The Metabolism of trans‐Cyclohexan‐1,2‐diol by an Acinetobacter Species

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Abstract
Acinetobacter TD63 was 1 of some 30 organisms isolated by elective culture with trans-cyclohexane-1,2-diol as sole C source. The great majority of these isolates displayed the same growth spectrum as Nocardia globerula CL1 and Acinetobacter NCIB 9871 being capable of utilizing trans-cyclohexane-1,2-diol, 2-hydroxycyclohexane-1-one, cyclohexanol, cyclohexanone, 1-oxa-2-oxocycloheptane and adipate and were assumed to use well-described metabolic pathways. Acinetobacter TD63 was distinctive in being incapable of growth with cyclohexanol, cyclohexanone or 1-oxa-2-oxocycloheptane, and therefore it was hoped that it would display an alternative pathway for the oxidation of trans-cyclohexane-1,2-diol. Studies with cell extracts showed the presence of inducible dehydrogenase [EC 1.1.1-] for the conversion of trans-cyclohexane-1,2-diol to 2-hydroxycyclohexane-1-one and cyclohexane-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-hydroxycyclohexane-1-one into the lactone 1-oxa-2-oxo-7-hydroxycycloheptane that spontaneously rearranges to yield 6-oxohexanoate. An enzyme capable of attacking cyclohexane-1,2-dione (mono-enol) in the absence of an electron donor or O2 was detected. This enzyme catalyzes a keto-enol tautomerization between cyclohexane-1,2-dione (mono-enol) and cyclohexane-1,2-dione (mono-hydrate) and is not involved in the pathway of ring cleavage. 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.