The primary metabolome of psychrophilic and mesophilic green algae at low temperature
To understand low temperature responses, we analyzed the primary metabolome of both algal species acclimated to low growth temperatures (4°C, 10°C, 15°C – UWO241; 10°C, 15°C, 28°C – C. reinhardtii ). We detected 771 unique metabolites, 163 of which were positively identified based on their mass spectra and retention times (Kindet al. 2009). PCA analysis revealed species-specific differences in the primary metabolomes along both components, regardless of the culturing temperature (Figure 2). The metabolic status of C. reinhardtii was dependent on the culturing temperature and differed between both components. This contrasted with UWO241 where temperature had minimal effects on the overall metabolic status, and we observed only nominal separation between the cultures grown at different temperatures (Figure 2).
Differentially accumulated metabolites (DAMs) were defined as those exhibiting a 2-fold change in accumulation between at least two of the treatments (p<0.01, ANOVA, Tukey’s post-hoc). Approximately 50% of the metabolites (392 out of 771) were identified as DAMs, with significant differences between species (Table 1). Hierarchical clustering analysis (HCA) revealed the following trends (Figure 3A): (1) The metabolome ofC. reinhardtii responded strongly to growth temperature with 273 (35%) DAMs at 10°C compared to optimal temperature of 28°C. This response was temperature dependent, with cultures at 15°C exhibiting a similar metabolite profile but with a decreased magnitude of the response (72 DAMs, 9%) (Table 1; Figure 3A). (2) The metabolic profile of UWO241 was similar regardless of the culturing temperature. Cultures at 4°C had only 48 (6%) and 78 (10%) DAMs when compared to 10°C and 15°C, respectively (Table 1; Figure 3A). These findings indicate that the mesophile grown at low temperatures experiences cold stress and adjusts its metabolome accordingly. In contrast, the metabolome of the psychrophile is stable at temperatures between 4°C and 15°C.