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The edible oils extracted from microorganisms that are single-celled entities present at the bottom of the food chain are known as single cell oils. Different types of fungi and yeasts are the best producers with highest oil contents followed by various key algal groups with the capability of producing high levels of PUFA with nutritional significance. The potentiality of algae to produce PUFA has currently galvanized the interest in these fatty acids enriched single cell oils essential for the well being of mankind that are actually not available from plants or animals.
Although potential producers of single cell oils, opportunities for the biotechnological exploitation of the microorganisms are yet limited to the high-value products. Recently an attempt to produce a species of yeast, oil equivalent to cocoa-butter did not materialize due to a reduction in the price of cocoa butter in the world market and not due to inability of development of correct formulation of fatty acids. Production of PUFAs of both the n-3 and n-6 series from bacteria, fungi or algae are gaining better prospects in recent times. It is also observed that certain microbial PUFAs are devoid of other PUFAs, making the purification of desirable fatty acids quite easy than from other sources. Some microorganisms also generate precursors of prostaglandin and also prostaglandins themselves along with cerebroside lipids that are not usually regarded as of microbial origin.
Various microorganisms now have evolved to produce SCO as the commercial source of docosahexaenoic acid (DHA) and arachidonic acid (ARA). SCOs are now extensively used as dietary supplements in infant products. To improve lipid yields a better understanding of genetics and biochemistry of oil accumulation in microorganism is quite essential. Also an understanding of the mechanism involved in the polyunsaturated fatty acids (PUFAs) production is also highly desirable for increasing the oil content. A report on the biosynthetic machinery revealed that oil accumulation in oleaginous species accounts of lipid build up to more than 70% of the cell biomass. Whilst most of the microorganisms use a conventional fatty acid synthase (FAS) pathway for production of polyunsaturated fatty acids (PUFA) followed by a series of elongases and desaturases., it now appears to be via a polyketide synthase (PKS) system in Schizochytrium sp and probably in related thraustochytrid marine protists. It clearly represents a major deviation from the conventional mechanism of fatty acid biosynthesis, possibly as a way to decrease the amount of NADPH needed in the overall production process.