Abstract
The climate-active gas isoprene is the major volatile produced by a variety of trees and is released into the atmosphere in enormous quantities, on a par with global emissions of methane. While isoprene production in plants and its effect on atmospheric chemistry have received considerable attention, research into the biological isoprene sink has been neglected until recently. Here, we review current knowledge on the sources and sinks of isoprene and outline its environmental effects. Focusing on degradation by microbes, many of which are able to use isoprene as the sole source of carbon and energy, we review recent studies characterizing novel isoprene degraders isolated from soils, marine sediments and in association with plants. We describe the development and use of molecular methods to identify, quantify and genetically characterize isoprene-degrading strains in environmental samples. Finally, this review identifies research imperatives for the further study of the environmental impact, ecology, regulation and biochemistry of this interesting group of microbes.
Highlights
The climate-a ctive gas isoprene is the major volatile produced by a variety of trees and is released into the atmosphere in enormous quantities, on a par with global emissions of methane
The precursor molecules, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), are synthesized by either the mevalonate (MVA) pathway or the methylerythritol 4-p hosphate (MEP) pathway, which use as precursors acetyl-CoA, or pyruvate and glyceraldehyde 3-p hosphate, respectively [6] (Fig. 1)
DMAPP is the substrate for the key final step in the production of isoprene, catalysed by the Mg2+-requiring enzyme, isoprene synthase (ISPS)
Summary
Isoprene (2-m ethyl-1,3-b utadiene) is the most abundantly produced biogenic volatile organic compound (BVOC) in our biosphere with atmospheric emissions of around 500 Tg(C) per year. Since trees are the major source of isoprene globally [7], there is increasing interest in the potential impact on air quality of certain crop plants [16]. Isoprene is an important commodity chemical that is industrially produced from petroleum in substantial amounts (approximately 1 million tonnes globally per year). It is used for production of polyisoprene (synthetic rubber) and has received attention as a potential fuelstock. Approaches used to explore isoprene production in microbes have been recently reviewed by Ye et al [44] and include expression of isoprene synthase genes from plants in Escherichia coli, Saccharomyces and Synechococcus, and enhancing carbon flux to DMAPP in microbes
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