulfite reduction is catalyzed by dissimilatory sulfite reductase (EC 1.8.99.1), which reduces sulfite to sulfate.
• Dissimilatory sulfate reduction can be carried out by a special group of organisms called sulfate-reducing bacteria (SRB).

Both processes share some similarities, such as taking place under anaerobic conditions, starting with sulfate as the starting compound, acting as the final electron acceptor, being ATP-dependent, and involving the activation of sulfate to adenosine 5'-phosphosulphate.

Comparative Table: Assimilatory vs Dissimilatory Sulphate Reduction

Here is a table comparing the differences between assimilatory and dissimilatory sulphate reduction:

Both assimilatory and dissimilatory sulphate reduction processes take place under anaerobic conditions, use sulphate as the final electron acceptor, and are ATP-dependent. However, the main difference between the two processes is the end product and the purpose of the reduction: assimilatory sulphate reduction produces cysteine for biosynthesis, while dissimilatory sulphate reduction generates sulfide for energy generation.