DISCUSSION
Algae have the fastest growth and maximal reproductive potential under optimal conditions, while stress is viewed as a threat to cellular homeostasis and leads to decreased growth and fitness (Borowitzka 2018). The Antarctic alga UWO241 experiences low but very stable temperatures of 4-6°C year-round, but we found that the growth rate was faster at 10°C and 15°C (Figure 1). This indicates that the biochemical and metabolic processes operating in UWO241 are better adjusted to optimal growth temperatures between 10-15°C than the temperature it experiences in nature (4°C), which would be considered a stress for UWO241 based on growth rates alone. Nevertheless, our metabolomic analyses showed that, despite the slower growth rates, UWO241 is adapted for life at 4°C. This was reflected in the fact that light- and CO2-saturated rate of O2 evolution for UWO241 grown at 4°C are comparable to the photosynthetic rate of C. reinhardtii grown at 28°C (Pocock, Koziak, Rosso, Falk & Hüner 2007).