scholarly journals Directing Clostridium ljungdahlii fermentation products via hydrogen to carbon monoxide ratio in syngas

2019 ◽  
Vol 124 ◽  
pp. 95-101 ◽  
Author(s):  
Joshua Jack ◽  
Jonathan Lo ◽  
Pin-Ching Maness ◽  
Zhiyong Jason Ren
2020 ◽  
Vol 86 (14) ◽  
Author(s):  
Zi-Yong Liu ◽  
De-Chen Jia ◽  
Kun-Di Zhang ◽  
Hai-Feng Zhu ◽  
Quan Zhang ◽  
...  

ABSTRACT Bioethanol production from syngas using acetogenic bacteria has attracted considerable attention in recent years. However, low ethanol yield is the biggest challenge that prevents the commercialization of syngas fermentation into biofuels using microbial catalysts. The present study demonstrated that ethanol metabolism plays an important role in recycling NADH/NAD+ during autotrophic growth. Deletion of bifunctional aldehyde/alcohol dehydrogenase (adhE) genes leads to significant growth deficiencies in gas fermentation. Using specific fermentation technology in which the gas pressure and pH were constantly controlled at 0.1 MPa and 6.0, respectively, we revealed that ethanol was formed during the exponential phase, closely accompanied by biomass production. Then, ethanol was oxidized to acetate via the aldehyde ferredoxin oxidoreductase pathway in Clostridium ljungdahlii. A metabolic experiment using 13C-labeled ethanol and acetate, redox balance analysis, and comparative transcriptomic analysis demonstrated that ethanol production and reuse shared the metabolic pathway but occurred at different growth phases. IMPORTANCE Ethanol production from carbon monoxide (CO) as a carbon and energy source by Clostridium ljungdahlii and “Clostridium autoethanogenum” is currently being commercialized. During gas fermentation, ethanol synthesis is NADH-dependent. However, ethanol oxidation and its regulatory mechanism remain incompletely understood. Energy metabolism analysis demonstrated that reduced ferredoxin is the sole source of NADH formation by the Rnf-ATPase system, which provides ATP for cell growth during CO fermentation. Therefore, ethanol production is tightly linked to biomass production (ATP production). Clarification of the mechanism of ethanol oxidation and biosynthesis can provide an important reference for generating high-ethanol-yield strains of C. ljungdahlii in the future.


Fermentation ◽  
2020 ◽  
Vol 6 (2) ◽  
pp. 61 ◽  
Author(s):  
Alba Infantes ◽  
Michaela Kugel ◽  
Anke Neumann

The fermentation of synthesis gas, or syngas, by acetogenic bacteria can help in transitioning from a fossil-fuel-based to a renewable bioeconomy. The main fermentation products of Clostridium ljungdahlii, one of such microorganisms, are acetate and ethanol. A sensitive, robust and reproducible system was established for C. ljungdahlii syngas fermentation, and several process parameters and medium components (pH, gas flow, cysteine and yeast extract) were investigated to assess its impact on the fermentation outcomes, as well as real time gas consumption. Moreover, a closed carbon balance could be achieved with the data obtained. This system is a valuable tool to detect changes in the behavior of the culture. It can be applied for the screening of strains, gas compositions or media components, for a better understanding of the physiology and metabolic regulation of acetogenic bacteria. Here, it was shown that neither yeast extract nor cysteine was a limiting factor for cell growth since their supplementation did not have a noticeable impact on product formation or overall gas consumption. By combining the lowering of both the pH and the gas flow after 24 h, the highest ethanol to acetate ratio was achieved, but with the caveat of lower productivity.


Microbiology ◽  
2000 ◽  
Vol 81 (1) ◽  
pp. 69-78 ◽  
Author(s):  
Wytske de Vries ◽  
Willemina M. C. van Wijck-Kapteyn ◽  
S. K. H. Oosterhuis

Strains of Selenomonas ruminantium, Anaerovibrio lipolytica and Veillonella alcalescens contained cytochrome b. Peaks corresponding to cytochromes a and a carbon monoxide-binding pigment were also observed. By means of dual-wavelength experiments with crude membrane fractions it was established that cytochrome b functioned in anaerobic electron transport to fumarate. In V. alcalescens and one strain of S. ruminantium which reduced nitrate, anaerobic electron transport to nitrate was found. Glycerol 1-phosphate and NADH were active as hydrogen donors for cytochrome b reduction in glycerol-grown A. lipolytica, lactate and pyruvate were active in lactate-grown V. alcalescens, and NADH was active in lactose-grown S. ruminantium. Oxidative phosphorylation associated with these electron transfer systems might explain the high molar growth yields previously found for these micro-organisms. Fermentation products were measured in supernatant fluids of cultures grown in the presence and absence of nitrate. Nitrate did not influence the fermentation of lactose to lactate by S. ruminantium, and inhibited propionate formation by V. alcalescens.


2020 ◽  
Vol 86 (23) ◽  
Author(s):  
Zi-Yong Liu ◽  
De-Chen Jia ◽  
Kun-Di Zhang ◽  
Hai-Feng Zhu ◽  
Quan Zhang ◽  
...  

