Tolerance Capacity of Chlamydomonas VHLR Mutants for the Toxicity of Mercury
2020
Samadani, Mahshid | El-Khoury, Jonathan | Dewez, David
The toxicity effect of metals on Chlamydomonas strains having a higher tolerance level for oxidative stress is important to investigate for better understanding their tolerance capacity. In this study, the toxicity of HgCl₂ was determined on two very high light resistant (VHLᴿ) mutant strains of Chlamydomonas, CC-3723 and CC-3724, and on the wild-type CC-125. All strains were exposed to 1–7 μM of HgCl₂ during 24–72 h. The results showed that VHLᴿ mutants were less affected by the effect of HgCl₂ than CC-125, due to a better ability to detoxify the level of intracellular reactive oxygen species (ROS) generated by Hg. In particular, the effect of 3 μM of HgCl₂ inhibited completely the growth rate of CC-125 at 24 h, which was correlated with a high accumulation of Hg and a strong level of ROS. From 48 to 72 h, the growth rate was recovered for all strains, which was stronger for VHLᴿ mutants than the wild-type by 50% at 48 h, when compared to 24 h. In addition, the extracytoplasmic polyP level decreased significantly compared to the control for all strains treated to 3 μM of HgCl₂ during 24–48 h. These results suggested that the polyP did participate to the tolerance for Hg through its cellular sequestration. Furthermore, the analysis of cellular morphology showed that VHLᴿ mutants formed palmelloid colonies of 4–5 cells under 3 μM of HgCl₂ at 48 h, reducing the surface contact with Hg. Therefore, VHLᴿ mutants were more tolerant than the wild-type to the effect of low concentrations of HgCl₂ (1 and 3 μM).
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