Acyl lipids of three microalgae

Abstract

Acyl-lipid composition of Isochrysis galbana, Porphyridium cruentum and Phaeodactylum tricornutum from stationary-phase cultures has been analyzed by TLC and GC. Additionally, P. tricornutum from an outdoor tubular photobioreactor was also studied. Neutral (NLs) and glyco (GLs) lipids were found in similar amounts of ca 40–45% each, with phospholipids (PLs) representing ca 10–20%. The major lipid classes were triacylglycerol (TAG), monogalactosylaylglycerols (MGD), and galactosylacylglycerols (DGD), usually in that order. The P. tricornutum biomass taken from the bioreactor showed a distinctive acyl-lipid composition. GL content was nearly twice (56%) that of the indoor culture (31%) and NL content (31%) was nearly half that of the indoor culture (54%). These changes mainly involved TAG and MGD. The fatty acid composition of lipids in the outdoor culture generally remained unaffected, except for MGD, DGD, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), in which eicosapentaenoic acid (EPA) content was greatly increased. TAG, the main class of lipids, always contained a high proportion of EPA, 16:0 and 16:1. In the typical (SQD) composition, 14:0, 16:0 and 16:1 accounted for around 70% of fatty acids, with small amounts of polunsaturated fatty acids (PUFAs). The lipid classes which typically had the highest PUFA content in the microalgae were MGD and DGD. In P. tricornutum, these lipids characteristically contained a large proportion of 16:1, 16:2, 16:3 and 16:4. PC, which was composed of the main C 16 fatty acids and the major PUFAs, was usually the most abundant phospholipid. Phosphatidylgycerol showed an accumulation of 16:1 (probably a mixture of 16:1n7 and 16:1n3 trans) as a distinctive feature. Phosphatidylinositol was characterized by 16:0 and 16:1 (and 14:0 in I. galbana), which together accounted for over 50% of fatty acids, and significant presence of the main PUFAs. There was no consistent fatty acid pattern for PE in the three microalgae studied. PE was exceptional in I. galbana, containing 61% docosahexaenoic acid.