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See detailControl of hydrogen photoproduction by the proton gradient generated by cyclic electron flow in Chlamydomonas reinhardtii.
Tolleter, Dimitri; Ghysels, Bart ULg; Alric, Jean et al

in Plant Cell (2011), 23(7), 2619-30

Hydrogen photoproduction by eukaryotic microalgae results from a connection between the photosynthetic electron transport chain and a plastidial hydrogenase. Algal H(2) production is a transitory ... [more ▼]

Hydrogen photoproduction by eukaryotic microalgae results from a connection between the photosynthetic electron transport chain and a plastidial hydrogenase. Algal H(2) production is a transitory phenomenon under most natural conditions, often viewed as a safety valve protecting the photosynthetic electron transport chain from overreduction. From the colony screening of an insertion mutant library of the unicellular green alga Chlamydomonas reinhardtii based on the analysis of dark-light chlorophyll fluorescence transients, we isolated a mutant impaired in cyclic electron flow around photosystem I (CEF) due to a defect in the Proton Gradient Regulation Like1 (PGRL1) protein. Under aerobiosis, nonphotochemical quenching of fluorescence (NPQ) is strongly decreased in pgrl1. Under anaerobiosis, H(2) photoproduction is strongly enhanced in the pgrl1 mutant, both during short-term and long-term measurements (in conditions of sulfur deprivation). Based on the light dependence of NPQ and hydrogen production, as well as on the enhanced hydrogen production observed in the wild-type strain in the presence of the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone, we conclude that the proton gradient generated by CEF provokes a strong inhibition of electron supply to the hydrogenase in the wild-type strain, which is released in the pgrl1 mutant. Regulation of the trans-thylakoidal proton gradient by monitoring pgrl1 expression opens new perspectives toward reprogramming the cellular metabolism of microalgae for enhanced H(2) production. [less ▲]

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See detailClotridial hydrogenases and the biohydrogen production
Calusinska, Magdalena ULg; Hamilton, Christopher ULg; Masset, Julien ULg et al

Poster (2010, July 01)

Among the large variety of microorganisms capable of fermentative hydrogen production, strict anaerobes such as Clostridium spp. are one of the most widely studied. They produce hydrogen by butyric and ... [more ▼]

Among the large variety of microorganisms capable of fermentative hydrogen production, strict anaerobes such as Clostridium spp. are one of the most widely studied. They produce hydrogen by butyric and mixed-acid fermentations at optimal pH values ranging from 4.5 to 5.5. While fermentative conditions such as substrate type, pH, hydraulic and solid retention time, H2 partial pressure and the concentration of acids produced have been extensively studied and optimized, relatively little is known about the different forms of hydrogenases present in clostridia. Building on previous reports [1, 2] and by analyzing sequenced genomes, we found that [FeFe] hydrogenases are not a homogenous group of enzymes, but exist in multiple forms with different modular structures and are especially abundant in Clostridum spp. [3]. However, among the numerous studies performed on fermentative hydrogen production by Clostridium sp., only a few are specifically concerned with hydrogenases. Even there the authors focus on one type of [FeFe] hydrogenase, (CpI-like) without considering the existence of multiple forms of this enzyme within one species. Therefore, we focused our research on the better characterization of different forms of hydrogenases present in the genus Clostridium. Using newly designed degenerate primers, specific for clostridial hydrogenases, we amplified different hydrogenases from our species of interest. Further, by designing specific qPCR assays we have quantitatively targeted different hydrogenases. By analyzing differential gene expression, according to applied growth conditions, we believe to optimize the hydrogen production process in order to achieve better production rates. To conclude, we think that a a precise knowledge of hydrogen metabolism and hydrogenases is essential to optimization of the biohydrogen production process and should therefore be a goal for future research. [less ▲]

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See detailThe surprising diversity of clostridial hydrogenases: a comparative genomic perspective
Calusinska, Magdalena ULg; Happe, Thomas; Joris, Bernard ULg et al

in Microbiology (2010), 156

Among the large variety of micro-organisms capable of fermentative hydrogen production, strict anaerobes such as members of the genus Clostridium are the most widely studied. They can produce hydrogen by ... [more ▼]

Among the large variety of micro-organisms capable of fermentative hydrogen production, strict anaerobes such as members of the genus Clostridium are the most widely studied. They can produce hydrogen by a reversible reduction of protons accumulated during fermentation to dihydrogen, a reaction which is catalysed by hydrogenases. Sequenced genomes provide completely new insights into the diversity of clostridial hydrogenases. Building on previous reports, we found that [FeFe] hydrogenases are not a homogeneous group of enzymes, but exist in multiple forms with different modular structures and are especially abundant in members of the genus Clostridium. This unusual diversity seems to support the central role of hydrogenases in cell metabolism. In particular, the presence of multiple putative operons encoding multisubunit [FeFe] hydrogenases highlights the fact that hydrogen metabolism is very complex in this genus. In contrast with [FeFe] hydrogenases, their [NiFe] hydrogenase counterparts, widely represented in other bacteria and archaea, are found in only a few clostridial species. Surprisingly, a heteromultimeric Ech hydrogenase, known to be an energy-converting [NiFe] hydrogenase and previously described only in methanogenic archaea and some sulfur-reducing bacteria, was found to be encoded by the genomes of four cellulolytic strains: Clostridum cellulolyticum, Clostridum papyrosolvens, Clostridum thermocellum and Clostridum phytofermentans. [less ▲]

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See detailThe surprising diversity of clostridial hydrogenases: a comparative genomic perspective
Calusinska, Magdalena ULg; Happe, Thomas; Joris, Bernard ULg et al

in Microbiology (2010), 156

Among the large variety of micro-organisms capable of fermentative hydrogen production, strict anaerobes such as members of the genus Clostridium are the most widely studied. They can produce hydrogen by ... [more ▼]

Among the large variety of micro-organisms capable of fermentative hydrogen production, strict anaerobes such as members of the genus Clostridium are the most widely studied. They can produce hydrogen by a reversible reduction of protons accumulated during fermentation to dihydrogen, a reaction which is catalysed by hydrogenases. Sequenced genomes provide completely new insights into the diversity of clostridial hydrogenases. Building on previous reports, we found that [FeFe] hydrogenases are not a homogeneous group of enzymes, but exist in multiple forms with different modular structures and are especially abundant in members of the genus Clostridium. This unusual diversity seems to support the central role of hydrogenases in cell metabolism. In particular, the presence of multiple putative operons encoding multisubunit [FeFe] hydrogenases highlights the fact that hydrogen metabolism is very complex in this genus. In contrast with [FeFe] hydrogenases, their [NiFe] hydrogenase counterparts, widely represented in other bacteria and archaea, are found in only a few clostridial species. Surprisingly, a heteromultimeric Ech hydrogenase, known to be an energy-converting [NiFe] hydrogenase and previously described only in methanogenic archaea and some sulfur-reducing bacteria, was found to be encoded by the genomes of four cellulolytic strains: Clostridum cellulolyticum, Clostridum papyrosolvens, Clostridum thermocellum and Clostridum phytofermentans [less ▲]

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