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1.
Fermentative hydrogen production by strict anaerobes has been widely reported. There is a lack of information related to metabolic flux distribution and its variation with respect to fermentation conditions in the metabolic production system. This study aimed to get a better understanding of the metabolic network and to conduct metabolic flux analysis (MFA) of fermentative hydrogen production by a recently isolated Clostridium butyricum strain W5. We chose the specific growth rate as the objective function and used specific H2 production rate as the criterion to evaluate the experimental results with the in silico MFA. For the first time, we constructed an in silico metabolic flux model for the anaerobic glucose metabolism of C. butyricum W5 with assistance of a modeling program MetaFluxNet. The model was used to evaluate metabolic flux distribution in the fermentative hydrogen production network, and to study the fractional flux response to variations in initial glucose concentration and operational pH. The MFA results suggested that pH has a more significant effect on hydrogen production yield compared to the glucose concentration. The MFA is a useful tool to provide valuable information for optimization and design of the fermentative hydrogen production process.  相似文献   

2.
Laboratory mutagenesis of microorganisms offers the possibility of relating acquired mutations to improve the quality of microbial cultures. In the present study, a mutant strain, Clostridium tyrobutyricum ATCC 25755 DG-8, with significantly elevated α-amylase activity as well as resistant to the non-metabolizable and toxic glucose analog 2-deoxyglucose (2-DG) was obtained by implanting the low-energy nitrogen ion beam. DG-8 was further developed to produce hydrogen by simultaneous saccharification and fermentation (SSF) directly form cassava starch in batch fermentation mode, which to our knowledge is at the first attempt in genus Clostridium. Our results demonstrated that the increased activity of α-amylase would be attributed to the hydrogen over-producing. Higher hydrogen yield (3.2 mol/mol glucose) was achieved with the volumetric productivity of 0.41 L/h/L when the initial total sugar concentration of cassava starch rise up to 100 g/L. The present work will help to decrease the cost of hydrogen fermentation process and stimulate its industrial application in the near future.  相似文献   

3.
An integrated bio-hydrogen production system involving fermentative hydrogen production and product separation is proposed. In this process, microorganisms conduct ethanol-type fermentation and generate H2 gas in anaerobic bioreactor, and acetate is removed from fermentation broth by using a two chamber bipolar membrane electrodialysis as separation unit. A comparative study of fermentative hydrogen production of Ethanoligenens harbinese B49 in the integrated system with traditional fermentation process was carried out. Compared to traditional process, accumulated H2 elevated 23%, glucose utilization ratio increased by 135% and cell growth increased by 27% in the integrated system. The specific hydrogen production rate reached 2.2 mol H2/mol glucose, indicating that separation of acetate from fermentation system has a great role in promoting hydrogen producing capacity. Bipolar membrane electrodialysis showed high acetate separation efficiency and low glucose loss rate. In the integrated system, pH could be used to direct electrodialysis operation, since it has an exponential correlation with acetate concentration in fermentation broth. These results provide a new method for achieving efficient and stable H2 production with simultaneous glucose recovery and acetate inhibition release.  相似文献   

4.
The effects of FeSO4 and synthesized iron oxide nanoparticles (0–250 mg/L) on fermentative hydrogen production from glucose and sucrose, using Enterobacter cloacae were investigated, to find out the enhancement of efficiency. The maximum hydrogen yields of 1.7 ± 0.017 mol H2/mol glucose and 5.19 ± 0.12 mol H2/mol sucrose were obtained with 25 mg/L of ferrous iron supplementation. In comparison, the maximum hydrogen yields of 2.07 ± 0.07 mol H2/mol glucose and 5.44 ± 0.27 mol H2/mol sucrose were achieved with 125 mg/L and 200 mg/L of iron oxide nanoparticles, respectively. These results indicate that the enhancement of hydrogen production on the supplementation of iron oxide nanoparticles was found to be considerably higher than that of ferrous iron supplementation. The activity of E. cloacae in a glucose and sucrose fed systems was increased by the addition of iron oxide nanoparticles, but the metabolic pathway was not changed. The results revealed that the glucose and sucrose fed systems conformed to the acetate/butyrate fermentation type.  相似文献   

