Abstract
Depending on species, heavy metals, including copper (Cu), differentially affect algal growth and metabolism. Here, we aim to evaluate the differential responses of two green microalgae, Chlorella sorokiniana and Scenedesmus acuminatus, exposed to sub -lethal doses of Cu (25 and 50 mu M, respectively) for 7 days. The changes in growth, oxidative damage markers, and antioxidants were analysed. We found that S. acwninatus could acclimatise during long-term exposure to Cu stress. S. acuminatus accumulated lower Cu content and showed a slight decrease in H2O2 levels when compared to C. sorokiniana. Cu stress induced membrane damage in the two microalgae species, however, this increase was slightly lower in S. acuminatus. To mitigate Cu stress impact, C. sorkiniana markedly increased proline, polyphenols, flavonoids, tocopherols, glutathione levels, as well as the activities of GST, APX, GR and SOD enzymes, which could explain less -stress sensitivity. On the other hand, S. acuminatus exhibited significant increases in proline, polyphenol, and tocopherol contents. Activity levels of PDX, APX, GR and SOD enzymes, were also increased. These results suggest that the two microalgae differentially induced the antioxidant defence system to neutralise the oxidative damage induced by Cu stress. This study also provided new data for Cu tolerance and Cu removal abilities of two microalgal species, which commonly exist in surface water bodies, where low Cu uptake and efficient antioxidant defence system protected S. acuminatus against oxidative stress induced by Cu stress. This makes it feasible for treatment of Cu contaminated waters.