Catabolic Pathways and Enzymes Involved in the Anaerobic Degradation of Terpenes

Abstract

Monoterpenes are ubiquitous and, in contrast to other terpenes, their anaerobic mineralization has been studied, especially in denitrifying betaproteobacteria. Castellaniella defragrans has a degradation pathway for cyclic monoterpenes, with a limonene dehydrogenase and a ring-cleavage reaction known from anoxygenic phototrophic bacteria. Toxic monoterpene alcohols are transformed in the periplasm by the linalool dehydratase/isomerase (Ldi) to the less toxic myrcene. Thauera linaloolentis degrades linalool with a membrane-anchored linalool isomerase and the enzymes of the Atu/Liu pathways for acyclic monoterpenes. The development of a genetic system for Castellaniella defragrans together with physiological and biochemical studies have provided an excellent toolbox to study the monoterpene metabolism. On the horizon, Pseudomonas aeruginosa and other gammaproteobacterial pseudomonads are waiting for a thorough exploration of their monoterpene metabolism.