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ABSTRACT: A reactor-scale hydrogen (H2) productionvia the water-gas shift reaction of carbon monoxide (CO) and water was studied using the purple nonsulfur bacterium,Rhodopseudomonas palustris P4. The experiment was conducted in a two-step process: an aerobic/chemoheterotrophic cell growth step and a subsequent anaerobic
H2 production step. Important parameters investigated included the agitation speed, inlet CO concentration and gas retention
time. P4 showed a stable H2 production capability with a maximum activity of 41 mmol H2 g cell−1h−1 during the continuous reactor operation of 400 h. The maximal volumetric H2 production rate was estimated to be 41 mmol H2 L1h−1, which was about nine-fold and fifteen-fold higher than the rates reported for the photosynthetic bacteriaRhodospirillum rubrum andRubrivivax gelatinosus, respectively. This is mainly attributed to the ability of P4 to grow to a high cell density with a high specific H2 production activity. This study indicates that P4 has an outstanding potential for a continuous H2 productionvia the water-gas shift reaction once a proper bioreactor system that provides a high rate of gas-liquid mass transfer is developed.
Biotechnology and Bioprocess Engineering 04/2012; 10(3):270-274. · 1.28 Impact Factor
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ABSTRACT: During photo-fermentative H(2) production, the effects of carbon and nitrogen sources on nitrogenase and hydrogenase activity, poly-β-hydroxybutyrate accumulation were investigated. In succinate/ammonium sulfate medium, H(2) was not detected for the first 6h because high ammonium concentration considerably reduced the nitrogenase activity to below 5 nmol/g-dcw/h. After 24h, 99% of the ammonium was consumed, and the nitrogenase activity increased to 296 nmol/g-dcw/h, accelerating H(2) production. In contrast, the ammonium in succinate/glutamate medium was much less, which led to rapid H(2) production in the beginning. However, H(2) evolution was repressed over time by increased ammonium. In the presence of H(2), hydrogenase activity increased with time regardless of the nitrogen source, and consequently, H(2) production was reduced. Compared with succinate, H(2) production in acetate media was severely limited due to increased pH over 9. During extended cultivation, the PHB accumulated in acetate media was 7 times higher than in succinate media.
Bioresource technology 04/2012; 116:179-83. · 4.25 Impact Factor
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ABSTRACT: Rhodobacter sphaeroides is a purple nonsulfur photosynthetic bacterium that is considered a possible source of H(2) production. R. sphaeroides KD131, which was isolated from sea mud in South Korea, was found to produce high levels of H(2). Here we report the complete and annotated genome sequence of R. sphaeroides KD131.
Journal of bacteriology 12/2008; 191(3):1118-9. · 3.94 Impact Factor
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ABSTRACT: For the newly isolated H2-producing chemoheterotrophic bacterium Citrobacter amalonaticus Y19, anaerobic glucose metabolism was studied in batch cultivation at varying initial glucose concentrations (3.5- 9.5 g/l). The carbon-mass and energy balances were determined and utilized to analyze the carbon metabolic-pathways network. The analyses revealed (a) variable production of major metabolites (H2, ethanol, acetate, lactate, CO2, and cell mass) depending on initial glucose levels; (b) influence of NADH regeneration on the production of acetate, lactate, and ethanol; and (c) influence of the molar production of ATP on the production of biomass. The results reported in this paper suggest how the carbon metabolic pathway(s) should be designed for optimal H2 production, especially at high glucose concentrations, such as by blocking the carbon flux via lactate dehydrogenase from the pyruvate node.
