Changes in fatty acid profiles of thermo-intolerant and thermo-tolerant marine diatoms during temperature stress

Fatty acid composition and degree of fatty acid saturation during temperature stress in thermo-intolerant (Phaeodactylum tricornutum) and thermo-tolerant (Chaetoceros muelleri) marine diatoms were investigated. A greater number of fatty acids were observed in C. muelleri than in P. tricornutum regardless of treatment. The major fatty acids detected were 14:0, 16:0, 16:1, 16:2, 16:3, 18:0, 18:1(n-9)c, 18:2(n-6) and 20:5(n-3) with additional fatty acids 18:1(n-9)t and 20:4(n-6) detected in C. muelleri. Short duration (2 h) temperature increase above optimal growth temperature had a greater effect on fatty acid composition in C. muelleri than in P. tricornutum and the degree of fatty acid saturation was affected more by temperature in C. muelleri than in P. tricornutum during both short and long duration (24 h) treatments. Total protein assay results suggest that P. tricornutum, but not C. muelleri, was undergoing stress under our growing conditions although lipids in both diatoms were affected by increased temperature. Immunodetection of proteins with anti-rubisco indicates that the rubisco large subunit was undergoing greater turnover in C. muelleri than in P. tricornutum. However, the integrity of rubisco as a suitable indicator of lipid status needs further study. This work supports the hypothesis that a particular temperature, and not treatment duration, has the greater effect on changes in fatty acid composition. Furthermore, changes in fatty acid composition and degree of fatty acid saturation occurred more quickly in the diatoms in response to increased temperature than previously observed in nutrient starvation studies. Since diatom lipids represent an important resource for growth and reproduction of marine animals, the rapid alteration of their lipid composition under temperatures normally encountered in marine environments warrants further study.