5.
Electro-fermentation has been recently proposed as a new operational mode of bioprocess control using polarized electrodes. This paper aims to evaluate how polarized electrodes are affecting microbial metabolic fermentative pathways, with a special focus on how the bacterial populations are affected during hydrogen production by dark fermentation. Four different potentials were applied on the working electrode in batch electro-fermentation tests operated with mixed culture and using glucose as a substrate. Two different metabolic behaviours for H2 production were observed in electro-fermentation. The first one led to a higher H2 production compared to conventional fermentation with a strong selection of Clostridium sp. The second behaviour led to lower H2 production along with ethanol, and strongly correlated with the selection of Escherichia and Enterobacter genera. However, the effect of the applied potential on population selection was mostly non-linear and no simple relationship was found between these two parameters. Overall, electro-fermentation process has shown its potential as a new type of control for mixed-culture bioprocesses with significant effects of polarized electrodes on glucose fermentation.  相似文献   

6.
A mesophilic alkaline tolerant fermentative microbe was isolated from estuarine sediment samples and designated as Clostridium butyricum TM-9A, based on 16S rRNA gene sequence. Batch experiments were conducted for investigation of TM-9A strain for its growth and hydrogen productivity from glucose, in an iron containing basal solution supplemented with yeast extract as organic nitrogen source. Hydrogen production started to evolve when cell growth entered exponential phase and reached maximum production rate at late exponential phase. Maximum hydrogen production was observed at 37 °C, initial pH of 8.0 in the presence of 1% glucose. Optimization of process parameters resulted in increase in hydrogen yield from 1.64 to 2.67 mol of H2/mol glucose. Molar yield of H2 increased further from 2.67 to 3.1 mol of H2/mol of glucose with the decrease in hydrogen partial pressure, obtained by lowering the total pressure in the head space of the batch reactor. Acetate and butyrate were the measure volatile fatty acids generated during hydrogen fermentation. TM-9A strain produced hydrogen efficiently from a range of pentose and hexose sugars including di-, tri and poly-saccharides like; xylose, ribose, glucose, rhamnose, galactose, fructose, mannose, sucrose, arabinose, raffinose, cellulose, cellobiose and starch.  相似文献   

7.
This study evaluates the effect of pH (4-7) on fermentative biohydrogen production by utilizing three isolated Clostridium species. Fermentative batch experiments show that the maximum hydrogen yield for Clostridium butyricum CGS2 (1.77 mmol/mmol glucose) is achieved at pH 6, whereas a high hydrogen production with Clostridium beijerinckii L9 (1.72 mmol/mmol glucose) and Clostridium tyrobutyricum FYa102 (1.83 mmol/mmol glucose) could be achieved under uncontrolled pH conditions (initial pH of 6.4-6.6 and final pH of 4-4.2). Low hydrogen yields (0-0.6 mmol/mmol glucose) observed at pH 4 are due likely to inhibitory effects on the microbial growth, although a low pH can be thermodynamically favorable for hydrogen production. The low hydrogen yields (0.12-0.64 mmol/mmol glucose) observed at pH 7 are attributed not only to thermodynamically unfavorable, but also metabolically unfavorable for hydrogen production. The relatively high levels of lactate, propionate, or formate observed at pH 7 reflect presumably the high enzymatic activities responsible for their production, together with the low hydrogenase activity, resulting in a low hydrogen production. A correlation analysis of the data from present and previous studies on biohydrogen production with pure Clostridium cultures and mixed microflora indicates a close relation between the hydrogen yield (YH2) and the (YH2)/(2(YHAc+YHBu)) ratio, with the observed correlation coefficient (0.787) higher than that (0.175) between YH2 and the molar ratio of butyrate to acetate (B/A). Based on the (YH2)/(2(YHAc+YHBu)) ratios observed at different pHs, a control of pH at 5.5-6.8 would seem to be an effective means to enhance the fermentative biohydrogen production.  相似文献   

8.
In view of increasing attempts for the production of renewable energy, the production of biohydrogen energy by a new mesophilic bacterium Clostridium sp. YM1 was performed for the first time in the dark fermentation. Experimental results showed that the fermentative hydrogen was successfully produced by Clostridium sp. YM1 with the highest cumulative hydrogen volume of 3821 ml/L with a hydrogen yield of 1.7 mol H2/mol glucose consumed. Similar results revealed that optimum incubation temperature and pH value of culture medium were 37 °C and 6.5, respectively. The study of hydrogen production from glucose and xylose revealed that this strain was able to generate higher hydrogen from glucose compared to that from xylose. The profile of volatile fatty acids produced showed that hydrogen generation by Clostridium sp. YM1 was butyrate-type fermentation. Moreover, the findings of this study indicated that an increase in head space of fermentation culture positively enhanced hydrogen production.  相似文献   

