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 T was isolated from a rice paddy soil in Dehong, Yunnan, China. Strain ZYK T is a facultative anaerobe and grows in up to 150, 000 ppm O 2. The comparative genomics analysis of strain ZYK T implies that it shares more orthologues with B. subtilis subsp. subtilis NCIB 3610 T (ANIm values, 85.4-86.7%) than with B. azotoformans NBRC 15712 T (ANIm values, 84.4-84.7%), although B. azotoformans NBRC 15712 T (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 T were iso-C 14:0 (17.8%), iso-C 15:0 (17.8%), and C 16:0 (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 T (=DSM 26460 T =CGMCC 1.5179 T). Strain ZYK T 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 T 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.