The characteristics of desaturation of Trichoderma sp. AM076 and formation of 9,12,15-hexadecatrienoic acid (16 :3ω1) through Δ15 desaturation of 9,12-hexadecadienoic acid

We investigated the characteristics of desaturation in Trichoderma sp. AM076. Although 6,9,12- octadecatrienoic acid (18:3ω6) was detected when Trichoderma sp. AM076 was cultivated in the presence of 6,9-octadecadienoic acid (18:2w9), the desaturation products of 6,9,12-octadecatrienoic acid (18 :3ω6) and 6- octadecenoic acid (18:1Δ6) were not detected. These results suggest that the double bonds at the Δ6 position of 18:3ω6 and 18 :1Δ6 disturb their Δ15 and Δ9 desaturation, respectively. This fungus also introduced a double bond at the Δ15 position of 9,12-hexadecadienoic acid (16:2ω4), thereby yielding a novel C16 polyunsaturated fatty acid (PUFA) identified as 9,12,15-hexadecatrienoic acid (16:3ω1). Further investigations revealed that the mutant having enhanced accumulation of linolenic aid (18:3ω3) accumulates 16:3ω1 as one of the major PUFAs, together with 9,12-octadecadienoic acid (16 :2ω4), when grown with palmitoleic acid (16 :1ω7). These results suggest that, in this strain, the reaction that catalyzes the conversion of linoleic acid to linolenic acid, similar to the conversion of 16 :2ω4 to 16:3ω1, is not ω3 desaturation but Δ15 desaturation.