Journal of Microbiology and Biotechnology 04/2008; 18(3):532-8. · 1.38 Impact Factor
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ABSTRACT: No phosphatidylcholine (PC) was detected in the membrane of Rhodobacter sphaeroides pmtA mutant (PmtA1) lacking phosphatidylethanolamine (PE) N-methyltransferase, whereas PE in the mutant was increased up to the mole % comparable to the combined level of PE and PC of wild type. Neither the fatty acid composition nor the fluidity of membrane was altered by pmtA mutation. Consistently, aerobic and photoheterotrophic growth of PmtA1 were not different from wild type. However, PmtA1 showed an extended lag phase (15 h) after the growth transition from aerobic to photoheterotrophic conditions, indicating the PC requirement for the efficient formation of intracytoplasmic membrane (ICM). Interestingly, the B800-850 complex of PmtA1 was decreased more than twofold in comparison with wild type, whereas the level of the B875 complex comprising the fixed photosynthetic unit was not changed. Since puc expression is not affected by pmtA mutation, PC appears to be required for the proper formation of the B800-850 complex in the ICM of R. sphaeroides.
Journal of Microbiology and Biotechnology 03/2007; 17(2):373-7. · 1.38 Impact Factor
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ABSTRACT: Thermophilic H2 production from glucose was studied at 55-64 degrees C for 234 days using a continuous trickling biofilter reactor (TBR) packed with a fibrous support matrix. Important parameters investigated included pH, temperature, hydraulic retention time (HRT), and glucose concentration in the feed. The optimal pH and temperature were 5.5 and 60 degrees C, respectively. With decreasing HRT or increasing inlet glucose concentration, volumetric H2 production rate increased but the H2 production yield to glucose decreased gradually. The biogas composition was almost constant at 53 +/- 4% (v/v) of H2 and 47 +/- 4% (v/v) of CO2. No appreciable CH4 was detected when the reactor was under a normal operation. The carbon mass balance showed that, in addition to cell mass, lactate, n-butyrate, CO2, and acetate were major products that comprised more than 85% of the carbon consumed. The maximal volumetric H2 production rate and H2 yield to glucose were 1,050 +/- 63 mmol H2/l.d and 1.11 +/- 0.12 mol H2/mol glucose, respectively. These results indicate that the thermophilic TBR is superior to most suspended or immobilized reactor systems reported thus far. This is the first report on continuous H2 production by a thermophilic TBR system.
Biotechnology and Bioengineering 01/2005; 88(6):690-8. · 3.95 Impact Factor
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ABSTRACT: The genes coding for two PII-like proteins, GlnB and GlnK, which play key roles in repressing the nitrogenase expression in the presence of ammonium ion, were interrupted from the chromosome of Rhodobacter sphaeroides. The glnB–glnK mutant exhibits the less ammonium ion-mediated repression for nitrogenase compared with its parental strain, which results in more H2 accumulation by the mutant under the conditions. Rhodospirillum rubrum produces H2 by both nitrogenase and hydrogenase. R. rubrum containing the recombinant pRK415 with an insert of hydC coding for its own Fe-only hydrogenase showed twofold higher accumulation of H2 in the presence of pyruvate under photoheterotrophic conditions, which was not observed in the absence of pyruvate. The same was true with R. rubrum containing the recombinant pRK415 cloned with hydA coding for Fe-only hydrogenase of Clostridium acetobutylicum. Thus, Fe-only hydrogenase requires pyruvate as an electron donor for the production of H2.
International Journal of Hydrogen Energy.
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ABSTRACT: For the newly isolated chemoheterotrophic bacterium Citrobacter amalonaticus Y19, anaerobic glucose metabolism and hydrogen (H2) production pathway were studied using batch cultivation and an in silico metabolic-flux analysis. Batch cultivation was conducted under varying initial glucose concentration between 1.5 and 9.5 g/L with quantitative measurement of major metabolites to obtain accurate carbon material balance. The metabolic flux of Y19 was analyzed using a metabolic-pathway model which was constructed from 81 biochemical reactions. The linear optimization program MetaFluxNet was employed for the analysis. When the specific growth rate of cells was chosen as an objective function, the model described the batch culture characteristics of Ci. amalonaticus Y19 reasonably well. When the specific H2 production rate was selected as an objective function, on the other hand, the achievable maximal H2 production yield ( glucose) and the metabolic pathway enabling the high H2 yield were identified. The pathway involved non-native NAD(P)-linked hydrogenase and H2 production from NAD(P)H which were supplied at a high rate from glucose degradation through the pentose phosphate pathway.
International Journal of Hydrogen Energy.
