Production of DHA in Microalgae in Low pH Medium
Methods for production of highly unsaturated fatty acids by marine microorganisms, including the heterotrophic marine dinoflagellate Crypthecodinium, using low levels of chloride ion are disclosed. Specifically, methods of increasing production of highly unsaturated fatty acids by marine microorganisms while growing in low chloride media by manipulating sodium ion and potassium ion levels. The invention also relates to methods of production of highly unsaturated fatty acids by marine organisms at low pH levels, and includes methods for generation of low pH tolerant strains.
1 . A method of producing docosahexaenoic acid (DHA) by culturing heterotrophic microalgae of the class Dinophyceae in a culture medium, wherein the culture medium has a pH of less than about 6.0, and wherein the microalgae produces at least about 0.04 g DHA per liter of 7-day culture.
2 . The method of claim 1 , wherein the microalgae is of the genus Crypthecodinium.
3 . The method of claim 1 , wherein the microalgae is of the species Crypthecodinium cohnii.
4 . The method of claim 1 , wherein the pH is less than or equal to about 5.5.
5 . The method of claim 1 , wherein the pH is less than or equal to about 5.0.
6 . The method of claim 1 , wherein the pH is or equal to about 4.5.
7 . The method of claim 1 , wherein the medium further comprises:
(a) chloride ion at a concentration of less than or equal to about 2 g/l; and
(b) potassium ion at a concentration of greater than or equal to about 0.25 g/L.
8 . The method of claim 7 , wherein the concentration of chloride ion is less than or equal to about 1.0 g/l.
9 . The method of claim 7 , wherein the concentration of chloride ion is less or equal to than about 0.3 g/l.
10 . The method of claim 7 , wherein the concentration of potassium ion is greater than or equal to about 0.4 g/L.
11 . The method of claim 7 , wherein the concentration of potassium ion is greater than or equal to about 0.8 g/L.
12 . The method of claim 7 , wherein a source of potassium ion is potassium sulfate.
13 . The method of claim 7 , wherein the medium further comprises sodium ion at a concentration of from about 1 g/L to about 8 g/l.
14 . The method of claim 13 , wherein the concentration of sodium ion is from about 1.5 g/l to about 5 g/L.
15 . The method of claim 13 , wherein a source of sodium ion is sodium sulfate.
16 . The method of claim 13 , wherein the concentration of potassium ion is about 0.8 g/L, the concentration of sodium ion is about 3.2 g/L and the pH is about 5.0.
17 . The method of claim 13 , wherein the concentration of potassium ion is about 0.8 g/L, the concentration of sodium ion is about 3.2 g/L and the pH is about 4.5.
18 . A biomass produced by the method of claim 1 .
19 . The method of claim 1 , wherein the microalgae produces at least about 0.10 g DHA per 10 9 cells.
20 . The method of claim 1 , wherein the microalgae produces at least about 0.20 g DHA per 10 9 cells.
21 . The method of claim 1 , further comprising recovering a DHA-containing lipid from the microalgae.