Fractionation of selenium isotopes during biofortification of Saccharomyces cerevisiae and the influence of metabolic labeling with 15 N

Isotope fractionation of metals/metalloids in biological systems is an emerging research area that demands the application of state-of-the-art analytical chemistry tools and provides data of relevance to life sciences. In this work, Se uptake and Se isotope fractionation were measured during the biofortification of baker’s yeast ( Saccharomyces cerevisiae )—a product widely used in dietary Se supplementation and in cancer prevention. On the other hand, metabolic labeling with 15 N is a valuable tool in mass spectrometry-based comparative proteomics. For Se-yeast, such labeling would facilitate the assessment of Se impact on yeast proteome; however, the question arises whether the presence of 15 N in the microorganisms affects Se uptake and its isotope fractionation. To address the above-mentioned aspects, extracellularly reduced and cell-incorporated Se fractions were analyzed by hydride generation–multi-collector inductively coupled plasma–mass spectrometry (HG MC ICP–MS). It was found that extracellularly reduced Se was enriched in light isotopes; for cell-incorporated Se, the change was even more pronounced, which provides new evidence of mass fractionation during biological selenite reduction. In the presence of 15 N, a weaker preference for light isotopes was observed in both, extracellular and cell-incorporated Se. Furthermore, a significant increase in Se uptake for 15 N compared to 14 N biomass was found, with good agreement between hydride generation microwave plasma–atomic emission spectrometry (HG MP–AES) and quadrupole ICP–MS results. Biological effects observed for heavy nitrogen suggest 15 N-driven alteration at the proteome level, which facilitated Se access to cells with decreased preference for light isotopes. Graphical abstract