Lipid and fatty acid composition of freshwater cyanobacteria

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Abstract
Four species of freshwater cyanobacteria (Anabaena cylindrica, Anacystis nidulans, Nostoc canina and Nostoc muscorum) contained as major lipid classes monogalactosyldiacylglycerols, digalactosyldiacylglycerols, sulphoquinovosyldiacylglycerols and phosphatidylglycerols. Unlike photosynthetic eukaryotes, cyanobacteria incubated for 7 d in the dark suffered no decrease in the concentrations of these classes, except for N. muscorum. Growth, photosynthesis and nitrogen fixation were 30-40% lower after dark incubation. The nitrogen-fixing cyanobacteria, Anabaena cylindrica, N. canina and N. muscorum, contained alcohol glycosides and a highly-polar unknown glycolipid at high concentrations. The proportion of these two lipid classes decreased in the dark in N. muscorum alone. Extracts from Anacystis nidulans and N. canina, and to a lesser extent N. muscorum, contained sterols, whose concentration increased after dark incubation. Anabaena cylindrica contained considerable concentrations of linolenic acid in its total lipid, which did not decrease on dark incubation, and was not present mainly in monogalactosyldiacylglycerols as in photosynthetic eukaryotes. Palmitoleic acid, which is primarily confined to phosphatidylglycerols in photosynthetic eukaryotes, was distributed among the major lipid classes of N. canina.