The relationship between cellular protein content and selenium accumulation in freshwater microalgae

Variability in the bioconcentration of selenium (Se) by primary producers at the base of the food web results in uncertainty in predictions of bioaccumulation and ecological risk to higher trophic level organisms. Water chemistry, speciation of Se, and periphyton community composition have all been suggested as factors that contribute to variability in bioconcentration by primary producers; however, the role of physiological composition of periphyton species in influencing the bioconcentration of Se has not been previously evaluated. To determine if a relationship exists between algal protein content and Se accumulation, Parachlorella kessleri, Chlorella vulgaris, and Raphidocelis subcapitata were exposed to Se (as selenate) and analyzed for total protein and tissue Se content in the exponential and stationary growth phases. Protein content and Se accumulation in R. subcapitata in the stationary phase were also measured under two light intensities. No relationship between cellular protein content and Se accumulation was found for algae in the exponential phase; however, a strong relationship was found in the stationary phase among species and for R. subcapitata under differing light intensities. Absolute Se accumulations by P. kessleri, C. vulgaris, and R. subcapitata in the stationary phase were statistically different; however, the concentrations of Se in protein were similar across species. These results suggest that cellular protein content in microalgae influences Se bioconcentration and that algal protein content may improve Se bioaccumulation modeling in food webs.