9.
Genome-scale model was applied to analyze the anaerobic metabolism of Escherichia coli. Three different methods were used to find deletions affecting fermentative hydrogen production: flux balance analysis (FBA), algorithm for blocking competing pathways (ABCP), and manual selection. Based on these methods, 81 E. coli mutants possessing one gene deletion were selected and cultivated in batch experiments. Experimental results of H2 and biomass production were compared against the results of FBA. Several gene deletions enhancing H2 production were found. Correctness of gene essentiality predictions of FBA for the selected genes was 78% and 77% in glucose and galactose media, respectively. 33% of the mutations that were predicted by FBA to increase H2 production had a positive effect in experiments. Batch cultivation is a simple and straightforward experimental way to screen improvements in H2 production. However, the ability of FBA to predict the H2 production rate cannot be evaluated by batch experiments. Metabolic network models provide a method for gaining broader understanding of the complicated metabolic system of a cell and can aid in prospecting suitable gene deletions for enhancing H2 production.  相似文献   

10.
Biomass of the green algae has been recently an attractive feedstock source for bio-fuel production because the algal carbohydrates can be derived from atmospheric CO2 and their harvesting methods are simple. We utilized the accumulated starch in the green alga Chlamydomonas reinhardtii as the sole substrate for fermentative hydrogen (H2) production by the hyperthermophilic eubacterium Thermotoga neapolitana. Because of possessing amylase activity, the bacterium could directly ferment H2 from algal starch with H2 yield of 1.8–2.2 mol H2/mol glucose and the total accumulated H2 level from 43 to 49% (v/v) of the gas headspace in the closed culture bottle depending on various algal cell-wall disruption methods concluding sonication or methanol exposure. Attempting to enhance the H2 production, two pretreatment methods using the heat-HCl treatment and enzymatic hydrolysis were applied on algal biomass before using it as substrate for H2 fermentation. Cultivation with starch pretreated by 1.5% HCl at 121 °C for 20 min showed the total accumulative H2 yield of 58% (v/v). In other approach, enzymatic digestion of starch by thermostable α-amylase (Termamyl) applied in the SHF process significantly enhanced the H2 productivity of the bacterium to 64% (v/v) of total accumulated H2 level and a H2 yield of 2.5 mol H2/mol glucose. Our results demonstrated that direct H2 fermentation from algal biomass is more desirably potential because one bacterial cultivation step was required that meets the cost-savings, environmental friendly and simplicity of H2 production.  相似文献   

11.
The biochemical hydrogen potential (BHP) tests were conducted to investigate the metabolism of glucose fermentation and hydrogen production performance of four Clostridial species, including C. acetobutylicum M121, C. butyricum ATCC19398, C. tyrobutyricum FYa102, and C. beijerinckii L9. Batch experiments showed that all the tested strains fermented glucose, reduced medium pH from 7.2 to a value between 4.6 and 5.0, and produced butyrate (0.37–0.67 mmol/mmol-glucose) and acetate (0.34–0.42 mmol/mmol-glucose) as primary soluble metabolites. Meanwhile, a significant amount of hydrogen gas was produced accompanied with glucose degradation and acid production. Among the strains examined, C. beijerinckii L9 had the highest hydrogen production yield of 2.81 mmol/mmol-glucose. A kinetic model was developed to evaluate the metabolism of glucose fermentation of those Clostridium species in the batch cultures. The model, in general, was able to accurately describe the profile of glucose degradation as well as production of biomass, butyrate, acetate, ethanol, and hydrogen observed in the batch tests. In the glucose re-feeding experiments, the C. tyrobutyricum FYa102 and C. beijerinckii L9 isolates fermented additional glucose during re-feeding tests, producing a substantial amount of hydrogen. In contrast, C. butyricum ATCC19398 was unable to produce more hydrogen despite additional supply of glucose, presumably due to the metabolic shift from acetate/butyrate to lactate/ethanol production.  相似文献   

12.
Inoculum pre-treatment is a crucial aspect of hydrogen fermentation processes to establish the required microbial community for hydrogen production. This paper models and optimizes two hybrid techniques of inoculum pre-treatment for fermentative hydrogen production: 1pH and Autoclave (PHA); 2pH and heat shock (PHS) using Response Surface Methodology (RSM). Coefficients of determination (R2) of 0.93 and 0.90 were obtained for PHA and PHS respectively and the optimized pre-treatment conditions gave hydrogen yields up to 1.35 mol H2/mol glucose and 0.75 mol H2/mol glucose, thus a 37.75% and 15.38% improvement on model predictions for PHA and PHS respectively.  相似文献   

