Osmium tetroxide is commonly used as a fixative to prepare biological specimens for electron microscopy. More information on Osmium is found in the Os entry in the EAWAG-BBD Biochemical Periodic Table. [http://www.ncbi.nlm.nih.gov/pubmed/14001842|Woolfolk and Whiteley (1962)] reported that extracts of Micrococcus lactilyticus (now Veillonella atypica) reduced Osmium tetroxide to Osmate (OsO4-) and reduced Osmium dioxide and Osmium(III) chloride to Osmium metal. The authors also observed reduction of Osmium tetroxide by extracts of Desulfovibrio desulfuricans.