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Author: search.filters.author.Taikhao, SamartSubject: search.filters.subject.hydrogen production

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    Increasing Hydrogen Production Efficiency of N2-Fixing Cyanobacterium Anabaena siamensis TISTR 8012 by Cell Immobilization
    (2017-01-01)
    Taikhao, Samart
    ;
    Phunpruch, Saranya
    H<inf>2</inf> produced by cyanobacteria is one of the interesting alternative energy carriers for the future. The filamentous N<inf>2</inf>-fixing cyanobacterium Anabaena siamensis TISTR 8012 is a potential microorganism for H<inf>2</inf> production. It can produce H<inf>2</inf> via both photosynthesis and nitrogen fixation processes. This study aimed to increase the efficiency of H<inf>2</inf> production by immobilization of A. siamensis cells. The result showed that H<inf>2</inf> production rate by A. siamensis grown in BG11<inf>0</inf> medium was higher than that in BG11 and Allen-Arnon media due to an increase of the heterocyst cells. The sulfur deprivation during adaptation period for 24 hours increased its H<inf>2</inf> production rate. The optimal conditions for H<inf>2</inf> production by immobilized cells were immobilization with alginate and using 150 gel beads in 20 mL glass vial. In immobilized cells, an addition of 0.5% fructose resulted in a 2-fold increase of H<inf>2</inf> production rate. Finally, the reducing agents β-mercaptoethanol and methylviologen enhanced H<inf>2</inf> production rate with 3.092 and 2.426 μmolH<inf>2</inf> mg chl a<sup>-1</sup> h<sup>-1</sup>, respectively, in A. siamensis immobilized cells whereas NADH, dithiothreitol and sodium dithionite were not capable of increasing H<inf>2</inf> production rate.
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    Effect of Metal Cofactors of Key Enzymes on Biohydrogen Production by Nitrogen Fixing Cyanobacterium Anabaena siamensis TISIR 8012
    (2017-01-01)
    Taikhao, Samart
    ;
    Phunpruch, Saranya
    In N<inf>2</inf>-fixing cyanobacteria, three enzymes are involved in the H<inf>2</inf> metabolism. Nitrogenase catalyzes the N<inf>2</inf> fixation which produces H<inf>2</inf> as a by-product. The produced H<inf>2</inf> is taken up to protons and electrons by an activity of uptake hydrogenase. Reversible enzyme catalyzes both reactions of the H<inf>2</inf> evolution and the H<inf>2</inf> uptake. These enzymes are all metalloenzyme. The cyanobacterial nitrogenase normally requires molybdenum and iron as cofactors; however nitrogenase of few cyanobacterial species is dependent on vanadium. The cyanobacterial uptake and reversible hydrogenase requires nickel and iron as cofactors. This research aimed to investigate the effect of these metal cofactors on H<inf>2</inf> production and hydrogenase activity by N<inf>2</inf>-fixing cyanobacterium Anabaena siamensis TISTR 8012 isolated from rice paddle field in Thailand. The result showed that A. siamensis cells incubated in N-deprived BG11 medium (BG11<inf>0</inf>) gave clearly higher H<inf>2</inf> production rate and hydrogenase activity than those in normal BG11 medium. Under nitrogen deprivation, an increase of iron, nickel, and molybdenum concentrations obviously enhanced H<inf>2</inf> production rate. But only higher iron concentrations increased hydrogenase activity, indicating that the iron metal assisted in the function of reversible hydrogenase activity. In addition, vanadium seemed not to be a metal cofactor of key enzymes involving in H<inf>2</inf> production in A. siamensis. The optimal concentrations of iron, nickel and molybdenum ions for H<inf>2</inf> production rate by A. siamensis were 60 μM, 4 μM and 4 μM, respectively. The highest H<inf>2</inf> production rate of 0.057 μmolH<inf>2</inf> mg chl a<sup>-1</sup> h<sup>-1</sup> was observed in cells incubated in BG11<inf>0</inf> medium supplemented with 4 μM nickel ion.