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Identification of bidirectional hydrogenase genes and their co-transcription in unicellular halotolerant cyanobacterium Aphanothece halophytica
(2016-04-01)
Phunpruch, Saranya
;
Taikhao, Samart
;
Incharoensakdi, Aran
The halotolerant cyanobacterium Aphanothece halophytica has been shown to produce H<inf>2</inf> via dark fermentation of accumulated glycogen under anoxic condition. One set of hox genes encoding a bidirectional hydrogenase is present in A. halophytica. In this study, the nucleotide sequence and the transcriptional analysis of hox genes in A. halophytica were investigated. The results revealed that A. halophytica contained five structural genes, hoxE, hoxF, hoxU, hoxY, and hoxH, without an insertion of other open reading frames (ORFs). The conserved cysteine motifs of iron-sulfur clusters involved in an electron transfer were found in all Hox subunits. The nucleotide and deduced amino acid sequences of hox genes in A. halophytica showed the highest identity and similarity to those of Halothece sp. PCC 7418. By reverse transcription polymerase chain reaction (RT-PCR) analysis, hox genes in A. halophytica were co-transcribed as a single operon. Under nitrogen-deprived condition, the transcripts of hoxH, glgB, coxA, ndhB, and psaA were upregulated whereas those of glgP and narB were downregulated which resulted in an increase of H<inf>2</inf> production, H<inf>2</inf>ase activity, glycogen content, and dark respiration rate.
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Dark fermentative hydrogen production by the unicellular halotolerant cyanobacterium Aphanothece halophytica grown in seawater
(2015-02-01)
Taikhao, Samart
;
Incharoensakdi, Aran
;
Phunpruch, Saranya
Biohydrogen is an environmentally friendly alternative energy carrier that can be produced by a number of different microorganisms. The unicellular halotolerant cyanobacterium Aphanothece halophytica is one of the high potential H<inf>2</inf> producers. Under dark fermentation, it is capable of producing H<inf>2</inf> by the bidirectional hydrogenase activity via the catabolism of glycogen stored during photosynthesis. This work aimed to cultivate A. halophytica in natural seawater containing high salinity and minerals, with an addition of some essential nutrients, and to investigate effects of various nutritional and physical factors on its dark fermentative H<inf>2</inf> production. A. halophytica was able to grow in natural seawater added with NaNO<inf>3</inf>. Cells grown in seawater supplemented with as little as 1.76 mM NaNO<inf>3</inf> showed similar growth to those cultivated in normal BG11 supplemented with Turk Island salt solution. H<inf>2</inf> production was the highest when incubating the cells in seawater without any supplementation of NaNO<inf>3</inf>. Under this condition, the highest rate of dark fermentative H<inf>2</inf> production of 82.79 ± 3.47 nmol H<inf>2</inf> mg-1 dry weight h−1 was found in cells incubated at 35 °C, pH 6 with the supplementation of 378 mmolC L−1 glucose, 0.25 M NaCl, and 0.4 μM Fe3+. Long-term H<inf>2</inf> accumulation of 1,864 ± 81 nmol H<inf>2</inf> mg−1 dry weight was observed after 8 days of dark incubation under anoxic condition, and the high yield of H<inf>2</inf> was sustained at least up to 14 days, suggesting the possibility of utilizing natural seawater to grow A. halophytica for long-term production of H<inf>2</inf>.
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Factors affecting biohydrogen production by unicellular halotolerant cyanobacterium Aphanothece halophytica
(2013-04-01)
Taikhao, Samart
;
Junyapoon, Suwannee
;
Incharoensakdi, Aran
;
Phunpruch, Saranya
The effects of several physiological parameters on H<inf>2</inf> production rate in the unicellular halotolerant cyanobacterium Aphanothece halophytica were investigated. Under nitrogen deprivation, the growth of cells was inhibited, but H<inf>2</inf> production rate was enhanced approximately fourfold. Interestingly, cells grown under sulfur deprivation exhibited a decrease in cell growth, H<inf>2</inf> production rate, and bidirectional hydrogenase activity. Glucose was the preferred sugar source for H<inf>2</inf> production by A. halophytica, but H<inf>2</inf> production decreased at high glucose concentrations. H<inf>2</inf> production rate was optimum when cells were grown in the presence of 0. 75 M NaCl, or 0. 4 μM Fe3+, or 1 μM Ni2+. The optimum light intensity and temperature for H<inf>2</inf> production were 30 μmol photons m-2 s-1 and 35 °C, respectively. A two-stage culture of A. halophytica was performed in order to overcome the reduction of cell growth in N-free medium. In the first stage, cells were grown in normal medium to accumulate biomass, and in the second stage, H<inf>2</inf> production by the obtained biomass was induced by growing cells in N-free medium supplemented with various chemicals for 24 h. A. halophytica grown in N-free medium containing various MgSO<inf>4</inf> concentrations had a high H<inf>2</inf> production rate between 11. 432 and 12. 767 μmol H<inf>2</inf> mg chlorophyll a (chl a)-1 h-1, a 30-fold increase compared to cells grown in normal medium. The highest rate of 13. 804 μmol H<inf>2</inf> mg chl a-1 h-1 was obtained when the N-free growth medium contained 0. 4 μM Fe3+. These results suggested the possibility of using A. halophytica and some other halotolerant cyanobacteria thriving under extreme environmental conditions in the sea as potential sources for H<inf>2</inf> production in the future. © 2012 Springer Science+Business Media B.V.

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