Growth and pigment variation of 92 green algal strains (Scenedesmaceae) under salinity stress

Freshwater microalgae often encounter transitional environments such as estuaries and lagoons, where fluctuating salinity imposes stress that disrupts osmotic imbalance, induces ion toxicity, and promotes excessive production of reactive oxygen species in algal cells. To withstand these conditions, microalgae employ physiological strategies, including ion transport regulation, osmolyte accumulation, and antioxidant defense systems. Carotenoids, in particular, serve dual roles as accessory pigments in photosynthesis and as potent antioxidants that scavenge singlet molecular oxygen and peroxyl radicals, thereby protecting cellular components. Beyond their ecological function, carotenoids are of biotechnological interest due to their commercial value as natural antioxidants. Members of the family Scenedesmaceae, a group of freshwater green algae, show diverse stress tolerances mediated by secondary metabolite production. In this study, we investigated growth and pigment variation in 92 Scenedesmaceae strains under control (0 psu) and salinity stress (30 psu) conditions over 4 weeks. Five strains demonstrated notably high pigment productivity efficiency under control conditions, while 46 strains survived salinity stress. Remarkably, eight strains accumulated higher pigment levels under salinity stress than in control conditions. Phylogenetic analysis revealed that adaptation to salinity stress is species- or strain-specific. These findings provide new insights into the mechanisms of salinity adaptation in green algae and underscore their potentials for biotechnological applications.