Toxicity and biochemical transformation of selenium species in rotifer (Brachionus plicatilis) enrichments

Selenium (Se) is an essential nutrient and the chemical forms of Se present in food affect both its bioavailability and its toxicity. The aim of this study was to evaluate the effects of the rotifer enrichment with three sources of selenium supplementation: selenite (Se(IV)), selenomethionine (SeMet) and selenized yeast (SelPlex). For this purpose, rotifers were exposed to each source of selenium at two concentrations during 6 days (2 culture cycles of 3 days). The toxicity order for the three sources of Se was SelPlex > SeMet > Se(IV). Modelling calculations showed that SeMet and Selplex uptake followed a first-order kinetic model. Nevertheless, uptake of Se(IV) displayed a linear pattern with increasing exposure time. Speciation data revealed that the predominant form in rotifers was SeMet. Indeed, rotifers metabolized and chemically transformed Se(IV) into SeMet. If the source of Se assayed is Se(IV), rotifers with Se levels similar to those in copepods and high content of SeMet can be accomplished when they are exposed to 2 mg of Se per million rotifers for 12 h. For SeMet and SelPlex treatments, 0.2 mg of Se per million rotifers in 3 and 6 h, respectively, were required.