Uptake of dissolved organic selenides by marine phytoplankton

Abstract

Se is present in multiple oxidation states in nature, each of which has unique chemical and biological reactivities. As a consequence, the rate of Se incorporation into food webs or its role as either a limiting nutrient or a toxic substance is a function of complex biogeochemistry. In particular, little is understood about the accumulation of dissolved organic selenides by phyto- or bacterioplankton. We assessed the bioavailability of dissolved organic selenides to marine and estuarine phytoplankton by presenting various algal species with filtered lysates of the diatom, Thalassiosira pseudonana, grown on media amended with radiolabeled selenite (75Se[IV]). Species known to accumulate selenite effectively also accumulated Se from radiolabeled cell lysates and to approximately the same extent. When exposed to a 4.5-nM solution of lysate Se, T. pseudonana, Heterocapsa triquetra (Dinophyceae), Tetraselmis levis (Prasinophyceae), Synechococcus bacillus (Cyanobacteria), and Dunaliella tertiolecta (Chlorophyceae) incorporated 42%-53%, 42%, 30%, 32%, and 4% of the dissolved Se, respectively. Se cell contents of T. pseudonana, T. levis, and D. tertiolecta grown in media containing 4.5 nM lysate Se were very similar to Se content of cells grown in 4.5 nM selenite. Our results suggest that recycling of Se(-II) may be more important than previously thought. Consequently, uptake of organic selenides by phytoplankton may need to be considered in models predicting Se incorporation into aquatic food webs, given that it is a significant fraction of dissolved Se in estuarine and oceanic waters.