Omega-cyclohexyl fatty acids in acidophilic thermophilic bacteria. Studies on their presence, structure, and biosynthesis using precursors labeled with stable isotopes and radioisotopes

Abstract

Omega-Cyclohexyl undecanoic acid and omega-cyclohexyl tridecanoic acid were found in 10 strains of acido-thermophilic bacteria isolated from different Japanese hot springs. These unusual fatty acids were found in the esterified form in glyceride type complex lipids and constituted 74 to 93% of the total fatty acids in the bacteria. The fatty acids other than omega-cyclohexyl fatty acids found were 14-methyl hexadecanoic acid (3 to 15%) and 15-methyl hexadecanoic acid (1 to 6%), and trace amounts of straight chain and methyl-branched tetra- and penta-decanoic acids. Biosynthesis of omega-cyclohexyl fatty acids increased with increase in the concentration of glucose in the culture medium. The metabolism of omega-cyclohexyl fatty acids was studied using deuterium-labeled precursors by mass fragmentation analysis. The deuterium of [2-D]glucose was specifically incorporated into position 2 of the cyclohexyl ring of the fatty acids, indicating that the ring was synthesized from the glucose molecule. Radioactivity was efficiently incorporated into the omega-cyclohexyl fatty acids from labeled glucose, shikimate, and cyclohexyl carboxylate. These findings indicate that omega-cyclohexyl fatty acids are synthesized with glucose through shikimic acid and probably cyclohexyl carboxylyl-CoA derivative as the intermediates.