Rhodopseudomonas Palustris WP3-5 Research Articles

Relationship between cell growth, hydrogen production and poly-β-hydroxybutyrate (PHB) accumulation by Rhodopseudomonas palustris WP3-5

Rhodopseudomonas palustris WP3-5 accumulated PHB in growth phase, and PHB could be utilized as another carbon and energy source when its content reached maximum value. Microorganism ceased growing when nitrogen source was exhausted, and used excessive energy to produce more hydrogen in the stationary phase. Rps. palustris WP3-5 could not synthesize PHB under low concentration of carbon source because substrate was degraded rapidly, and there were no difference of hydrogen production between wild-type strain and its PHB synthase-deficient mutant Rps. palustris M23. When concentration of carbon source was three times higher, cumulated hydrogen volume and substrate conversion efficiency of Rps. palustris WP3-5 were better than Rps. palustris M23. This result coincided with other experiments in different culture conditions. But when using malate as carbon source, Rps. palustris WP3-5 had lower substrate degrading rate and cumulated hydrogen volume, and PHB was not accumulated. Rps. palustris WP3-5 used most energy to produce hydrogen in the stationary phase and PHB content was below 10% cell dry weight, accounting for less than 5% of the substrate electrons utilized. This portion of energy might partially be redistributed to synthesize soluble microbial product (SMP). Therefore, the competition relationship between hydrogen production and PHB accumulation was insignificant.

Correlation between bio-hydrogen production and polyhydroxybutyrate (PHB) synthesis by Rhodopseudomonas palustris WP3-5

The aim of this study was to determine the competition between H2 production and polyhydroxybutyrate (PHB) accumulation of Rhodopseudomonas palustris WP3-5 when grown on six different substrates. From the results, strain WP3-5 can utilize acetate, propionate, malate, and lactate to produce H2 but can only synthesize PHB on acetate and propionate. The substrate conversion efficiency (SCE) on acetate and propionate increased significantly after the maximum PHB content was achieved, illustrating a competition for reducing power when PHB synthesis occurred. However, when strain WP3-5 was cultivated at suboptimal pH values on acetate, the synthesized PHB prevented strain WP3-5 from the stress of the inappropriate pH and retained H2 producing efficiency as at optimal pH value. Consequently, although PHB synthesis does compete with H2 production in R. palustris WP3-5, it is still conducive to H2 production when strain WP3-5 is in a stressful condition.

Bio-hydrogen production enhancement by co-cultivating Rhodopseudomonas palustris WP3-5 and Anabaena sp. CH3

Photobiological H 2 production is a promising method for renewable energy development. An innovative system that co-cultivating Rhodopseudomonas palustris WP3-5 and Anabaena sp. CH3 was carried out to estimate the effect of co-cultivation on H 2 production enhancement. H 2 production prolongation and enhancement were observed due to the light and metabolic compatibility of these two strains. Co-culture system served by acetate and fructose as carbon source can accumulate H 2 in 140.8 mL, almost double than the sum of individuals. Moreover, the enhancement of H 2 production was significantly affected by the mixed ratio of two strains. The mixed ratio (WP3-5:CH3) of 1:2 showed a highest H 2 production rate in 44.8 mL-H 2/L-culture/h, and both 2:1 and 1:2 exhibited a relatively high substrate conversion efficiency during the latest period of cultivation, whereas the mixed ratio of 1:1 and 3:1 only revealed a prolongation in H 2 production due to metabolic compatibility of two strains.

Photo fermentative hydrogen production using dominant components (acetate, lactate, and butyrate) in dark fermentation effluents

Engineering strategies were applied to promote the phototrophic H 2 production of an indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5 using major components (i.e., acetate, butyrate, and lactate) of dark fermentation effluents as carbon sources. First, performance of cell growth and photo-H 2 production on each carbon source was examined individually. It appeared that acetate was the most effective carbon source for photo-H 2 production, giving an overall H 2 production rate and H 2 yield of 12.68 ml/h/l and 67.1%, respectively. Next, the effect of substrate concentration of each carbon source on photo-hydrogen production was investigated. Kinetic models were developed to describe the correlation between maximum specific growth rate/specific H 2 production rate and the substrate concentration. The results show that using acetate and lactate as the carbon source, the kinetics for the cell growth and photo-hydrogen production can be described by Monod-type and Michaelis–Menten models, respectively, whereas substrate inhibition occurred when using butyrate as the carbon source. The continuous cultures were also conducted at a hydraulic retention time of 96 h using synthetic dark fermentation soluble metabolites (with a 5 and 10 fold dilution) as the influent. The phototrophic H 2 production efficiency was stably maintained for over 30 days with an overall H 2 yield 10.30 and 11.97 mol H 2/mol sucrose, when using 5-fold and 10-fold diluted dark fermentation effluent, respectively, as the substrate for dark fermentation. This demonstrates the feasibility of using the sequential dark and photo fermentation for high-yield biohydrogen production.

