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Acclimation of Microalgae to Wastewater Environments Involves Increased Oxidative Stress Tolerance ActivityA wastewater environment can be particularly toxic to eukaryotic microalgae. Microalgae can adapt to these conditions but the specific mechanisms that allow strains to tolerate wastewater environments are unclear. Furthermore, it is unknown whether the ability to acclimate microalgae to tolerate wastewater is an innate or species-specific characteristic. Six different species of microalgae (Chlamydomonas debaryana, Chlorella luteoviridis, Chlorella vulgaris, Desmodesmus intermedius, Hindakia tetrachotoma, Parachlorella kessleri) that had never previously been exposed to wastewater conditions were acclimated over an eight week period in secondary-treated municipal wastewater. With the exception of C. debaryana, acclimation to wastewater resulted in significantly higher growth rate and biomass productivity. With the exception of C. vulgaris, total chlorophyll content was significantly increased in all acclimated strains, while all acclimated strains showed significantly increased photosynthetic activity. The ability of strains to acclimate was species-specific, with two species, C. luteoviridis and P. kessleri, able to acclimate more efficiently to the stress than C. debaryana and D. intermedius. Metabolic fingerprinting of the acclimated and non-acclimated microalgae using Fourier transform infrared spectroscopy was able to differentiate strains on the basis of metabolic responses to the stress. In particular, strains exhibiting greater stress response and altered accumulation of lipids and carbohydrates could be distinguished. The acclimation to wastewater tolerance was correlated with higher accumulation of carotenoid pigments and increased ascorbate peroxidase activity.