Transcriptomic and Physiological Responses of the Green Microalga Chlamydomonas reinhardtii during Short-Term Exposure to Subnanomolar Methylmercury Concentrations

The
effects of short-term exposure to subnanomolar methyl-mercury
(MeHg) concentrations, representative of contaminated environments,
on the microalga Chlamydomonas reinhardtii were assessed using both physiological end points and gene expression
analysis. MeHg bioaccumulated and induced significant increase of
the photosynthesis efficiency, while the algal growth, oxidative stress,
and chlorophyll fluorescence were unaffected. At the molecular level,
MeHg significantly dysregulated the expression of genes involved in
motility, energy metabolism, lipid metabolism, metal transport, and
antioxidant enzymes. Data suggest that the cells were able to cope
with subnanomolar MeHg exposure, but this tolerance resulted in a
significant cost to the cell energy and reserve metabolism as well
as ample changes in the nutrition and motility of C.
reinhardtii. The present results allowed gaining new
insights on the effects and uptake mechanisms of MeHg at subnanomolar
concentrations in aquatic primary producers.