Antioxidant and antimicrobial effects of Spirulina platensis supplemented with magnesium and zinc

This study was carried out to investigate the effect of different levels of magnesium (Mg) and zinc (Zn) on the growth, bioaccumulative capacity, protein and amino acid content, phytochemical content, antioxidant activity and antimicrobial activity of S. platensis, a cyanobacterium. The aim is to produce Spirulina by exposing it to mineral stress conditions to enrich its magnesium and zinc content while enhancing the production of organic and bioactive compounds, followed by evaluating its antioxidant and antimicrobial activity. These results show that magnesium and zinc mineral enrichment did not significantly affect Spirulina cell density throughout the experiment. Optic density values in the control group (0,230 ± 0,000) were generally similar or close to those of the mineral enrichment treatments, while the control group had the highest protein content (70,34%). The total phenol content of the magnesium-enriched groups was significantly higher than that of the zinc-enriched and control groups. Spirulina biomass enriched with Zn-5 mg/L, showed the highest degree of DPPH inhibition 101,346±9,274% for the methanol extract and 103,941±13,81% for the ethanol extract. All extracts showed antimicrobial activity against E. coli, K. pneumonia, S. aureus, B. cereus, C. albicans and A. flavus at a concentration of 100 mg/mL. Gram-positive S. aureus was the most sensitive bacterial species to Mg-200 mg/L methanolic extracts, followed by Zn-5 mg/L and Mg-100 mg/L with inhibition zones of 20 ± 1,31; 20 ± 0,00 and 19,5 ± 0,61 mm diameter, respectively.