دانلود رایگان مقاله اسیدهای چرب ضروری برای قارچ های روغنی مورتیرلا آلپینا

Abstract

Oleaginous fungus Mortierella alpina 1S-4 accumulates arachidonic acid (20:4ω6) as a major polyunsaturated fatty acid. However, 20:4ω6 is not essential for the growth of M. alpina 1S-4, because various mutants that produce no 20:4ω6 were isolated. M. alpina JT-180, a Δ12 desaturation-defective mutant that was derived from M. alpina 1S-4 by treatment with a chemical mutagen, accumulates Mead acid (20:3ω9) instead of 20:4ω6. p-Anisidine was found to be a Δ6 desaturation inhibitor in this study. The concentration of 0.1 mg/ml of p-anisidine had an inhibitory effect on the growth of M. alpina JT-180. The addition of p-anisidine to the medium caused M. alpina JT-180 to produce only monoenoic acids such as oleic acid (18:1ω9) and eicosenoic acid (20:1ω9) as unsaturated fatty acids. The effects of exogenous fatty acids were investigated when M. alpina JT-180 was cultivated in medium containing p-anisidine. The addition of linoleic acid (18:2ω6) and 6Z,9Z-octadecadienoic acid (18:2ω9) restored the growth of M. alpina JT-180 cultivated on the medium containing p-anisidine, but palmitic acid (16:0), 18:1ω9, and vaccenic acid (18:1ω7) had no effect. For the growth of oleaginous fungus M. alpina, 18-carbon length fatty acids with more than two double bonds are considered to be essential.

3. Results and discussion

3.1. Inhibition of fatty acid desaturase in M. alpina by p-anisidine Δ6 desaturase activity was defined as a desaturase index. i.e., the ratio of 18:2ω6 to 18:3ω6þ20:3ω6þ20:4ω6 in total mycelial fatty acids, since the desaturation reaction is not reversible and 20:4ω6 is not further metabolized in the fungus (Yamada et al., 1987; Sakuradani et al., 2013). Therefore, the desaturation index increases when the desaturase activity is reduced and the substrate 18:2ω6 for Δ6 desaturase is not consumed through Δ6 desaturation. Table 1 shows that p-anisidine supplementation caused increases in stearic acid (18:0), oleic acid (18:1ω9), and 18:2ω6, and decreases in 20:3ω6 and 20:4ω6. Addition of p-anisidine to the culture medium is considered to cause Δ6 desaturation inhibition through an increase in the Δ6 desaturase index. Similarly, the supplementation of methyl p-coumarate and propyl gallate caused inhibition of the Δ6 desaturase activity (Kawashima et al., 1996a, 1996b). On the other hand, the supplementation of (þ)-sesamine, which is a specific inhibitor of Δ5 desaturase, hardly influenced the fatty acid composition, except for the levels of 20:3ω6 and 20:4ω6, and caused a remarkable decrease in only the Δ5 desaturase index (Shimizu et al., 1991).