Role of iron in gene expression and in the modulation of copper uptake in a freshwater alga: Insights on Cu and Fe assimilation pathways

Metal uptake and toxicity can generally be related to its aqueous speciation and to the presence of competitive ions as described by the biotic ligand model. Beyond these simple chemical interactions at the surface of aquatic organisms, several internal biological feedback mechanisms can also modulate metal uptake. This is particularly important for essential elements for which specific transport systems were developed over the course of evolution. Based on the results of short-term Cu2+ uptake experiments and on the analysis of the expression of certain genes involved in Cu and Fe homeostasis, we studied the effects of Fe3+ on Cu2+ uptake by the freshwater green alga Chlamydomonas reinhardtii. We observed a significant increase in Cu2+ uptake rate in algal cells acclimated to a low Fe3+ medium up to 4.7 times greater compared to non-acclimated algal cells. The overexpression of the ferroxidase FOX1 and permease FTR1 genes suggests an activation of the high affinity Fe3+ assimilation system, which could constitute a plausible explanation for the increase in Cu2+ uptake rate in acclimatized algae. We show that Fe availability can have a significant impact on Cu uptake. Our observations reinforce the importance of considering physiological factors to better predict metal bioavailability.

Automated summary

Metal uptake and toxicity are influenced by its aqueous speciation and competitive ions, as well as internal biological feedback mechanisms. This study found that the uptake rate of Cu2+ significantly increased in algal cells acclimated to a low Fe3+ environment, up to 4.7 times higher compared to non-acclimated cells. The overexpression of certain genes suggests the activation of a high affinity Fe3+ assimilation system, which may explain the increase in Cu2+ uptake rate in acclimatized algae.