Crystallizing bacterial extracellular protein reveals paths of silver mineralization for recovery

Heavy metal pollution calls for green recovery strategies. In response to metal stress, bacteria secrete extracellular proteins (ECPs), but the specific role of an individual extracellular protein (ECP) in silver ion (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 ppm 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 complete silver recovery from aqueous medium in 1.5 h. This previously unrecognized single-protein mediated biomineralization mechanism reveals specific ECPs as programmable bio-lixiviants, offering a low-energy, solvent-free route to metal recovery and expanding the toolkit for biometallurgy and environmental remediation.