Formation of Isobutene from 3-Hydroxy-3-Methylbutyrate by Diphosphomevalonate Decarboxylase

Gogerty, David S.; Bobik, Thomas A.

doi:10.1128/aem.01917-10

Cited by 35 publications

(43 citation statements)

References 33 publications

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“…Natural alkene sources are mainly emissions from hydrocarbon reservoirs and hydrothermal sites (11) as well as from burning and pyrolysis of organic materials (21,55). In addition, traces of isobutene could be produced from side reactions occurring in the metabolism of isovaleric acid and 3,3-HMB (14,15). Most important, of course, isobutene and isoamylene are also present in oil derivatives such as gasoline (24).…”

Section: Discussionmentioning

confidence: 99%

Formation of Alkenes via Degradation of tert -Alkyl Ethers and Alcohols by Aquincola tertiaricarbonis L108 and Methylibium spp

Schäfer

Muzica

Schuster

et al. 2011

Appl Environ Microbiol

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Bacterial degradation pathways of fuel oxygenates such as methyl tert-butyl and tert-amyl methyl ether (MTBE and TAME, respectively) have already been studied in some detail. However, many of the involved enzymes are still unknown, and possible side reactions have not yet been considered. In Aquincola tertiaricarbonis L108, Methylibium petroleiphilum PM1, and Methylibium sp. strain R8, we have now detected volatile hydrocarbons as by-products of the degradation of the tert-alkyl ether metabolites tert-butyl and tert-amyl alcohol (TBA and TAA, respectively). The alkene isobutene was formed only during TBA catabolism, while the beta and gamma isomers of isoamylene were produced only during TAA conversion. Both tert-alkyl alcohol degradation and alkene production were strictly oxygen dependent. However, the relative contribution of the dehydration reaction to total alcohol conversion increased with decreasing oxygen concentrations. In restingcell experiments where the headspace oxygen content was adjusted to less than 2%, more than 50% of the TAA was converted to isoamylene. Isobutene formation from TBA was about 20-fold lower, reaching up to 4% alcohol turnover at low oxygen concentrations. It is likely that the putative tert-alkyl alcohol monooxygenase MdpJ, belonging to the Rieske nonheme mononuclear iron enzymes and found in all three strains tested, or an associated enzymatic step catalyzed the unusual elimination reaction. This was also supported by the detection of mdpJK genes in MTBE-degrading and isobutene-emitting enrichment cultures obtained from two treatment ponds operating at Leuna, Germany. The possible use of alkene formation as an easy-to-measure indicator of aerobic fuel oxygenate biodegradation in contaminated aquifers is discussed.The extensive use of methyl tert-butyl ether (MTBE) and related compounds as fuel oxygenates has resulted in contamination of numerous groundwater sites in the United States and Europe (13,26,33,51). Although MTBE is now banned in some countries and may be phased out in others (52), it will persist at polluted sites for a long time due to its poor biodegradability. Despite this enormous environmental prevalence, only a few strains capable of growth on MTBE, ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME) have been found, and fuel oxygenate metabolism has not been elucidated in full detail (20,30,31,46). Since the pioneering works of Salanitro et al. and Steffan et al. (42,43,48), it is generally agreed that aerobic MTBE degradation proceeds via a monooxygenase-catalyzed ether cleavage resulting in formation of tert-butyl alcohol (TBA). The latter is hydroxylated to the corresponding diol, 2-methyl-1,2-propanediol (MPD), which is further oxidized to 2-hydroxyisobutyric acid (2-HIBA). This branched carboxylic acid is then introduced into common metabolic routes after isomerization to 3-hydroxybutyric acid (39). Since ETBE shares the tert-butyl structure with MTBE, it should have a similar degradation path via TBA (8, 30). The biochemistry of TAME catabol...

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Section: Discussionmentioning

confidence: 99%

Formation of Alkenes via Degradation of tert -Alkyl Ethers and Alcohols by Aquincola tertiaricarbonis L108 and Methylibium spp

Schäfer

Muzica

Schuster

et al. 2011

Appl Environ Microbiol

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“…However, higher alcohols, like isobutanol, possess several advantages, such as a lower hygroscopicity, vapor pressure, and corrosivity, full compatibility with existing engines and pipelines, and a higher energy density, allowing safer handling and more efficient use than ethanol (15). Furthermore, isobutanol can serve as a precursor for the production of isobutene (34), which nowadays is exclusively produced in large scale by petroleum refining and is used as a gasoline additive and for the production of butyl rubber and specialty chemicals (20).…”

mentioning

confidence: 99%

Corynebacterium glutamicum Tailored for Efficient Isobutanol Production

Blombach

Riester

Wieschalka

et al. 2011

Appl Environ Microbiol

280

209

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We recently engineered Corynebacterium glutamicum for aerobic production of 2-ketoisovalerate by inactivation of the pyruvate dehydrogenase complex, pyruvate:quinone oxidoreductase, transaminase B, and additional overexpression of the ilvBNCD genes, encoding acetohydroxyacid synthase, acetohydroxyacid isomeroreductase, and dihydroxyacid dehydratase. Based on this strain, we engineered C. glutamicum for the production of isobutanol from glucose under oxygen deprivation conditions by inactivation of L-lactate and malate dehydrogenases, implementation of ketoacid decarboxylase from Lactococcus lactis, alcohol dehydrogenase 2 (ADH2) from Saccharomyces cerevisiae, and expression of the pntAB transhydrogenase genes from Escherichia coli. The resulting strain produced isobutanol with a substrate-specific yield (Y P/S ) of 0.60 ؎ 0.02 mol per mol of glucose. Interestingly, a chromosomally encoded alcohol dehydrogenase rather than the plasmid-encoded ADH2 from S. cerevisiae was involved in isobutanol formation with C. glutamicum, and overexpression of the corresponding adhA gene increased the Y P/S to 0.77 ؎ 0.01 mol of isobutanol per mol of glucose. Inactivation of the malic enzyme significantly reduced the Y P/S , indicating that the metabolic cycle consisting of pyruvate and/or phosphoenolpyruvate carboxylase, malate dehydrogenase, and malic enzyme is responsible for the conversion of NADH؉H ؉ to NADPH؉H ؉ . In fed-batch fermentations with an aerobic growth phase and an oxygen-depleted production phase, the most promising strain, C. glutamicum ⌬aceE ⌬pqo ⌬ilvE ⌬ldhA ⌬mdh(pJC4ilvBNCD-pntAB)(pBB1kivd-adhA), produced about 175 mM isobutanol, with a volumetric productivity of 4.4 mM h ؊1 , and showed an overall Y P/S of about 0.48 mol per mol of glucose in the production phase.

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“…It has been shown that 3-hydroxyisovalerate can be converted to isobutene as a side-activity of mevalonate diphosphate decarboxylase (Figure 4). [62][63] Also, patent applications describe isobutanol dehydration as a side activity of engineered oleate hydratase and other hydratases. [48][49] Fermentative production of isobutanol is described in section 0.…”

Section: Isobutenementioning

confidence: 99%