Low-Temperature Affected LC-PUFA Conversion and Associated Gene Transcript Level in Nannochloropsis oculata CS-179

Nannochloropsis oculata CS-179, a marine eukaryotic unicellular microalga, is rich in long-chain polyunsaturated fatty acids （LC-PUFAs）. Culture temperature affected cell growth and the composition of LC-PUFAs. At an initial cell density of 1.5 × 106 cell mL-1, the highest growth was observed at 25℃ and the cell density reached 3 × 107 cell mL-1 at the beginning of loga-rithmic phase. The content of LC-PUFAs varied with culture temperature.The highest content of LC-PUFAs （43.96%） and EPA （36.6%） was gained at 20℃. Real-time PCR showed that the abundance of Δ6-desaturase gene transcripts was significantly different among 5 culture temperatures and the highest transcript level （15℃） of Nanoc-D6D took off at cycle 21.45. The gene transcript of C20-elongase gene was higher at lower temperatures （10, 15, and 20℃）, and the highest transcript level （20℃） of Nanoc-E took off at cycle 21.18. The highest conversion rate （39.3%） of Δ6-desaturase was also gained at 20℃. But the conversion rate of Nanoc-E was not detected. The higher content of LC-PUFAs was a result of higher gene transcript level and higher enzyme activity. Compared with C20-elongase gene, Δ6-desaturase gene transcript and enzyme activity varied significantly with temperature. It will be useful to study the mechanism of how the content of LC-PUFAs is affected by temperature.