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2.
BackgroundAcetogenic bacteria are able to use CO 2 as terminal electron acceptor of an anaerobic respiration, thereby producing acetate with electrons coming from H 2. Due to this feature, acetogens came into focus as platforms to produce biocommodities from waste gases such as H 2 + CO 2 and/or CO. A prerequisite for metabolic engineering is a detailed understanding of the mechanisms of ATP synthesis and electron-transfer reactions to ensure redox homeostasis. Acetogenesis involves the reduction of CO 2 to acetate via soluble enzymes and is coupled to energy conservation by a chemiosmotic mechanism. The membrane-bound module, acting as an ion pump, was of special interest for decades and recently, an Rnf complex was shown to couple electron flow from reduced ferredoxin to NAD + with the export of Na + in Acetobacterium woodii. However, not all acetogens have rnf genes in their genome. In order to gain further insights into energy conservation of non-Rnf-containing, thermophilic acetogens, we sequenced the genome of Thermoanaerobacter kivui. ResultsThe genome of Thermoanaerobacter kivui comprises 2.9 Mbp with a G + C content of 35% and 2,378 protein encoding orfs. Neither autotrophic growth nor acetate formation from H 2 + CO 2 was dependent on Na + and acetate formation was inhibited by a protonophore, indicating that H + is used as coupling ion for primary bioenergetics. This is consistent with the finding that the c subunit of the F 1F O ATP synthase does not have the conserved Na + binding motif. A search for potential H +-translocating, membrane-bound protein complexes revealed genes potentially encoding two different proton-reducing, energy-conserving hydrogenases (Ech). ConclusionsThe thermophilic acetogen T. kivui does not use Na + but H + for chemiosmotic ATP synthesis. It does not contain cytochromes and the electrochemical proton gradient is most likely established by an energy-conserving hydrogenase (Ech). Its thermophilic nature and the efficient conversion of H 2 + CO 2 make T. kivui an interesting acetogen to be used for the production of biocommodities in industrial micobiology. Furthermore, our experimental data as well as the increasing number of sequenced genomes of acetogenic bacteria supported the new classification of acetogens into two groups: Rnf- and Ech-containing acetogens. 相似文献
3.
Acetogenic bacteria recently attracted attention because they reduce carbon dioxide (CO 2) with hydrogen (H 2) to acetate or to other products such as ethanol. Besides gases, acetogens use a broad range of substrates, but conversion of the sugar alcohol mannitol has rarely been reported. We found that the thermophilic acetogenic bacterium Thermoanaerobacter kivui grew on mannitol with a specific growth rate of 0.33 h −1 to a final optical density (OD 600) of 2.2. Acetate was the major product formed. A lag phase was observed only in cultures pre-grown on glucose, not in those pre-grown on mannitol, indicating that mannitol metabolism is regulated. Mannitol-1-phosphate dehydrogenase (MtlD) activity was observed in cell-free extracts of cells grown on mannitol only. A gene cluster (TKV_c02830–TKV_c02860) for mannitol uptake and conversion was identified in the T. kivui genome, and its involvement was confirmed by deleting the mtlD gene (TKV_c02860) encoding the key enzyme MtlD. Finally, we overexpressed mtlD, and the recombinant MtlD carried out the reduction of fructose-6-phosphate with NADH, at a high V MAX of 1235 U mg −1 at 65°C. The enzyme was thermostable for 40 min at 75°C, thereby representing the first characterized MtlD from a thermophile. 相似文献
4.
