Anatoly A. Tsygankov

Hydrogen production from tofu wastewater by Rhodobacter sphaeroides immobilized in agar gels

Hydrogen production from the wastewater of tofu factory was examined by using anoxygenic phototrophic bacterium Rhodobacter sphaeroides immobilized in agar gels. The maximum rate of hydrogen production observed from the wastewater was 2.1 l h−1 m2 gel which was even slightly higher than that from a glucose medium (as control). The hydrogen production lasted up to 50 h. The yield of hydrogen was 1.9 ml⧸mlwastewater or 0.24 ml⧸mg carbohydrates contained in the wastewater. This yield corresponds to53% or 65% of that from the glucose medium, according to the different expressions of the yield. The TOC (total organic carbon) removal ratio in 85 h reached 41% which was comparable to that from the glucose medium. The immobilization protected the bacterium from the inhibitory effect of ammonium ion.

Hydrogen photoproduction under continuous illumination by sulfur-deprived, synchronous Chlamydomonas reinhardtii cultures

Unsynchronized Chlamydomonas reinhardtii cells subsequently deprived of sulfur produce H2 under continuous illumination in the laboratory for 3– 4 days. However, cultures grown outdoors will be exposed to day-and-night cycles that may synchronize their growth and cell division. While it is clear that only insigni6cant amounts of H2 can be produced by sulfur-deprived cells during the night period, little work has been done to examine the e7ects of the light=dark cycles preceding sulfur deprivation on subsequent H2 photoproduction. We show that (a) C. reinhardtii cells exhibit synchronized growth and cell division in the presence of acetate, (b) cells with the highest speci6c rates of H2 photoproduction also have the highest rates of biomass accumulation, and (c) the highest rates of starch and protein degradation coincide with the highest rates of formate and acetate accumulation, but not with H2 photoproduction. This work shows that it is possible to maximize the production of H2 by sulfur-depriving synchronized cultures at about 4 h after the beginning of the light period. ? 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.

Photobioreactor with photosynthetic bacteria immobilized on porous glass for hydrogen photoproduction

A photobioreactor was constructed with porous glass as an immobilization matrix. The reactor was a rectangular glass chamber (inner dimensions: 125 × 50 × 2.5 mm) containing a porous glass sheet (125 × 50 × 0.5 mm) on which Rhodobacter sphaeroides RV was immobilized (11.2 mg dry wt./ml porous glass). The maximum rate of hydrogen evolution was 1.3 ml/h/ml porous glass. The conversion efficiency of succinate into hydrogen reached 75%. Stable and efficient hydrogen evolution continued for up to 40 d.

Prolongation of H2 photoproduction by immobilized, sulfur-limited Chlamydomonas reinhardtii cultures

Two approaches to prolong the duration of hydrogen production by immobilized, sulfur-limited Chlamydomonas reinhardtii cells are examined. The results demonstrate that continuous H2 photoproduction can occur for at least 90 days under constant flow of TAP medium containing micromolar sulfate concentrations. Furthermore, it is also possible to prolong the duration of H2 production by cycling immobilized cells between minus and plus sulfate conditions.

Accumulation of poly-(hydroxybutyrate) by a non-sulfur photosynthetic bacterium, Rhodobacter sphaeroides RV at different pH

SummaryEffect of pH of culture media on intracellular accumulation of poly-(hydroxybutyrate) (PHB) by a non-sulfur photosynthetic bacterium, Rhodobacter sphaeroides strain RV was studied in pH-stat cultures. Sub-optimal pH for growth, 8.0 or 8.5 gave the higher content of PHB rather than optimal pH 7.5 for growth. These results show that growth and PHB accumulation of the bacteria can be controlled by pH of culture media.

Chlamydomonas Flavodiiron Proteins Facilitate Acclimation to Anoxia During Sulfur Deprivation

The flavodiiron proteins (FDPs) are involved in the detoxification of oxidative compounds, such as nitric oxide (NO) or O2 in Archaea and Bacteria. In cyanobacteria, the FDPs Flv1 and Flv3 are essential in the light-dependent reduction of O2 downstream of PSI. Phylogenetic analysis revealed that two genes (flvA and flvB) in the genome of Chlamydomonas reinhardtii show high homology to flv1 and flv3 genes of the cyanobacterium Synechocystis sp. PCC 6803. The physiological role of these FDPs in eukaryotic green algae is not known, but it is of a special interest since these phototrophic organisms perform oxygenic photosynthesis similar to higher plants, which do not possess FDP homologs. We have analyzed the levels of flvA and flvB transcripts in C. reinhardtii cells under various environmental conditions and showed that these genes are highly expressed under ambient CO2 levels and during the early phase of acclimation to sulfur deprivation, just before the onset of anaerobiosis and the induction of efficient H2 photoproduction. Importantly, the increase in transcript levels of the flvA and flvB genes was also corroborated by protein levels. These results strongly suggest the involvement of FLVA and FLVB proteins in alternative electron transport.

