BIOSYNTHESIS OF EUKARYOTIC LIPID MOLECULAR-SPECIES BY THE CYANOBACTERIUM SPIRULINA-PLATENSIS

This report brings evidence that a prokaryotic photosynthetic organism can synthesize eukaryotic molecular species of glycerolipids. When Sp irulina platensis PCC 8005 was supplemented with oleic acid, the sum o f the percentages of 18 carbon (C18) fatty acids in monogalactosyldiac ylglycerol (MGDG), the major lipid class, became largely higher than 5 0 mol%. This was absolutely unexpected from the well-known structure o f cyanobacterial lipids. In these organisms, C18 fatty acids usually a ccount for less than 50 mol% because they are esterified on carbon 1 o f the glycerol, exclusively. This classical feature was 99% confirmed in control as well as in palmitate-supplemented cultures. The major mo lecular species of MGDG, which resulted from the different distributio ns of fatty acids on carbons 1 and 2 of glycerol, were C18/C16 type, b elonging to the so-called ''prokaryotic'' type of lipids. By contrast, the molecular species of MGDG from oleate-supplemented cultures consi sted of only 74 mol% of C18/C16 and the complementary 26 mol% were C18 /C18, the so-called ''eukaryotic'' type of lipids, Furthermore, such C 18/C18 lipids were also evidenced as traces (< 1%) in control cultures . These results underline the fact that the fatty acid specificity of 1-monoacylglycerol-3-phosphate-acyltransferase (in Spirulina) is not a s absolute as the widely accepted concept of prokaryotic lipid would s uggest. Oleate, supplemented at high concentration, can be compelled t o act as a substrate for the acyltransferase and this results in the a ppearance of C18/C18 ''eukaryotic'' lipids in a prokaryotic organism.