title: Temperature- and time-dependent changes in the structure and composition of glycolipids during the growth of the green sulfur photosynthetic bacterium Chlorobaculum tepidum.
abstract: The green sulfur photosynthetic bacterium Chlorobaculum (Cba.) tepidum (previously known as Chlorobium tepidum), which grows at an optimal temperature of around 45 °C, biosynthesized unique disaccharide rhamnosylgalactosyldiacylglyceride (RGDG) having a methylene-bridged palmitoleyl (17:Cyc) and a palmitoyl group (16:0) as the two acyl chains in a molecule [RGDG(17:Cyc,16:0)], together with the corresponding monosaccharide monogalactosyldiacylglyceride (MGDG). Here, we report changes in the structure and composition of the glycolipids that are dependent upon the temperature and period of cultivation. With a decrease in temperature to 25 °C, the two major glycolipids were almost completely eliminated, and MGDG with a palmitoleyl (16:1) and a (16:0) group concomitantly became the major glycolipid. MGDG(16:1,16:0) corresponded to the removal of an α-rhamnosyl and a cyclopropyl methylene group from RGDG(17:Cyc,16:0) and the lack of the CH(2) group in MGDG(17:Cyc,16:0). The structural conversion was almost reversible when the Cba. tepidum adapted to low and high temperatures was cultured again at 45 and 25 °C, respectively. Moreover, during this cultivation, the structure and composition of glycolipids were sequentially changed: MGDG(16:1,16:0), MGDG(17:Cyc,16:0), and RGDG(17:Cyc,16:0) predominated in the exponential, stationary and late phases of the cultivation, respectively. On the basis of these time-dependent changes, the unique disaccharide RGDG(17:Cyc,16:0) was thought to be created by the site-specific transfer of an α-rhamnosyl group to MGDG(17:Cyc,16:0) after insertion of a methylene group into the precursor MGDG(16:1,16:0). These culturing temperature- and time-dependent changes in glycolipids at the molecular level allow us to discuss their biosynthesis as well as physiological function in green photosynthetic bacteria.
authors.affiliation: Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Mizoguchi
authors.forename: Taichi
authors.initials: T
authors.lastname: Yoshitomi
authors.forename: Jiro
authors.initials: J
authors.lastname: Harada
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
mesh_terms: D041883:Chlorobium / Q000254:growth & development / Q000378:metabolism* / Q000502:physiology; D002851:Chromatography, High Pressure Liquid; D006017:Glycolipids / Q000737:chemistry*; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D010788:Photosynthesis; D021241:Spectrometry, Mass, Electrospray Ionization; D013696:Temperature; D013997:Time Factors
chemical_list: D006017:Glycolipids