LAUSR

Abstract Co-deprivation of some photosynthetic electron transport mineral pairs is sought for enhancing antioxidant accumulation in a local isolate of Arthrospira (Spirulina) platensis, to improve their nutritional value and economic feasibility. The omitted element pairs were iron and sulfur (‑FeS), manganese and iron (‑MnFe) and nitrogen and sulfur (‑NS); chosen on the basis of their strong mediation in redox activities (Fe, Mn or S) or as sinks (N or S) of photosynthetic electrons. Antioxidant contents were estimated in 15 days old cells as growth of Arthrospira was not deteriorated by depriving the studied mineral pairs on the one hand and older cells tend to accumulate secondary compounds than younger ones whose bioenergetics are diverted into vegetative growth on the other hand. Iron‑sulfur, followed by iron‑manganese deprivation, induced the highest rates of photosynthtic oxygen evolution and respiratory oxygen uptake. Nitrogen‑sulfur starved cells, however, seem just survived as the increment of their dry mass relative to the inoculum was insignificant; they exhibited the lowest rates of photosynthesis with significantly enhanced respiration. A positive correlation between dry mass allocation and antioxidant accumulation can be deduced in the following order: ‑FeS > ‑FeMn > ‑NS. Vitamins A and tocopherols exhibited significant rise per unit dry mass (about fourfold that of the control) at ‑FeS while total antioxidants, reducing power and phenolics were more than doubled. FeMn pair deprivation sustained growth but did not enhance the accumulation of the targeted antioxidants. Under NS deprivation, neither Vitamin A nor tocopherols was enhanced although total antioxidants, reducing power and total phenolics were significantly higher than in control cultures. Soluble carbohydrates and free amino acids did not exhibit significant alterations in response to the imposed deprivations, indicating that enhancing the antioxidant accumulation did not take place at the expense of growth or primary metabolism in Arthrospira.