Carbon monoxide fermentation to ethanol by Clostridium autoethanogenum in a bioreactor with no accumulation of acetic acid

Abubackar, Haris Nalakath; Veiga, María C.; Kennes, Christian

doi:10.1016/j.biortech.2015.02.113

Cited by 119 publications

(66 citation statements)

References 28 publications

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“…A counterargument is that ethanol formation from CO-rich BOF gas appears to be favored when the pH in the growth medium is pH 6 rather than pH 5.5 (87,88), i.e., conditions under which ethanol formation via acetic acid reduction to acetaldehyde is less favored (see above). However, these findings were not backed by a more recent study that showed that during growth of C. autoethanogenum on CO at pH 4.7, mainly ethanol was formed, whereas at pH 6 ethanol and acetate were generated in almost equal amounts (89).…”

Section: H 2 Activationmentioning

confidence: 63%

Energy Conservation Associated with Ethanol Formation from H ₂ and CO ₂ in Clostridium autoethanogenum Involving Electron Bifurcation

et al. 2015

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Most acetogens can reduce CO 2 with H 2 to acetic acid via the Wood-Ljungdahl pathway, in which the ATP required for formate activation is regenerated in the acetate kinase reaction. However, a few acetogens, such as Clostridium autoethanogenum, Clostridium ljungdahlii, and Clostridium ragsdalei, also form large amounts of ethanol from CO 2 and H 2 . How these anaerobes with a growth pH optimum near 5 conserve energy has remained elusive. We investigated this question by determining the specific activities and cofactor specificities of all relevant oxidoreductases in cell extracts of H 2 /CO 2 -grown C. autoethanogenum. The activity studies were backed up by transcriptional and mutational analyses. Most notably, despite the presence of six hydrogenase systems of various types encoded in the genome, the cells appear to contain only one active hydrogenase. The active [FeFe]-hydrogenase is electron bifurcating, with ferredoxin and NADP as the two electron acceptors. Consistently, most of the other active oxidoreductases rely on either reduced ferredoxin and/or NADPH as the electron donor. An exception is ethanol dehydrogenase, which was found to be NAD specific. Methylenetetrahydrofolate reductase activity could only be demonstrated with artificial electron donors. Key to the understanding of this energy metabolism is the presence of membrane-associated reduced ferredoxin:NAD ؉ oxidoreductase (Rnf), of electron-bifurcating and ferredoxin-dependent transhydrogenase (Nfn), and of acetaldehyde:ferredoxin oxidoreductase, which is present with very high specific activities in H 2 /CO 2 -grown cells. Based on these findings and on thermodynamic considerations, we propose metabolic schemes that allow, depending on the H 2 partial pressure, the chemiosmotic synthesis of 0.14 to 1.5 mol ATP per mol ethanol synthesized from CO 2 and H 2 . IMPORTANCEEthanol formation from syngas (H 2 , CO, and CO 2 ) and from H 2 and CO 2 that is catalyzed by bacteria is presently a much-discussed process for sustainable production of biofuels. Although the process is already in use, its biochemistry is only incompletely understood. The most pertinent question is how the bacteria conserve energy for growth during ethanol formation from H 2 and CO 2 , considering that acetyl coenzyme A (acetyl-CoA), is an intermediate. Can reduction of the activated acetic acid to ethanol with H 2 be coupled with the phosphorylation of ADP? Evidence is presented that this is indeed possible, via both substrate-level phosphorylation and electron transport phosphorylation. In the case of substrate-level phosphorylation, acetyl-CoA reduction to ethanol proceeds via free acetic acid involving acetaldehyde:ferredoxin oxidoreductase (carboxylate reductase).

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Section: H 2 Activationmentioning

confidence: 63%

Energy Conservation Associated with Ethanol Formation from H ₂ and CO ₂ in Clostridium autoethanogenum Involving Electron Bifurcation

et al. 2015

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“…Abubackar and co-workers found that the presence of tungsten significantly improved alcohol production and increased the ethanol/acetate ratio in C. autoethanogenum grown on CO, while the presence of selenium did either not improve ethanol production or even reduce it under the experimental conditions used in their study. 84,85 Metalloenzymes and the presence of trace metals play thus a key role in ethanol production and are expected to have a similar influence in the bioconversion of gaseous C1 substrates to higher alcohols such as butanol and hexanol.…”

Section: Effect Of Medium Compositionmentioning

confidence: 99%

H‐B‐E (hexanol‐butanol‐ethanol) fermentation for the production of higher alcohols from syngas/waste gas

