Formation of Tellurium Nanocrystals with Anaerobic Growth of Bacteria that use Te-Oxyanions as Respiratory Electron Acceptors

U.S. Geological Survey, Menlo Park, CA 94025; Department of Physics, New Mexico State University, Las Cruces, NM 88001; Department of Molecular & Cellular Biology and Advanced Food & Materials Network-Networks of Centres of Excellence, University of Guelph, Guelph, Ontario, Canada, N1G 2W1

^* To whom correspondence should be addressed. Email: roremlan{at}usgs.gov.

	Abstract

Certain toxic elements support the metabolism of diverse prokaryotes by serving as respiratory electron acceptors for growth. Here we demonstrate that two anaerobes previously shown capable of respiring oxyanions of selenium also achieve growth by reduction of either tellurate [Te(VI)] or tellurite [Te(IV)] to elemental tellurium [Te(0)]. This reduction achieves a sizeable Te stable isotopic fractionation ( = - 0.4 to - 1.0 per mil per atomic mass unit) and results in the formation of unique crystalline Te(0) nanoarchitectures as endproducts. The Te(0) crystals occur both internally within, but mainly externally from the cells and each microorganism forms a distinctly different structure. Those formed by Bacillus selenitireducens initially are nanorods ( 10 nm diameter x 200 nm length), that cluster together forming larger ( 1,000 nm) rosettes composed of numerous individual shards ( 100 nm width x 1,000 nm length). In contrast, Sulfurospirillum barnesii forms extremely small irregularly-shaped nanospheres (diameter < 50 nm) that coalesce into larger composite aggregates. Energy dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED) indicate that both biominerals are composed entirely of Te and are crystalline, while Raman spectroscopy confirms they are in the elemental state. These Te-biominerals have specific spectral signatures (UV-Vis, Raman) that also provide clues to their internal structure. Use of microorganisms to generate Te-nanomaterials may be an alternative for bench-scale syntheses. Additionally, they may also generate products with unique properties unattainable by conventional physical/chemical methods.