Author(s):  
Alba Infantes ◽  
Michaela Kugel ◽  
Anke Neumann

ABSTRACTThe fermentation of synthesis gas, or syngas, which consists mainly of CO, CO2 and H2 by acetogenic bacteria has the potential to help in transitioning from a fossil-fuel-based to a renewable bio-economy. Clostridium ljungdahlii, one of such microorganisms, has as main fermentation products acetate and ethanol. Multiple research efforts have been directed towards understanding how the metabolism and the product formation of this, and other acetogenic bacteria, can be directed towards increasing productivities and yields; nonetheless, transferring those findings to a particular set-up can prove challenging. This study used a well-established and robust fed-batch fermentation system with C. ljungdahlii to look into the effects of different fermentation pH profiles, gas flow, and the supplementation with additional yeast extract or cysteine on growth, product formation ratios, yields, and productivities, as well as gas consumption. Neither yeast extract nor cysteine supplementation had a noticeable impact on cell growth, product formation or overall gas consumption. The lowering of the pH proved mainly detrimental, with decreased productivities and no improvement in ethanol ratios. The most notable shift towards ethanol was achieved by the combination of lowering both the pH and the gas flow after 24 h, but with the caveat of lower productivity. The obtained results, unexpected to some extent, highlight the necessity for a better understanding of the physiology and the metabolic regulation of acetogenic bacteria in order for this process to become more industrially relevant.


2012 ◽  
Vol 36 (5) ◽  
pp. 591-595 ◽  
Author(s):  
Seok-In Yun ◽  
Seong-Joo Gang ◽  
Hee-Myong Ro ◽  
Min-Jin Lee ◽  
Woo-Jung Choi ◽  
...  

2002 ◽  
Vol 184 (21) ◽  
pp. 5903-5911 ◽  
Author(s):  
Gerrit Voordouw

ABSTRACT Sulfate-reducing bacteria, like Desulfovibrio vulgaris Hildenborough, use the reduction of sulfate as a sink for electrons liberated in oxidation reactions of organic substrates. The rate of the latter exceeds that of sulfate reduction at the onset of growth, causing a temporary accumulation of hydrogen and other fermentation products (the hydrogen or fermentation burst). In addition to hydrogen, D. vulgaris was found to produce significant amounts of carbon monoxide during the fermentation burst. With excess sulfate, the hyd mutant (lacking periplasmic Fe-only hydrogenase) and hmc mutant (lacking the membrane-bound, electron-transporting Hmc complex) strains produced increased amounts of hydrogen from lactate and formate compared to wild-type D. vulgaris during the fermentation burst. Both hydrogen and CO were produced from pyruvate, with the hyd mutant producing the largest transient amounts of CO. When grown with lactate and excess sulfate, the hyd mutant also exhibited a temporary pause in sulfate reduction at the start of stationary phase, resulting in production of 600 ppm of headspace hydrogen and 6,000 ppm of CO, which disappeared when sulfate reduction resumed. Cultures with an excess of the organic electron donor showed production of large amounts of hydrogen, but no CO, from lactate. Pyruvate fermentation was diverse, with the hmc mutant producing 75,000 ppm of hydrogen, the hyd mutant producing 4,000 ppm of CO, and the wild-type strain producing no significant amount of either as a fermentation end product. The wild type was most active in transient production of an organic acid intermediate, tentatively identified as fumarate, indicating increased formation of organic fermentation end products in the wild-type strain. These results suggest that alternative routes for pyruvate fermentation resulting in production of hydrogen or CO exist in D. vulgaris. The CO produced can be reoxidized through a CO dehydrogenase, the presence of which is indicated in the genome sequence.


Author(s):  
Al W. Stinson

The stratified squamous epithelium which lines the ruminal compartment of the bovine stomach performs at least three important functions. (1) The upper keratinized layer forms a protective shield against the rough, fibrous, constantly moving ingesta. (2) It is an organ of absorption since a number of substances are absorbed directly through the epithelium. These include short chain fatty acids, potassium, sodium and chloride ions, water, and many others. (3) The cells of the deeper layers metabolize butyric acid and to a lesser extent propionic and acetic acids which are the fermentation products of rumen digestion. Because of the functional characteristics, this epithelium is important in the digestive process of ruminant species which convert large quantities of rough, fibrous feed into energy.Tissue used in this study was obtained by biopsy through a rumen fistula from clinically healthy, yearling holstein steers. The animals had been fed a typical diet of hay and grain and the ruminal papillae were fully developed. The tissue was immediately immersed in 1% osmium tetroxide buffered to a pH of 7.4 and fixed for 2 hrs. The tissue blocks were embedded in Vestapol-W, sectioned with a Porter-Blum microtome with glass knives and stained with lead hydroxide. The sections were studied with an RCA EMU 3F electron microscope.


2000 ◽  
Vol 12 (4) ◽  
pp. 354-357
Author(s):  
David R Smart ◽  
Paul D Mark

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