A Study On The Compositions Of Fatty Acid, Neutral Lipids And Isotope Fractionation In Five Microalgae

Lipids which are called as ocean biomarkers are widely used in the Geochemical researches. Many factors impact the preservation of the lipids in the sediment. In this research, we incubate five marine microalgae, and first examine the composition of lipids during different growth phases. Then we study the differences between membrane lipids and metabolic storage lipids. Theδ13C composition of the five microalgae are also determined during different growth phases in order to analyse the alteration of carbon isotope during different periods. The main results and conclusions are listed as follows:1. The compositions of fatty acids and neutral in five microalgae during different growth phases14∶0,16∶3,16∶2,16∶1,16∶0,18∶3,18∶2,18∶1,18∶0,20∶5,22∶6 are the primary fatty acids in the five microalgae.Platymonas helgolanidica, Dunallelia salina, Alexandrium tamarense have more fatty acids in logarithmic phase than in stationary phase, especially 16∶0,18∶0 and 22∶6 change significantly during the growth phase. Concentrations of 16∶0,16∶1 and 20∶5 in Phaeodactylum tricornutum, Synechocoocus sp. during the logarithmic phase are as twice as stationary phase.2. The compositions of membrane lipids and intracellular lipidsThe concentrations of fatty acids are less in the intracellular lipids. The saturated fatty acids 16∶0 and 18∶0 are the primary fatty acids. We can also find 14∶0 in the two parts of algae, but its concentration is low.With the onset of logarithmic phase, the composition of membrane lipids is more complex than the intracellular lipids. Saturated fatty acids are the main fatty acids during the whole growth phase, the concentrations and species of unsaturated fatty acids are less than of saturated fatty acids.In the stationary phase, the species of fatty acids in the five algae increase, and we can find more unsaturated fatty acids. The main membrane fatty acids are 16∶0 , 18∶2,18∶1 and 18∶0. During this phase, the concentration of unsaturated fatty acids is more than saturated fatty acids. The concentration of membrane lipids is lower than the intracellular lipids.3. Stable isotopic compositionFatty acids extracted from Platymonas helgolanidica and Dunallelia salina during stationary phase are depleted in 13C relative to it in the logarithmic phase. The range is opposited in Alexandrium tamarense, Phaeodactylum tricornutum and Synechocoocus sp..Membrane polyunsaturated fatty acids, 20∶5,18∶2 and 16∶2, are slightly enriched in 13C in the logarithmic phase. Membrane saturated fatty acids of Platymonas helgolanidica and Dunallelia salina are enriched in 13C during logarithmic phase, oppositely these lipids of Alexandrium tamarense, Phaeodactylum tricornutum and Synechocoocus sp are enriched in 13C in stationary phase.Intracellular lipids in Platymonas helgolanidica and Dunallelia salina are enriched in 13C related to membrane lipids during logarithmic phase. This range is reversed in stationary phase.δ13C of individual compounds of different resources varies from 0 to 1‰.Membrane lipids in Platymonas helgolanidica and Dunallelia salina are enriched in 13C related to intracellular lipids during logarithmic phase, vary by up to 0.5‰. In stationary phase, 18∶1 of Phaeodactylum tricornutum and 18∶0 of Synechocoocus sp are depleted in 13C relative to it in intracellular lipids.δ13C of individual compounds of different resources varies from 0 to 4‰.