K. Krishna Rao

The potential applications of cyanobacterial photosynthesis for clean technologies.

Natural photosynthesis may be adapted to advantage in the development of clean energy technologies. Efficient biocatalysts that can be used in solar energy conversion technologies are the cyanobacteria. Photobioreactors incorporating cyanobacteria have been used to demonstrate (a) the production of hydrogen gas, (b) the assimilation of CO2 with the production of algal biomass, (c) the excretion of ammonium, and (d) the removal of nitrate and phosphate from contaminated waters.

Outdoor production of Phaeodactylum tricornutum biomass in a helical reactor

The production of microalga Phaeodactylum tricornutum in an outdoor helical reactor was analysed. The influence of temperature, solar irradiance and air flow rate on the yield of the culture was evaluated. Biomass productivities up to 1.5 g l(-1) per day and photosynthetic efficiency up to 14% were obtained by maintaining the cultures below 30 degrees C, dissolved oxygen levels less than 400% Sat. (with respect to air saturated culture) and controlling the cell density in order to achieve an average irradiance within the culture below 250 microE m(-2) s(-1). Under these conditions, the fluorescence parameter, Fv/Fm, which reflects the maximal efficiency of PSII photochemistry, remained roughly 0.6-0.7 and growth rates up to 0.050 h(-1) were achieved. The average irradiance and the light/dark cycle frequency, were the variables determining the behaviour of the cultures. A hyperbolic relationship between growth rate and biomass productivity with the average irradiance was observed, whereas both biomass productivity and photosynthetic efficiency linearly increased with the light/dark cycle frequencies. Optimum design and operational conditions which maximise the production of P. tricornutum biomass in outdoor helical reactors were determined.

Light induced H2 evolution in a hydrogenase-TiO2 particle system by direct electron transfer or via rhodium complexes

Three different hydrogenases (isolated from Clostridium pasteurianum, Desulfovibrio desulfuricans strain Norway 4 and D. baculatus 9974) added to a suspension of TiO2 (anatase) powder are able to catalyze H2 evolution under band gap illumination of the semiconducting particles, and in the presence of EDTA or methanol as electron donor. This H2 production can be obtained by the direct electron transfer from the conduction band of the TiO2 particles to the active site of the enzyme at pHs higher than 7. This mediator-independent charge transfer is more efficient with C. pasteurianum and D. baculatus 9974 hydrogenases, and in the presence of methanol. Rhodium tris- and bis-bipyridyl complexes can act efficiently as electron carriers from the supporting particles to the adsorbed enzyme molecules in cases where the direct transfer is inefficient.

An Automated Helical Photobioreactor Incorporating Cyanobacteria for Continuous Hydrogen Production

A laboratory-scale, helical tubular photobioreactor, made of polyvinyl chloride tubing, was constructed to study photobiological H2 production by cyanobacteria catalyzed by cellular nitrogenase. The photobioreactor was connected to a computer, with specially written software and hardware, for automated control of the biochemical and environmental processes regulating H2 evolution. A basic photobioreactor unit with a photostage volume of 4.35 L and containing Anabaena azollae grown in 98% air + 2% CO2 gas mixture produced H2 at a rate of 13 mL H2·h−1·L−1 culture suspension when the gas phase was changed to Ar. The H2 production was sustained for 6 h. No H2 evolution was observed in the presence of photosynthetic O2.

A hollow fibre photobioreactor for continuous production of hydrogen by immobilized Cyanobacteria under partial vacuum

Abstract Photoproduction of hydrogen by the nitrogen-fixing cyanobacterum Anabaena variabilis was measured in partial vacuum. The rates of hydrogen production under vacuum were compared with those under an argon atmosphere in vials. Hydrogen production was dependent on the residual pressure of gases remaining in the partial vacuum and required light. The adhesion of cyanobacterial cells to hydrophilic and hydrophobic hollow fibres was studied. The degree of immobilization of the cells on the hollow fibres was assessed by examining cell attachment using scanning electron microscopy. A laboratory-scale photobioreactor for production of hydrogen by immobilized cyanobacterium A. variabilis was assembled. The photobioreactor was designed such that the cyanobacterial growth medium passes from the outside of the fibres into the inner lumen space. Photoproduction of hydrogen at rates of 0.02–0.2 ml H 2 per mg dry weight of cyanobacterial biomass per hour was observed for 5 months.

