Accumulation of CdS nanoparticles by yeasts in a fed-batch bioprocess

The yeasts Schizosaccharomyces pombe and Candida glabrata were successfully cultivated in a fed-batch process at cadmium levels up to 100 mg l(-1). S. pombe incorporated 20 mg C dg(-1) dry biomass within 24h. C. glabrata accumulated 8 mg C dg(-1) dry biomass in 24h. The higher Cd uptake from S. pombe cells correlate with the elevated glucose concentrations during and at the end of the cultivation. Analysis of the cells with energy-filtering transmission electron microscopy-element specific imaging (EFTEM-ESI) revealed that cadmium is not precipitated outside the cells or at the cell wall but evenly distributed inside the cell plasma. As Cd is highly toxic this indicates that Cd is immobilized by an intracellular detoxification mechanism. Size exclusion chromatography showed that Cd is associated to a protein fraction between 25 and 67 kDa which corresponds to the theoretical molecular weight of CdS nanoparticles of 35 kDa coated with phytochelatins. This structure has been proposed in literature.