Skeletonema marinoi, Sarno & Zingone, 2005

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

2.6. Changes in the endometabolome composition of S. marinoi in response to the short- and long-term salinity stresses

Both P. tricornutum and T. pseudonana were subjected to salinity stress of 60 PSU. However, S. marinoi showed no further growth at salinities of 60 or 55 PSU. For this reason, the analysis of the endometabolome composition for this diatom was investigated in response to the increase in salt concentration to 50 PSU where it still grew.

Similar to the results obtained for two other diatoms, salinity stress led to significant changes in the endometabolome composition ( Fig. 3 ). Consitently with the data from the other diatoms, increase in cell count normalized metabolite concentrations was also observed for S. marinoi as a response to the salinity stress.

An increase in amino acid content, especially in proline and 4-hydroxyproline, was detected in salinity stressed cultures of S. marinoi (Table S3). Interestingly, conversely to results obtained for P. tricornutum and T. pseudonana , no saccharide accumulation was detected for S. marinoi in response to the elevation of the salt content at any time point. However, the up-regulation of both myo- and scylloinositols and putatively identified glyceryl-glycoside was observed for S. marinoi in response to the long-term salinity stress. Also, similar to the two other diatoms, the concentration of pyrrole-2-carboxylic acid was increased in stressed cultures of S. marinoi at both analyzed time points.

Furthermore, an increase in the content of four different acylcarnitines was observed for this diatom in response to the short-term salinity stress. Butyrylcarnitine and propionylcarnitine were also detected in P. tricornutum , two others unique to S. marinoi were acetylcarnitine and isovalerylcarnitine. Moreover, similar to P. tricornutum , content of cysteinolic acid increased in salinity stressed cultures at both analyzed time points ( Table 1).

Similar to T. pseudonana , an increase in glycine betaine content was observed in high-salinity cultures of S. marinoi . Statistically significant up-regulation of glycine betaine was detected at both time points for this diatom.

Overall, the number of significantly dysregulated compounds detected with GC-MS increased from 21 to 51 over time of salinity stress adaptation (Fig. S14, S16). Almost all significantly increased metabolites after 24 h were also significantly up-regulated 96 h after the treatment (19 out of 21). Conversely, the number of metabolites detected with LC-MS 24 h after the stress was higher than at 96 h time point (62 compounds detected for the 24 h time point, compared to 22 detected for the 96 h time point) (Fig. S15, S17). In turn, 18 out of 22 up-regulated metabolites after 96 h were the same as at 24 h. Down-regulation was detected only with LC-MS for three compounds 96 h after the treatment. Two of these metabolites (one of them leucine) were elevated 24 h after the stress exhibiting a transient maximum.

Figures

Fig. 3. Pairwise PCA plots for S. marinoi 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 4–5 (see Experimental 5.13.). (For interpretation of the colours in this figure legend, the reader is referred to the Web version of this article.)