Properties of the docosahexaenoic acid-producer Schizochytrium mangrovei Sk-02: effects of glucose, temperature and salinity and their interaction

Abstract

A number of variables potentially affecting docosahexaenoic acid (DHA) formation in Schizochytrium mangrovei Sk-02 were studied in shaken flasks using yeast extract (10 g l-1) as a nitrogen source. Usage of fructose, galactose, glucose, glycerol and mannose (60 g l-1) in yeast extract-containing media resulted in production of 3–4 g l-1 DHA, with a lower value for galactose. The highest DHA-content (28% w/w) was observed with glycerol. Disaccharides (maltose and lactose) resulted in poor growth. At a fixed glucose level (60 g l-1), biomass and DHA-levels reached a maximum at 25 g l-1 artificial sea salts (ASS). Replacement of ASS by various sodium salts reduced biomass and DHA-yields. Initial medium pH (4–7) had little effect on biomass or DHA-formation, but increasing temperature (25–40°C) negatively affected biomass and DHA-content, though not the ratio of saturated to unsaturated fatty acids. In addition, various combinations of glucose (45, 60 and 75 g-1), temperature (25 and 30°C) and salinity (5, 15 and 25 g l-1 ASS) were tested. In general, both biomass and DHA-levels (as g l-1) increased with increasing glucose, whereas DHA-, but not biomass levels were negatively affected by temperature. The DHA-weight content decreased with temperature. The effect of salinity was not clearly defined. Maximal DHA-level obtained was 4.7 g l-1 (75 g l-1 glucose, 15–25 g l-1 ASS and 25°C). We calculate that in a standard medium, only 42% of glucose consumed was directly converted into fatty acids.