Taking the Heat: The Effect of Growth Temperature on Lipids of the Diatoms

Abstract

Diatoms are one of the largest groups of primary producers in the oceans, and because of their environmental and increasing economic importance, more information is being revealed about their lipid biochemistry. Mass spectrometry techniques were used to examine the lipids of diatoms, with particular focus on how growth temperature would affect different lipid classes. Galactolipid-associated fatty acid composition and regiochemistry was examined in a selection of diatoms. Two centric diatoms, Skeletonema marinoi and Thalassiosira weissflogii, and one pennate diatom, Phaeodactylum tricornutum, contained primarily C20/C16 (sn-1/sn-2) and C18/C16 forms of the galactolipids. The other pennate diatoms, Haslea ostrearia and Navicula perminuta, contained primarily C18/C16 or C18/C18 forms of these lipids. This shows a split in galactolipid profiles that does not correspond with the phylogeny of these organisms and their plastids.

The effect of different growth temperatures on the galactolipid fatty acids of H. ostrearia and P. tricornutum was also examined. At 20C, H. ostrearia and P. tricornutum were rich in eicosapentaenoic acid (EPA; C20:5) at the sn-1 position and C16 fatty acids at the sn-2 position of the galactolipids. At 30C, however, H. ostrearia and P. tricornutum contained no EPA or other C20 fatty acids, but rather contained higher percentages of C18 fatty acids at sn-1. When exposed to a higher growth temperature, both species cope by eliminating the longest and shortest fatty acid chains, as well as decreasing the total number of unsaturations, possibly reflecting a difference in their autecologies.

Finally, the hydrocarbons produced by P. tricornutum at 20 and 30C were examined. Innate production of hydrocarbons in diatoms could eventually lead to these organisms being used as direct sources of biofuels. P. tricornutum produced a number of different hydrocarbons, namely octane, undecane, nonadecane, and heneicosane at 20C. At 30C, however, the alkanes produced were heptadecane, octadecane, nonadecane, and eicosane, as well as three alkenes: heptadecene, octadecene, and nonadecene. The hydrocarbons produced are indeed in the ranges of hydrocarbons seen in petroleum fuels, like gasoline and diesel, and temperature does have a large impact on the hydrocarbons are produced.