Feeding microbial communities with both organic and inorganic substrates can improve sustainability and feasibility of chain elongation processes. Sustainably produced H 2, CO 2, and CO can be co-fed to microorganisms as a source for acetyl-CoA, while a small amount of an ATP-generating organic substrate helps overcome the kinetic hindrances associated with autotrophic carboxylate production. Here, we operated two semi-continuous bioreactor systems with continuous recirculation of H 2, CO 2, and CO while co-feeding an organic model feedstock (lactate and acetate) to understand how a mixotrophic community is shaped during carboxylate production. Contrary to the assumption that H 2, CO 2, and CO support chain elongation via ethanol production in open cultures, significant correlations ( p < 0.01) indicated that relatives of Clostridium luticellarii and Eubacterium aggregans produced carboxylates (acetate to n-caproate) while consuming H 2, CO 2, CO, and lactate themselves. After 100 days, the enriched community was dominated by these two bacteria coexisting in cyclic dynamics shaped by the CO partial pressure. Homoacetogenesis was strongest when the acetate concentration was low (3.2 g L −1), while heterotrophs had the following roles: Pseudoramibacter, Oscillibacter, and Colidextribacter contributed to n-caproate production and Clostridium tyrobutyricum and Acidipropionibacterium spp. grew opportunistically producing n-butyrate and propionate, respectively. The mixotrophic chain elongation community was more efficient in carboxylate production compared with the heterotrophic one and maintained average carbon fixation rates between 0.088 and 1.4 g CO 2 equivalents L −1 days −1. The extra H 2 and CO consumed routed 82% more electrons to carboxylates and 50% more electrons to carboxylates longer than acetate. This study shows for the first time long-term, stable production of short- and medium-chain carboxylates with a mixotrophic community. 相似文献
5.
Little is known about the contributions of biomass feedstock storage to the net greenhouse gas emissions from cellulosic biofuels. Direct emissions of methane and nitrous oxide during decomposition in storage may contribute substantially to the global warming potential of biofuels. In this study, laboratory-scale bales of switchgrass and corn stover were stored under a range of moisture (13.0–32.9%) and temperature (5–35 °C) conditions and monitored for O 2 consumption and CO 2, CH 4, and N 2O production over 8 weeks. Gas concentrations and emissions rates were highly variable within and between experimental groups. Stover bales produced higher CO 2 concentrations ( P = 0.0002) and lower O 2 ( P < 0.0001) during storage than switchgrass bales. Methane concentrations (1.8–2100 ppm) were inversely correlated with bale moisture ( P < 0.05), with emissions rates ranging from 4.4–914.9 μg kg −1 DM day −1. Nitrous oxide concentrations ranged from 0 to 31 ppm, and emissions from switchgrass bales inversely correlated with temperature and moisture ( P < 0.0001). Net global warming potential from each treatment (0–2.4 gCO 2e kg −1 DM) suggests that direct emission of methane and nitrous oxide from aerobically stored feedstocks have a small effect on net global warming potential of cellulosic biofuels. 相似文献
6.
Species of the genus Blautia are typical inhabitants of the human gut and considered as beneficial gut microbes. However, their role in the gut microbiome and their metabolic features are poorly understood. Blautia schinkii was described as an acetogenic bacterium, characterized by a functional Wood–Ljungdahl pathway (WLP) of acetogenesis from H 2 + CO 2. Here we report that two relatives, Blautia luti and Blautia wexlerae do not grow on H 2 + CO 2. Inspection of the genome sequence revealed all genes of the WLP except genes encoding a formate dehydrogenase and an electron-bifurcating hydrogenase. Enzyme assays confirmed this prediction. Accordingly, resting cells neither converted H 2 + CO 2 nor H 2 + HCOOH + CO 2 to acetate. Carbon monoxide is an intermediate of the WLP and substrate for many acetogens. Blautia luti and B. wexlerae had an active CO dehydrogenase and resting cells performed acetogenesis from HCOOH + CO 2 + CO, demonstrating a functional WLP. Bioinformatic analyses revealed that many Blautia strains as well as other gut acetogens lack formate dehydrogenases and hydrogenases. Thus, the use of formate instead of H 2 + CO 2 as an interspecies hydrogen and electron carrier seems to be more common in the gut microbiome. 相似文献
8.
The aim of this study was to evaluate the influence of different carbon dioxide (CO 2) concentrations on the distribution of carbon forms in the culture medium and the biomass production and biomolecules productivity of the strain Chlorella fusca LEB 111. In this study, experiments were carried out in which C. fusca cultures were exposed to different CO 2 concentrations, 0.03% (0.08 ml CO2 ml medium−1 days −1), 5% (0.18 ml CO2 ml medium−1 days −1), and 15% vol/vol CO 2 (0.54 ml CO2 ml medium−1 days −1). Among the carbon chemical species distributions in the culture medium, bicarbonate was predominant (94.2–98.9%), with the highest quantitative percentage in the experiment receiving a 15% CO 2 injection. C. fusca LEB 111 cultivated with 15% CO 2 showed the highest biomass productivity (194.3 mg L −1 days −1) and CO 2 fixation rate (390.9 mg L −1 days −1). The carbohydrate productivity in the culture that received 15% CO 2 was 46.2% higher than the value verified for the culture with the addition of CO 2 from the air (0.03% CO 2). In addition, CO 2 concentration providing increases of 0.03–15% to C. fusca cultures resulted in a 31.6% increase in the lipid productivity. These results showed that C. fusca can be used for CO 2 bioconversion and for producing biomass with potential applications for biofuels and bioproducts. 相似文献
9.
