Metabolism of 2-Methylpropene (Isobutylene) by the Aerobic Bacterium Mycobacterium sp. Strain ELW1

Abstract

An aerobic bacterium (Mycobacterium sp. strain ELW1) that utilizes 2-methylpropene (isobutylene) as a sole source of carbon and energy was isolated and characterized. Strain ELW1 grew on 2-methylpropene (growth rate ‫؍‬ 0.05 h ؊1 ) with a yield of 0.38 mg (dry weight) mg 2-methylpropene ؊1 . Strain ELW1 also grew more slowly on both cis-and trans-2-butene but did not grow on any other C 2 to C 5 straight-chain, branched, or chlorinated alkenes tested. Resting 2-methylpropene-grown cells consumed ethene, propene, and 1-butene without a lag phase. Epoxyethane accumulated as the only detected product of ethene oxidation. Both alkene consumption and epoxyethane production were fully inhibited in cells exposed to 1-octyne, suggesting that alkene oxidation is initiated by an alkyne-sensitive, epoxide-generating monooxygenase. Kinetic analyses indicated that 1,2-epoxy-2-methylpropane is rapidly consumed during 2-methylpropene degradation, while 2-methyl-2-propen-1-ol is not a significant metabolite of 2-methylpropene catabolism. Degradation of 1,2-epoxy-2-methylpropane by 2-methylpropene-grown cells led to the accumulation and further degradation of 2-methyl-1,2-propanediol and 2-hydroxyisobutyrate, two sequential metabolites previously identified in the aerobic microbial metabolism of methyl tert-butyl ether (MTBE) and tert-butyl alcohol (TBA). Growth of strain ELW1 on 2-methylpropene, 1,2-epoxy-2-methylpropane, 2-methyl-1,2-propanediol, and 2-hydroxyisobutyrate was fully inhibited when cobalt ions were omitted from the growth medium, while growth on 3-hydroxybutyrate and other substrates was unaffected by the absence of added cobalt ions. Our results suggest that, like aerobic MTBE-and TBA-metabolizing bacteria, strain ELW1 utilizes a cobalt/cobalamin-dependent mutase to transform 2-hydroxyisobutyrate. Our results have been interpreted in terms of their impact on our understanding of the microbial metabolism of alkenes and ether oxygenates.T he compound 2-methylpropene (isobutylene) is one of four butene (C 4 H 8 ) isomers and is the simplest branched alkene. Annually, in excess of 10 million tons of this gas are produced worldwide, mainly from cracking of petroleum. 2-Methylpropene is used as feedstock for high-volume petrochemicals, including ether fuel oxygenates, such as methyl tert-butyl ether (MTBE); high-octane gasoline blending components, such as 2,2,4-trimethylpentane (isooctane); and butyl rubber (1). The industrial importance of 2-methylpropene has stimulated interest in its biological production as an alternative to nonrenewable petroleum sources. Many microorganisms that can generate this gas have been identified (2, 3), including MTBE-metabolizing bacteria (4). It can also be produced directly by several enzymes (5-8). In contrast to these microbial and enzymatic production routes, little is known about the microbial degradation of 2-methylpropene, and no microorganisms have previously been reported to grow on this gas.From their outset, studies of aerobic microbial metabolism of gaseous alkenes have f...

Activity-Based Protein Profiling of Ammonia Monooxygenase in Nitrosomonas europaea

“…Several n-alkynes, including 1-octyne, inactivate the alkeneoxidizing enzyme system of the 2-methylpropene metabolizing strain, Mycobacterium sp. ELW1 (43). The well-studied alkane hydroxylase in Pseudomonas oleovorans GPo1 is also irreversibly inactivated by 17OD (44)(45)(46).…”

Isolation of isoprene degrading bacteria from soils, development of isoA gene probes and identification of the active isoprene‐degrading soil community using DNA‐stable isotope probing

“…Interestingly, conjugation with glutathione in Rhodococcus sp. AD45 contrasts with other alkene utilizers, which often overcome the toxicity of epoxides by forming coenzyme M conjugates or by hydrolysis (Ensign, 2001;Kottegoda et al, 2015). The genes encoding the monooxygenase (isoABCDEF) and two subsequent enzymes, together with two additional genes of unknown function, were cloned and sequenced (van Hylckama Vlieg et al, 2000).…”

Formation of Developmentally Toxic Phenanthrene Metabolite Mixtures by Mycobacterium sp. ELW1

“…1-Octyne (~7 µmol in the aqueous media) was used as a control to inhibit the alkene monooxygenase involved in isobutene oxidation to reduce PHE transformation and better understand the mechanism of transformation. 44 Preparation of stock gas-phase 1-octyne and determination of optimal 1-octyne aqueous concentration is explained in detail in the Supporting Information. 1-Octyne controls and PHE-only controls were prepared with 0.033, 0.068, 0.14, and 0.84 µmol PHE.…”

“…ELW1 was isolated from stream sediment using isobutene (2-methylpropene) as the single source of carbon for growth and energy. 44 PCR sequencing of the 16S rRNA gene of ELW1 indicates that it is a Mycobacterium strain. 44 The ability of ELW1 to utilize isobutene as a growth substrate has potential for the in situ stimulation of endogenous microbial populations through isobutene and oxygen addition, and may lead to a novel method to promote the initial oxidation of PAHs for subsurface bioremediation, through co-metabolic transformations.…”