Abstract
BackgroundThe betaproteobacterium Thauera linaloolentis 47LolT was isolated on the tertiary monoterpene alcohol (R,S)-linalool as sole carbon and energy source under denitrifying conditions. Growth experiments indicated the formation of geraniol and geranial. Thus, a 3,1-hydroxyl-Δ1-Δ2-mutase (linalool isomerase) activity may initiate the degradation, followed by enzymes of the acyclic terpene utilization (Atu) and leucine/isovalerate utilization (Liu) pathways that were extensively studied in Pseudomonas spp. growing on citronellol or geraniol.ResultsA transposon mutagenesis yielded 39 transconjugants that could not grow anaerobically on linalool and nitrate in liquid medium. The deficiencies were apparently based on gene functions required to overcome the toxicity of linalool, but not due to inactivation of genes in the degradation pathway. Growing cultures formed geraniol and geranial transiently, but also geranic acid. Analysis of expressed proteins detected several enzymes of the Atu and Liu pathways. The draft genome of T. linaloolentis 47LolT had atu and liu genes with homology to those of Pseudomonas spp..ConclusionThe in comparison to monoterpenes larger toxicity of monoterpene alcohols is defeated by several modifications of the cellular structure and metabolism in Thauera linaloolentis 47LolT. The acyclic terpene utilization pathway is used in T. linaloolentis 47LolT during growth on (R,S)-linalool and nitrate under anoxic conditions. This is the first experimental verification of an active Atu pathway outside of the genus Pseudomonas.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0693-8) contains supplementary material, which is available to authorized users.
Highlights
The betaproteobacterium Thauera linaloolentis 47LolT was isolated on the tertiary monoterpene alcohol (R,S)-linalool as sole carbon and energy source under denitrifying conditions
Growth studies revealed the regioselective formation of geraniol from linalool in the stationary phase, while linalool and geranial were detected in geraniol-grown cultures. These findings suggested the presence of a linalool isomerase, a 3,1hydroxyl-Δ1-Δ2-mutase [14]
Transposon insertion mutagenesis Five thousand nine hundred sixteen transconjugants were screened on solid medium for denitrifying growth on acetate or linalool as carbon source, presenting a gene coverage of 74 % for an average gene size of 1000 bp. 92 mutants had a growth deficiency on linalool, a mutation frequency of 0.0155 was observed
Summary
The betaproteobacterium Thauera linaloolentis 47LolT was isolated on the tertiary monoterpene alcohol (R,S)-linalool as sole carbon and energy source under denitrifying conditions. Linalool (C10H18O, 3,7-dimethylocta-1,6-dien-3-ol), a tertiary monoterpene alcohol, is the main constituent in essential oils of lavender and coriander. It is a fragrance of flowers [1, 2]. As tertiary alcohols cannot be directly oxidized to ketones, microorganisms initiate their metabolism with oxidation reactions by oxygenases at other parts of the molecule [3] or with isomerizations without molecular oxygen. The latter case has been described for the betaproteobacterium Castellaniella defragrans 65Phen. A pathway for geranic acid degradation was not found in the genome of C. defragrans
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