Structural and spectral features of selenium nanospheres produced by Se-respiring bacteria

Certain anaerobes grow by respiring selenium oxyanions, which are in turn reduced to elemental selenium [Se(0)]. From the study of 3 different species of Se-respiring bacteria we report that, while they can form large (∼500 nm) intracellular particles of Se, most of the Se granules accumulated is extracellular. These external ∼300 nm granules consist of stable, uniform nanospheres whose structure, as determined by electron diffraction and EDS, corresponds to monoclinic Se(0). The optical properties of the purified particles revealed large differences between Se(0) produced by the different bacteria, which in turn was distinct from Se(0) formed via abiotic means. Our study points to the bacterial synthesis of unique nanospheres that internally contain different compacted forms and/ or chain arrangements of Se.