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Silver toxicity is a problem that microorganisms face in medical and environmental settings. Through exposure to silver compounds, some bacteria have adapted to growth in high concentrations of silver ions. Such adapted microbes may be dangerous as pathogens but, alternatively, could be potentially useful in nanomaterial-manufacturing applications. While naturally adapted isolates typically utilize efflux pumps to achieve metal resistance, we have engineered a silver-tolerant Escherichia coli strain by the use of a simple silver-binding peptide motif. A silver-binding peptide, AgBP2, was identified from a combinatorial display library and fused to the C terminus of the E. coli maltose-binding protein (MBP) to yield a silver-binding protein exhibiting nanomolar affinity for the metal. Growth experiments performed in the presence of silver nitrate showed that cells secreting MBP-AgBP2 into the periplasm exhibited silver tolerance in a batch culture, while those expressing a cytoplasmic version of the fusion protein or MBP alone did not. Transmission electron microscopy analysis of silver-tolerant cells revealed the presence of electron-dense silver nanoparticles. This is the first report of a specifically engineered metal-binding peptide exhibiting a strong in vivo phenotype, pointing toward a novel ability to manipulate bacterial interactions with heavy metals by the use of short and simple peptide motifs. Engineered metal-ion-tolerant microorganisms such as this E. coli strain could potentially be used in applications ranging from remediation to interrogation of biomolecule-metal interactions in vivo .

Here, we exploit the ability of electrodeposition to decouple materials nucleation and growth to investigate how engineered biomineralizing proteins control inorganic morphogenesis. Using a silver-binding designer protein at concentrations proximal to its equilibrium dissociation constant, we produce rosettelike silver particles instead of the pentagonal twinned crystals obtained without additive or with a wild-type protein that nonspecifically adsorbs to silver. We correlate the difference in silver growth habit to specific interactions between the designer protein and the {111} faces of polycrystalline silver nuclei. Our results suggest that electrodeposition is a powerful tool to interrogate protein−inorganic interactions and to screen solid-binding proteins for shape-changing activity.

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