Possible Evolutionary Significance of Polyunsaturated Fatty Acids in Blue–Green Algae

Abstract

AMONG eukaryotes, α-linolenic acid (18 : 3α) and certain related polyunsaturated fatty acids occur as major fatty acids only in photosynthetic organisms¹, where they are concentrated in chloroplasts as components of the acyl lipids². Photosynthetic bacteria, by contrast contain saturated and monounsaturated fatty acids exclusively, a character which they share with nearly all non-photosynthetic bacteria^3–5. Blue–green algae are the only prokaryotes which photosynthesize as do green plants, and their fatty acid composition is thus of particular interest from the evolutionary standpoint. Many filamentous blueαgreen algae have been shown to contain polyunsaturated fatty acids^6,8,9, but these compounds are absent from three unicellular blue–green algae so far examined: Anacystis nidulans, Anacystis marina and Synechococcus cedrorum^6,7,9. This has prompted us to undertake a more extensive survey of the fatty acid composition of blue–green algae, with particular attention to unicellular representatives.