Comparative immunochemistry of bacterial, algal and plant ferredoxins.

1. Antibodies were produced in rabbits to the 4Fe-4S ferrodoxins from Bacillus stearothermophilus, the 2 [4Fe-4S] ferredoxin from Clostridium pasteurianum, and the 2Fe-2S ferredoxins from the blue-green algia Spirulina maxima, the green alga Scenedesmus obliquus, and the higher plant Beta vulgaris. The antibodies were tested for immunoprecipitation activity with seven bacterial, twelve blue-green algal, six eukaryotic algal and six higher plant ferredoxins. 2. Antibodies to the bacterial ferredoxins reacted to a significant extent only with their homologous proteins. On the other hand, antibodies to the plant and algal ferredoxins showed cross-reaction with other ferredoxins. There was a correlation between the degrees of immunoprecipitation and the similarity in amino acid sequences. These results suggest that the method can be used as a marker in taxonomic studies. 3. The interaction of the antibodies with the five native ferredoxins was compared with the reactions with their apoproteins. In each case the degree of interaction was different. This behaviour was interpreted as due to an influence of tertiary structure on the antibody-antigen interaction.

Immobilization of Rhodobacter capsulatus on Cellulose Beads and Water Treatment Using a Photobioreactor

Abstract A photobioreactor containing cells of the purple non-sulphur bacterium Rhodobacter capsulatus immobilized on cellulose beads removed organic carbon, ammonium ion, and phosphate ion from a diluted growth medium over a period of 19–22 d with a residence time of 20.6 or 10.3 h at 35 (±1)°C and continuous light of 60 μE·m −2 ·s −1 .

Biological activity of synthetic molybdenum-iron-sulphur, iron-sulphur and iron-selenium analogues of ferredoxin-type centres

The molybdenum-iron-sulphur cluster [Fe6Mo2S8(SCH2CH2OH)9]3-, which contains two Fe3MoS4 cubane-like centres, is the best plausible analogue available to date for the molybdenum site of the nitrogenase enzymes. The iron-sulphur cluster [Fe4S4(S . CH2CH2OH)4]2- and the iron-selenium cluster [Fe4Se4(S . CH2CH2OH)4]2- are structural analogues of the ferredoxin Fe4S4 active centre. All three clusters would replace ferredoxin and mediate electron transfer to Clostridium pasteurianum hydrogenase in a H2-evolving system with sodium dithionite as the electron donor. The clusters would not replace hydrogenases which themselves are unable to evolve H2 from reduced ferredoxins. The molybdenum-iron-sulphur cluster would also replace ferredoxin in a chloroplast-ferredoxin-hydrogenase H2 evolving system.

Immobilized Photosynthetic Membranes and Cells for the Production of Fuels and Chemicals

Photosynthesis by plants, algae, cyanobacteria (bluegreen algae) and photosynthetic bacteria converts large quantities of solar radiation into chemical energy in the form of carbohydrates, lipids, proteins, ammonia, hydrogen, ATP, pyridine nucleotides, etc. The importance of photosynthetic processes as energy converters lies in the facts that the substrates used such as water, CO2 and N2 are ubiquitous and inexpensive.

Purification and sequence determination of two ferredoxins from Dunaliella salina

Abstract A ferredoxin was purified from the halophyte Dunaliella salina by standard procedures. This preparation was found to be heterogeneous by amino-terminal analysis and was resolved into two fractions by chemical modification and chromatography. The primary structure of both ferredoxins consists of 95 amino acid residues which include five cysteines. There are 16 amino acid differences in the sequences of the two ferredoxins. The amino-terminal of one of the ferredoxins is serine whereas all other plant and algal ferredoxins so far sequenced have alanine at the aminoterminus. The sequences of the two ferredoxins from this halophyte resemble those of other chloroplast ferredoxins but do not show any special homology to Halobacterium ferredoxin.