The very long-chain polyunsaturated fatty acids (vlcPUFAs) eicosapentaenoic (EPA), docosahexaenoic acid (DHA), and arachidonic acid (AA) are well known for their nutritional importance. As they confer flexibility, fluidity, and selective permeability properties to cellular membranes, they have been shown to be vital for brain development and beneficial for the cardiovascular system and for other im­portant nutraceutical and pharmaceutical targets in human and animal health (Funk 2001; de Urquiza 2000; Colquhoun 2001). For example, vlcPUFAs are found in many different product applications including formulas for infants, adult dietary supplements, animal feed, food additives, and pharmaceutical precursors. These ap­plications represent an extensive market for vlcPUFAs: the world wholesale market for infant formula alone is estimated to be about $ 10 billion per annum (Ward and Singh 2005).

Animals lack the capability to synthesize vlcPUFAs, and therefore these essen­tial fatty acids must be obtained from food/feed. Typically sources of PUFAs are oil-rich fish such as eel, mackerel, herring, salmon, and sardines (Ward and Singh 2005). Due to concerns over declining fish stocks and the potential for fish oils to be contaminated by a range of pollutants, the possibilities for obtaining these fatty acids from other sources have been investigated (Qi et al. 2004). Interestingly, the vlcPUFAs in oil-rich fish originate from marine microalgae that are eaten by the fish. Algal genes encoding relevant enzymes have been identified, and recently several groups have reported progress on using these genes to produce DHA and ARA in transgenic plants, including crops such as soybean, linseed, tobacco, and the model species Arabidopsis (Qi et al. 2004; Abbadi et al. 2004). By adding addi­tional genes to those that are needed to produce ARA and EPA, production of DHA has been established in soybean, Brassica juncea, and Arabidopsis (Robert et al. 2005; Wu etal. 2005).

An alternative approach is to use directly the algae that are the most efficient primary producers of the vlcPUFAs. Algae groups that contain vlcPUFAs include diatoms, crysophytes, cryptophytes, and dinoflagellates (Cohen etal. 1995; Behrens and Kyle 1996). High amounts of DHA, for example, are produced in the algae Crypthecodinium cohnii, Thraustochytrium spp., Schizochytrium spp, Isochrysis galbana, and Crypthecodinium spp. (Ward and Singh 2005). The algae Porphyrid — ium cruentum and Parietochloris incise accumulate AA (Zhang et al. 2002; Guil — Guerrero et al. 2000) and several species have been suggested for the production of EPA including Nitzschia spp., Nannochloropsis spp., Navicula spp., Phaeodatylum spp., and Porphyridium spp. (Tan and Johns 1996; Sukenik 1991; Molina Grima et al. 2003; Cohen et al. 1995). For additional information about the content of vlcPUFAs in different microalgae see Barclay et al. (1994), Wen and Chen (2003), and Ward and Singh (2005). A slight inconvenience with using algal feedstocks di­rectly for the production of vlcPUFAs is that in many species the accumulation of these fatty acids involves their presence in lipids other than triacylglycerides such as galactolipids. This makes their isolation more complicated. For vlcPUFA produc­tion directly from microalgae it has been estimated that the cost of producing EPA from Phaeodactylum tricornutum cultured in photobioreactors is about $ 4602 kg-1 (Molina Grima et al. 2003).