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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−1 dry weight h−1 and H<inf>2</inf> accumulation at 356.21 ± 6.04 μmol H<inf>2</inf> g−1 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 cm3 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.
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Effects of the Photosystem II Inhibitors CCCP and DCMU on Hydrogen Production by the Unicellular Halotolerant Cyanobacterium Aphanothece halophytica
(2019-01-01)
Pansook, Sunisa
;
Incharoensakdi, Aran
;
Phunpruch, Saranya
The unicellular halotolerant cyanobacterium Aphanothece halophytica is a potential dark fermentative producer of molecular hydrogen (H<inf>2</inf>) that produces very little H<inf>2</inf> under illumination. One factor limiting the H<inf>2</inf> photoproduction of this cyanobacterium is an inhibition of bidirectional hydrogenase activity by oxygen (O<inf>2</inf>) obtained from splitting water molecules via photosystem II activity. The present study aimed to investigate the effects of the photosystem II inhibitors carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on H<inf>2</inf> production of A. halophytica under light and dark conditions and on photosynthetic and respiratory activities. The results showed that A. halophytica treated with CCCP and DCMU produced H<inf>2</inf> at three to five times the rate of untreated cells, when exposed to light. The highest H<inf>2</inf> photoproduction rates, 2. 26 ± 0. 24 and 3. 63 ± 0. 26 μmol H<inf>2</inf>g-1 dry weight h-1, were found in cells treated with 0.5 μM CCCP and 50 μM DCMU, respectively. Without inhibitor treatment, A. halophytica incubated in the dark showed a significant increase in H<inf>2</inf> production compared with cells that were incubated in the light. Only CCCP treatment increased H<inf>2</inf> production of A. halophytica during dark incubation, because CCCP functions as an uncoupling agent of oxidative phosphorylation. The highest dark fermentative H<inf>2</inf> production rate of 39. 50 ± 2. 13 μmol H<inf>2</inf>g-1 dry weight h-1 was found in cells treated with 0.5 μM CCCP after 2 h of dark incubation. Under illumination, CCCP and DCMU inhibited chlorophyll fluorescence, resulting in a low level of O<inf>2</inf>, which promoted bidirectional hydrogenase activity in A. halophytica cells. In addition, only CCCP enhanced the respiration rate, further reducing the O<inf>2</inf> level. In contrast, DCMU reduced the respiration rate in A. halophytica.

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