Cell wall-specific ω-hydroxy fatty acids in some freshwater green microalgae

Abstract

Ester-bound lipids from the cell walls of the green algae, Tetraedron minimum, Scenedesmus communis and Pediastrum boryanum, were analysed by gas chromatography-mass spectrometry. The double bond positions of the C 30, C 32 and C 34 mono- and C 30 and C 32 diunsaturated ω-hydroxy fatty acids obtained were determined by derivatisation with dimethyl disulphide (DMDS) prior to mass spectrometric identification. All unsaturated ω-hydroxy fatty acids have a double bond located at the ω9-position, whilst the C 30 and C 32 diunsaturated acids have a second double bond at the ω19 and ω18 positions, respectively. Unsaturated ω-hydroxy fatty acids are released upon saponification of the isolated cell walls in all three algae, but the distribution patterns of these compounds differ between species. ω-Hydroxy fatty acids are the main building blocks of the highly cross-linked constituent of the cell walls, herein termed algaenan, in which linear chains of esterified monomers are ether cross-linked at the position of the double bonds. Because none of these monomeric compounds were observed in the cytosolic fraction of the cells, it is believed that they are rapidly secreted and incorporated in the aliphatic cell walls of these algae.