title: Formation of tellurium nanocrystals during anaerobic growth of bacteria that use Te oxyanions as respiratory electron acceptors.
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 to be 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 stable-Te-isotopic fractionation (isotopic enrichment factor [epsilon] = -0.4 to -1.0 per ml per atomic mass unit) and results in the formation of unique crystalline Te(0) nanoarchitectures as end products. The Te(0) crystals occur internally within but mainly externally from the cells, and each microorganism forms a distinctly different structure. Those formed by Bacillus selenitireducens initially are nanorods ( approximately 10-nm diameter by 200-nm length), which cluster together, forming larger ( approximately 1,000-nm) rosettes composed of numerous individual shards ( approximately 100-nm width by 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 and selected area electron diffraction indicate that both biominerals are composed entirely of Te and are crystalline, while Raman spectroscopy confirms that they are in the elemental state. These Te biominerals have specific spectral signatures (UV-visible light, Raman) that also provide clues to their internal structures. The 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.
authors.affiliation: .S. Geological Survey, Menlo Park, California 94025, USA.
authors.forename: Shaun M
authors.initials: SM
authors.lastname: Baesman
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Bullen
authors.forename: James
authors.initials: J
authors.lastname: Dewald
authors.forename: Donghui
authors.initials: D
authors.lastname: Zhang
authors.forename: Seamus
authors.initials: S
authors.lastname: Curran
authors.forename: Farhana S
authors.initials: FS
authors.lastname: Islam
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Beveridge
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Oremland
mesh_terms: D000693:Anaerobiosis; D001407:Bacillus / Q000254:growth & development / Q000378:metabolism*; D004579:Electron Transport; D020565:Epsilonproteobacteria / Q000378:metabolism*; D008854:Microscopy, Electron; D053758:Nanoparticles; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman; D013691:Tellurium / Q000737:chemistry / Q000378:metabolism*
chemical_list: C026660:tellurous acid; D013691:Tellurium