Tatsuki Wakayama

Enhancement of hydrogen production by a photosynthetic bacterium mutant with reduced pigment.

A novel mutant MTP4 was created from the wild-type strain Rhodobacter sphaeroides RV by UV irradiation for the enhancement of hydrogen production. The amount of light absorbed by MTP4 was lower than that by the wild-type strain at any wavelengths ranging from 350 to 1000 nm. This nature enables the illumination of cells in the deeper parts of a reactor. The contents of bacteriochlorophylls and carotenoids of the chromatophores prepared from MTP4 under the conditions for hydrogen production were reduced to 41 and 49% of those from the wild-type strain RV, respectively. Analysis of the light-harvesting (LH) complexes by SDS-PAGE showed that the amounts of LH1s and reaction centers (RCs) in MTP4 were retained, whereas that of LH2s was much less than that in RV. Although MTP4 had less pigments, its growth rate was equivalent to that of RV over a wide range of light intensities. MTP4 produces hydrogen with a stable manner. Using a plate-type reactor, it produced 50% more hydrogen than RV. A novel method of pigment reduction was found to be effective for the enhancement of hydrogen production per unit reactor.

Simulation of the daily sunlight illumination pattern for bacterial photo-hydrogen production.

Methods of illumination to simulate the daily sunlight irradiation pattern were studied in relation to photohydrogen production using the photosynthetic bacterium Rhodobacter sphaeroides RV. Three illumination patterns were compared, in which the light intensity was changed in 1, 3, or 6 steps. As a control, outdoor experiments were also carried out over a 3-d period in Tsukuba, August 1996. Outdoors, hydrogen production by Rba. sphaeroides RV was dependent on the sunlight intensity: the total volume of hydrogen produced per day varied from 14 to 28 l.m(-2), while the total light energy ranged from 5.5 to 6.4 kWh.m(-2). d(-1). The maximum hydrogen production rate was 2.8 l.m(-2).h(-1) under a 4.5-cm light path and the average light energy conversion efficiency was 1.1%. Indoors, the hydrogen production rate was found to be independent of the mode of illumination among the three patterns employed. The maximum hydrogen production rate was 3.3 l.m(-2).h(-1) with a light energy conversion efficiency of 1.0%, and it was concluded that the single-step illumination method provides an appropriate simulation of sunlight. Saturation of hydrogen production occurs during high light intensity around noon and this plays a key role in the simulation.

Hydrogen production by combining two types of photosynthetic bacteria with different characteristics

Abstract The double-layer photobioreactor using two types of photosynthetic bacteria, Rhodobacter sphaeroides RV and its reduced-pigment mutant, MTP4, was developed for efficient hydrogen production. The two types of bacteria had different characteristics on light energy, hydrogen production rate and conversion efficiency. MTP4 produced hydrogen more efficiently under high light conditions and RV did so under low light conditions. Illuminated light toward the surface of a photobioreactor quasi-exponentially declines as it penetrates into the reactor. When two types of bacteria were placed using the developed reactor according to this light distribution, the hydrogen production rate reached 3.64 l/m 2 / h at a light intensity of 500 W/m 2 in 24 h and the conversion efficiency of light energy to hydrogen was 2.18%. These values were 33% higher than those of only using RV. The low light in the deep part of the reactor was utilized efficiently, resulting in a higher hydrogen production rate.

Hydrogen production by four cultures with participation by anoxygenic phototrophic bacterium and anaerobic bacterium in the presence of NH4

Hydrogen production by suspended culture, entrapped culture of Rhodobacter sphaeroides and Clostridium butyricum, and entrapped co-culture of these two bacteria in the presence of NH_4+ was investigated and compared. Hydrogen production by suspended culture of Rhodobacter sphaeroides was most affected by NH_4+ among the four cultures studied. Nevertheless, hydrogen production rate was the highest after the NH_4+ was removed metabolically. Hydrogen production by entrapped culture of Rb. sphaeroides was not readily inhibited by NH_4+ compared with that by suspended culture, and the hydrogen production rate was also kept high. Hydrogen production by entrapped culture of C. butyricum was not inhibited by NH_4+ in the initial period of time, but NH_4+ had some influence on hydrogen production by this culture in the later period. The hydrogen production rate from this culture was low compared with that from the culture of Rb. sphaeroides as expected theoretically. The former was only 1 of 5.6 of the latter, on average. The pattern of NH_4+ effect on the hydrogen production by co-culture of these two bacteria was similar to that by the single culture of C. butyricum. Nevertheless, hydrogen production by co-culture was enhanced by 160% compared with that by the single culture of anaerobic bacterium.

Metal-mediated coordination polymer nanotubes of 5,10,15,20-tetrapyridylporphine and tris(4-pyridyl)-1,3,5-triazine at the water–chloroform interface

Coordination polymer nanotubes have been prepared by using the Hg2+-mediated co-assembly of two ligands, tetrapyridylporphine (TPyP) and tris(4-pyridyl)-1,3,5-triazine (TPyTa), at the water-chloroform interface.

