Extremely Thermophilic Routes to Microbial Electrofuels

Hawkins, Aaron S.; Han, Young-Tak; Lian, Hong; Loder, Andrew J.; Menon, Angeli Lal; Iwuchukwu, Ifeyinwa J.; Keller, Matthew W.; Leuko, Therese T.; Adams, Michael W. W.; Kelly, Robert M.

doi:10.1021/cs2003017

Cited by 41 publications

(34 citation statements)

References 87 publications

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“…It is important to note that the low metabolic activity of P. furiosus at 72°C was sufficient to provide the ATP needed for carbon dioxide fixation. These results are a significant step forward toward the overall goal of incorporating into P. furiosus the complete M. sedula 3-HP/4-HB pathway, in which two molecules of carbon dioxide are reduced to acetyl-CoA that can then be converted into a variety of valuable products including biofuels (6). Clearly, there will be a balance between using a fixed carbon source (sugar) via the low metabolic activity of the host to produce ATP and the high catalytic activity of the heterologous enzymes to generate the desired product.…”

Section: Resultsmentioning

confidence: 93%

“…3A). The incorporation of electrons from hydrogen gas and the carbon from carbon dioxide into a single desired product is essentially the paradigm for electrofuels (6). P. furiosus grows by fermenting sugars (such as the disaccharide maltose) to acetate, carbon dioxide, and hydrogen and can also use pyruvate as a carbon source (12).…”

Section: Resultsmentioning

confidence: 99%

“…This circumvents the overall low efficiency experienced in generating both plant and algal photosynthetic products (5). Moreover, such electron sources can potentially be used to reduce carbon dioxide directly to produce liquid fuels or "electrofuels" (6) or to produce industrial chemicals without a sugar intermediate. However, although significant advances have been made in manipulating microorganisms to produce various fuels from organic substrates (4,7,8), the engineering of microorganisms to use carbon dioxide and hydrogen gas has not been reported.…”

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confidence: 99%

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Exploiting microbial hyperthermophilicity to produce an industrial chemical, using hydrogen and carbon dioxide

Keller

Schut

Lipscomb

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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119

103

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Microorganisms can be engineered to produce useful products, including chemicals and fuels from sugars derived from renewable feedstocks, such as plant biomass. An alternative method is to use low potential reducing power from nonbiomass sources, such as hydrogen gas or electricity, to reduce carbon dioxide directly into products. This approach circumvents the overall low efficiency of photosynthesis and the production of sugar intermediates. Although significant advances have been made in manipulating microorganisms to produce useful products from organic substrates, engineering them to use carbon dioxide and hydrogen gas has not been reported. Herein, we describe a unique temperature-dependent approach that confers on a microorganism (the archaeon Pyrococcus furiosus, which grows optimally on carbohydrates at 100°C) the capacity to use carbon dioxide, a reaction that it does not accomplish naturally. This was achieved by the heterologous expression of five genes of the carbon fixation cycle of the archaeon Metallosphaera sedula, which grows autotrophically at 73°C. The engineered P. furiosus strain is able to use hydrogen gas and incorporate carbon dioxide into 3-hydroxypropionic acid, one of the top 12 industrial chemical building blocks. The reaction can be accomplished by cell-free extracts and by whole cells of the recombinant P. furiosus strain. Moreover, it is carried out some 30°C below the optimal growth temperature of the organism in conditions that support only minimal growth but maintain sufficient metabolic activity to sustain the production of 3-hydroxypropionate. The approach described here can be expanded to produce important organic chemicals, all through biological activation of carbon dioxide.

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Exploiting microbial hyperthermophilicity to produce an industrial chemical, using hydrogen and carbon dioxide

Keller

Schut

Lipscomb

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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119

103

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“…The identification and biochemical characteristics of many of the enzymes in this cycle have been reported by Fuchs and coworkers (1,28,30,44,50,54), mostly focusing on a member of the Sulfolobales, Metallosphaera sedula (27). Supporting genome sequence information (6) and complementary transcriptomic data for growth of M. sedula under autotrophic and heterotrophic conditions helped elucidate the components of this cycle (5,25). This extremely thermoacidophilic archaeon, which grows optimally at 73°C and pH 2, can utilize organic carbon (peptides) or CO 2 as its carbon source and metal sulfides, organic carbon, and/or H 2 as an energy source (4).…”