The factors influencing direct photohydrogen production and anaerobic fermentation hydrogen production combination bioreactors

A system that combines fermentative and photosynthetic bacteria makes combined organic wastewater treatment and energy recycling possible. This study introduces a method to separates useful byproduct, such as volatile fatty acids, to serve as the substrate for a serial photobioreactor from the outlet of anaerobic hydrogen fermentation reactor using a ceramic membrane system. Batch experiments were applied to investigate the metabolic characteristics of Rhodopseudomonas palustris WP3-5 under various conditions during photobioreactor operation. The results indicate that a higher temperature (35 °C) improved poly-β-hydroxybutyric acid (PHB) content and hydrogen accumulation. Maximal hydrogen accumulation and reduced PHB synthesis occurred at lower temperature (25 °C) at an initial pH of 6.8.. Glutamate and peptone were more suitable nitrogen sources for hydrogen production than glutamine and NH 4Cl. Photohydrogen production results, using various anaerobic fermentation effluents with a dilution ratio of 0.4X, illustrated that an increased photohydrogen production rate (HPR) could be obtained using an anaerobic fermentation influent with an initial C/N ratio of 4. The result obtained when an anaerobic hydrogen fermentation reactor was connected to the serial photobioreactor showed that when the anaerobic hydrogen fermentation reactor outlet dilution increased from 2.5- to 5-fold, HPR increased. The HPR of the three bioreactors in the serial photobioreactor were 269.2, 345.6 and 256.7 mL-H 2/L-reactor/day. A UV-sterilizer, which was placed between the fermentation reactor and photobioreactor, resulted in the longer (336 h) operating duration.

Enhancement of photohydrogen production using phbC deficient mutant Rhodopseudomonas palustris strain M23

This study used a DNA recombination method to knock out the poly-β-hydroxybutyrate (PHB) synthesis gene phbC in the photosynthetic bacterium Rhodopseudomonas palustris WP3-5. The experimental results indicated that the mutant strain Rps. palustris M23 could be successfully screened. Fluorescent observation with Nile blue staining showed no significant PHB granule accumulation in the mutant cells. Batch mode experiments using acetic acid as a carbon source revealed a 29.1% and 25.9% hydrogen gas content from M23 and WP3-5, respectively. However, this trend did not appear when using propionic acid as carbon source. Under continuous operation, the hydrogen gas content from M23 could be maintained above 72%. The average hydrogen production rates of the WP3-5 and M23 strains were 264 mL-H 2/L/day and 457 mL-H 2/L/day, respectively. The total biogas volume collected from M23 was 1.7 times higher than that from the wild type.

Engineering strategies for the enhanced photo-H 2 production using effluents of dark fermentation processes as substrate

The major obstacle of combining dark and photo fermentation for high-yield biohydrogen production is substrate inhibition while using dark fermentation effluent as the sole substrate. To solve this problem, the dark fermentation broth was diluted with different dilution ratio to improve photo-H 2 production performance of an indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5. The best photo-H 2 production performance occurred at a dilution ratio of 1:2, giving a highest overall H 2 production rate of 10.72 ml/l/h and a higher overall H 2 yield of 6.14 mol H 2/mol sucrose. The maximum H 2 content was about 88.1% during the dilution ratio of 1:2. The photo-H 2 production performance was further improved by supplying yeast extract and glutamic acid as the nutrient. The results indicate that the overall H 2 production rate and H 2 yield increased to 17.02 ml/l/h and 10.25 mol H 2/mol sucrose, respectively. Using a novel solar-energy-excited optical fiber photobioreactor (SEEOFP) with supplementing tungsten filament lamp (TL) irradiation, the overall H 2 production rate was improved to 17.86 ml/l/h. Meanwhile, the power consumption by combining SEEOFP and TL was about 37.1% lower than using TL alone. This study demonstrates that using optimal light sources and proper dilution of dark fermentation effluent, the performance of photo-H 2 production can be markedly enhanced along with a reduction of power consumption.

Phototrophic hydrogen production in photobioreactors coupled with solar-energy-excited optical fibers

