Briefly explain how *Bacillus subtilis* detoxifies lead in contaminated soil, mentioning the key enzymes involved and the environmental factors that affect its efficiency.
Answer
*Bacillus subtilis* binds lead ions using surface proteins and secretes the lead‑binding peptide subtilosin, which precipitates Pb²⁺ as insoluble lead‑sulphide. The key enzymes are the lead‑binding protein (Lbp) and the ATPase pump (Pb-ATPase) that expel Pb²⁺ from the cytoplasm. Efficiency is influenced by soil pH (optimal around 6.5–7.5), temperature (30–35 °C), and the presence of competing metal ions such as Zn²⁺ and Cu²⁺.
Step-by-step solution
- 1. Lead ions diffuse into the soil medium.
- 2. Surface proteins of *B. subtilis* bind Pb²⁺ forming a complex.
- 3. The lead‑binding protein (Lbp) transfers Pb²⁺ to the ATPase pump.
- 4. Pb-ATPase expels Pb²⁺ from the cell, where it reacts with sulphide to precipitate PbS.
- 5. Environmental pH, temperature and competing ions modulate binding efficiency.
Common mistake: Assuming the detoxification is solely enzymatic without binding proteins
Concept tested: Microbial bioremediation of heavy metals
Published · How this solution was prepared and checked
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