K. K. Rao

Actual and potential rates of hydrogen photoproduction by continuous culture of the purple non-sulphur bacterium Rhodobacter capsulatus

Abstract The influence of (NH4)2SO4 concentration and dilution rate (D) on actual and potential H2 photoproduction has been studied in ammonium-limited chemostat cultures of Rhodobacter capsulatus B10. The actual H2 production in a photobioreactor was maximal (approx. 80 ml h−1 l−1) at D = 0.06 h−1 and 4 mM (NH4)2SO4. However, it was lower than the potential H2 evolution (calculated from hydrogen evolution rates in incubation vials), which amounted to 100–120 ml h−1 l−1 at D = 0.03–0.08 h−1. Taking into account the fact that H2 production in the photobioreactor under these conditions was not limited by light or lactate, another limiting (inhibiting) factor should be sought. One possibility is an inhibition of H2 production by the H2 accumulated in the gas phase. This is apparent from the non-linear kinetics of H2 evolution in the vials or from its inhibition by the addition of H2; initial rates were restored in both cases after the vials had been refilled with argon. The actual H2 production in the photobioreactor at D = 0.06 h−1 was shown to increase from approximately 80 ml h−1 l−1 to approximately 100 ml h−1 l−1 under an argon flow at 100 ml min−1. Under maximal H2 production rates in the photobioreactor, up to 30% of the lactate feedstock was utilised for H2 production and 50% for biomass synthesis.

Hydrogen photoproduction by Rhodobacter sphaeroides immobilised on polyurethane foam

H2 photoproduction by Rhodobacter sphaeroides GL-1 immobilised on polyurethane foam in a continuous flow photobioreactor was shown to occur for prolonged periods. Under optimal conditions (300 W m−2; dilution rate 0.023 h−1) the rate of H2 production was 0.21 ml h−1 ml−1 foam matrix with an efficiency for lactic acid to H2 conversion of 86%. The duration of the process (35 days of operation) showed no major limitations.

H2 photoproduction by batch culture of Anabaena variabilis ATCC 29413 and its mutant PK84 in a photobioreactor

Hydrogen production by Anabaena variabilis ATCC 29413 and of its mutant PK84, grown in batch cultures, was studied in a photobioreactor. The highest volumetric H(2) production rates of native and mutant strains were found in cultures grown at gradually increased irradiation. The native strain evolved H(2) only under an argon atmosphere with the actual rate as high as the potential rate (measured in small vials under optimal conditions). In this case 61% of oxygenic photosynthesis was used for H(2) production. In contrast the mutant PK84 produced H(2) during growth under CO(2)-enriched air. Under these conditions at the maximum rate of H(2) production (10 mL h(-1) L(-1)), 13% of oxygenic photosynthesis was used for H(2) production and the actual H(2) production was only 33% of the potential. Under an atmosphere of 98% argon + 2% CO(2) actual H(2) production by mutant PK84 was 85% of the potential rate and 66% of oxygenic photosynthesis was used for H(2) production. Hydrogen production under argon + CO(2) by the mutant was strictly light-dependent with saturation at about 300 microE m(-2) s(-1). However, the rate of photosynthesis was not saturated at this irradiation. At limiting light intensities (below 250 microE m(-2) s(-1)) 33-58% of photosynthesis was used for H(2) production. Hydrogen evolution by PK84 under air + 2% CO(2) was also stimulated by light; but was not saturated at 332 microE m(-2) s(-1) and did not cease completely in darkness. The rate of oxygen photoevolution was also not saturated. A mechanism for increasing cyanobacterial hydrogen production is proposed.

Hydrogen production by Anabaena variabilis PK84 under simulated outdoor conditions

Hydrogen production by autotrophic, vanadium-grown cells of Anabaena variabilis PK84, a cyanobacterial mutant impaired in the utilization of molecular hydrogen, has been studied under simulated outdoor conditions. The cyanobacterium was cultivated in an automated helical tubular photobioreactor (4.35 L) under air containing 2% CO(2), with alternating 12-h light (36 degrees C) and 12-h dark (14 degrees to 30 degrees C) periods. A. variabilis steadily produced H(2) directly in the photobioreactor during continuous cultivation for 2.5 months. The maximum H(2) production by the continuously aerated culture under light of 332 microE. s(-1). m(-2) was 230 mL per 12-h light period per photobioreactor and was observed at a growth density corresponding to 3.6 to 4.6 microgram Chl a. mL(-1) (1.2 to 1.6 mg dry weight. mL(-1)). Replacement of air with an argon atmosphere enhanced H(2) evolution by a factor of 2. This stimulatory effect was caused mainly by N(2) deprivation in the cell suspension. A short-term decrease of the CO(2) concentration in the air suppressed H(2) evolution. Anoxygenic conditions over the dark periods had a negative effect on H(2) production. The peculiarity of hydrogen production and some physiological characteristics of A. variabilis PK84 during cultivation in the photobioreactor under a light-dark regime are investigated.