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confidence: 92%

“…In animals, MCE and MCM are involved in glyoxylate regeneration (31) and metabolism of propionate, branched-chain amino acids, Transcriptional response analysis. To identify the genes encoding MCE and MCM in the M. sedula genome, a whole-genome oligonucleotide microarray for M. sedula was used to follow the transcriptomes for growth under autotrophic and heterotrophic conditions (5,25). Briefly, M. sedula cells were grown aerobically at 70°C in a shaking oil bath (70 rpm) under autotrophic or heterotrophic conditions on a chemically defined medium (DSM 88) at pH 2.0.…”

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confidence: 99%

Epimerase (Msed_0639) and Mutase (Msed_0638 and Msed_2055) Convert ( S )-Methylmalonyl-Coenzyme A (CoA) to Succinyl-CoA in the Metallosphaera sedula 3-Hydroxypropionate/4-Hydroxybutyrate Cycle

Han

Hawkins

Adams

et al. 2012

Appl Environ Microbiol

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ABSTRACTCrenarchaeotal genomes encode the 3-hydroxypropionate/4-hydroxybutyrate (3-HP/4-HB) cycle for carbon dioxide fixation. Of the 13 enzymes putatively comprising the cycle, several of them, including methylmalonyl-coenzyme A (CoA) epimerase (MCE) and methylmalonyl-CoA mutase (MCM), which convert (S)-methylmalonyl-CoA to succinyl-CoA, have not been confirmed and characterized biochemically. In the genome ofMetallosphaera sedula(optimal temperature [Topt], 73°C), the gene encoding MCE (Msed_0639) is adjacent to that encoding the catalytic subunit of MCM-α (Msed_0638), while the gene for the coenzyme B12-binding subunit of MCM (MCM-β) is located remotely (Msed_2055). The expression of all three genes was significantly upregulated under autotrophic compared to heterotrophic growth conditions, implying a role in CO2fixation. Recombinant forms of MCE and MCM were produced inEscherichia coli; soluble, active MCM was produced only if MCM-α and MCM-β were coexpressed. MCE is a homodimer and MCM is a heterotetramer (α2β2) with specific activities of 218 and 2.2 μmol/min/mg, respectively, at 75°C. The heterotetrameric MCM differs from the homo- or heterodimeric orthologs in other organisms. MCE was activated by divalent cations (Ni2+, Co2+, and Mg2+), and the predicted metal binding/active sites were identified through sequence alignments with less-thermophilic MCEs. The conserved coenzyme B12-binding motif (DXHXXG-SXL-GG) was identified inM. sedulaMCM-β. The two enzymes together catalyzed the two-step conversion of (S)-methylmalonyl-CoA to succinyl-CoA, consistent with their proposed role in the 3-HP/4-HB cycle. Based on the highly conserved occurrence of single copies of MCE and MCM inSulfolobaceaegenomes, theM. sedulaenzymes are likely to be representatives of these enzymes in the 3-HP/4-HB cycle in crenarchaeal thermoacidophiles.

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Electrofuels

Benton

Coyler

Hickman

et al. 2014

Encyclopedia of Inorganic and Bioinorganic Chemistry

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Electrofuels are high‐energy compounds produced by the electrochemical reduction of compounds such as carbon dioxide or water. Microorganisms can act as biocatalysts for these reactions, during which they accept electrons either directly or indirectly from electrodes in bioelectrochemical systems ( BESs ). These microbes store this electrical energy by producing extracellular compounds instead of biomass. The electricity that drives this process may be harvested from intermittent renewable sources such as solar or wind. Thus, electrosynthesis could simultaneously sequester CO 2 and store renewable energy sources in designer chemicals, materials, or in convenient, high‐energy‐dense fuels for use in our transportation and electrical grid sectors. Butanol appears to be an ideal electrofuel target because it is considered a “drop‐in” fuel that can be used in our current energy infrastructure. Several challenges still face the production of electrofuels. The stability, structure, and conductivity of materials used as electrodes, the efficiency of electron transfer between these electrodes and microbes, and the diffusion of substrates (e.g., CO 2 ) into and products (e.g., butanol) out of the microbes all need to be optimized for efficient microbial electrosynthesis. A complete life‐cycle assessment of the environmental impact of any electrofuel also needs to be conducted before its widespread use.

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Extremely Thermophilic Routes to Microbial Electrofuels

Cited by 41 publications

References 87 publications

Exploiting microbial hyperthermophilicity to produce an industrial chemical, using hydrogen and carbon dioxide

Exploiting microbial hyperthermophilicity to produce an industrial chemical, using hydrogen and carbon dioxide

Epimerase (Msed_0639) and Mutase (Msed_0638 and Msed_2055) Convert ( S )-Methylmalonyl-Coenzyme A (CoA) to Succinyl-CoA in the Metallosphaera sedula 3-Hydroxypropionate/4-Hydroxybutyrate Cycle

Electrofuels

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