A variety of glycolipids in green photosynthetic bacteria

The compositions of glycolipids in the following seven strains of green photosynthetic bacteria were investigated at the molecular level using LC-MS coupled with an evaporative light scattering detector: Chlorobium (Chl.) limicola strains Larsen (30 A degrees C as the optimal cultivation temperature) and DSM245 (30 A degrees C), Chlorobaculum (Cba.) tepidum strain ATCC49652 (45 A degrees C), Cba. parvum strain NCIB8327 (30 A degrees C), Cba. limnaeum strain 1549 (30 A degrees C), Chl. phaeovibrioides DSM269 (30 A degrees C), and Chloroflexus (Cfl.) aurantiacus strain J-10-fl (55 A degrees C). Dependence of the molecular structures of glycolipids including the chain-length of their acyl groups upon bacterial cultivation temperatures was clearly observed. The organisms with their optimal temperatures of 30, 45, and 55 A degrees C dominantly accumulated glycolipids possessing the acyl chains in the range of C-15-C-16, C-16-C-17, and C-18-C-20, respectively. Cba. tepidum with an optimal temperature of 45 A degrees C preferred the insertion of a methylene group to produce finally a C-17-cyclopropane chain. Cfl. aurantiacus cultured optimally at 55 A degrees C caused a drastic increase in the chain-length. Notably, the length of such acyl groups corresponded to that of the esterifying chain in the 17-propionate residues of self-aggregative bacteriochlorophylls-c/d/e, indicating stabilization of their supramolecular structures through hydrophobic interactions among those hydrocarbon chains. Based on the detailed compositions of glycolipids, a survival strategy of green photosynthetic bacteria grown in the wide range of temperatures is discussed.