## 3 Results and Discussion
### Fatty Acid Composition of Lipids from C. variabilis RSM09  
Obtaining a suitable lipid composition for biofuel generation is just as crucial as increasing the overall volume of lipids generated from microalgae. The lipid generated from microalgal species typically has a lipid profile that is mainly composed of C16 and C18 fatty acids, comparable to that of vegetable oils, making it appropriate for the generation of biodiesel [35]. The lipids extracted from _C. variabilis_ RSM09 under three different photoperiods were utilized for transesterification. The FAME analysis was performed by GC-FID. A representative chromatogram of the FAME analysis using GC-FID is depicted in Figure 10. The FAME profiles of _C. variabilis_ RSM09 under three different photoperiods are shown in Table 1.  
Figure 8: Growth curve of _C. variabilis_ RSM09 under 5000 Lux of light intensity in different photoperiods (12:12, 18:6, and 24:0 h L/D cycles). Error bars show \(\pm\) S.D. of three replicates.  
Figure 9: Dry weight and lipid content of _C. variabilis_ RSM09 under 5000 Lux of light intensity in different photoperiods (12:12, 18:6, and 24:0 h L/D cycles). Different letters represent statistically significant difference (\(p\) < 0.05).  
According to photoperiod acclimation, all cultured microalgae had patterns of fluctuation in the concentration of identical fatty acid classes. Palmitic (16:0), linoleic (C18:2), and linolenic (C18:3) acids were predominant in _C. variabilis_ RSM09 under all photoperiods. These results were in accordance with those of [PERSON] et al. [39] and [PERSON] et al. [40]. Within biodiesel production, feedstock must possess a high lipid content and a suitable fatty acid profile. The ratio of various fatty acids significantly influences the overall properties of the fuel [41]. The fatty acid methyl ester (FAME) profile of _C. variabilis_ RSM09 reveals  
Figure 10: GC-FID chromatogram for FAME analysis of lipids extracted from _C. variabilis_ RSM09 under different photoperiods—(**A**) 12:12 (L/D cycle), (**B**) 18:6 (L/D cycle), and (**C**) 24:0 (L/D cycle).  
that its primary fatty acids are palmitic acid (C16:0), linoleic acid (C18:2), and linoleic acid (C18:3). Among the other components, the percentage of palmitic acid is the highest, at 45.09%, 42.27%, and 70.50% of dry weight under different photoperiods of 12:12, 18:6, and 24:0 h L/D, respectively. [PERSON] et al. [41] indicated that the high abundance of palmitic acid in biodiesel contributes to its elevated cetane number and exceptional oxidative stability. In addition, cultivated microalgae under 24:0 h L/D had a higher value of SFA than those under 18:6 h and 12:12 h L/D, whereas cultivated microalgae under 18:6 h L/D had a higher value of MFA and PFA than the others. The results indicated that decreasing light duration was associated with increased MUFA and PUFA and decreased SFA. The alteration in the fatty acid composition of microalgae exposed to different light durations might be explained by the fact that these lipids, being the principal component of chloroplast membranes, play a vital role in the formation of the photosynthetic apparatus of the algae [39]. According to [PERSON] et al. [42], PUFAs are crucial for maintaining the function of the photosynthetic membrane and are also crucial for acclimating to low-light conditions. On the other hand, the biosynthesis of SFA requires high amounts of photosynthetically produced ATP and NADPH, and high chlorophyll a content may help to support high SFA production [43]. Thus, the change in fatty acid composition in this study may be one adaptive response of _C. variabilis_ RSM09 under various light durations.