The culture conditions for high‐yield production of docosahexaenoic acid (DHA) by Schizochytrium sp. strain SR21 were investigated in a fermenter. With increasing carbon (glucose) and nitrogen (corn steep liquor and ammonium sulfate) sources (up to 12% glucose) in the medium, DHA productivity increased without a decrease in growth rate, i.e., 2.0, 2.7, and 3.3 g DHA/L/d with 6, 10, and 12% glucose, respectively. Eventually, 48.1 g dry cells/L and 13.3 g DHA/L were produced in 4 d with 12% glucose. DHA productivity was decreased with 15% glucose, i.e., 3.1 g/L/d. With 12% glucose, the lipid content was 77.5% of dry cells, and DHA content was 35.6% of total fatty acids. The lipid was composed of about 95% neutral lipid and 5% polar lipid. In polar lipids, the contents of phosphatidylcholine (PC), phosphatidylethanolamine, and phosphatidylinositol were 74, 11, and 5%, respectively. The PC profile was simple, 70% of PC molecules were 1‐palmitoyl‐2‐DHA‐PC and 1.2‐di‐DHA‐PC. These results indicate that Schizochytrium sp. strain 21 is an excellent source for microbial DHA production, including not only the acid form of DHA but also 2‐DHA‐PC.

A marine microbe (strain SR21) from the coral reef area of the Yap Islands was isolated by a screening test for polyunsaturated fatty acids and was found to accumulate lipid that contained 22:5n‐6 docosapentaenoic acid (DPA) as well as 22:6n‐3 docosahexaenoic acid (DHA). Strain SR21 was identified as genusSchizochytrium in Labyrinthulomycota, owing to its ultrastructural character and life cycle, which is composed of vegetative cell, zoosporangium, and zoospore stages. After cultural optimization, both in flask and fermenter, the highest DHA and DPA productivities of 2.0 and 0.44 g/L per day, respectively, were obtained in a medium of 60 g/L glucose and corn steep liquor/ammonium sulfate in a half salt concentration of seawater in fermenter culture at 28°C and pH 4. This productivity was almost twice that obtained with flask culture, indicating its high resistance to mechanical stirring. The lipid extracted from the cell was about 50% of the dry cell weight and was composed of 93% triacylglycerol (TG). DHA content of the lipid was 34% of total fatty acids. The TG profile was simple, and the content of the most dominant TG, 1,3‐dipalmitoyl‐2‐DHA‐TG, was 27%. TG that contained DHA and n‐6‐DPA amounted to 57 and 17%, respectively, of total TG molecules. Strain SR21 was revealed to be an excellent source of microbial DHA and n‐6 DPA.

The culture conditions for arachidonic acid (AA) production by Mortierella alpina 1S-4 were investigated by means of a morphological study with the aims of obtaining a high AA yield and scale-up. In a 50-L jar fermentor study, a medium containing 3.1% soy flour and 1.8% glucose with 0.3% KH 2 PO 4 , 0.1% Na 2 SO 4 , 0.05% CaCl 2 ⋅2H 2 O and 0.05% MgCl 2 ⋅6H 2 O was found to be optimum. The AA yield reached 9.8 g/L/7 d, and the major morphology was small pellets (1-2 mm). However, in the case of the only addition of KH 2 PO 4 , the major morphology was filaments. The apparent viscosity increased to 2240 cp, thereby requiring a high agitation speed to maintain adequate oxygen tension, which caused mycelial damage due to shear stress and therefore a decrease in the AA yield. When a medium with Na 2 SO 4 , CaCl 2 , and MgCl 2 was used, the major morphology was large pellets (2-3 mm), and mass transfer limitation through the pellet wall caused a decrease in the AA yield. Based on these results, a scale-up study was carried out under the optimal conditions described above. An AA yield of 10.9 g/L/8 d was obtained in a 10-kL industrial fermentor, and the major morphology was small pellets.

In this study, a new marine oil that contains 45% docosahexaenoic acid (DHA, 22:6n-3) and 13% docosapentaenoic acid (DPA, 22:5n-6) was administered to rats. The metabolism and distribution of DPA in rats was investigated. In experiment 1, the effects of DHA and n-6 fatty acids (linoleic acid, LA; arachidonic acid, AA; and DPA) on AA contents were investigated in vivo. LA group: LA 25%, DHA 30%; LA-DPA group: LA 15%, DPA 10%, DHA 35%; LA-AA-DPA group: LA 10%, AA 5%, DPA 10%, DHA 35% were administered to rats for 4 wk. In the liver, the AA content in the LA-DPA and LA-AA-DPA groups was significantly higher than in the LA group. The decreased AA contents in the LA group might be caused by DHA administration. Although DHA also was administered in the LA-DPA and LA-AA-DPA groups, the AA contents in these two groups did not decrease. These results suggested that DPA retroconverted to AA, blunting the decrease in AA content caused by DHA administration. To conduct a detailed investigation on DPA metabolism and its relation with AA and DHA, rat hepatocytes were cultured with purified DPA and DHA for 24 h. We discovered the retroconversion of DPA to AA occurred only when AA content was decreased by a high DHA administration; it did not occur when AA content was maintained at a normal level.

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