Economically Important Protists

Pinguiophyceae

(contributed by Bob Bidigare, bidigare@soest.hawaii.edu)

Kawachi, M., I. Inouye, D. Honda, C. J. O'Kelly, J. C. Bailey, R. R.
Bidigare and R. A. Andersen. 2002. The Pinguiophyceae classis nova, a new
class of photosynthetic stramenopiles whose members produce large amounts
of omega-3 fatty acids. Phycol. Res. (in press).

Carotenoids are lipid-soluble isoprenoids found in a wide variety of aquatic organisms, including microalgae and photosynthetic bacteria, as well as certain crustacean invertebrates. Certain carotenoids (e.g., astaxanthin, zeaxanthin and beta-carotene) function as photo-protective pigments in microalgae. These pigments protect the photosynthetic apparatus (as well as other cellular components) from photo-destruction by dissipating excess light energy as heat or fluorescence. The oxygen-containing carotenoids (i.e. xanthophylls) are high-value products that are currently used as fish, shrimp, and poultry feed ingredients for enhancing the pigmentation of animal flesh and egg yolks. These compounds have tremendous potential as pharmaceutical and nutraceutical products since they have been shown to have strong anti-oxidant activity as well as being very effective for the preventive treatment of cancer and age-related macular degeneration. Of the wide range of natural pigments available from microalgae, the xanthophylls remain the most lucrative. The astaxanthin market, for example, is currently estimated at >130 million dollars per year. While other xanthophylls (e.g., lutein and zeaxanthin) are also in demand by industry, economical production systems are not currently available. Certain species of green algae (chlorophytes) synthesize large quantities of carotenoids under conditions of nutrient depletion, high salt, and/or high irradiance. For example, Haematococcus and Dunaliella, are known to accumulate astaxanthin and lutein/zeaxanthin when grown under "stressful" conditions, respectively. While Haematococcus is currently used as a commercial source of astaxanthin , other chlorophytes (including Dunaliella) hold promise as rich sources of lutein and zeaxanthin.

Polyunsaturated fatty acids (PUFAs) are gaining recognition as important components of the human diet. PUFAs have been implicated in lowering the incidence of certain cardiovascular diseases, improving neural and retinal development in infants, and slowing the growth of cancerous cells. Two important omega-3 PUFAs, eicosapentaenoic acid (20:5, n-3; EPA) and docosahexaenoic acid (22:6, n-3; DHA), are commonly found in marine fish oils, which has led to use of fish oil as a nutraceutical. However, because of oxidative stability problems and the presence of undesirable fatty acids, fish oil is not an ideal source for these PUFAs. Microalgae represent an excellent source of diverse PUFAs. Of the wide range of PUFAs potentially available from microalgae, EPA and DPA (n-3) remain the most lucrative. Certain species of golden-brown algae synthesize large quantities of PUFAs. For example, Schizochytrium sp. can be grown heterotrophically and is currently used as a commercial source of DHA and DPA (n-6). The latter is retro-converted in mammals via b-oxidation to arachidonic acid (20:4, n-6), an important omega-6 fatty acid which serves as a precursor for prostaglandins and other bioactive compounds which regulate growth and reproductive functions. The Pinguiophyceae, a novel class of golden-brown algae (Kawachi et al., 2002), accumulate large quantities of PUFAs and hold promise as a rich source of EPA.