Abstract
Green photosynthetic bacteria have a unique light-harvesting antenna system called chlorosome. The envelope of a chlorosome consists of monolayer of glyco/phospholipids containing proteins. These glyceroglycolipids were reported to be monogalactosyldiacylglycerol (MGDG) and rhamnosylgalactosyldiacylglycerol (RGDG), but not characterized at the molecular level, especially for their fatty acids. In this study, we elucidated the molecular structures and compositions of MGDG and RGDG extracted from Chlorobium (Chl.) tepidum using combination of liquid-chromatography with electrospray-ionization mass spectrometry and evaporative-light-scattering detection. Major two fatty acids in MGDG and RGDG were determined to be cyclopropane acid (C17:1) and saturated acid (C16:0). Their covalently linked positions with glycerol moieties were determined by selective hydrolysis of the esters using a lipase. Moreover, we investigated changes in the glycolipid composition of the cells of Chl. tepidum grown at different temperatures, indicating that the composition drastically changed with lowering the culturing temperature.
