Identification and Functional Analysis of Delta-9 Desaturase, a Key Enzyme in PUFA Synthesis, Isolated from the Oleaginous Diatom Fistulifera

Oleaginous microalgae are one of the promising resource of nonedible biodiesel fuel (BDF) feed stock alternatives. Now a challenge task is the decrease of the long-chain polyunsaturated fatty acids (PUFAs) content affecting on the BDF oxidative stability by using gene manipulation techniques. However, only the limited knowledge has been available concerning the fatty acid and PUFA synthesis pathways in microalgae. Especially, the function of Delta(9) desaturase, which is a key enzyme in PUFA synthesis pathway, has not been determined in diatom. In this study, 4 Delta(9) desaturase genes (fD9desA, fD9desB, fD9desC and fD9desD) from the oleaginous diatom Fistulifera were newly isolated and functionally characterized. The putative Delta(9) acyl-CoA desaturases in the endoplasmic reticulum (ER) showed 3 histidine clusters that are well-conserved motifs in the typical Delta(9) desaturase. Furthermore, the function of these Delta(9) desaturases was confirmed in the Saccharomyces cerevisiae ole1 gene deletion mutant (Delta ole1). All the putative Delta(9) acyl-CoA desaturases showed Delta(9) desaturation activity for C16:0 fatty acids; fD9desA and fD9desB also showed desaturation activity for C18:0 fatty acids. This study represents the first functional analysis of Delta(9) desaturases from oleaginous microalgae and from diatoms as the first enzyme to introduce a double bond in saturated fatty acids during PUFA synthesis. The findings will provide beneficial insights into applying metabolic engineering processes to suppressing PUFA synthesis in this oleaginous microalgal strain.