Nitrate and phosphate ion removal from water by Phormidium laminosum immobilized on hollow fibres in a photobioreactor

Abstract Removal of nitrate and phosphate ions from water, by using the thermophilic cyanobacterium Phormidium laminosum, immobilized on cellulose hollow fibres in the tubular photobioreactor at 43 °C, was studied by continuously supplying dilute growth medium for 7 days and then secondarily treated sewage (STS) for 12 days. The concentrations of NO−3 and PO3−4 in the effluent from the dilute growth medium decreased from 5.0 mg N/l to 3.1 mg N/l, and from 0.75 mg P/l to 0.05 mg P/l respectively, after a residence time of 12 h. The concentrations of NO−3 and PO3−4 in the effluent from STS decreased from 11.7 mg N/l to 2.0 mg N/l, and from 6.62 mg P/l to 0.02 mg P/l respectively, after a residence time of 48 h. The removal rates of nitrogenous␣and phosphate ions from STS were 0.24 and 0.11 mmol day−1 l reactor−1 respectively, under the same conditions. Although, among nitrogenous ions, nitrate and ammonium ions were efficiently removed by P.␣laminosum, the nitrite ion was released into the effluent when STS was used as influent. Treatment of water with thermophilic P. laminosum immobilized on hollow fibres thus appears to be an appropriate means for the removal of inorganic nitrogen and phosphorus from treated wastewater.

Hydrogen photoproduction by three different nitrogenases in whole cells of Anabaena variabilis and the dependence on pH

Abstract Mo, V and Fe nitrogenases were induced in Anabaena variabilis. The influence of neutral and alkaline pHs on nitrogenase activity and rates of H2 photoproduction by whole cells was investigated to establish the optimum activity for H2 evolution under varying growth and H2 production conditions. Growth rates in batch cultures at pH 7 with Mo- or V-nitrogenases were three times higher than the Fe-nitrogenase cultures. The Mo-nitrogenase activity decreased from pHs 7 to 9, and at pH 10, the culture was unable to grow. Fe-nitrogenase cells (no Mo or V) showed similar behaviour over pH 7–8. Cultures expressing V-nitrogenase exhibited the highest resistance to alkaline pHs and grew even at pH 10; H2 evolution was practically independent of the culture at pH 7–9. With cells grown under more alkaline conditions, the pH optimum for the H2 production was more alkaline; the maximal rates of H2 photoproduction were observed with V-nitrogenase containing cells.

Anabaena variabilisProduction of hydrogen by an mutant in a photobioreactor under aerobic outdoor conditions

Publisher Summary This chapter describes the principal possibility of hydrogen production in an outdoor photobioreactor (PhBR) incorporating a cyanobacterial mutant of Anabaena variabilis (PK84) under aerobic conditions. It describes the research in which a computer-controlled helical tubular PhBR was operated over 4 summer months. A maximum rate of 80 mL H2 per hr per reactor volume (4.35 L) was obtained on a bright day (400 W.m 2) from a batch culture. Also, the culture was grown in chemostat mode at dilution rate D of 0.02 h–1. The maximum efficiency of conversion of light to chemical energy of H2 in the PhBR was 0.33% and 0.14% on a cloudy and a sunny day, respectively. This chapter demonstrates long term, continuous, and stable hydrogen production in a helical photobioreactor incorporating the cyanobacterium A. variabilis PK84 under aerobic outdoor conditions.

The complete amino acid sequence of the Spirulina platensis ferredoxin

Abstract The complete amino acid sequence of ferredoxin from the Spirulina platensis , a blue green non-filamentous algae has been determined. The amino acid sequence differs from the reported sequence of Wada et al. (1) at residue 9. Our results indicate that the residue is Asn while Wada et al. have reported it to be Asp. In addition, residues 86 and 87 have been determined in our study while Wada et al. have assumed these residues by homology to other ferredoxins which have been sequenced. Modifications of the automated sequence procedure previously described (2) were again found to be useful for peptide sequencing.

Amino acid sequence of the spirulina maxima ferredoxin, a ferredoxin from a procaryote

Abstract The amino acid sequence of the Spirulina maxima ferredoxin has been determined. Spirulina maxima is a blue green algae and is a procaryote. The ferredoxins of the plant-algal type sequenced to date have all been isolated from eucaryotes. The S. maxima ferredoxin was composed of 98 amino acids arranged in a single polypeptide chain. The sequences of the various procaryote-eucaryote ferredoxins are compared and the differences discussed.

Ferredoxins in the evolution of photosynthetic systems from anaerobic bacteria to higher plants

Ferredoxins are present in a wide range of organisms, from the primitive anaerobic bacteria to higher plants and animals, where they function in diverse electron transfer processes. They are relatively small proteins with molecular weights of 6000 to 12000, contain 2–8 Fe atoms and an equivalent amount of inorganic sulphur per molecule, and they transfer electrons at low redox potentials.Anaerobic bacteria, like the clostridia, contain 8 Fe ferredoxins with a peptide chain of 55 amino acid residues which could be arranged in two similar halves suggesting the evolution of the molecule, from a prototype of 26 amino acid residues, by gene duplication. Since these ferredoxins contain a high predominance of certain amino acids detected in meteorites and lunar samples and synthesized under simulated prebiotic environment and since iron and sulphus could be incorporated easily into the apoprotein in anaerobic conditions, the ferredoxin molecule could have been formed in the early periods of the origin of life. From the available chemical compositions and amino acid sequences of various ferredoxins the following evolutionary scheme can be postulated: anaerobic bacteria→green photosynthetic bacteria→red photosynthetic bacteria→sulphate reducing bacteria→blue-green algae→green algae and higher plants.