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Abstract

Monoterpenes are a class of volatile organic compounds synthesized by plants. Their characteristic scent possesses antimicrobial and anti-herbivore properties. In industry monoterpenes are added to various foods, cosmetics and household products as flavour and fragrance and also as antimicrobial agent. Below toxic concentrations, certain bacteria can utilize monoterpenes as source of carbon and energy. Monoterpene biosynthesis is mediated by a wide range of terpene synthases. These enzymes are widely distributed in plants, fungal and bacteria species and they usually possess similar properties and reaction mechanisms. Under denitrifying conditions, the betaproteobacterium Castellaniella defragrans 65Phen is capable of metabolizing monoterpenes as sole carbon and energy source. Linalool dehydratase/isomerase (ldi) a bifunctional enzyme of C. defragrans, mineralizes the hydration of acyclic monoterpene, β-myrcene to (3S)-linalool and the isomerization of (3S)-linalool to geraniol. The deletion mutant C. defragrans 65Phen-RIF Δldi grows on (R,S)-linalool but not β-myrcene or geraniol. In cell free protein extracts, the formation of monocyclic monoterpene, terpinolene from (R,S)-linalool had been observed. The biotransformation of linalool required ATP and divalent metal ion cofactors (manganese and magnesium). Here it was shown that the monoterpene cyclase is a soluble enzyme and has a preference for Mn2+ ions over Mg2+ ions. Phosphate buffers caused a slight inhibition of the activity of the enzyme. The accumulated terpinolene product was further metabolised to undetermined secondary metabolites. We suggest a presence of a terpene cyclase reaction to line the degradation of linalool with a recently suggested monocyclic monoterpene degradation pathway in C. defragrans 65Phen.