Catabolism of citronellol and related acyclic terpenoids in pseudomonads

Abstract

Terpenes are a huge group of natural compounds characterised by their predominantly pleasant smell. They are built up by isoprene units in cyclic or acyclic form and can be functionalised by carbonyl, hydroxyl or carboxyl groups and by presence of additional carbon-carbon double bonds (terpenoids). Currently, much more than 10,000 terpenoid compounds are known, and many thereof are present in different iso- and stereoforms. Terpenoids are secondary metabolites and can have important biological functions in living organisms. In many cases, the biological functions of terpenoids are not known at all. Nevertheless, terpenoids are used in large quantities as perfumes and aroma compounds for food additives. Terpenoids can be also precursors and building blocks for synthesis of complex chiral compounds in chemical and pharmaceutical industry. Unfortunately, only few terpenoids are available in large quantities at reasonable costs. Therefore, characterisation of suited biocatalysts specific for terpenoid compounds and development of biotransformation processes of abundant terpenoids to commercially interesting derivates becomes more and more important. This minireview summarises knowledge on catabolic pathways and biotransformations of acyclic monoterpenes that have received only little attention. Terpenoids with 20 or more carbon atoms are not a subject of this study.

Persistency assessment and aerobic biodegradation of selected cyclic sesquiterpenes present in essential oils

“…A few reports exist on the occurrence of sesquiterpenes in the geosphere, including a study by Elias et al [16] that provides evidence that the degradation of sesquiterpenoids begins with aromatization. Terpene-degrading bacteria able to transform 2-methylisoborneol [17], (þ/À)-geosmin [18], cedrol [19,20], cedrene [21], and farnesol [15] have been identified, with the latter reported to have a similar catabolic pathway to the monoterpene homologue, citronellol. However, data from ready and inherent biodegradability tests is scarce.…”

“…The catabolic pathways and associated enzymology for a number of monoterpenes have also been studied. These include camphor [11], a-pinene [11,12], 1,8-cineole [11], limonene [11,13], menthol [14], menthone [14], citronellol [15], and b-myrcene [15].…”

Anaerobic Degradation of Benzene and Polycyclic Aromatic Hydrocarbons

“…This would lead to a branched alkyl chain, where a side chain had to be cleaved off either before or after the second ring-opening reaction. Strategies for the removal of side chains are for example known for degradation pathways of acyclic terpenoids [Forster-Fromme and Jendrossek, 2010] or steroid compounds [Philipp, 2011;Wipperman et al, 2014]. The thn operon includes two genes coding for a potential lyase ThnQS with similarities (34% identity, 51% similarities) to the putative 3-hydroxy-3-isohexenyl-glutaryl-CoA: acetate lyase AtuA from the citronellol-degrading Pseudomonas citronellolis Jendrossek, 2006, 2010].…”

The Pseudomonas aeruginosa Isohexenyl Glutaconyl Coenzyme A Hydratase (AtuE) Is Upregulated in Citronellate-Grown Cells and Belongs to the Crotonase Family

“…They are also characterized by (many) important biological properties, including antimicrobial, antineoplastic, antifungal, antiviral, antihyperglycemic, anti-inflammatory, and antiparasitic activities. Terpenes consist of isoprene units combined in a cyclic or acyclic form and are produced in large quantities (ϳ10 5 tons/ year) (1). Introduction of additional carbon-carbon double bonds in terpenes or incorporation of heteroatoms, such as oxygen, results in the formation of terpenoids.…”

“…In particular, the acyclic terpene utilization (Atu) pathway in P. aeruginosa broadens the catabolic capabilities of the species to the utilization of acyclic monoterpenes (1,4). The Atu pathway has been found to involve seven proteins (AtuA, AtuB, AtuCF, AtuD, AtuE, AtuG, AtuH) (5,6).…”