Mechanisms For Ethanol Tolerance In Arthrobacter Simplex Based On Analysis Of Membrane Lipids

In this study, Arthrobacter simplex TCCC 11037-UV15X1-2(UV15X1-2), a ethanol tolerant mutant used in steroids 1-en-dehydrogenation process, was selected. For a deep understanding and a wide application of the tolerant mechanisms, we investigated the content and composition of fatty acids and phospholipids of cell membrane of ASP after adding ethanol. By analysis of content and composition of cell membrane lipids, we came up with conclusions as follows.The UV15X1-2 was proved to be tolerant to ethanol:the OD600 of medium was much higher than that of control group when concentrations of ethanol were below 4%(v/v), which indicated that the cell growth was promoted by ethanol. However, when ethanol was higher than 6%(v/v), the OD600 of medium decreased compared to control, which meant the growth of cells was inhibited.The lipid fluidity(LFU) increased from 0.36 to 0.44,0.76,0.74,1.03,1.08, respectively, with the increase of concentrations of ethanol(0,2,4,6,8,10%, v/v). Meanwhile, the LFU increased with the proceeding time prolonged. However, cells can decrease the LFU by self-recovery when removed ethanol.The isomerization of cis to trans unsaturated fatty acids in ASP cell membrane to increase the stability can be activated in the short term(3 h) after addition of ethanol, allowing cells to get through the shock of ethanol. When ethanol was removed, the cis/trans value of unsaturated fatty acids can recover to the same as the initial, suggesting that the isomerization is a reversible process.Both saturated fatty acids and PC tend to organize as a bilayer, which makes them ideally suited to preserving membrane integrity. Therefore, strain cells can tolerate the long term(>3 h) shock of ethanol by synthesizing saturated fatty acids and PC. When ethanol was removed, the content of saturated fatty acids and PC remained unchanged, which means the synthesis of saturated fatty acids and PC is a irreversible process.