The effect of growth temperature on the long-chain alkenes composition in the marine coccolithophorid Emiliania huxleyi

The hydrocarbon fraction of a pure culture of Emiliania huxleyi, composed o f a mixture of C-31, C-33, C-37 and C-38 polyunsaturated n-alkenes, appeare d strongly dependent on the growth temperature of the alga between 8 degree s C and 25 degrees C. The total hydrocarbon content increased linearly with decreasing temperatures. C-37 and C-38 alkenes (which accounted for more t han 90% of the total hydrocarbons) showed distinct changes in distribution compared to C-31 and C-33 alkenes, suggesting different biological synthese s and/or functions for these two groups of compounds. C-37 and C-38 alkenes and C-37 methyl ketones (alkenones) all showed a trend to lower proportion s of the two diunsaturated isomers and to higher proportions of the corresp onding trienes with decreasing temperature. Unlike the alkenone unsaturatio n ratio (U-37(k')), ratios based on the C-37 and C-38 alkadi- and trienes c ould be linearly related to the growth temperature of E. huxleyi only betwe en 15 degrees C and 25 degrees C. The modifications in the distribution of alkenes induced by varying temperature appeared, however, to be twice as fa st as the modifications undergone by the alkenones. Although structurally a nd biochemically related, the distinct evolutions of alkenes and alkenones in response to changes in growth temperature might indicate that these two classes of compounds play two distinct physiological functions. The non-sys tematic linearity of relationships to temperature of parameters based on al kenes distribution suggested that these compounds are of limited use as pal eotemperature indicator in the marine environment in contrast with the alke nones. (C) 2000 Elsevier Science Ltd. All rights reserved.