Chlorosome lipids from Chlorobium tepidum: Characterization and quantification of polar lipids and wax esters

We have extracted polar lipids and waxes from

isolated chlorosomes from the green sulfur bacterium

Chlorobium tepidum and determined the fatty acid composition

of each lipid class. Polar lipids amounted to 4.8 mol

per 100 mol bacteriochlorophyll in the chlorosomes, while

non-polar lipids (waxes) were present at a ratio of 5.9 mol

per 100 mol bacteriochlorophyll. Glycolipids constitute

60 % of the polar lipids while phosphatidylglycerol,

diphosphatidylglycerol, phosphatidylethanolamine, and an

aminoglycosphingolipid make up respectively 15, 3, 8 and

12 %. A novel glycolipid was identified as a rhamnose

derivative of monogalactosyldiacylglycerol, while the

other major glycolipid was monogalactosyldiacylglycerol.

Tetradecanoic acid was the major fatty acid in the aminoglycosphingolipid,

while the other polar lipids contained

predominantly hexandecanoic acid. The chlorosome waxes

are esters of unbranched fatty acids and fatty alcohols with

14 or 16 carbon atoms, joined to form molecules with

between 28 and 32 carbon atoms. The stoichiometry

between lipids and bacteriochlorophyll suggests that much

of the chlorosome surface is covered by protein.