Nutrient metal interactions and adaptive responses of Dunaliella tertiolecta to zinc and copper toxicity under phosphorus limitation

Heavy metal pollution is a major environmental concern, especially in phosphorus-limited aquatic habitats. The growth of algae is negatively impacted by a variety of stressors, including fluctuations in heavy metal concentrations, phosphorus starvation, or a deficiency of dissolved inorganic phosphorus. This study examines how the microalga Dunaliella tertiolecta helps reduce zinc (Zn²⁺) and copper (Cu²⁺) toxicity in phosphorus-deficient circumstances, which simulates the typical circumstances of aquatic habitats, including its existence and absence of the element. Under both phosphorus-sufficient (+ P) and phosphorus-limited (-P) circumstances, controlled laboratory studies were carried out using Zn²⁺ and Cu²⁺ concentrations ranging from 5 to 25 mg/L. Different heavy metal concentrations were permitted in the study, and there were enough biological replicates for statistical analysis using the ANOVA test. The EC50 of both elements was approximately 15 mg/L. The physiological response of D. tertiolecta to metal exposure was evaluated by measuring growth inhibition, chlorophyll content, and photosynthetic activity. The results show that both metals’ harmful effects were exacerbated by phosphorus deficiency, with Cu2+ showing significantly more toxicity than Zn2+. Under phosphorus-limited conditions, the maximum concentration of Cu2+ (25 mg/L) resulted in a higher drop at the end of the experiment in growth rate which reaching around 85%, a decline in chlorophyll content of up to 91%, and a suppression of photosynthetic activity of about 40%. Moreover, O₂ evolution was significantly decreased in cultures that were starved of phosphorus, and metal toxicity further inhibited photosynthesis, especially at concentrations higher than 10 mg/L. Phosphorus’s contribution to algal resistance to metal stress was demonstrated by the way it lessened these effects. The study additionally highlights D. tertiolecta’s potential for bioremediation applications, as dietary circumstances influence the organism’s ability to resist and alleviate metal stress. These findings suggest that phosphorus availability is an important element in determining the level of heavy metal toxicity and provide new insights into nutrient-metal interactions in aquatic settings.