Anaerobic degradation of cyclohexane-1,2-diol by a new Azoarcus species

Abstract

A bacterium, strain 22Lin, was isolated on cyclohexane-1,2-diol as sole electron donor and carbon source and nitrate as electron acceptor. Cells are motile rods and are facultatively anaerobic. A phylogenetic comparison based on the total 16S rRNA gene sequence allowed the assignment of the isolate to the genus Azoarcus. Cyclohexanol, cyclohexanone, cyclohexane-1,3-diol, and cyclohexane-1,3-dione, which are oxidized by a different denitrifying strain, did not support denitrifying growth of isolate 22Lin. On the contrary, cyclohexanol (I₅₀ = 37 μM) and cyclohexanone (I₅₀ = 28 μM) inhibited growth on cyclohexane-1,2-diol, but not on acetate. NAD was reduced by crude extracts of strain 22Lin in the presence of cyclohexane-1,2-dione, but not in the presence of cyclohexanone or cyclohexane-1,3-dione. The formation of 6-oxohexanoate from cyclohexane-1,2-dione and of adipate during NAD reduction suggests that strain 22Lin possesses a carbon–carbon hydrolase that transforms cyclohexane-1,2-dione into 6-oxohexanoate. This pathway was once observed in an aerobic pseudomonad that was lost and could not be reisolated. Here, the application of strictly anoxic enrichment conditions enabled the reisolation of another strain (22Lin) that uses this pathway.