Phaeodactylum tricornutum, Bohlin, 1897

Nikitashina, Vera, Stettin, Daniel & Pohnert, Georg, 2022, Metabolic adaptation of diatoms to hypersalinity, Phytochemistry (113267) 201, pp. 1-13 : 4

2.5. Changes in the endometabolome composition of P. tricornutum in response to the short- and long-term salinity stresses

For P. tricornutum , salinity stress also triggered significant changes in endometabolome composition. Separation between stressed and control cultures was observed in the PCA analysis of GC-MS and LC-MS data for both time points ( Fig. 2 ).

In response to the short-term salinity stress, the statistical analysis revealed an increase in content for the majority of the dysregulated compounds normalized to cell count. Only for one out of 69 dysregulated compounds detected with GC-MS down-regulation was shown, all 89 statistically significant compounds detected with LC-MS were up-regulated (Fig. S10, S11).

Among metabolites detected with GC-MS, the highest increase was observed for a putatively identified glyceryl-glycoside in response to short- and long-term salinity stresses. Interestingly, up-regulation of the same metabolite was also detected for T. pseudonana at both time points but with comparatively lower fold changes.

As for T. pseudonana , mainly amino acids and saccharides were among the identified up-regulated compounds. Also, similarly to T. pseudonana , up-regulation of pyrrole-2-carboxylic and threonic acid, ectoine, and its precursor N γ- acetyldiaminobutyrate was detected for this alga ( Table 1).

In contrast to T. pseudonana , increased concentrations of methyl palmitate, putrescine, and butyrylcarnitine were detected for P. tricornutum in response to the short-term salinity stress. Interestingly, in response to the long-term salinity stress butyrylcarnitine was not present among significantly up-regulated compounds, but increase in content of another acylcarnitine – propionylcarnitine was detected. Furthermore, statistically significant increase in the content of cysteinolic and pipecolinic acids, methionine, and adenosine was detected 96 h but not 24 h after the salinity stress for P. tricornutum (Table S2).

No clear pattern was found for the long-term adaptation. The amount of significantly dysregulated compounds detected with GC-MS decreased from 69 to 49 during the 96 h salinity stress adaptation of the algae (Fig. S12). For the LC-MS analysis, the number of statistically significantly changed metabolites conversely rose from 89 to 113 in course of time (Fig. S13).

PCA also showed two different trends for GC- and LC-MS analysis. According to the GC-MS results, the endometabolome composition of P. tricornutum was affected to a larger extent by the cultivation time than by salinity elevation ( Fig. 2E ). Cultures extracted at different time points were located further from each other than control and treated cultures from the same time point. Whereas, for LC-MS the clustering of treated and control cultures can be observed. High variation among stressed cultures at 24 h led to overlap with both control at 24 h and stressed cultures at 96 h ( Fig. 2F ).

Figures

Fig. 2. Pairwise PCA plots for P. tricornutum endometabolome samples extracted 24 (A, B) and 96 (C, D) hours after the salinity stress treatment. PCA plots of all data analyzed together (E, F). Panels A, C, and E show results from GC-MS. Panels B, D, and F result from the analysis of LC-MS data; the number of replicates analyzed is 5. (For interpretation of the colours in this figure legend, the reader is referred to the Web version of this article.)