Characterization of growth and arachidonic acid production of Parietochloris incisa comb. nov (Trebouxiophyceae, Chlorophyta)

Arachidonic acid (AA) is a precursor of biologically active prostaglandines and leukotrienes. The commercial source for AA at present is a fungus, but the recently discovered coccoid green alga, Parietochloris incisa comb. nov., in which over 90% of total AA is deposited in triacylglycerols, makes this species a potential candidate for commercial production of AA. We investigated the effect of the light-regime on cell-AA content and on culture productivity, by manipulating the intensity of the light source, the length of the light-path (LPL), and the population density of cultures grown in flat plate glass reactors under both controlled laboratory conditions (continuously illuminated) as well as outdoors. The effect of nitrogen deprivation on culture content of AA and its productivity was also studied. In all experiments, the longer light-path reactors with the highest areal volumes (L m^-2) yielded the highest culture-AA or the highest amount of AA harvested per illuminated reactor surface. Highest culture content of AA was obtained in cultures exposed to strong light and nitrogen-deprivation. In contrast, highest cell-AA content was obtained in cultures receiving the lowest light-dose. Maximum culture content of AA obtained in the laboratory was 2667 mg L^-1, reached after a 38-day growth period (of which the final 17 days took place in nitrogen-free medium), under continuous exposure to 2000 μmol photon m^-2 s^-1. Maximal culture content of AA outdoors was significantly lower compared with the maximum obtained in the laboratory.