Bacillus subtilis is employed to remediate soils contaminated with lead ($P{b}^{2+}$). Describe in detail (i) the biochemical pathway it uses to detoxify lead, (ii) the enzymes involved, and (iii) the environmental factors affecting the efficiency of this bioremediation.

Step-by-step solution

1. Recognise that Bacillus subtilis binds $P{b}^{2+}$ to its cell wall through metal‑binding ligands, forming a surface complex.
2. Explain that intracellular $P{b}^{2+}$ is reduced to $PbS$ by the enzyme sulfide:quinone oxidoreductase, which uses hydrogen sulfide generated from cysteine metabolism.
3. State that additional precipitation occurs via phosphatase activity, converting $P{b}^{2+}$ to insoluble lead‑phosphate (Pb${}_3$(PO${}_4$)${}_2$).
4. Identify key enzymes: sulfide:quinone oxidoreductase and phosphatase.
5. List environmental factors: soil pH (optimal 6–7), moisture (70–80 % RH), sulfur availability (from organic matter), and presence of other divalent metals that can compete for binding sites.

Concept tested: Microbial lead bioremediation

Published 23 September 2026 · How this solution was prepared and checked