Resistance to heavy metals in algae isolated from an extreme acidic environment, Rio Tinto (SW, Spain)

Rio Tinto, a river located in south-western Spain, is characterized by its extreme physico-chemical conditions in terms of low pH (mean 2.2) and high concentrations of heavy metals. It contains an unexpected diversity of photosynthetic eukaryotes. We have isolated a strain of Chlamydomonas sp., an acidophilic species belonging to the phylum Chlorophyta. It has been cultured in BG11 media in the presence of copper, cobalt or zinc in order to evaluate the effects of these metals both on the photosynthesis and on the overall growth.

When exposed to different doses of metals, considerable changes were observed in its growth as compared to metal-free controls. At the lowest concentrations tested, a small decrease in growth was observed. However, the algae still maintained morphology and green colour similar to the control. Metal concentrations were progressively increased reaching the lethal doses 50 (LD₅₀). At these high concentrations, cells became colourless and some even lost their flagella from the first day.

Our experiments suggest that our Chlamydomonas sp. isolate is particularly resistant to zinc.

We have also observed a decrease in the amount of chlorophyll per cell linked to an increment in metal concentration. This leads us to think that metals could be affecting the viability of the cells by decreasing the yields in photosynthesis.

Studies using this organism could provide valuable information with application in the fields of biotechnology and bioremediation.