Volatile organic compounds from arctic bacteria of the Cytophaga-Flavobacterium-Bacteroides group: a retrobiosynthetic approach in chemotaxonomic investigations

Abstract

Volatile organic compounds emitted by different marine arctic strains of the Cytophaga-Flavobacterium-Bacteroides group were investigated by using a modified closed-loop stripping apparatus (CLSA). Seven of nine strains emitted volatiles, dominated by methyl ketones, in specific patterns. The methyl ketones were aliphatic saturated, or unsaturated, and comprised 12 to 18 C-atoms, sometimes with terminal Me branches. They were identified by GC/MS, retention-index calculations, derivatization with dimethyl disulfide for C=C bond location, and GC/FTIR to elucidate their uniform (Z)-configuration. The proposed structures of all methyl ketones were subsequently confirmed by synthesis, while the absolute configuration of chiral volatiles was elucidated by stereoselective synthesis. From retrobiosynthetic considerations, it was found that strain ARK10267 uses mainly valine, and strain ARK10063 mainly isoleucine for formation of starters for the ketone biosynthesis, which is correlated to fatty acid biosynthesis. Four strains (ARK10223, ARK10044, ARK10141, and ARK10146) use leucine. These separations are supported by phylogenetic affiliations based on 16S rRNA. Strain ARK10255b, in the course of this study found to be not a member of the Cytophaga-Flavobacterium-Bacteroides phylum, did not emit aliphatic ketones of medium chain length, but methionine-derived 4-(methylsulfanyl)butan-2-one and corresponding 4-(methylsulfanyl)butan-2-ol. Most of the compounds described have not been reported previously from nature.