ACCUMULATION OF A NOVEL GLYCOLIPID AND A BETAINE LIPID IN CELLS OF RHODOBACTER-SPHAEROIDES GROWN UNDER PHOSPHATE LIMITATION

Cells of the photosynthetic bacterium Rhodobacter sphaeroides grown un der phosphate-limiting conditions accumulated nonphosphorous glycolipi ds and lipids carrying head groups derived from amino acids. Concomita ntly, the relative amount of phosphoglycerolipids decreased from 90 to 22 mol% of total polar lipids in the membranes. Two lipids, not detec table in cells grown under standard conditions, were synthesized durin g phosphate-limited growth. Fast atom bombardment mass spectroscopy, e xact mass measurements, H-1 NMR spectroscopy, sugar composition analys is, and methylation analysis of the predominant glycolipid led to the identification of the novel compound 1,2-di-O-acyl-3-O-[alpha-D-glucop yranosyl-(1 -> 4)-O-beta-D-galactopyranosyl]glycerol. The second lipid was identified as the betaine lipid di-O-acyl-[4'-(N,N,N-trimethyl)ho moserine]glycerol by cochromatography employing an authentic standard from Chlamydomonas reinhardtii, fast atom bombardment mass spectroscop y, exact mass measurements, and 1H NMR spectroscopy. Prior to this obs ervation, the occurrence of this lipid was thought to be restricted to lower plants and algae. Apparently, these newly synthesized nonphosph orous lipids, in addition to the sulfo- and the ornithine lipid also f ound in R. sphaeroides grown under optimal conditions, take over the r ole of phosphoglycerolipids in phosphate-deprived cells. (C) 1995 Acad emic Press, Inc.