Crystallizing extracellular protein reveals paths for silver mineralization and recovery

Heavy metal pollution calls for green recovery strategies. In response to metal stress, bacteria secret extracellular proteins (ECPs), but the specific role of individual ECP in silver (Ag2+) mineralization and recovery remains unexplored. Here, we investigated how a single ECP from silver-hypertolerant Enterobacter cloacae mediates Ag²⁺ mineralization. Proteomics (LC-MS/MS, MALDI-TOF) identified the 15.6 kDa protein as an inosine-monophosphate dehydrogenase (ImpD) homolog, whose secretion peaks in medium containing 15.9 mg L⁻¹ Ag²⁺. Partially purified ImpD crystallized at 20–30 °C. Time-resolved in-situ crystallography and X-ray diffraction captured monomers assembling into donut-shaped hexamers that weave into thread-like lattices; these ordered scaffolds template orientation-specific nucleation of Ag-rich crystals, enabling quantitative silver capture from solution. This previously unrecognized single-protein mediated biomineralization mechanism reveals ECPs as programmable bio-lixiviants, offering a low-energy, solvent-free route to selective metal recovery and expanding the toolkit for biometallurgy and environmental remediation.