Light shade bands for the improvement of solar hydrogen production efficiency by Rhodobacter sphaeroides RV

Abstract At mid-day, the sunlight provides excessive energy for photo-hydrogen production by photosynthetic bacteria. Conversion efficiency from light energy to hydrogen decreased under high illumination. To overcome this problem, we examined a method to spatial dispersion of the high illumination. The new photobioreactor using the light shade bands set on the surface of the reactor was developed for efficient hydrogen production. Spatial dispersion gave remarkable effect on conversion efficiency under the excessive light condition. Indoors, the 1.0 cm width of light shade bands gave the best conversion efficiency (2.1%). Actual use of the sunlight, the 1.5 cm width of light shade bands provided the best conversion efficiency (1.4%). Light inhibition was successfully suppressed by the light shade bands in both experiments. The dispersed light energy could be used for other energy conversion device as solar cells.

Enhanced hydrogen production by a mutant of Rhodobacter sphaeroides having an altered light-harvesting system

A stable mutant of the photosynthetic bacterium Rhodobacter sphaeroides with an altered light-harvesting (LH) system (P3 mutant) was obtained by UV irradiation and characterized. The mutant exhibited a 2.7-fold decrease in the core antennal (LH1) content and 1.6-fold increase in peripheral antennal (LH2) content compared to the wild-type strain. The H2 evolution rates in the P3 mutant under 800- and 850-nm light, corresponding to the absorption maxima of LH2, were 1.5 times higher than in the wild-type strain. The wild-type absorption spectrum was restored in the P3 mutant when a 1.1-kb PCR-amplified fragment containing the puf promoter and pufQBA genes was ligated into a pRK-415 derivative and introduced into it. The transformant showed lower H2 production rates at 800 and 850 nm than the P3 strain carrying the control plasmid, indicating that the accelerated H2 production in the P3 mutant was a result of alterations in the LH system.

Entrapment of Rhodobacter sphaeroides RV in cationic polymer/agar gels for hydrogen production in the presence of NH4+

Cationic polyelectrolytes (chitosan, poly-L-lysine (PLL), polyethyleneimine (PEI) and trimethylammonium glycol chitosan iodide (TGCI)) were used to entrap anoxygenic phototrophic bacteria in order to prevent the inhibitory effect of NH4+ on hydrogen production. When combined with agar gel, chitosan and PLL demonstrated no obvious repressive effect on hydrogen production by Rhodobacter sphaeroides under light-anaerobic conditions with lactate and glutamate as the carbon and nitrogen sources, respectively. On the other hand, both PEI and TGCI exerted a detrimental effect on hydrogen production under these conditions. Hydrogen production in the presence of NH4+ by the bacteria entrapped in the complex gel containing chitosan and agar improved considerably compared to that in the control containing only agar. Evidence shows that chitosan improves the hydrogen production via various effects. Diffusion tests demonstrated that the addition of chitosan increased to some extent the resistance to the diffusion of positively charged NH4+, but had no effect on negatively charged lactate. A buffer effect in the complex gels was also revealed.

Biomolecular device for photoinduced hydrogen production

In order to construct a molecular device for photoinduced hydrogen production, a model has been designed and first results in the framework of this multicomponent system are presented. This device should involve Photosystem 1, Photosystem 2 and hydrogenase in a modular configuration which allows to combine appropriate proteins from various-mainly thermophilic-organisms. Parts of this modular system can be easily exchanged and separately characterized and optimized. Here the optimization of one component of this device, the hydrogenase from Thiocapsa roseopersicina, is shown. The isolated hydrogenase was deposited as Langmuir-Blodgett (LB) film on quartz glass and ITO electrodes, respectively, and its activity was measured in dependence of counter ions, presence of oxygen and number of immobilized layers. While poly-L-lysine or poly-butyl-viologen as counter ion in the subphase stabilized the protein complex on quartz glass (up to about 30 mN/m surface pressure), Ca 2+ resulted in a dramatic activity loss at a much lower surface pressure (15 mN/m). Also, the presence of even smallest amounts of oxygen or an excess amount of protein on an ITO electrode resulted in a significant decrease of the hydrogen production as did the increase in the number of layers-as shown by electrochemical measurements.

Photoinduced hydrogen evolution by use of porphyrin, EDTA, viologens and hydrogenase in solutions and Langmuir?Blodgett films

Abstract Photoinduced hydrogen evolution was investigated by use of a zinc porphyrin, EDTA, viologens and hydrogenase (H2ase) in the solutions and Langmuir–Blodgett (LB) films. An almost linear increase of hydrogen evolution rate was observed with the increase of H2ase concentrations from 1 to 5 μg / ml . For the zinc porphyrin, EDTA and methyl viologen, when their concentrations increased to a given value, hydrogen evolution did not show obvious increase. Phospholipid-porphyrin mixed LB films were prepared and used as photosensitizer for the photoinduced hydrogen evolution. Spectroscopic studies of the deoxygenated solutions indicated a “new” absorption band (in the solutions) or sharp peaks (in the LB films) when the sample solutions were irradiated, which was ascribed to the formation of an excited complex of porphyrin–EDTA (or -EDTA breakdown products). This excited complex was unstable to air.