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Author: search.filters.author.Pansook, SunisaSubject: search.filters.subject.Aphanothece halophytica

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    Simazine Enhances Dark Fermentative H2 Production by Unicellular Halotolerant Cyanobacterium Aphanothece halophytica
    (2022-07-15)
    Pansook, Sunisa
    ;
    Incharoensakdi, Aran
    ;
    Phunpruch, Saranya
    The halotolerant cyanobacterium Aphanothece halophytica is a potential H<inf>2</inf> producer that induces H<inf>2</inf> evolution under nitrogen deprivation. H<inf>2</inf> is mainly produced via the catabolism of stored glycogen under dark anaerobic condition. H<inf>2</inf> evolution is catalyzed by O<inf>2</inf>-sensitive bidirectional hydrogenase. The aim of this study was to improve H<inf>2</inf> production by A. halophytica using various kinds of inhibitors. Among all types of inhibitors, simazine efficiently promoted the highest H<inf>2</inf> production under dark conditions. High simazine concentration and long-term incubation resulted in a decrease in cell and chlorophyll concentrations. The optimal simazine concentration for H<inf>2</inf> production by A. halophytica was 25 µM. Simazine inhibited photosynthetic O<inf>2</inf> evolution but promoted dark respiration, resulting in a decrease in O<inf>2</inf> level. Hence, the bidirectional hydrogenase activity and H<inf>2</inf> production was increased. A. halophytica showed the highest H<inf>2</inf> production rate at 58.88 ± 0.22 µmol H<inf>2</inf> g<sup>−1</sup> dry weight h<sup>−1</sup> and H<inf>2</inf> accumulation at 356.21 ± 6.04 μmol H<inf>2</inf> g<sup>−1</sup> dry weight after treatment with 25 µM simazine under dark anaerobic condition for 2 and 24 h, respectively. This study demonstrates the potential of simazine for the enhancement of dark fermentative H<inf>2</inf> production by A. halophytica.
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    Enhanced dark fermentative H2 production by agar-immobilized cyanobacterium Aphanothece halophytica
    (2019-10-01)
    Pansook, Sunisa
    ;
    Incharoensakdi, Aran
    ;
    Phunpruch, Saranya
    Cell immobilization is one of the techniques used to improve H<inf>2</inf> productivity in cyanobacteria. In this study, H<inf>2</inf> production by immobilized cells of unicellular halotolerant cyanobacterium Aphanothece halophytica was investigated and optimized. The results showed that immobilized cells of A. halophytica had higher H<inf>2</inf> production than free cells under nitrogen-deprived condition. Among various support material types used, agar-immobilized cells showed the highest H<inf>2</inf> production rate. Under nitrogen deprivation, the optimal conditions of cell immobilization for H<inf>2</inf> production were 3% (w/v) agar concentration, 0.2 mg dry cell weight per mL of gel solution, and 0.125 cm<sup>3</sup> of agar cube. The optimum pH of medium and incubation temperature for H<inf>2</inf> production by agar-immobilized cells were pH 7.4 and 40 °C, respectively. Using a large glass vial and headspace volume resulted in enhancement of H<inf>2</inf> production by agar-immobilized cells. Finally, H<inf>2</inf> production by agar-immobilized cells was analyzed for three consecutive cycles. H<inf>2</inf> production could be maintained at the highest level after two cycles when half of immobilized cells were replaced with fresh immobilized cells. These findings indicate that the enhanced H<inf>2</inf> production of the unicellular halotolerant cyanobacterium A. halophytica can be achieved by immobilization method, thus providing the possibility to improve H<inf>2</inf> production by cyanobacteria in the future.