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.