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Microbial metabolism of isoprene: a much-neglected climate-active gas.

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.

SUBMITTER: Murrell JC

PROVIDER: S-EPMC7657509 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:A series of iminopyridyl-based ligands, 6-[(Ar)N=C(R)]-2-C6H5N [(Ar = 2,6-Me2-C6H3, R = Me (L1); Ar = 2,6-iPr2-C6H3, R = Me (L2); Ar = 2,6-Me2-C6H3, R = H (L3); Ar = 2,6-iPr2-C6H3, R = H (L4); Ar = 3,5-(CF3)2-C6H3, R = Me (L5); Ar = C6F5, R = Me (L6)], and their corresponding iron (II) complexes were developed to investigate their application in the controlled coordinative polymerization of isoprene. The modulation of steric and electronic properties within this family of ligands/pre-catalysts has shown to influence the stereo-selectivity and activity of the polymerization of isoprene after activation. Upon activation with various co-catalysts such as AliBu3/[Ph3C][B(C6F5)4], AlEt3/[Ph3C][B(C6F5)4] or MAO, the resulting catalysts produced polyisoprenes with an excellent conversion (>99% of 500-5000 equiv.) within less than 1 h (TOF > 500 h-1) and having a variety of stereo-/regio-regularities. The presence of electron-donating and withdrawing groups drastically impacted the activity and the stereoselectivity of the catalysts during the course of the polymerization of isoprene. When activated with AliBu3/[Ph3C][B(C6F5)4], the complexes {6-[(2,6-Me2-C6H3)N=C(Me)]-2-C6H5N}FeCl2 (C1) and {6-[(2,6-iPr2-C6H3)N=C(Me)]-2-C6H5N}FeCl2 (C2) exhibited moderate trans-1,4 selectivity (>67%) while the iron-based systems bearing related aldiminopyridyl ligands {6-[(2,6-Me2-C6H3)N=C(H)]-2-C6H5N}FeCl2 (C3) and {6-[(2,6-iPr2-C6H3)N=C(H)]-2-C6H5N}FeCl2 (C4) were found to afford significant cis-1,4 selectivity at low temperature (>86% at -40 °C). On the other hand, the ternary {6-[(3,5-(CF3)2-C6H3)N=C(Me)]-2-C6H5N}FeCl2 (C5) or {6-[(C6F5)N=C(Me)]-2-C6H5N}FeCl2 (C6)/AliBu3/[Ph3C][B(C6F5)4] catalytic combinations showed exceptional activity for the polymerization of isoprene (TOF > 1,000,000 h-1), albeit providing less stereoselectivity.

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