Chlorella fusca LEB 111 and Spirulina sp. LEB 18 cultivated in brewery effluent: Phytohormonal profiles and associated effects on seed germination and lettuce performance under drought

Brewery wastewater can serve as a nutrient source for microalgal cultivation, while microalgae contain bioactive compounds, including phytohormones, with potential to influence plant development and stress responses. This study characterized the phytohormonal profiles of Chlorella fusca LEB 111 and Spirulina sp. LEB 18 biomass cultivated in brewery wastewater and evaluated their association with the effects of aqueous extracts on seed germination and root development of barley and lettuce, as well as on lettuce physiological responses and fresh weight under drought stress. Both species were successfully cultivated in the effluent, with Spirulina sp. reaching higher biomass productivity. Their biomasses displayed distinct phytohormonal profiles: Spirulina sp. contained higher auxin and gibberellin concentrations, whereas C. fusca showed higher concentrations of salicylic and jasmonic acids. In the seed bioassays, Spirulina sp. extract increased barley germination by 58% and approximately doubled root length relative to the control. Under severe drought, Chlorella -treated lettuce maintained fresh weight comparable to well-watered plants, with values 46.5% higher than the drought-stressed control, and showed an electron transport rate 25% higher than the same control. Because phytohormones were quantified in dried biomass rather than in the aqueous extracts applied to seeds and plants, these relationships should be interpreted as associations rather than direct evidence of causation. Overall, brewery-wastewater-grown C. fusca and Spirulina sp. exhibited distinct phytohormonal profiles associated with complementary plant responses, supporting further investigation of these biomasses as sources of functionally differentiated biostimulants.