This strain has been used for several past studies, and was concomitantly being tested in outdoor mass culture by another subcontractor (the University of Hawaii; principal investigator Dr. Edward Laws; discussed in Section III). Therefore, this strain was subjected to more extensive testing than the other strains in this subcontract. In one experiment reported for this strain, the

effects of light intensity on productivity were determined in batch cultures (i. e., in the Plexiglas culture apparatus described earlier without culture replacement and dilution). The maximum productivity observed for this strain (21 to 22 g dry weighPm — •d-) was observed at a total daily illumination of 63-95 kcal (representing approximately 40%-60% of full sunlight in southern California during the summer). This value was slightly higher than the productivity observed with a total daily illumination of 70% full sunlight (17.1 g dry weighHm-2^d-1). Productivities under N-limiting, continuous growth mode conditions were between 7 and 11 g dry weighHm-2^d-1. Likewise, productivities under N-sufficient, continuous growth mode conditions were reduced relative to batch cultures.

In addition to measuring overall productivities, the levels of protein, carbohydrate, lipid, and ash were determined for cells grown under the various conditions described earlier. Illumination of the cultures from 40% to 70% of full sunlight did not have a large impact on the cellular composition. Growth of P. tricornutum cells under N-deficient conditions resulted in a reduction of the protein content from 55% (in N-sufficient cells) to 25% of the cellular dry weight. Carbohydrate content increased from 10.5% to 15.1%, and the mean lipid content increased from 19.8% to 22.2%, although these differences in carbohydrate and lipid contents did not appear to be statistically significant. At one stage of the experiment, however, a time course of N deficiency led to a consistent rise in lipid content from 19.9% to 30.8% over the course of 7 days. The actual rate of lipid production did not increase, however, because the overall productivity of the cultures was reduced under N-deficient growth.