Regulation of nitrogenase in the photosynthetic bacterium Rhodobacter sphaeroides containing draTG and nifHDK genes from Rhodobacter capsulatus.

The photosynthetic bacteria Rhodobacter capsulatus and Rhodospirillum rubrum regulate their nitrogenase activity by the reversible ADP-ribosylation of nitrogenase Fe-protein in response to ammonium addition or darkness. This regulation is mediated by two enzymes, dinitrogenase reductase ADP-ribosyl transferase (DRAT) and dinitrogenase reductase activating glycohydrolase (DRAG). Recently, we demonstrated that another photosynthetic bacterium, Rhodobacter sphaeroides, appears to have no draTG genes, and no evidence of Fe-protein ADP-ribosylation was found in this bacterium under a variety of growth and incubation conditions. Here we show that four different strains of Rba. sphaeroides are incapable of modifying Fe-protein, whereas four out of five Rba. capsulatus strains possess this ability. Introduction of Rba. capsulatus draTG and nifHDK (structural genes for nitrogenase proteins) into Rba. sphaeroides had no effect on in vivo nitrogenase activity and on nitrogenase switch-off by ammonium. However, transfer of draTG from Rba. capsulatus was sufficient to confer on Rba. sphaeroides the ability to reversibly modify the nitrogenase Fe-protein in response to either ammonium addition or darkness. These data suggest that Rba. sphaeroides, which lacks DRAT and DRAG, possesses all the elements necessary for the transduction of signals generated by ammonium or darkness to these proteins.

The effect of sulfur compounds on H2 evolution/consumption reactions, mediated by various hydrogenases, in the purple sulfur bacterium, Thiocapsa roseopersicina.

The influence of reduced sulfur compounds (including stored S0) on H2 evolution/consumption reactions in the purple sulfur bacterium, Thiocapsa roseopersicina BBS, was studied using mutants containing only one of the three known [NiFe] hydrogenase enzymes: Hox, Hup or Hyn. The observed effects depended on the kind of hydrogenase involved. The mutant harbouring Hox hydrogenase was able to use S2O32−, SO32−, S2− and S0 as electron donors for light-dependent H2 production. Dark H2 evolution from organic substrates via Hox hydrogenase was inhibited by S0. Under light conditions, endogenous H2 uptake by Hox or Hup hydrogenases was suppressed by S compounds. СО2-dependent H2 uptake by Hox hydrogenase in the light required the additional presence of S compounds, unlike the Hup-mediated process. Dark H2 consumption via Hyn hydrogenase was connected to utilization of S0 as an electron acceptor and resulted in the accumulation of H2S. In wild type BBS, with high levels of stored S0, dark H2 production from organic substrates was significantly lower, but H2S accumulation significantly higher, than in the mutant GB1121(Hox+). There is a possibility that H2 produced via Hox hydrogenase is consumed by Hyn hydrogenase to reduce S0.

Immobilization of the purple non-sulfur bacterium Rhodobacter sphaeroides on glass surfaces

A method for improving the adsorption of bacteria on glass surfaces was developed. The modification of a glass surface by LS-2480 greatly increased the number of bacteria that were immobilized. The conditions for bacteria immobilization on the modified glass surface were optimized.

Hydrogen Photoproduction by Immobilized N2-Fixing Cyanobacteria: Understanding the Role of the Uptake Hydrogenase in the Long-Term Process

ABSTRACT We have investigated two approaches to enhance and extend H2 photoproduction yields in heterocystous, N2-fixing cyanobacteria entrapped in thin alginate films. In the first approach, periodic CO2 supplementation was provided to alginate-entrapped, N-deprived cells. N deprivation led to the inhibition of photosynthetic activity in vegetative cells and the attenuation of H2 production over time. Our results demonstrated that alginate-entrapped ΔhupL cells were considerably more sensitive to high light intensity, N deficiency, and imbalances in C/N ratios than wild-type cells. In the second approach, Anabaena strain PCC 7120, its ΔhupL mutant, and Calothrix strain 336/3 films were supplemented with N2 by periodic treatments of air, or air plus CO2. These treatments restored the photosynthetic activity of the cells and led to a high level of H2 production in Calothrix 336/3 and ΔhupL cells (except for the treatment air plus CO2) but not in the Anabaena PCC 7120 strain (for which H2 yields did not change after air treatments). The highest H2 yield was obtained by the air treatment of ΔhupL cells. Notably, the supplementation of CO2 under an air atmosphere led to prominent symptoms of N deficiency in the ΔhupL strain but not in the wild-type strain. We propose that uptake hydrogenase activity in heterocystous cyanobacteria not only supports nitrogenase activity by removing excess O2 from heterocysts but also indirectly protects the photosynthetic apparatus of vegetative cells from photoinhibition, especially under stressful conditions that cause an imbalance in the C/N ratio in cells.