Green fluorescent protein revolutionized cellular optical microscopy by enabling clonable fluorescent contrast. Cellular electron microscopy lacks a similar clonable contrast tool. Naturally occurring cellular mechanisms for processing inorganic ions into nanoparticles represent a potential source of clonable nanoparticles. Herein we characterize the selenium (Se) and tellurium (Te) nanoparticles produced by a bacterium that tolerates ordinarily toxic concentrations of Se. The bacterium was recently isolated from roots of an Se hyperaccumulator plant <i>Stanleya pinnata</i>, Structure and cellular ultrastructure determined by electron tomography shows the nanoparticles as intracellular, of narrow dispersity, symmetrically irregular and without any observable membrane or structured protein shell. Protein mass spectrometry of fractionated soluble cytosolic material with selenite reducing capability identified nitrite reductase and glutathione reductase or close homologues as NADPH dependent candidate enzymes for the reduction of selenite to zerovalent Se nanoparticles. <i>In vitro</i> enzymology with commercially sourced glutathione reductase revealed that the enzyme catalyzes NADPH dependent reduction of selenite to zerovalent selenium nanoparticles. The disappearance of the enzyme as determined by protein assay during nanoparticle formation suggests that glutathione reductase is entombed in the nanoparticles whose formation it catalyzes. By lowering the concentration of NADPH, the size of the Se nanoparticles may also be controlled. In aggregate, we suggest that enzymes like the ones producing the Se nanoparticles identified here possess many of the attributes desired of a clonable nanoparticle system, such as precursor reduction, nanoparticle retention and size control of the nanoparticle at the enzyme site. Most notably, the particles appear to be naked and exposed to cytosol.

Progress toward clonable inorganic nanoparticles

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.