13.
A hydrogen producing facultative anaerobic alkaline tolerant novel bacterial strain was isolated from crude oil contaminated soil and identified as Enterobacter cloacae DT-1 based on 16S rRNA gene sequence analysis. DT-1 strain could utilize various carbon sources; glycerol, CMCellulose, glucose and xylose, which demonstrates that DT-1 has potential for hydrogen generation from renewable wastes. Batch fermentative studies were carried out for optimization of pH and Fe2+ concentration. DT-1 could generate hydrogen at wide range of pH (5–10) at 37 °C. Optimum pH was; 8, at which maximum hydrogen was obtained from glucose (32 mmol/L), when used as substrate in BSH medium containing 5 mg/L Fe2+ ion. Decrease in hydrogen partial pressure by lowering the total pressure in the fermenter head space, enhanced the hydrogen production performance of DT-1 from 32 mmol H2/L to 42 mmol H2/L from glucose and from 19 mmol H2/L to 33 mmol H2/L from xylose. Hydrogen yield efficiency (HY) of DT-1 from glucose and xylose was 1.4 mol H2/mol glucose and 2.2 mol H2/mol xylose, respectively. Scale up of batch fermentative hydrogen production in proto scale (20 L working volume) at regulated pH, enhanced the HY efficiency of DT-1 from 2.2 to 2.8 mol H2/mol xylose (1.27 fold increase in HY from laboratory scale). 84% of maximum theoretical possible HY efficiency from xylose was achieved by DT-1. Acetate and ethanol were the major metabolites generated during hydrogen production.  相似文献   

14.
An NADH dehydrogenase encoded by the nuo cluster was isolated and impaired by knocking out the nuoB gene in Enterobacter aerogenes to examine its effect on hydrogen production. Three nuoB-deleted mutant strains were constructed from the wild-type strain E. aerogenes IAM1183 and two recombinant strains, IAM1183-A (ΔhycA) and IAM1183-O (ΔhybO), from which the hycA and hybO genes had already been deleted previously, respectively. Compared with the performance of the wild-type strain, the overall hydrogen production of the mutants IAM1183-B (ΔnuoB), IAM1183-AB (ΔhycAnuoB) and IAM1183-BO (ΔhybOnuoB) was increased by 49.2%, 54.0%, and 52.4% in batch culture, respectively. The hydrogen yields from glucose by the three mutants IAM1183-B, IAM1183-AB, IAM1183-BO were 1.38, 1.49, and 1.39 mol H2/mol glucose, respectively, while it was 1.16 mol H2/mol glucose in the wild-type strain. Metabolic flux analysis indicated that all three mutants exhibited reduced fluxes to lactate production, and enhanced fluxes toward the generation of hydrogen, acetate, ethanol, succinate and 2,3-butanediol. Both the formate pathway and the NADH pathway contributed to increased hydrogen production in the mutant strains. The assay of 4 NADH-mediated enzyme activities (H2ase, LDH, ADH and BDDH) was in accordance with the redistributions of the metabolic fluxes in the mutant strains.  相似文献   

15.
A novel hydrogen-producing strain was isolated from gamma irradiated digested sludge and identified as Clostridium butyricum INET1. The fermentative hydrogen production performance of the newly isolated C. butyricum INET1 was characterized. Various carbon sources, including glucose, xylose, sucrose, lactose, starch and glycerol were used as substrate for hydrogen production. The operational conditions, including temperature, initial pH, substrate concentration and inoculation proportion were evaluated for their effects on hydrogen production, and the optimal condition was determined to be 35 °C, initial pH 7.0, 10 g/L glucose and 10% inoculation ratio. Cumulative hydrogen production of 218 mL/100 mL and hydrogen yield of 2.07 mol H2/mol hexose was obtained. The results showed that C. butyricum INET1 is capable of utilizing different substrates (glucose, xylose, sucrose, lactose, starch and glycerol) for efficient hydrogen production, which is a potential candidate for fermentative hydrogen production.  相似文献   

16.
Dark fermentation is a promising biological method for hydrogen production because of its high production rate in the absence of light source and variety of the substrates. In this study, hydrogen production potential of four dark fermentative bacteria (Clostridium butyricum, Clostridium pasteurianum, Clostridium beijerinckii, and Enterobacter aerogenes) using glucose as substrate was investigated under anaerobic conditions. Batch experiments were conducted to study the effects of initial glucose concentration on hydrogen yield, hydrogen production rate and concentration of volatile fatty acids (VFA) in the effluents. Among the four different fermentative bacteria, C. butyricum showed great performance at 10 g/L of glucose with hydrogen production rate of 18.29 mL-H2/L-medium/hand specific hydrogen production rate of 3.90 mL-H2/g-biomass/h. In addition, it was found that the distribution of volatile fatty acids was different among the fermentative bacteria. C. butyricum and C. pasteurianum had higher ratio of acetate to butyrate compared to the other two species, which favored hydrogen generation.  相似文献   