Energy crops for biofuel production, especially switchgrass ( Panicum virgatum), are of interest from a climate change perspective. Here, we use outputs from a crop growth model and life cycle assessment (LCA) to examine the global warming intensity (GWI; g CO 2 MJ −1) and greenhouse gas (GHG) mitigation potential (Mg CO 2 year −1) of biofuel systems based on a spatially explicit analysis of switchgrass grown on marginal land (abandoned former cropland) in Michigan, USA. We find that marginal lands in Michigan can annually produce over 0.57 hm 3 of liquid biofuel derived from nitrogen-fertilized switchgrass, mitigating 1.2–1.5 Tg of CO 2 year −1. About 96% of these biofuels can meet the Renewable Fuel Standard (60% reduction in lifecycle GHG emissions compared with conventional gasoline; GWI ≤37.2 g CO 2 MJ −1). Furthermore, 73%–75% of these biofuels are carbon-negative (GWI less than zero) due to enhanced soil organic carbon (SOC) sequestration. However, simulations indicate that SOC levels would fail to increase and even decrease on the 11% of lands where SOC stocks >>200 Mg C ha −1, leading to carbon intensities greater than gasoline. Results highlight the strong climate mitigation potential of switchgrass grown on marginal lands as well as the needs to avoid carbon rich soils such as histosols and wetlands and to ensure that productivity will be sufficient to provide net mitigation. 相似文献
10.
The marine diatom Thalassiosira pseudonana grown under air (0.04% CO2) and 1 and 5% CO2 concentrations was evaluated to determine its potential for CO2 mitigation coupled with biodiesel production. Results indicated that the diatom cultures grown at 1 and 5% CO2 showed higher growth rates (1.14 and 1.29 div day−1, respectively) and biomass productivities (44 and 48 mgAFDWL−1 day−1) than air grown cultures (with 1.13 div day−1 and 26 mgAFDWL−1 day−1). The increase of CO2 resulted in higher cell volume and pigment content per cell of T. pseudonana. Interestingly, lipid content doubled when air was enriched with 1–5% CO2. Moreover, the analysis of the fatty acid composition of T. pseudonana revealed the predominance of monounsaturated acids (palmitoleic-16:1 and oleic-18:1) and a decrease of the saturated myristic acid-14:0 and polyunsaturated fatty acids under high CO2 levels. These results suggested that T. pseudonana seems to be an ideal candidate for biodiesel production using flue gases. 相似文献
11.
Trophic links between fermentation and methanogenesis of soil derived from a methane‐emitting, moderately acidic temperate fen (pH 4.5) were investigated. Initial CO 2:CH 4 production ratios in anoxic microcosms indicated that methanogenesis was concomitant to other terminal anaerobic processes. Methane production in anoxic microcosms at in situ pH was stimulated by supplemental H 2–CO 2, formate or methanol; supplemental acetate did not stimulate methanogenesis. Supplemental H 2–CO 2, formate or methanol also stimulated the formation of acetate, indicating that the fen harbours moderately acid‐tolerant acetogens. Supplemental monosaccharides (glucose, N‐acetylglucosamine and xylose) stimulated the production of CO 2, H 2, acetate and other fermentation products when methanogenesis was inhibited with 2‐bromoethane sulfonate 20 mM. Glucose stimulated methanogenesis in the absence of BES. Upper soil depths yielded higher anaerobic activities and also higher numbers of cells. Detected archaeal 16S rRNA genes were indicative of H 2–CO 2‐ and formate‐consuming methanogens ( Methanomicrobiaceae), obligate acetoclastic methanogens ( Methanosaetaceae) and crenarchaeotes (groups I.1a, I.1c and I.3). Molecular analyses of partial sequences of 16S rRNA genes revealed the presence of Acidobacteria, Nitrospirales, Clamydiales, Clostridiales, Alpha‐, Gamma‐, Deltaproteobacteria and Cyanobacteria. These collective results suggest that this moderately acidic fen harbours phylogenetically diverse, moderately acid tolerant fermenters (both facultative aerobes and obligate anaerobes) that are trophically linked to methanogenesis. 相似文献
12.
