Microbial production of n-3 docosapentaenoic acid and development of its utilization

N-3-二十二碳五烯酸(DPA)对冠状动脉硬化的抑制活性是其前体二十碳五烯酸(EPA)的10-20倍，但其生理作用尚不清楚，商业应用市场较小。本研究的目的是开发微生物DPA的生产体系。首先，我们分离了一批海洋微生物，并对它们的DPA产量进行了评价。其中一株为Thraustochytrium sp.菌株KK17-3的DPA含量为胞内脂肪酸总量的1-3%。通过对培养条件的优化，进一步提高了其DPA产量。为了分离和利用与多不饱和脂肪酸生物合成相关的基因，我们试图阐明海洋微生物中DPA的生物合成途径。结果，发现了一条包括饱和脂肪酸伸长的新途径。这表明n-6DPA而不是n-3DPA是该途径的最终产物二十二碳六烯酸(DHA)生物合成的中间体。然而，我们也发现迷宫微生物含有与高等植物和真菌中的Delta-12和Delta-6同源的常规类型的去饱和酶。这可能表明n-3DPA和EPA是沿着与大多数真核生物相同的途径生物合成的。事实上，n-3DPA可以通过哺乳动物类型的伸长酶延长EPA而产生。

n-3 Docosapentaenoic acid (DPA) exhibits suppressive effect for coronary arteriosclerosis at 10-20 times higher activity than that of eicosapentaenoic acid (EPA), a precursor of DPA.However, its physiological role has yet to be elucidated enough and market for its commercial use remains small. One of the obstacles is the lack of source to provide inexpensive and an enough amount of DPA.The aim of this study was to develop the production system of microbial DPA.First, we isolated a number of marine microbes producing polyunsaturated fatty acids and evaluated their DPA productivity. One of them, Thraustochytrium sp. strain KK17-3, contained DPA at the level of 1-3% of total intracellular fatty acids. We further improved its DPA productivity through optimization of culture condition. In order to isolate and utilize genes involving to the biosynthesis of polyunsaturated fatty acids, we tried to elucidate biosynthetic pathway of DPA in the marine microbe. As a result, a novel pathway including elongation of saturated fatty acids was found. This implied that n-6 DPA, but not n-3 DPA, was an intermediate for biosynthesis of docosahexaenoic acid (DHA), a final product of the pathway. However, we have also found that the Labyrinthula microbes contain conventional type of desaturases that are homologous to delta-12 and delta-6 desaturases from higher plants and fungi. This might indicate that n-3 DPA as well as EPA is biosynthesized along with the pathway identical to those of the most of eukaryotes. Indeed, n-3 DPA could be generated through an elongation of EPA by mammalian type of elongase.