Arachidonic acid production by the red algaPorphyridium cruentum

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Abstract
The single‐celled alga,Porphyridium cruentum, was assessed by means of chromatographic separation and mass spectral analysis of its fatty acids to be a potentially competetive source of arachidonic (5,8,11,14‐eicosatetraenoic) acid. Models for both cell growth and production of the prostaglandin precursor at various temperatures and light intensities are presented. Increasing the light intensity within the range 1700–8000 lux increases the cell growth rate without affecting the arachidonic acid yield per cell; increasing the cultivation temperature from 18°C to ca. 32°C lowers the yield of arachidonic acid per cell but increases the rate of its production per unit volume and time. The increase of the weight ratio of arachidonic:palmitic acids at low temperatures is interpreted as a means of controlling the microviscosities of cellular membranes. In addition, the arachidonic acid content of cells decreases with the culture's age, despite increases in unit cell dry weight. The maximum rate of 0.46 mg arachidonic acid L−1h−1was calculated by means of the model to occur at ca. 32°C and 8000 lux in liquid cultures of 12 × 109cells/L. Estimates of the cost of producing arachidonic acid by means of this alga range from $0.15/g to $1.00/g of arachidonic acid. Cells grown at 18°C in the presence of 0.3% linoleic acid swelled and produced gorlic (13‐cyclopent‐2‐enyltridec‐6‐enoic) acid and another compound not normally observed. An estimated threefold increase of arachidonic acid content also occurred, but no significant lipogenesis was induced at 23°C in the presence of 1% kerosene or 0.3% palmitic, stearic, oleic, or linoleic acids.