Cyanobacterium aponinum PCC 10605 (Cyan10605), a thermophilic, halotolerant single-cell cyanobacterium, can grow under extreme conditions including high temperature and high salinity. While the impact of stress on growth and the production of biotechnologically high-value compounds like exopolysaccharides and phycocyanin have been studied, the responses of lipid metabolism of Cyan10605 under stress conditions remain unclear. Here, we present the alterations in membrane and nonpolar lipids in Cyan10605 cells during growth under high temperature, salt stress, phosphate and nitrogen deprivation, and extended cultivation time. The degree of acyl unsaturation in all membrane lipid classes decreased at high temperature, while sulfolipids accumulated up to ~ 50 mol% of membrane lipids at the expense of galactolipids in cells grown in artificial seawater medium. The membrane lipid composition under phosphate deprivation remained similar, with low amounts of phosphatidylglycerol, while the proportion of sulfolipid was increased under nitrogen starvation. After extended cultivation, large amounts of membrane lipids were degraded. Triacylglycerol containing saturated acyl groups accumulated at high temperatures, while under phosphate deprivation, the TAG content remained similar, but fatty acid phytyl esters increased. Nitrogen deprivation caused an increase in TAG but a decrease in phytyl esters. After extended cultivation, triacylglycerol and phytyl esters accumulated to the highest amounts. Under all stress conditions, the content of acyl-plastoquinols decreased. Cyan10605 contains a multifunctional acyltransferase related to Synechocystis sp. PCC 6803 Slr2103. This enzyme is presumably involved in nonpolar lipid synthesis since it produced TAG and FAPE after expression in Escherichia coli. These results show that membrane lipids and nonpolar lipids are involved in the metabolic response of Cyan10605 to adapt to extreme growth conditions. Small amounts of fatty acids derived from membrane lipids are deposited in the form of TAG and FAPE, but not in acyl-plastoquinols, during extended cultivation, indicating that the synthesis of nonpolar lipid classes is differentially regulated. Knowledge about lipid changes during adaptation to different growth conditions is crucial for biotechnological applications including the use of Cyan10605 for biodiesel production and the optimization of growth in outdoor or mass cultivation settings.
陈子硕 et al. (Wed,) studied this question.