Fatty acid desaturation-defective mutants of an arachidonic-acid-producing fungus, Mortierella alpina 1S-4

SUMMARY: Three mutants, which were defective in the desaturation of fatty acids, were isolated from an arachidonic-acidproducing fungus, Mortierella alpina 1S-4, after treating wild-type spores with N-methyl-N′-nitro-N-nitrosoguanidine. They were designated Mut44, Mut48 and Mut49. Mut44 was a mutant with low Δ5-desaturase activity. It accumulated a high level of dihomo-λ-linolenic acid (DGLA) (28.6%, w/w) but a low level of arachidonic acid (Ara) (10.6%), compared with the wild type, which had levels of 6.3 and 47.0%, respectively. Mut48 was unable to desaturate oleic acid (18:1) to linoleic acid (18:2), i.e. Δ12-desaturation, and therefore a large amount of 18:1 (49.5%) accumulated and no fatty acid of the ω-6 family was detected. In addition, several fatty acids of the ω-9 family, such as 5,8,11-cis-eicosatrienoic acid, were found. In Mut49, 18:2 (46%) accumulated markedly, but only small amounts of DGLA and Ara were detected. Thus, Mut49 was considered to be defective in Δ6-desaturation. These mutants showed a somewhat longer lag phase than the wild type on cultivation at both 28 and 12 °C.