Sulfur chemolithotrophy: Which organism is capable of oxidizing elemental sulfur or reduced sulfur compounds to sulfates under acidic conditions?

Introduction / Context:
Industrial and environmental microbiology frequently leverage sulfur-oxidizing bacteria for bioleaching and acid mine drainage studies. Identifying the correct genus for sulfur oxidation to sulfate is foundational knowledge.

Given Data / Assumptions:

• Target reaction: S(0), S2O3^2−, or other reduced sulfur → sulfate (SO4^2−).
• Acid-tolerant chemolithotrophs are classic agents of this oxidation.
• Distractors include sulfate-reducers and phototrophs that do not carry out extensive sulfur oxidation to sulfate aerobically.

Concept / Approach:
Thiobacillus thiooxidans (now Acidithiobacillus thiooxidans) is a sulfur-oxidizing chemolithoautotroph that thrives at low pH and oxidizes sulfur to sulfuric acid (sulfate). In contrast, Desulfotomaculum reduces sulfate to sulfide, and the listed phototrophs use different electron donors and pathways.

Step-by-Step Solution:
Match the biochemical function: sulfur oxidation → sulfate. Recall archetypal genus: Thiobacillus/Acidithiobacillus thiooxidans. Eliminate sulfate reducers (Desulfotomaculum) and phototrophs (Rhodospirillum, Rhodomicrobium). Select the sulfur oxidizer: T. thiooxidans.

Verification / Alternative check:
Bioleaching operations and AMD systems measure sulfate and acidity increases correlated with A. thiooxidans activity.

Why Other Options Are Wrong:
Desulfotomaculum – performs sulfate reduction, not oxidation.

Rhodospirillum/Rhodomicrobium – phototrophic metabolism not centered on sulfur oxidation to sulfate in acidic aerobic systems.

Methanobrevibacter – methanogenesis, unrelated to sulfur oxidation.

Common Pitfalls:
Confusing sulfur-oxidizers with purple sulfur bacteria that use sulfide under anoxygenic phototrophy; the product profile and conditions differ.

Final Answer:
Thiobacillus thiooxidans (Acidithiobacillus thiooxidans).