So, what is the specific purpose of the cyclopropanation of an unsaturated lipid acyl chain? From the chemical reactivity perspective, it is known that double bonds are more susceptible to oxidation and ozonolysis than the cyclopropane rings and thus the LCFAs are more stable compared to LUFA . Beside the chemical stability, there might be some roles of LCFAs to protect the cell membrane from drastic physical change, which is detrimental for the functional behaviours of the cell membrane. The earlier work by Poger et al. compared the role of cyclopropane ring and C=C unsaturated bond on the fluidity and ordering of the lipid membrane . They proposed, the LCFAs enhance the membrane fluidity by influencing the lipid packing and increasing the gauche defect formation. It was claimed that the effect is partly due to steric hindrance originated by the methylene bridge. Although the above study provided important insights about the role of the cyclopropane rings in maintaining the packing density and fluidity of a single component lipid membrane, the actual role is far from understood in real cell membrane of the bacteria, such as E. coli, Lactobacillus, etc., where tens of different types of lipids are present and in inhospitable situation, like at low temperature when the membrane exists in gel phase. Therefore, it is important to understand how LCFAs stabilize a realistic cell membrane which is exposed to a drastic change of temperature.