Effect of temperature on the growth, total lipid content and fatty acid composition of recently isolated tropical microalgae Isochrysis sp, Nitzschia closterium, Nitzschia paleacea, and commercial species Isochrysis sp (clone T ISO)

The effect of temperature from 10 degrees C to 35 degrees C on the growth, total lipid content, and fatty acid composition of three species of tropical marine microalgae, Isochrysis sp., Nitzschia closterium, N. paleacea (formerly frustulum), and the Tahitian Isochrysis sp. (T.ISO), was investigated. Cultures of N. closterium, Isochrysis sp. and T.ISO grew very slowly at 35 degrees C, while N. closterium did not grow at temperatures higher than 30 degrees C or lower than 20 degrees C. N. paleacea was low-temperature tolerant, with cells growing slowly at 10 degrees C. N. paleacea produced the highest percentage of lipids at 10 degrees C, while the other species produced maximum amounts of lipid at 20 degrees C. None of the species maintained high levels of polyunsaturated fatty acids (PUFAs) at high growth temperature and there was a significant inverse relationship between the percentage of PUFAs and temperature for N. paleacea. A curved relationship was found between temperature and percentage of PUFA for N. closterium and tropical Isochrysis sp., with the maximum production of PUFA at 25 degrees C and 20 degrees C, respectively. The two Nitzschia species produced higher levels of the essential fatty acid eicosapentaenoic acid [20:5(n-3)] at lower growth temperatures, but the two Isochrysis species had little change in percentage of 20:5(n-3) with temperature. Only T.ISO had the highest percentage of 22:6(n-3) at lowest growth temperature (11.4% total fatty acids at 10 degrees C).