CO 2 electrochemical reduction (CO 2RR) can mitigate environmental issues while providing valuable products, yet challenging in activity, selectivity, and stability. Here, a CuS-Bi 2S 3 heterojunction precursor is reported that can in situ reconstruct to Cu-doped Bismuth (CDB) electrocatalyst during CO 2RR. The CDB exhibits an industrial-compatible current density of −1.1 A cm −2 and a record-high formate formation rate of 21.0 mmol h −1 cm −2 at −0.86 V versus the reversible hydrogen electrode toward CO 2RR to formate, dramatically outperforming currently reported catalysts. Importantly, the ultrawide potential region of 1050 mV with high formate Faradaic efficiency of over 90% and superior long-term stability for more than 100 h at −400 mA cm −2 can also be realized. Experimental and theoretical studies reveal that the remarkable CO 2RR performance of CDB results from the doping effect of Cu which optimizes adsorption of the *OCHO and boosts the structural stability of metallic bismuth catalyst. This study provides valuable inspiration for the design of element-doping electrocatalysts to enhance catalytic activity and durability. 相似文献
13.
Acetogens such as Clostridium ljungdahlii can play a crucial role reducing the human CO 2 footprint by converting industrial emissions containing CO 2, CO and H 2 into valuable products such as organic acids or alcohols. The quantitative understanding of cellular metabolism is a prerequisite to exploit the bacterial endowments and to fine-tune the cells by applying metabolic engineering tools. Studying the three gas mixtures CO 2 + H 2, CO and CO + CO 2 + H 2 (syngas) by continuously gassed batch cultivation experiments and applying flux balance analysis, we identified CO as the preferred carbon and electron source for growth and producing alcohols. However, the total yield of moles of carbon (mol-C) per electrons consumed was almost identical in all setups which underlines electron availability as the main factor influencing product formation. The Wood–Ljungdahl pathway (WLP) showed high flexibility by serving as the key NAD + provider for CO 2 + H 2, whereas this function was strongly compensated by the transhydrogenase-like Nfn complex when CO was metabolized. Availability of reduced ferredoxin (Fd red) can be considered as a key determinant of metabolic control. Oxidation of CO via carbon monoxide dehydrogenase (CODH) is the main route of Fd red formation when CO is used as substrate, whereas Fd red is mainly regenerated via the methyl branch of WLP and the Nfn complex utilizing CO 2 + H 2. Consequently, doubled growth rates, highest ATP formation rates and highest amounts of reduced products (ethanol, 2,3-butanediol) were observed when CO was the sole carbon and electron source. 相似文献
14.
Accumulation of formate to millimolar levels was observed during the growth of Methanobacterium formicicum species on H 2–CO 2. Hydrogen was also produced during formate metabolism by M. formicicum. The amount of formate accumulated in the medium or the amount H 2 released in gas phase was influenced by the bicarbonate concentration. The formate hydrogenlyase system was constitutive but regulated by formate. When methanogenesis was inhibited by addition of 2-bromoethane sulfonate, M. formicicum synthesized formate from H 2 plus HCO
inf3
sup-
or produced H 2 from formate to a steady-state level at which point the Gibbs free energy (G) available for formate synthesis or H 2 production was approximately -2 to -3 kJ/reaction. Formate conversion to methane was inhibited in the presence of high H 2 pressure. The relative rates of conversion of formate and H 2 were apparently controlled by the G available for formate synthesis, hydrogen production, methane production from formate and methane production from H 2. Results from 14C-tracer tests indicated that a rapid isotopic exchange between HCOO - and HCO
inf3
sup-
occurred during the growth of M. formicicum on H 2–CO 2. Data from metabolism of 14C-labelled formate to methane suggested that formate was initially split to H 2 and HCO
inf3
sup-
and then subsequently converted to methane. When molybdate was replaced with tungstate in the growth media, the growth of M. formicicum strain MF on H 2–CO 2 was inhibited although production of methane was not Formate synthesis from H 2 was also inhibited. 相似文献
15.
