Antioxidant assessment of wastewater-cultivated Chlorella sorokiniana in Drosophila melanogaster

Microalgae play a critical role as a sustainable and abundant source of natural antioxidant compounds, leading to a potential market for microalgae-based food or feed supplements. Currently, this market development is limited by high cost of biomass production due to the large quantities of water and nutrients required for microalgae cultivation. It has been demonstrated that this barrier could be overcome by microalgae cultivated in wastewater containing nutrients. However, there is a pressing need to investigate how the wastewater medium influences antioxidant characteristics of microalgae. This study examined the antioxidant effects of wastewater-cultivated microalgae Chlorella sorokiniana (C. sorokiniana) using Drosophila melanogaster (fruit fly) as the animal model. Characteristics representing antioxidant properties such as fly lifespan, behavioral activities and stress resistance capacities, together with the potential underlying antioxidant mechanism were assessed. Results showed that flies fed on 4 mg/mL wastewater-cultivated C. sorokiniana had significantly extended median lifespan (55 days vs 49 days for control), and improved locomotor activity with increased step size and longer travel distance, although no significant differences in struggling activity was observed. Moreover, C. sorokiniana diet provided flies with protective responses to both H₂O₂-induced oxidative stress and anoxia-induced disturbance on brain ion homeostasis. These aforementioned effects were associated with the mRNA up-regulation of endogenous stress-defense genes such as Cu/Zn-superoxide dismutase (SOD1) and catalase (CAT) as well as the down-regulation of Methuselah (MTH) gene. Finally, flies fed on C. sorokiniana demonstrated similar feeding behavior and boundary preference, suggesting that C. sorokiniana supplementation did not cause starvation. This study demonstrated that C. sorokiniana grown on wastewater still maintained antioxidant properties in fruit fly, further providing new insights into the feasibility of wastewater-grown microalgae as a natural antioxidant alternative.