Humic Acid Mitigates Viability Reduction, Lipids and Fatty Acids of Dunaliella salina and Nannochloropsis salina Grown under Nickel Stress

摘要

The evaluation of Humic Acid (HA) to mitigate the viability reduction, lipids and fatty acid s of Dunaliella salina Teodoresco and Nannochloropsis salina Hibberd cultivated in nickel contaminated media has been studied. The results revealed that toxicity of nickel decreased the cell viability to 40 and 30% of the control for D. salina and N. salina , respectively. Total fatty acid /lipid content has been reduced in both strains to about 28 and 20% of the control in the same order. Nickel induced alterations in the fatty acid composition in both investigated microalgae. An obvious increase was detected in the proportions of saturated profiles accompanied by a decrease in the unsaturated ones, except for C18:2 of N. salina which appeared to accumulate in the cells. Upon HA addition, the toxicity of nickel was significantly reduced (p≤0.05), cell viability enhanced to 25 and 15% for D. salina and N. salina , respectively. Total fatty acid /lipid content became 20 and 10% correspondingly. Concerning fatty acid composition, the response of the examined species appeared the same; both saturated and unsaturated fatty acid concentrations tend to be more or less around the control values. The study demonstrated a mitigation effect of HA towards the toxicity caused by nickel contamination. This mitigation has been explained through two ways. (a) The formation of HA-Ni²⁺, a complex of high molecular weight and hence the metal was less bioavailable. (b) HA absorbed into the algal cell surface causing a protection from NiCl₂ stress.