Extremophiles in biotechnology: Thiobacillus thiooxidans (Acidithiobacillus thiooxidans) exhibits an optimum pH for growth in which range?

Introduction / Context:
Acidophilic sulfur-oxidizing bacteria such as Thiobacillus (now Acidithiobacillus) thiooxidans are instrumental in bioleaching and acid mine drainage studies. Knowing their pH preference is essential for both industrial applications and environmental management.

Given Data / Assumptions:

• Acidithiobacillus thiooxidans oxidizes reduced sulfur compounds to sulfuric acid.
• It is highly acidophilic and thrives at very low pH.
• Neutral or alkaline pH inhibits growth of strict acidophiles.

Concept / Approach:
These organisms show optimal activity in the strongly acidic range, where proton gradients and enzyme systems are adapted to low pH. The commonly cited optimum is around pH 2–3.5, enabling efficient sulfur oxidation and metal solubilization in heap leaching or biooxidation reactors.

Step-by-Step Solution:
Identify the organism as a strict acidophile.Recall typical optimal pH range ~2–3.5 for growth and metabolism.Select the matching option “2.0–3.5.”

Verification / Alternative check:
Process guidelines for bioleaching maintain low pH to favor Acidithiobacillus species and suppress neutrophiles, corroborating the optimal range.

Why Other Options Are Wrong:

• 0.5–6.0: overly broad and unrealistic for a defined optimum.
• 6.5–7.5 (neutral) and 9.0–9.5 (alkaline): inhibitory for this acidophile.
• 7.8–8.4: typical for alkaline conditions, not suitable.

Common Pitfalls:
Confusing acid-tolerant organisms with strict acidophiles; assuming broad pH tolerance.

Final Answer:
2.0–3.5.