Biotransformation and distribution of selenium in cultures of a salt-marsh yeast

Abstract

The essentiality and toxicity of selenium makes its biogeochemical cycling and global distribution of great interest for human health. Selenium-reducing yeast and fungi are important contributors to the selenium cycle, yet there have been few studies of both particulate Se accumulation and Se volatilization by an environmental yeast isolate. This study quantified the distribution of selenium in liquid, solid (cell-associated), and volatile fractions of cultures of a salt-marsh yeast isolate, Rhodotorula mucilaginosa-13B. More than 20% of amended selenite accumulated in cell pellets, while 1% was dispersed in volatile form. Elemental selenium only accumulated during the exponential and stationary growth phases of live cultures. Electron microscopy images indicated the location of particles both within and outside of cells and suggested changes to cellular ultrastructure resulting from internal particulate Se accumulation. Additionally, distribution results indicated several other minor interactions among cells, media and the various species of selenium present in the cultures. We conclude that strain 13B may play a complex and substantial role in the distribution and speciation of selenium in its environment, with its primary contributions to the selenium cycle clearly resulting from its ability to reduce selenium oxyanions to elemental selenium.