A novel solar-energy-excited optical fiber (SEEOF) photobioreactor (PBR) was developed to enhance the phototrophic H 2 production by Rhodopseudomonas palustris WP3-5 using acetate (HAc) as the sole carbon source. The PBR was illuminated by combinative light sources, including an internal illumination with optical fiber excited by solar energy (OF(sunlight)) as well as external irradiation of tungsten filament lamp (TL). The photo-H 2 producing performance of the SEEOF photobioreactor was further improved by using an innovative light dependent resistor (LDR) system, which could maintain sufficient and continual light supply. The results show that combination of OF(sunlight)/TL was more effective than the TL/TL illumination system, leading to a 138% and 136% increase in cumulative H 2 production ( V H 2 ) and H 2 yield ( Y H 2 ) , respectively. The LDR-coupled SEEOF photobioreactor was able to solve the problems of diurnal variation in solar light intensity, enabling the control of a constant total light irradiation intensity on the PBR surface. Combining OF(sunlight)/TL with LDR, the V H 2 and Y H 2 were nearly 27% higher than without LDR. For bioreactor scale up from 50 to 1800 ml working volume, the LDR-coupled SEEOF photobioreactor worked well during daytime, leading to a marked improvement in phototrophic H 2 production with a V H 2 and Y H 2 of 3606 ml and 2.45 mol H 2/mol HAc, respectively. Moreover, continuous cultures operated at a hydraulic retention time (HRT) of 48 h show a high hydrogen production rate of 32.4 ml/l/h with stable operation for over 15 days. This optimal performance of LDR-coupled SEEOF photobioreactor is superior to most reported results and is a favorable choice of electricity-saving PBR strategy to improve photo-H 2 production efficiency.

Biohydrogen production using sequential two-stage dark and photo fermentation processes

A two-stage process combining dark/photo fermentation was used to increase the overall hydrogen yield from sucrose and also to reduce the chemical oxygen demand (COD) in the effluent. Dark-H 2 fermentation was conducted using Clostridium pasteurianum CH 4, giving a maximum H 2 production yield of 3.80 mol H 2/mol sucrose. The soluble metabolites resulting from dark fermentation, consisting of butyric and acetic acid, were further used for H 2 production in the subsequent photo fermentation. Using soluble products from dark fermentation as substrate, Rhodopseudomonas palustris WP3-5 could produce H 2 phototrophically, elevating the total hydrogen yield from 3.80 (dark fermentation) to 10.02 mol H 2/mol sucrose (dark/photo fermentation). Meanwhile, a 72.0% COD removal was also achieved. When the photobioreactor was illuminated with side-light optical fibers and was supplemented with 2.0% (w/v) of clay carriers, the overall H 2 yield of the two-stage process was further enhanced to 14.2 mol H 2/mol sucrose with a nearly 90% COD removal. Continuous photo fermentation was also carried out at 96 h HRT using effluent from dark fermentation as the feed. The continuous culture maintained stable for nearly 10 days with an average H 2 yield of 10.21 mol H 2/mol sucrose. This demonstrates the feasibility of using the two-stage process combining dark and photo fermentation for simultaneous hydrogen production and COD removal.

Combining enzymatic hydrolysis and dark–photo fermentation processes for hydrogen production from starch feedstock: A feasibility study

In this work, an integrated enzymatic hydrolysis and dark–photo fermentation were employed to enhance the performance of H 2 production from starch feedstock. The starch feedstock was first hydrolyzed in sequencing batch reactor containing indigenous starch hydrolytic bacterium Caldimonas taiwanensis On1, producing reducing sugar at a yield and rate of 0.5 g reducing sugar/g starch and 1.17 g reducing sugar/h/L, respectively, under the optimal condition of pH 7.0, 55 °C and 1.0 vvm (air volume per reactor volume per minute) aeration rate. The hydrolyzed starch was continuously introduced to dark fermentation bioreactor, where the hydrolysate was converted to H 2 at a rate of 0.22 L/h/L by Clostridium butyricum CGS2 at pH 5.8–6.0, 37 °C and 12 h HRT. The resulting effluent from dark fermentation became the influent of continuous photo H 2 production process inoculated with Rhodopseudomonas palustris WP3-5 under the condition of 35 °C, 100 W/m 2 irradiation, pH 7.0 and 48 h HRT. Combining enzymatic hydrolysis, dark fermentation and photo fermentation led to a marked improvement of overall H 2 yield (up to 16.1 mmol H 2/g COD or 3.09 mol H 2/mol glucose) and COD removal efficiency (ca. 54.3%), suggesting the potential of using the proposed integrated process for efficient and high-yield bioH 2 production from starch feedstock.

Improved phototrophic H 2 production with Rhodopseudomonas palustris WP3-5 using acetate and butyrate as dual carbon substrates

An indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5 was used to produce hydrogen phototrophically from acetate (HAc) and butyrate (HBu), which are the major soluble products from acidogenic dark fermentation. Statistical experimental design methodology was applied to identify optimal composition of the two carbon substrates in the medium, leading to better H 2 production performance of R. palustris WP3-5. Three performance indexes were used to assess the effectiveness of the phototrophic H 2 production; they were H 2 yield ( Y H 2 ), maximum H 2 production rate ( R max) and maximum cumulative H 2 evolution ( H max). An overlay contour plot was used to determine the optimal concentration range of HAc and HBu, taking into account all three performance indexes (i.e., R max, H max, and Y H 2 ) simultaneously. With the response surface analysis, R. palustris WP3-5 could produce H 2 efficiently with the best R max, H max, and Y H 2 of 39.5 ml/h, 2738 ml, and 51.6%, respectively. This performance is superior to most reported values in the literature, indicating that the statistical experimental design is an effective tool to improve phototrophic H 2 production with R. palustris WP3-5.

