Characterization and Potential Applications of a Selenium Nanoparticle Producing and Nitrate Reducing Bacterium Bacillus oryziterrae sp. nov.

A novel nitrate- and selenite reducing bacterium strain ZYK was isolated from a rice paddy soil in Dehong, Yunnan, China. Strain ZYK is a facultative anaerobe and grows in up to 150, 000 ppm O. The comparative genomics analysis of strain ZYK implies that it shares more orthologues with B. subtilis subsp. subtilis NCIB 3610 (ANIm values, 85.4-86.7%) than with B. azotoformans NBRC 15712 (ANIm values, 84.4-84.7%), although B. azotoformans NBRC 15712 (96.3% 16S rRNA gene sequence similarity) is the closest Bacillus species according to 16S rRNA gene comparison. The major cellular fatty acids of strain ZYK were iso-C (17.8%), iso-C (17.8%), and C (32.0%). The polar lipid profile consisted of phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol and an unidentified aminophospholipid. Based on physiological, biochemical and genotypic properties, the strain was considered to represent a novel species of the genus Bacillus, for which the name Bacillus oryziterrae sp. nov. is proposed. The type strain is ZYK (=DSM 26460 =CGMCC 1.5179). Strain ZYK can reduce nitrate to nitrite and ammonium and possesses metabolic genes for nitrate reduction including nar, nap and nrf. Biogenic selenium nanoparticles of strain ZYK show a narrow size distribution and agree with the gaussian distribution. These selenium nanoparticles show significant dose-dependent inhibition of the lung cancer cell line H157, which suggests potential for application in cancer therapy.