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Modified natural seawater as growth medium for the halotolerant cyanobacterium Aphanothece halophytica to increase lipid content for biodiesel production
(2025-02-01)
Thongtha, Sitthichai
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Aryusuk, Kornkanok
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Kittiwongwattana, Chokchai
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Incharoensakdi, Aran
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Phunpruch, Saranya
Biodiesel derived from cyanobacterial oils becomes attractive as an efficient renewable energy. The present study aims to optimize growth and lipid production of the halotolerant unicellular cyanobacterium Aphanothece halophytica cultivated in natural seawater. In this study A. halophytica was able to grow in natural seawater when supplemented with low concentration of NaNO<inf>3</inf>, whereas no growth occurred without supplementation. The specific growth rate of 0.230 day-1 and cell concentration of 25.17 x 106 cells mL-1 were achieved in A. halophytica cultivated in natural seawater supplemented with 17.6 mM NaNO<inf>3</inf> and Turk Island salt solution (suitable natural seawater; SNSW) for 14 days. This growth rate was comparable to that of cells grown in normal BG11 plus Turk Island salt solution. The lipid content and fatty acid profiles of A. halophytica varied with changes in NaCl concentrations. The highest lipid content of 50.47 % and lipid productivity of 48.33 mg L-1 day-1 were obtained in cultures supplemented with 1.89 mmol C-atom L-1 glucose and 0.75 M NaCl. The optimal medium pH and cultivation temperature for lipid production was 7.5 and 25-35 °C, respectively. When cultivating A. halophytica in optimized SNSW with various NaCl concentrations, the highest contents of linoleic and linolenic acids, and the lowest contents of palmitic, stearic, and oleic acids were observed with 0.75 M NaCl. In contrast, cultures grown in optimized SNSW with 0.5 M NaCl showed fatty acid methyl ester profiles rich in monounsaturated fatty acids, which are favorable for high-quality biodiesel production.
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Enhanced dark fermentative H2 production by agar-immobilized cyanobacterium Aphanothece halophytica
(2019-10-01)
Pansook, Sunisa
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Incharoensakdi, Aran
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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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Identification of bidirectional hydrogenase genes and their co-transcription in unicellular halotolerant cyanobacterium Aphanothece halophytica
(2016-04-01)
Phunpruch, Saranya
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Taikhao, Samart
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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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Factors affecting biohydrogen production by unicellular halotolerant cyanobacterium Aphanothece halophytica
(2013-04-01)
Taikhao, Samart
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Junyapoon, Suwannee
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Incharoensakdi, Aran
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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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