Enhancing phototrophic hydrogen production of Rhodopseudomonas palustris via statistical experimental design

An indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5 was used to produce hydrogen via photo-fermentation. Response surface methodology was used to optimize the concentration of three critical medium components (butyric acid (HBu), glutamic acid, and FeCl 3 ) having major impacts on the cell growth and H 2 production of R. palustris WP3-5. Four performance indexes (PIs), namely, H 2 yield ( Y H 2 ), maximum H 2 production rate ( R max ) , overall H 2 production rate ( R overall ) , and lag time ( λ ) were used to assess the effectiveness of the phototrophic H 2 production. A new overlay 3-D contour surface plot was developed to determine optimal conditions for R max , R overall , and λ in the system, while maintaining a high H 2 yield ( Y H 2 = 5.5 mol H 2 / mol HBu) simultaneously. The overlay optimal regions of the three double responses ( Y H 2 - R max , Y H 2 - R overall , and Y H 2 - λ ) were identified. Using R max as the PI, the response surface analysis attained an optimal concentration of 1832, 607, and 54 mg/l for butyric acid, glutamic acid, and FeCl 3 , respectively, giving an expected R max and Y H 2 value of 24.9 ml/h/l and 5.74 mol H 2 / mol HBu, respectively. This optimal performance is superior to most of the reported values in the literature, indicating that the statistical experimental design was an effective tool leading to marked improvement in phototrophic H 2 production with the R. palustris WP3-5 strain.

Feasibility study on bioreactor strategies for enhanced photohydrogen production from Rhodopseudomonas palustris WP3-5 using optical-fiber-assisted illumination systems

A novel photobioreactor (PBR) was utilized to produce H 2 by indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5 using acetate as the sole carbon source. The PBR was illuminated by combinative light sources including side-light optical fibers (internal light source) as well as external irradiation of halogen lamp and/or tungsten filament lamp. A fill and draw (F/D) operation of PBR was shown to improve the performance of photoH 2 production over the performance of batch and continuous cultures under similar operation conditions. For medium improvement, the PBR was conducted under different concentrations of carbon source (acetate) and nitrogen source (glutamic acid). The results show that the highest overall H 2 production rate ( v H 2 ) and H 2 yield ( Y H 2 ) occurred when the acetate concentration was 32.5 mmol/l and the glutamic acid concentration was 400 mg/l. The optimal acetate and glutamic acid concentration led to a v H 2 and Y H 2 of 20.9 ml/h l and 2.47 mol H 2/mol acetate, respectively. The H 2 production rate and yield was further enhanced to as high as 38.2 ml/h l and 3.15 mol H 2/mol acetate, respectively, while using a ternary-light-source (TLS) system, combining optical fiber, halogen lamp, and tungsten filament lamp (i.e., the OF/HL/TL system). Meanwhile, the high H 2 production efficiency with TLS system was stably maintained for nearly 30 day under the F/D operations.

Enhancing phototropic hydrogen production by solid-carrier assisted fermentation and internal optical-fiber illumination

Three strategies were applied to promote the phototrphic H 2 production of an indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5 using acetate as the sole carbon substrate. First, a small amount of solid carriers (e.g., activated carbon, silica gel, and clay) was supplemented to fermentation broth to stimulate cell growth and H 2 production. Second, the acetate concentration leading to optimal production of H 2 was identified. Finally, an innovative optical-fiber illuminating system was designed to facilitate the efficiency of the photobioreactor. The results show that addition of clay and silica gel was effective in promoting H 2 production, resulting in 67.2–50.9% and 37.2–32.5% increases in H 2 production rate ( v H 2 ) and H 2 yield ( Y H 2 ), respectively. For clay-supplemented batch cultures, the optimal acetate concentration was 1000 mg COD/l, leading to a v H 2 and Y H 2 value of 28.5 ml/h/l and 2.97 mol H 2/mol acetate, respectively. Moreover, combination of internal optical-fiber illumination system, clay addition, and optimal acetate concentration further elevated the v H 2 and Y H 2 to a maximum level of 43.8 ml/h/l and 3.63 mol H 2/mol acetate, respectively. These values are considerably higher than most reported results from relevant studies. Meanwhile, the results of continuous cultures operated at 36 h HRT (hydraulic retention time) show that the high phototrophic H 2 production efficiency was stably maintained for over 17 days with a steady-state v H 2 and Y H 2 of 44.0 ml/h/l and 3.57 mol H 2/mol acetate, respectively.