Changes of microalgal cells morphology and structure under different
Except for the classes of lipid, fatty acids (FA) composition also played a vital role in the evaluation of biodiesel quality. The FA composition of both microalgae under different light intensities showed in Table 3, which dominant by species of C16 and C18 FAME, comprising 94% to 99% of the total fatty acids in lipid. The abundance of C16:0 and C18:1 were all higher in both microalgae, while C18:3 was found to be abundant in Chlorella sp. L1 and C18:2 in M. dybowskii Y2. Nonetheless, all of the above-mentioned FA components were good choices for the production of biodiesel ( Knothe, 2009). Under HL, the content of C16:0 increased and C18:3 exhibited an initial rise in LL and then decreased, these changes were in accordance with the observation that the emergence of lipid bodies and disappearance of most thylakoid membrane. C18:3 were tightly associated with thylakoid membrane, so the decrease under HL fully indicated that the photosynthetic membranes experienced oxidative stress. Additionally, the content of C22:4, C22:5 and C22:6 declined, this phenomenon had also been observed in other microalgae ( Zhukova, 2007, Solovchenko et al., 2008 and Guedes et al., 2010). The de novo synthesis of C16:0 occurred actively in PMSF to cope with high light for the reason that it were energy-consuming ones, therefore it could utilized excessive energy ( Zhukova, 2007). Studies of Neochloris oleoabundans under high light intensity (300 μmol photon m−2 s−1) found the percentages of C16:0, C18:1 strongly increased ( Sun et al., 2014). The results of Pavlova lutheri also showed that cultures possess a higher fraction of PUFA in polar classes under low light intensity, while an increase in triacylglycerols under a higher light intensity ( Guedes et al., 2010). The raised PUFA content under increasing light intensities may be attributed to the enhancement of fluidity and the ability of harvesting light in microalgae to defend the damage, while the decreased content indicate the degradation of membrane system for the serious photooxidative damage under HL ( Becker et al., 2010, Guedes et al., 2010 and Liu et al., 2012). In addition, the decrease of UFA under HL also confirmed the damage of microalgae. Zhukova (2007) put forward that membrane lipid contained more UFA while storage lipid (TAG) contained more SFA in symbiotic dinoflagellates FA analyses which was in accord with the results in this study. Collectively, it clearly demonstrated that high light intensity could induce the production of useful fatty acids (i.e., C16:0, C18:1) that were the primary components of neutral lipids.