Enzymatic and non-enzymatic antioxidants in Dunaliella microalgae can diminish toxicity of polycyclic aromatic hydrocarbons in favor of valuable metabolites production

In Dunaliella tertiolecta and Dunaliella salina species, production of valuable metabolites such as soluble sugar and proteins, and proline as non-enzymatic antioxidant, as well as ascorbate peroxidase, guaiacol peroxidase, catalase and peroxidase as enzymatic antioxidant against the toxicity of two common PAHs (Polycyclic Aromatic Hydrocarbons) including phenanthrene and anthracene was evaluated. The results showed that toxicological parameters including growth rate, chlorophyll a content, lipid peroxidation (malondialdehyde production) were different for both Dunaliella species exposed to different concentrations (0, 3000, 6000 and 9000 µgL-1) of Phenanthrene and Anthracene in the culture media. There was a more inhibitory effect of Phenanthrene and Anthracene on cell number and chlorophyll a in D. salina than D. tertiolecta. Therefore, D. salina is more sensitive to PAHs stress than D. tertiolecta. Phenanthrene and Anthracene caused lipid peroxidation or malondialdehyde production but increased non-enzymatic metabolites such as sugar, proline and soluble protein as well as activity of enzymatic antioxidant such as ascorbate peroxidase, peroxidase which scavenge produced reactive oxygen species (ROS) due to their toxicity. It is concluded that Phenanthrene and Anthracene had dose and species dependent effect on D. salina and D. tertiolecta. These PAHs was more toxic for D. salina than D. tertiolecta. Therefore, these species specially D. tertiolecta may be suggested as the good candidates to remove PAHs contaminations such as Phenanthrene and Anthracene from the aquatic environments. The positive correlation between growth rate of Dunaliella and chlorophyll content under PAHs stress were observed. Inversely, negative correlation between proline, sugar, protein content and growth rate showed their importance to PAHs resistance. Also, major role of antioxidants to PAHs resistance can be inferred by positive correlation of non-enzymatic antioxidants with enzymatic antioxidants.