Response of Arthrospira platensis to nitrogen depletion and the effect of aqueous extracts on tumor and non-tumor cells

The microalgae Arthrospira platensis (AP), commonly known as Spirulina, has gained widespread popularity as a food supplement in recent years. AP is particularly abundant in protein, B vitamins, iron, magnesium, potassium, and various antioxidants. In this study we aimed to evaluate the effect of nitrate limitation in the AP culture medium on AP growth and composition. In addition, the cytotoxicity of the respective aqueous AP extracts on three different mammalian cell-lines (HepG2, Caco2, L929) was tested. AP was cultivated over a 10-day period under nitrogen-rich (Nrich: 1.8 g/L) and nitrogen-deficient (Nlimited: 0.2-0.4 g/L) conditions in two separate experiments, each with three biological replicates (three bioreactors). Throughout the cultivation, the kinetic progress of dry biomass, pH, pigment content, the levels of essential elements (sulphur, phosphate, and nitrate) and the composition of elements in the harvested biomass was determined. While the biomass slightly but significantly differed, the phycocyanin concentration differed considerably (around 10-fold higher in the Nrich medium, p < 0.05). Aqueous extracts of the Nrich medium had significantly stronger effects on the cell membrane integrity and the metabolic activity of the cells than extracts of the Nlimited medium. Particularly was the finding that AP had a significantly stronger toxic effect on the two tumour cell types (HepG2, Caco2) than on the non-tumour cells (L929). This study underscores the significance of nitrate content in the cultivation media of AP.