Selenite transport and its inhibition in the unicellular green alga Chlamydomonas reinhardtii

Abstract

The influence of time, ambient concentration, and medium composition on selenite (Se(IV)) uptake by the unicellular green alga Chlamydomonas reinhardtii has been investigated. The aims of the performed experiments were to describe the kinetics of accumulation, to characterize transport capacities, to identify key nutrients influencing absorption, and to establish links between speciation and bioavailability. Our results suggested that the adsorbed fraction was negligible compared to the absorbed one. Over the short time scale considered, the absorption was linear with time, with an estimated conductance of approximately 0.2 nmol/m2/h/nM. Uptake was proportional to ambient levels in a broad range of intermediate concentrations (from nM to microM). However, conductances were higher at low concentrations (< nM) and then decreased with increasing concentrations (> microM). These results suggested that a specific but rapidly saturated transport system was involved at low concentrations, coupled with a nonspecific one that was only saturated at high ambient concentrations (approximately mM). The latter could involve transporters used by anionic macronutrients, which is supported by the fact that increasing sulfate and nitrate concentrations induced significant inhibition of Se(IV) uptake. Finally, Se(IV) speciation changes caused by varying pH did not significantly affect bioavailability.

Organic selenium, selenate, and selenite accumulation by lake plankton and the alga Chlamydomonas reinhardtii at different pH and sulfate concentrations

“…We measured a significant ( p < 0.05) pH effect on Se accumulation by C. reinhardtii (Figure B) following 12 h of exposure to 63 nM Se(IV). In contrast, 2 other studies on this algal species reported no clear influence of pH on Se(IV) accumulation (Morlon et al [pH 5–8]; Riedel and Sanders [pH 5–9]). The pH effect that we measured can be explained by the fact that Se(IV) speciation changes markedly as pH increases from 7 to 9 because the protonated form (HSeO 3 – ) is progressively replaced by the deprotonated form (SeO 3 2– ) up to pH 8.4 (p K a ), at which point approximately 50% of each Se(IV) species is present (thermodynamic calculation using MINEQL+; Schecher and McAvoy ).…”

“…Kelly Lake (Figure ) differed somewhat from the other lakes in that adding Se(VI) concentrations (solid triangles in Figure ) to Org‐Se concentrations (solid squares in Figure ) overpredicted [Se] in organisms from this lake. The high SO 4 concentrations in this lake (4 mM) likely competed with those of inorganic Se, thereby reducing the accumulation of inorganic Se species at the base of the food chain (Figure C; Morlon et al ; Fournier et al ; Ponton and Hare ). To explain these trends seen in nature, we explored the influence of Se speciation, SO 4 , and H + on [Se] in the green alga C reinhardtii .…”

“…These observations can be explained by the chemical similarities between inorganic Se and SO 4 ions (Reich and Hondal ) that can lead to competition at biological uptake sites and thereby reduce Se uptake. Lake water pH could also influence the protonation state of Se(IV) and its bioaccumulation (Riedel and Sanders ; Morlon et al ), although this hypothesis remains to be rigorously tested.…”

“…In the field, Ponton and Hare (2013) reported that the Org-Se concentrations in lake water best predicted those in larvae of the phantom midge Chaoborus; although adding Se (VI) concentrations raised slightly the strength of the correlations for some lakes. At high sulfate (SO 4 ) concentrations, the accumulation of inorganic Se species is reported to be reduced in the field (Ponton and Hare 2013) and in the laboratory for both Se(IV) (Morlon et al 2006) and Se(VI) (Fournier et al 2010). These observations can be explained by the chemical similarities between inorganic Se and SO 4 ions (Reich and Hondal 2016) that can lead to competition at biological uptake sites and thereby reduce Se uptake.…”

Effect of continuous application of inorganic nitrogen fertilizer on selenium concentration in vegetables grown in the Taihu Lake region of China

“…Others have identified that Se concentration of rice roots had a close negative correlation to nitrate concentration (R 2 =0.7252), due to anion-anion interactions (Xu et al 2010). Similarly, nitrate was also found to inhibit selenite uptake in the unicellular green alga Chlamydomonas reinhardtii (Morlon et al 2006).…”