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Author: search.filters.author.Chinchusak, NattanonSubject: search.filters.subject.Aphanothece halophytica

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    Dark fermentative hydrogen production and transcriptional analysis of genes involved in the unicellular halotolerant cyanobacterium Aphanothece halophytica under nitrogen and potassium deprivation
    (2023-01-06)
    Chinchusak, Nattanon
    ;
    Incharoensakdi, Aran
    ;
    Phunpruch, Saranya
    The unicellular halotolerant cyanobacterium Aphanothece halophytica is known as a potential hydrogen (H<inf>2</inf>) producer. This study aimed to investigate the enhancement of H<inf>2</inf> production under nutrient deprivation. The results showed that nitrogen and potassium deprivation induced dark fermentative H<inf>2</inf> production by A. halophytica, while no differences in H<inf>2</inf> production were found under sulfur and phosphorus deprivation. In addition, deprivation of nitrogen and potassium resulted in the highest H<inf>2</inf> production in A. halophytica due to the stimulation of hydrogenase activity. The effect of adaptation time under nitrogen and potassium deprivation on H<inf>2</inf> production was investigated. The results showed that the highest H<inf>2</inf> accumulation of 1,261.96 ± 96.99 µmol H<inf>2</inf> g dry wt<sup>−1</sup> and maximum hydrogenase activity of 179.39 ± 8.18 µmol H<inf>2</inf> g dry wt<sup>−1</sup> min<sup>−1</sup> were obtained from A. halophytica cells adapted in the nitrogen- and potassium-deprived BG11 medium supplemented with Turk Island salt solution (BG11<inf>0</inf>-K) for 48 h. An increase in hydrogenase activity was attributed to the decreased O<inf>2</inf> concentration in the system, due to a reduction of photosynthetic O<inf>2</inf> evolution rate and a promotion of dark respiration rate. Moreover, nitrogen and potassium deprivation stimulated glycogen accumulation and decreased specific activity of pyruvate kinase. Transcriptional analysis of genes involved in H<inf>2</inf> metabolism using RNA-seq confirmed the above results. Several genes involved in glycogen biosynthesis (glgA, glgB, and glgP) were upregulated under both nitrogen and potassium deprivation, but genes regulating enzymes in the glycolytic pathway were downregulated, especially pyk encoding pyruvate kinase. Interestingly, genes involved in the oxidative pentose phosphate pathway (OPP) were upregulated. Thus, OPP became the favored pathway for glycogen catabolism and the generation of reduced nicotinamide adenine dinucleotide phosphate (NADPH), which resulted in an increase in H<inf>2</inf> production under dark anaerobic condition in both nitrogen- and potassium-deprived cells.
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    Enhancement of dark fermentative hydrogen production in nitrogen-deprived halotolerant unicellular cyanobacterium Aphanothece halophytica by treatment with reducing agents
    (2022-12-01)
    Chinchusak, Nattanon
    ;
    Incharoensakdi, Aran
    ;
    Phunpruch, Saranya
    To enhance H<inf>2</inf> production by the halotolerant unicellular cyanobacterium Aphanothece halophytica, effect of various kinds of reducing sugar and reducing agent on H<inf>2</inf> production was investigated. The highest H<inf>2</inf> production rate of 55.80 ± 0.50 μmol H<inf>2</inf> g dry weight<sup>−1</sup> h<sup>−1</sup> was obtained when the cells were incubated in BG11<inf>0</inf> medium containing 0.189 mmol C-atom L<sup>−1</sup> glucose under dark anaerobic condition. This rate was 1.5 folds higher than that without glucose. Among ten reducing agents tested, β-mercaptoethanol, dithiothreitol, L-cysteine and sodium sulfide had high potential as an effective reducing agent to increase H<inf>2</inf> production by A. halophytica. Cells treated with 50 mM sodium sulfide showed the highest H<inf>2</inf> accumulation with 4815.59 ± 194.78 μmol H<inf>2</inf> g dry weight<sup>−1</sup> after 24 h of dark anaerobic incubation. An increase in H<inf>2</inf> production was ascribed to an increase of hydrogenase activity and a decrease of O<inf>2</inf> production rate. This H<inf>2</inf> production yield was approximately 20 folds higher than that without reducing agent. Furthermore, 50 mM sodium sulfide appeared to be non-toxic to A. halophytica cells, since the IC<inf>50</inf> of sodium sulfide was higher than 100 mM. The reduced ferredoxin at 1.5 μM-1.5 mM, NADH and NADPH at 0.15–1.5 mM could support in vitro [NiFe]-H<inf>2</inf>ase activity, demonstrating the ability of these compounds to provide electrons towards [NiFe]-H<inf>2</inf>ase in A. halophytica.