17.
Glycerol is an inevitable by-product from biodiesel synthesis process and could be a promising feedstock for fermentative hydrogen production. In this study, the feasibility of using crude glycerol from biodiesel industry for biohydrogen production was evaluated using seven isolated hydrogen-producing bacterial strains (Clostridium butyricum, Clostridium pasteurianum, and Klebsiella sp.). Among the strains examined, C. pasteurianum CH4 exhibited the best biohydrogen-producing performance under the optimal conditions of: temperature, 35 °C; initial pH, 7.0; agitation rate, 200 rpm; glycerol concentration, 10 g/l. When using pure glycerol as carbon source for continuous hydrogen fermentation, the average H2 production rate and H2 yield were 103.1 ± 8.1 ml/h/l and 0.50 ± 0.02 mol H2/mol glycerol, respectively. In contrast, when using crude glycerol as the carbon source, the H2 production rate and H2 yield was improved to 166.0 ± 8.7 ml/h/l and 0.77 ± 0.05 mol H2/mol glycerol, respectively. This work demonstrated the high potential of using biodiesel by-product, glycerol, for cost-effective biohydrogen production.  相似文献   

18.
Thermophilic dark fermentative hydrogen producing bacterial strain, TERI S7, isolated from an oil reservoir flow pipeline located in Mumbai, India, showed 98% identity with Thermoanaerobacterium thermosaccharolyticum by 16S rRNA gene analysis. It produced 1450–1900 ml/L hydrogen under both acidic and alkaline conditions; at a temperature range of 45–60 °C. The maximum hydrogen yield was 2.5 ± 0.2 mol H2/mol glucose, 2.2 ± 0.2 mol H2/mol xylose and 5.2 ± 0.2 mol H2/mol sucrose, when the respective sugars were used as carbon source. The cumulative hydrogen production, hydrogen production rate and specific hydrogen production rate by the strain TERI S7 with sucrose as carbon source was found to be 1704 ± 105 ml/L, 71 ± 6 ml/L/h and 142 ± 13 ml/g/h respectively. Major soluble metabolites produced during fermentation were acetic acid and butyric acid. The strain TERI S7 was also observed to produce hydrogen continuously up to 48 h at pH 3.9.  相似文献   

19.
Escherichia coli can produce H2 from glucose via formate hydrogen lyase (FHL). In order to improve the H2 production rate and yield, metabolically engineered E. coli strains, which included pathway alterations in their H2 production and central carbon metabolism, were developed and characterized by batch experiments and metabolic flux analysis. Deletion of hycA, a negative regulator for FHL, resulted in twofold increase of FHL activity. Deletion of two uptake hydrogenases (1 (hya) and hydrogenase 2 (hyb)) increased H2 production yield from 1.20 mol/mol glucose to 1.48 mol/mol glucose. Deletion of lactate dehydrogenase (ldhA) and fumarate reductase (frdAB) further improved the H2 yield; 1.80 mol/mol glucose under high H2 pressure or 2.11 mol/mol glucose under reduced H2 pressure. Several batch experiments at varying concentrations of glucose (2.5–10 g/L) and yeast extract (0.3 or 3.0 g/L) were conducted for the strain containing all these genetic alternations, and their carbon and energy balances were analyzed. The metabolic flux analysis revealed that deletion of ldhA and frdABdirected most of the carbons from glucose to the glycolytic pathway leading to H2 production by FHL, not to the pentose phosphate pathway.  相似文献   

20.
The present study focused on the influence of pH on the fermentative hydrogen production from the sugars of sweet sorghum extract, in a continuous stirred tank bioreactor. The reactor was operated at a Hydraulic Retention Time of 12 h and a pH range of 3.5–6.5. The maximum hydrogen production rate and yield were obtained at pH 5.3 and were 1752 ± 54 mL H2/d or 3.50 ± 0.07 L H2/L reactor/d and 0.93 ± 0.03 mol H2/mol glucose consumed or 10.51 L H2/kg sweet sorghum, respectively. The main metabolic product at this pH value was butyric acid. The hydrogen productivity and yield were still at high levels for the pH range of 5.3–4.7, suggesting a pH value of 4.7 as optimum for hydrogen production from an economical point of view, since the energy demand for chemicals is lower at this pH. At this pH range, the dominant fermentation product was butyric acid but when the pH culture sharply decreased to 3.5, hydrogen evolution ceased and the dominant metabolic products were lactic acid and ethanol.  相似文献   

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