Effect of seawater on the growth and composition of the freshwater microalga Chlorella sorokiniana

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This study aimed to adapt the edible freshwater microalga Chlorella sorokiniana to seawater using adaptive laboratory evolution. The strain was successfully acclimated to salinity levels up to 30 g·L −1 , maintaining biomass yields. Seawater adaptation altered the biochemical composition of the biomass through successive batch cultivation over 95 days. The protein content decreased from 54.2 to 49.6 g·100 g −1 , which correlated with a down-regulation in total amino acid synthesis, except for proline, which increased by 78.5%. Lipid levels remained stable at approximately 16.5 g·100 g −1 . The fatty acid profile shifted towards higher saturated and monounsaturated fatty acids ( p < 0.05). Pigment concentrations also increased, particularly carotenoids, rising from 3.36 to 4.38 mg·g −1 ( p < 0.05) to act as antioxidant defence mechanism. Morphological changes included a two-fold increase in cell diameter (from 276 to 4.85 μm) and a shift towards rounder, more spherical shapes, indicating structural adaptation to osmotic stress by minimising membrane exposure to the saline environment. The findings demonstrate the capacity of C. sorokiniana to be produced in seawater without compromising biomass yield, while also exhibiting favourable shifts in biochemical and morphological traits that support its potential as a sustainable food source.