Unlike gaseous C 1 feedstocks for acetogenic bacteria, there has been less attention on liquid C 1 feedstocks, despite benefits in terms of energy efficiency, mass transfer and integration within existing fermentation infrastructure. Here, we present growth of Eubacterium limosum ATCC8486 using methanol and formate as substrates, finding evidence for the first time of native butanol production. We varied ratios of methanol-to-formate in batch serum bottle fermentations, showing butyrate is the major product (maximum specific rate 220 ± 23 mmol-C gDCW -1day -1). Increasing this ratio showed methanol is the key feedstock driving the product spectrum towards more reduced products, such as butanol (maximum titre 2.0 ± 1.1 mM-C). However, both substrates are required for a high growth rate (maximum 0.19 ± 0.011 h -1) and cell density (maximum 1.2 ± 0.043 gDCW l -1), with formate being the preferred substrate. In fact, formate and methanol are consumed in two distinct growth phases – growth phase 1, on predominately formate and growth phase 2 on methanol, which must balance. Because the second growth varied according to the first growth on formate, this suggests butanol production is due to overflow metabolism, similar to 2,3-butanediol production in other acetogens. However, further research is required to confirm the butanol production pathway in E. limosum, particularly given, unlike other substrates, methanol likely results in mostly NADH generation, not reduced ferredoxin. 相似文献
16.
Desulfovibrio baarsii is a sulfate reducing bacterium, which can grown on formate plus sulfate as sole energy source and formate and CO 2 as sole carbon sources. It is shown by 14C labelling studies that more than 60% of the cell carbon is derived from CO 2 and the rest from formate. The cells thus grow autotrophically. Labelling studies with [ 14C]acetate, 14CO and [ 14C]formate indicate that CO 2 fixation does not proceed via the Calvin cycle. The labelling patterns of alanine, aspartate, glutamate, and glucosamine indicate that acetate (or activated acetic acid) is an early intermediate in formate and CO 2 assimilation; the methyl group of acetate is derived from formate, and the carboxyl group from CO 2 via CO; pyruvate is formed from acetyl-CoA by reductive carboxylation. The capacity to synthesize an acetate unit from two C 1-compounds obviously distinguishes D. baarsii from those Desulfovibrio species, which require acetate as a carbon source in addition to CO 2. 相似文献
17.
This paper focuses on modelling the growth rate and exopolysaccharides production of Anabaena sp. ATCC 33047, to be used in carbon dioxide removal and biofuels production. For this, the influence of dilution rate, irradiance
and aeration rate on the biomass and exopolysaccharides productivity, as well as on the CO 2 fixation rate, have been studied. The productivity of the cultures was maximum at the highest irradiance and dilution rate
assayed, resulting to 0.5 g bio l −1 day −1 and 0.2 g eps l −1 day −1, and the CO 2 fixation rate measured was 1.0 gCO 2 l −1 day −1. The results showed that although Anabaena sp. was partially photo-inhibited at irradiances higher than 1,300 μE m −2 s −1, its growth rate increases hyperbolically with the average irradiance inside the culture, and so does the specific exopolysaccharides
production rate. The latter, on the other hand, decreases under high external irradiances, indicating that the exopolysaccharides
metabolism hindered by photo-damage. Mathematical models that consider these phenomena have been proposed. Regarding aeration,
the yield of the cultures decreased at rates over 0.5 v/v/min or when shear rates were higher than 60 s −1, demonstrating the existence of thus existence of stress damage by aeration. The behaviour of the cultures has been verified
outdoors in a pilot-scale airlift tubular photobioreactor. From this study it is concluded that Anabaena sp. is highly recommended to transform CO 2 into valuable products as has been proved capable of metabolizing carbon dioxide at rates of 1.2 gCO 2 l −1 day −1 outdoors. The adequacy of the proposed equations is demonstrated, resulting to a useful tool in the design and operation
of photobioreactors using this strain. 相似文献
18.