Fernández-Naveira

Veiga

Kennes

2017

J of Chemical Tech & Biotech

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114

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CO, H2, and CO2 are major components of syngas and some industrial CO‐rich waste gases (e.g. waste gases from steel industries), besides some additional minor compounds. It was recently shown that those gases can be bioconverted, by acetogenic/solventogenic bacteria, into ethanol and higher alcohols such as butanol, but also hexanol, through the so‐called HBE fermentation. That process presents some advantages over existing chemical conversion processes. This paper reviews HBE fermentation from C1‐gases after briefly describing the more conventional ABE (acetone‐butanol‐ethanol) fermentation from carbohydrates by Clostridium acetobutylicum, in order to allow for comparison of both processes. Although acetone may appear in carbohydrate fermentation, alcohols are the only major end‐metabolites in the HBE process with Clostridium carboxidivorans. The few acetogenic bacteria known to metabolize C1‐gases and produce butanol or higher alcohols are described. Clostridium carboxidivorans has been used in most cases. Bioconversion of the gaseous substrates takes place in two stages, namely acidogenesis (production of acids) followed by solventogenesis (production of alcohols), characterized by different optimal fermentation conditions. Major parameters affecting each bioconversion stage as well as the overall fermentation process are analyzed. Although it has been claimed that acidification is required in ABE fermentation to initiate the solventogenic stage, strong acidification seems to some extent not to be a prerequisite for solventogenesis in the HBE process. Bioreactors potentially suitable for this type of bioconversion process are described as well. © 2017 Society of Chemical Industry

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“…Furthermore, some studies also confirm that C. autoethanogenum is a low productivity bacteria in ethanol production compared to other carboxidotrophic strains of Clostridium sp. despite its genetic modified strain has been developed for ethanol commercial scale production by LanzaTech [1,[12][13][14]. C. ragsdaleii and C. carbodixovorans are the recent isolated strains which their potential are still in the exploration [15,16].…”

Section: Introductionmentioning

confidence: 99%

Bioethanol Production via Syngas Fermentation

et al. 2018

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Abstract. Bioconversion of C-1 carbon in syngas through microbial fermentation presents a huge potential to be further explored for ethanol production. Syngas can be obtained from the gasification of lignocellulosic biomass, by which most of carbon content of the biomass was converted into CO and CO2. These gases could be further utilized by carbon-fixing microorganism such as Clostridium sp. to produce ethanol as the end product. In order to obtain an optimum process, a robust and high performance strain is required and thus high ethanol yield as the main product can be expected. In this study, series of batch fermentation was carried out to select high performance strains for ethanol production. Bottle serum fermentations were performed using CO-gas as the sole carbon source to evaluate the potential of some Clostridia species such as Clostridium ljungdahlii, C. ragsdalei, and C. carboxidovorans in producing ethanol at various concentration of yeast extract as the organic nitrogen source, salt concentration, and buffer composition. Strain with the highest ethanol production in the optimum media will be further utilized in the upscale fermentation.

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Carbon monoxide fermentation to ethanol by Clostridium autoethanogenum in a bioreactor with no accumulation of acetic acid

Cited by 119 publications

References 28 publications

Energy Conservation Associated with Ethanol Formation from H ₂ and CO ₂ in Clostridium autoethanogenum Involving Electron Bifurcation

Energy Conservation Associated with Ethanol Formation from H ₂ and CO ₂ in Clostridium autoethanogenum Involving Electron Bifurcation

H‐B‐E (hexanol‐butanol‐ethanol) fermentation for the production of higher alcohols from syngas/waste gas

Bioethanol Production via Syngas Fermentation

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Carbon monoxide fermentation to ethanol by Clostridium autoethanogenum in a bioreactor with no accumulation of acetic acid

Cited by 119 publications

References 28 publications

Energy Conservation Associated with Ethanol Formation from H 2 and CO 2 in Clostridium autoethanogenum Involving Electron Bifurcation

Energy Conservation Associated with Ethanol Formation from H 2 and CO 2 in Clostridium autoethanogenum Involving Electron Bifurcation

H‐B‐E (hexanol‐butanol‐ethanol) fermentation for the production of higher alcohols from syngas/waste gas

Bioethanol Production via Syngas Fermentation

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Product

Resources

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Energy Conservation Associated with Ethanol Formation from H ₂ and CO ₂ in Clostridium autoethanogenum Involving Electron Bifurcation

Energy Conservation Associated with Ethanol Formation from H ₂ and CO ₂ in Clostridium autoethanogenum Involving Electron Bifurcation