Omega-3/6 fatty acids: Alternative sources of production Owen P. Ward * , Ajay Singh Department of Biology, University of Waterloo, Waterloo, Ont., Canada N2L 3G1 Accepted 14 February 2005 Abstract Polyunsaturated fatty acids (PUFAs) are essential components of higher eukaryotes. Single cell oils (SCO) are now widely accepted in the market place and there is a growing awareness of the health benefits of PUFAs, such as g-linolenic acid (GLA), arachidonic acid (ARA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). ARA and DHA have also been used for fortification of infant formulae in many parts of the world. Fish oils are rich sources of DHA and EPA and a limited number of plant oilseeds are good sources of other PUFAs. Marine protists and dinoflagellates, such as species of Thraustochytrium, Schizochytrium and Crypthecodinium are the rich sources of DHA, whereas microalgae like Phaeodactylum and Monodus are good sources of EPA. Species of lower fungi Mortierella accumulate a high percentage of ARA in the lipid fraction. In this paper, various microbiological and enzymatic methods for synthesis of PUFAs are discussed. # 2005 Elsevier Ltd. All rights reserved. Keywords: Polyunsaturated fatty acids; Highlyunsaturated fatty acids; PUFA; HUFA; Omega-3; Omega-6; Eicosapentaenoic acid; Docosahexaenoic acid; Arachidonic acid; Single cell oil; Marine protists; Microalgae; Lower fungi; Microbial production; Enzymatic synthesis 1. Introduction Polyunsaturated fatty acids (PUFAs) are essential components of higher eukaryotes. They confer flexibility, fluidity and selective permeability properties to membranes. The brain is particularly rich in arachidonic acid (ARA) and docosahexaenoic acid (DHA), and the latter is also a ligand for the retinoid X-receptor [1]. Eicosapentaenoic acid (EPA) has a beneficial effect on the cardiovascular system. PUFAs contained in membrane phospholipids (PL) are precursors for synthesis of prostaglandins, leukotrienes and thrombox- anes which bind to specific G-protein-coupled receptors and signal cellular physiological responses to inflammation, vasodilation, blood pressure, pain and fever [2]. Conse- quently, PUFAs and their derivatives and analogues are important neutraceutical and pharmaceutical targets [3]. In 1989, we published a review in this Journal on ‘‘Omega-3 Fatty Acids: Alternative Sources of Production’’ [4]. Many exciting developments have occurred in this field in the past 15 years. This review attempts to update these developments. Single cell oils (SCO) are now widely accepted in the market place and there is a growing awareness of the health benefits of PUFAs, such that the market for specific products is predicted to expand and diversify. In addition, developments in processes for PUFA production are benefiting from advances in cell and molecular biology and recombinant technology. The major targets so far have been g-linolenic acid (GLA), ARA, DHA and EPA. While the term highly unsatursated fatty acids (HUFAs) is sometimes used to differenentiate higher from lower forms of PUFAs, in most cases we have retained the term PUFA. Strategies to develop processes for production of single cell oil should take account of lessons learned from attempts to commercialize processes for production of single cell proteins (SCP). During the period from 1960 to the mid- 1980s there was substantial activity in development and commercialization of processes to produce proteins from microorganisms as a source of food/feed for humans and animals. The general strategy to produce SCP by fermenta- tion failed dismally because of the lower cost of plant proteins,the stability of agricultural prices relative to industrial prices and the low value of food protein and particularly feed protein. Use of cheap hydrocarbon-based www.elsevier.com/locate/procbio Process Biochemistry 40 (2005) 3627–3652 * Corresponding author. Tel.: +1 519 888 4567x2427; fax: +1 519 746 0614. E-mail address: opward@sciborg.uwaterloo.ca (O.P. Ward). 1359-5113/$ – see front matter # 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2005.02.020