title: Hydrogen photoproduction by immobilized n2-fixing cyanobacteria: understanding the role of the uptake hydrogenase in the long-term process.
abstract: We have investigated two approaches to enhance and extend H2 photoproduction yields in heterocystous, N2-fixing cyanobacteria entrapped in thin alginate films. In the first approach, periodic CO2 supplementation was provided to alginate-entrapped, N-deprived cells. N deprivation led to the inhibition of photosynthetic activity in vegetative cells and the attenuation of H2 production over time. Our results demonstrated that alginate-entrapped ΔhupL cells were considerably more sensitive to high light intensity, N deficiency, and imbalances in C/N ratios than wild-type cells. In the second approach, Anabaena strain PCC 7120, its ΔhupL mutant, and Calothrix strain 336/3 films were supplemented with N2 by periodic treatments of air, or air plus CO2. These treatments restored the photosynthetic activity of the cells and led to a high level of H2 production in Calothrix 336/3 and ΔhupL cells (except for the treatment air plus CO2) but not in the Anabaena PCC 7120 strain (for which H2 yields did not change after air treatments). The highest H2 yield was obtained by the air treatment of ΔhupL cells. Notably, the supplementation of CO2 under an air atmosphere led to prominent symptoms of N deficiency in the ΔhupL strain but not in the wild-type strain. We propose that uptake hydrogenase activity in heterocystous cyanobacteria not only supports nitrogenase activity by removing excess O2 from heterocysts but also indirectly protects the photosynthetic apparatus of vegetative cells from photoinhibition, especially under stressful conditions that cause an imbalance in the C/N ratio in cells.
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, Finland.
authors.forename: Sergey
authors.initials: S
authors.lastname: Kosourov
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Leino
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, Finland.
authors.forename: Gayathri
authors.initials: G
authors.lastname: Murukesan
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, Finland.
authors.forename: Fiona
authors.initials: F
authors.lastname: Lynch
authors.affiliation: Division of Microbiology and Biotechnology, Department of Food and Environmental Sciences, University of Helsinki, Helsinki, Finland.
authors.forename: Kaarina
authors.initials: K
authors.lastname: Sivonen
authors.affiliation: Institute of Basic Biological Problems, RAS, Pushchino, Russia.
authors.forename: Anatoly A
authors.initials: AA
authors.lastname: Tsygankov
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, Finland.
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, Finland allahve@utu.fi.
authors.forename: Yagut
authors.initials: Y
authors.lastname: Allahverdiyeva
mesh_terms: D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D018914:Cells, Immobilized / Q000201:enzymology* / Q000378:metabolism*; D000458:Cyanobacteria / Q000201:enzymology* / Q000378:metabolism* / Q000528:radiation effects; D006859:Hydrogen / Q000378:metabolism*; D008027:Light; D009584:Nitrogen / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism*; D010788:Photosynthesis
chemical_list: D002245:Carbon Dioxide; D002244:Carbon; D006859:Hydrogen; D010088:Oxidoreductases; C029746:uptake hydrogenase; D009584:Nitrogen