The metabolism of trans-cyclohexan-1,2-diol by an Acinetobacter species

Abstract

1. Acinetobacter TD63 was one of some thirty organisms isolated by elective culture with trans-cyclohexan-1,2-diol as sole source of carbon. The great majority of these isolates displayed the same growth spectrum as Nocardia globerula CL1 and Acinetobacter NCIB 9871 being capable of utilizing trans-cyclohexan-1,2-diol, 2-hydroxycyclohexan-1-one, cyclohexanol, cyclohexanone,1-oxa-2oxocycloheptane and adipate and were assumed to use well described metabolic pathways. 2. Acinetobacter TD63 was distinctive in being incapable of growth with cyclohexanol, cyclohexanone or 1-oxa-2-oxocycloheptane and because of this it was hoped that it would display an alternative pathway for the oxidation of trans-cyclohexan-1,2-diol. 3. Studies with cell extracts have shown the presence of inducible dehydrogenase for the conversion of trans-cyclohexan-1,2-diol to 2-hydroxycyclohexan-1-one and cyclohexan-1,2-dione and of 6-oxohexanoate to adipate. These enzymes are linked into a metabolic sequence by the action of a monooxygenase of broad specificity but efficiently capable of converting 2-hydroxy-cyclohexan-1-one into the lactone 1-oxa-2-oxo-7-hydroxycycloheptane that spontaneously rearranges to yield 6-oxohexanoate. 4. An enzyme capable of attacking cyclohexan-1,2-dione (mono-enol) in the absence of an electron donor or oxygen has also been detected. Evidence has been presented indicating that this enzyme catalyses a keto-enol tautomerization between cyclohexan-1,2-dione (mono-enol) and cyclohexan-1,2-dione (mono-hydrate) and is not involved in the pathway of ring cleavage. 5. The failure of Acinetobacter TD63 to grow with cyclohexanol, cyclohexanone or 1-oxa-2-oxocycloheptane is due not to this organism possessing a distinctive metabolic sequence but to a narrow inducer specificity coupled with an inability to form a lactone hydrolase enabling it to cleave the stable 1-oxa-2-oxocycloheptane which is an intermediate in the established pathway of cyclohexanol and cyclohexanone oxidation.