The spatial successions of bacterial and archaeal communities in anaerobic digestion were investigated in a glucose-degrading five-compartment anaerobic baffled reactor (ABR). The distributions of H 2-producing acetogens, H 2-utilizing acetogens and methanogens in different anaerobic-digestion stages were quantitatively analyzed using functional probes. The results show that the acidogenesis stage and acetogenesis stage were located in the first two compartments, while the methanogenesis were located in the last two compartments. In acidogenesis/acetogenesis stage of anaerobic digestion, H 2-producing acetogens (19.7%) and H 2-utilizing acetogens (8.3%) were the dominant bacterial community. While in methanogenesis stage, methanogens became the dominant (40.2%) with H 2-producing acetogens and H 2-utilizing acetogens only accounting for 6.6% and 4.8%, respectively. With the bacterial population decreasing from 7.2 ± 0.5 × 10 12 cells mL −1 to 0.6 ± 0.3 × 10 12 cells mL −1 along water flowing direction, their diversity increased from 2.79 to 299. The acidogenic bacteria, such as Lactococcus sp., Uncultured Firmicutes bacterium, and Uncultured Clostridium sp., etc., dominated in the acidogenesis/acetogenesis stage, while Uncultured Desulfobacterales bacterium became dominant in the methanogenesis stage. A two-stage anaerobic process may be suitable for easily degradable organic matters removal. 相似文献
19.
Morphological and anatomical changes for first-order daughter cladodes (flattened stem segments) of a prickly pear cactus, Opuntia ficus-indica, were monitored to determine the effects of a doubled atmospheric CO 2 concentration on their development and mature form. For daughter cladodes developing in controlled environment chambers for 60 d, maximal elongation rates were similar under a photosynthetic photon flux density (PPFD) of 6 mol m −2 d −1 and a CO 2 concentration of 370 μl liter −1, an increased PPFD (10 mol m −2 d −1), and an increased PPFD and a doubled CO 2 concentration. These maximal rates, however, occurred at 20, 15, and 12 d, respectively. The maximal relative growth rate under the doubled CO 2 concentration was about twice that under the other conditions. For cladodes at 60 d as well as after 4 and 16 mo in open-top chambers, doubling the CO 2 concentration had no effect on final length or width. At 4 mo, cladodes under doubled C0 2 were 27% thicker, perhaps allowing the earlier production of second-order daughter cladodes. The chlorenchyma was then 31% thicker and composed of longer cells. At 16 mo, the difference in cladode thickness diminished, but the chlorenchyma remained thicker under doubled CO 2, which may contribute to greater net CO 2 uptake for O. ficus-indica under elevated CO 2 concentrations. Two other persistent differences were a 20% lower stomatal frequency and a 30% thicker cuticle with more epicuticular wax for cladodes under doubled CO 2, both of which may help reduce transpirational water loss. 相似文献
20.
Carbon dioxide (CO 2) stands out as sustainable feedstock for developing a circular carbon economy whose energy supply could be obtained by boosting the production of clean hydrogen from renewable electricity. H 2-dependent CO 2 gas fermentation using acetogenic microorganisms offers a viable solution of increasingly demonstrated value. While gas fermentation advances to achieve commercial process scalability, which is currently limited to a few products such as acetate and ethanol, it is worth taking the best of the current state-of-the-art technology by its integration within innovative bioconversion schemes. This review presents multiple scenarios where gas fermentation by acetogens integrate into double-stage biotechnological production processes that use CO 2 as sole carbon feedstock and H 2 as energy carrier for products' synthesis. In the integration schemes here reviewed, the first stage can be biotic or abiotic while the second stage is biotic. When the first stage is biotic, acetogens act as a biological platform to generate chemical intermediates such as acetate, formate and ethanol that become substrates for a second fermentation stage. This approach holds the potential to enhance process titre/rate/yield metrics and products' spectrum. Alternatively, when the first stage is abiotic, the integrated two-stage scheme foresees, in the first stage, the catalytic transformation of CO 2 into C 1 products that, in the second stage, can be metabolized by acetogens. This latter scheme leverages the metabolic flexibility of acetogens in efficient utilization of the products of CO 2 abiotic hydrogenation, namely formate and methanol, to synthesize multicarbon compounds but also to act as flexible catalysts for hydrogen storage or production. 相似文献
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