ReviewThe versatility of algae and their lipid metabolism
Introduction
Eukaryotic algae are a very varied group of organisms which, perhaps, is only to be expected because of the extraordinary range of habitats in which they can be found. They are important components of many ecosystems which range from hot springs to snow and encompass freshwater and marine habitats. They also form important symbiotic partners with fungi in the majority of lichens. The systematic classification of algae is based primarily on their pigment components and there are nine divisions. The largest groups are Chlorophyceae (green algae), Phaeophyceae (brown algae), Pyrrophyceae (dinoflagellates), Chrysophyceae (golden-brown algae), Bacillariophyceae (diatoms) and Rhodophyceae (red algae).
The lipids (and lipid metabolism) of algae have been described in several reviews beginning with the book by Hitchcock and Nichols [1]. Please consult Guschina and Harwood [2] and references therein, for recent sources.
Section snippets
The heterogeneity of algal fatty acids and lipids
As befits their variable morphology and habitats, eukaryotic algae contain a diverse composition of acyl lipids and their fatty acids. Indeed, even within divisions, individual algae contain a bewildering array of compositions. It should also be borne in mind that the number of algae which have been examined comprehensively is relatively few and, furthermore, as with other phyla certain species have become favourite experimental organisms. The latter may or may not be representative of their
Algae as sources of polyunsaturated fatty acids
We have already referred to the relatively high content of VLCPUFAs in many eukaryotic algae. This has commercial importance (Section 5). A summary of the biosynthesis of such acids is made in Fig. 2. There are several points to note. First, there may be alternative pathways to produce a given product. Thus, eustigmatophytes can synthesise EPA from linoleic acid either via α-linolenic or γ-linolenic acids [2]. Additionally, in the usual conversion of α-linolenic acid to EPA, there is an
Isolated algal enzymes for use in producing polyunsaturated fatty acids
There is much current interest in using novel fatty acid metabolising genes from algae in order to modify crops for the production of useful products [9]. In particular, this has focussed on efforts to use crops for the supply of EPA and DHA. In order to utilise the plant n-3 PUFA α-linolenic acid, three desaturases as well as two elongation steps are needed for the normal pathway (Fig. 2). Earlier work to identify suitable desaturases and elongases from various lower eukaryotes has been
Commercial uses of algal lipids
The first reported use of “microalgae” by humans is that by the Chinese who utilised Nostoc and other edible cyanobacteria as an emergency food source some 2000 years ago. However, it is only in the last 50 years that the commercial exploitation of eukaryotic algae has taken place. This initially focussed on algal biomass as a source of protein and the systematic examination of algae for biologically-active compounds and pharmaceuticals. More recently, algae have been used successfully to produce
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