GC-MS structural characterization of fatty acids from marine aerobic anoxygenic phototrophic bacteria.

The FA composition of 12 strains of marine aerobic anoxygenic phototrophic bacteria belonging to the genera Erythrobacter, Roseobacter, and Citromicrobium was investigated. GC-MS analyses of different types of derivatives were performed to determine the structures of the main FA present in these organisms. All the analyzed strains contained the relatively rare 11-methyloctadec-12-enoic acid, and three contained 12-methyl-octadec-11-enoic acid, which has apparently never been reported before. High amounts of the very unusual octadeca-5,11-dienoic acid were present in 9 of the 12 strains analyzed. A FA containing a furan ring was detected in three strains. Analytical data indicated that this FA was 10,13-epoxy-11-methyloctadeca-10,12-dienoic acid. A very interesting enzymatic peroxidation of the allylic carbon 10 of cis-vaccenic acid was observed in three strains. Deuterium labeling and GC-MS analyses enabled us to demonstrate that this enzymatic process involves the initial dioxygenase-mediated formation of 10-hydroperoxyoctadec-11(cis)-enoic acid, which is then isomerized to 10-hydroperoxyoctadec-11(trans)-enoic acid and converted to the corresponding hydroxyacids and oxoacids. Different biosynthetic pathways were proposed for these different compounds.