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ABSTRACT: Rhodopseudomonas palustris P4 can produce H2 either from CO by water-gas shift reaction or from various sugars by anaerobic fermentation. Fermentative H2 production by P4 is fast, but its yield is relatively low due to the formation of various organic acids. In order to increase H2 production yield from glucose, P4 was investigated for the photo-fermentation of acetate which is a major by-product of fermentative H2 production. Experiments were performed in batch modes using both light-grown and dark-grown cells. When the dark-grown P4 was challenged with light and acetate, H2 was produced with the consumption of acetate after a lag period of production was inhibited when a nitrogen source, especially ammonium, is present. When the dark-fermentation broth containing acetate was adopted for photo-fermentation with light-grown cells, H2 production and concomitant acetate consumption occurred without a lag period. The H2 yield was estimated as 2.4– acetate and the specific H2 production rate was as cell h. The fact that a single strain can perform both dark- and light-fermentation gives a great advantage in process development. Compared to a one-step dark-fermentation, the combined dark- and light-fermentation can increase the H2 production yield on glucose by two-fold.
International Journal of Hydrogen Energy.
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ABSTRACT: Increase in levels of photosynthetic spectral complexes by maintaining the plasmids harboring DNA encoding puhA, pufBA, or pucBAC in trans in Rhodobacter sphaeroides resulted in decrease of the photoheterotrophic production of H2. However, removal of B875 or B800–850 light-harvesting (LH) complexes affected H2 production differently. Lack of B875 complex following in-frame deletion of pufBA (mutant PUF1) not only slowed photoheterotrophic growth but also decreased H2 production, indicative of the essential requirement of the complex for LH process. However, the pucBA-deleted mutant, PUC1 lacking of B800–850 complex, increased H2 production in comparison with its parental cell by approximately twofold, given irradiated with light (10 W/m2) saturating the growth of wild type. The H2 production of PUC1 did not increase in proportion to the light intensity, which is also observed with wild type. Thus, we suggest that light is not limited for the H2 production of the cells under the experimental conditions employed in this work, but the cellular energy to be used for the formation of B800–850 complex may flow into the metabolism leading to the H2 production in PUC1.
International Journal of Hydrogen Energy.
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ABSTRACT: Rhodobacter sphaeroides KCTC 12085 is a natural isolate which shows a higher ability of photoheterotrophic H2 production compared with a laboratory strain R. sphaeroides 2.4.1. The H2 production by R. sphaeroides is observed only under light conditions. In order to render R. sphaeroides to produce H2 fermentatively as well, a 4.4-kb Rhodospirillum rubrum DNA encompassing a gene coding for pyruvate-formate lyase (PFL) with its putative maturation protein, and a 29.4-kb R. rubrum gene cluster including formate-hydrogen lyase (FHL) complex, its maturation proteins, a transcriptional activator for FHL, and Fe-only hydrogenase with its maturation proteins were cloned and mobilized into R. sphaeroides KCTC 12085. The recombinant R. sphaeroides evolved H2 during dark fermentative growth. The H2 production by the recombinant R. sphaeroides under photoheterotrophic conditions was elevated twofold to show 4 mol H2/mol of glucose compared with 2 mol H2/mol of glucose by its parental strain carrying empty vector. Interestingly, addition of hypophosphite, an inhibitor of PFL, to the recombinant R. sphaeroides under photoheterotrophic conditions still resulted in 3 mol H2/mol of glucose, suggestive of active H2 production not only by nitrogenase but also by Fe-only hydrogenase, which are insensitive to hypophosphite. The results further suggest the photoheterotrophic H2 production by FHL unless hypophosphite is present. Thus, the H2 production by the recombinant R. sphaeroides under photoheterotrophic conditions appears to be mediated by the concerted actions of FHL, Fe-only hydrogenase, and nitrogenase. The H2-evolving activity by the recombinant R. sphaeroides containing Fe-only hydrogenase of R. rubrum appears to depend on the presence its maturation proteins, suggestive of lack of such proteins in R. sphaeroides.
International Journal of Hydrogen Energy.
