Biofortification of <i>Arthrospira platensis</i> with Zinc: A Comparison of Chloride and Sulfate Salts

This study investigated the distinct effects of zinc chloride (ZnCl 2 ) and zinc sulfate (ZnSO 4 ) on the cyanobacterium Arthrospira platensis . The results demonstrated that ZnCl 2 promoted growth at concentrations up to 11 mg/l. In contrast, ZnSO 4 exhibited inhibitory effects at concentrations of 7.5 mg/l and above. Monod kinetic modeling confirmed a higher tolerance threshold for ZnCl 2 . Analysis of the enrichment factor revealed significantly greater zinc accumulation in samples treated with ZnCl 2 (24.62 ± 5.06 mg/kg) compared to those exposed to ZnSO 4 (19.47 ± 2.76 mg/kg), with accumulation plateauing beyond 7.5 mg/l for ZnSO 4 . Both zinc salts caused reductions in photosynthetic pigment and protein content at elevated concentrations, with ZnSO 4 exerting a more pronounced detrimental effect. Fourier‐transform infrared (FTIR) spectroscopy of isolated proteins revealed zinc‐induced structural modifications, evidenced by shifts in the amide I and II absorption bands, indicating alterations in protein secondary structure. Despite these structural changes, proteins isolated from zinc‐exposed biomass retained antioxidant activity. Collectively, these findings highlight the critical role of the anionic counterpart in modulating zinc toxicity and bioaccumulation in A. platensis . ZnCl 2 proved less harmful than ZnSO 4 , allowing higher growth limits and enhanced zinc uptake. This salt‐specific tolerance has important implications for selecting zinc compounds in the cultivation of A. platensis to optimize biomass yield and the production of zinc‐enriched bioactive substances.