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Title: Bacterial degradation of isoprene in the terrestrial environment
Author: El Khawand, Myriam
ISNI:       0000 0004 5371 308X
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2014
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Isoprene is a climate active gas emitted from natural and anthropogenic sources in quantities equivalent to the global methane flux to the atmosphere. 90 % of the emitted isoprene is produced enzymatically in the chloroplast of terrestrial plants from dimethylallyl pyrophosphate via the methylerythritol pathway. The main role of isoprene emission by plants is to reduce the damage caused by heat stress through stabilizing cellular membranes. Isoprene emission from microbes, animals, and humans has also been reported, albeit less understood than isoprene emission from plants. Despite large emissions, isoprene is present at low concentrations in the atmosphere due to its rapid reactions with other atmospheric components, such as hydroxyl radicals. Isoprene can extend the lifetime of potent greenhouse gases, influence the tropospheric concentrations of ozone, and induce the formation of secondary organic aerosols. While substantial knowledge exists about isoprene production and atmospheric chemistry, our knowledge of isoprene sinks is limited. Soils consume isoprene at a high rate and contain numerous isoprene-utilizing bacteria. However, Rhodococcus sp. AD45 is the only terrestrial isoprene-degrading bacterium characterized in any detail. A pathway for isoprene degradation involving a putative soluble monooxygenase has been proposed. In this study, we report the isolation of two novel isoprene-degrading bacteria and characterization of the isoprene gene clusters in their draft genomes. Using marker exchange mutagenesis, transcription assays and proteomics analyses, we provide conclusive evidence that isoprene is metabolized in Rhodococcus sp. AD45 through the induced activity of soluble isoprene monooxygenase, a close relative to well known soluble diiron center monooxygenase enzymes. Metabolic gene PCR assays based on a key component of isoprene monooxygenase were also developed to detect isoprene degraders in the environment. The diversity of active isoprene degraders in the terrestrial environment was investigated using DNA-stable isotope probing experiments combined with 454 pyrosequencing.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available