Gas Exchange in the Filamentous Cyanobacterium <i>Nostoc punctiforme</i> Strain ATCC 29133 and ItsHydrogenase-Deficient Mutant StrainNHM5

  • Pia Lindberg
    Department of Physiological Botany, Evolutionary Biology Centre, Commissariatà l’Energie Atomique (CEA), Uppsala University, SE-752 36 Uppsala, Sweden
  • Peter Lindblad
    Department of Physiological Botany, Evolutionary Biology Centre, Commissariatà l’Energie Atomique (CEA), Uppsala University, SE-752 36 Uppsala, Sweden
  • Laurent Cournac
    Direction des Sciences du Vivant, Département d’Ecophysiologie Végétale et de Microbiologie, Cadarache, DSV, DEVM, Laboratoire d'Ecophysiologie de la Photosynthèse, UMR 6191 CNRS CEA, Université Méditerranée CEA 1000, F-13108 Saint Paul lez Durance Cedex,France

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<jats:title>ABSTRACT</jats:title> <jats:p> <jats:italic>Nostoc punctiforme</jats:italic> ATCC 29133 is a nitrogen-fixing, heterocystous cyanobacterium of symbiotic origin. During nitrogen fixation, it produces molecular hydrogen (H <jats:sub>2</jats:sub> ), which is recaptured by an uptake hydrogenase. Gas exchange in cultures of <jats:italic>N.</jats:italic> <jats:italic>punctiforme</jats:italic> ATCC 29133 and its hydrogenase-free mutant strain NHM5 was studied. Exchange of O <jats:sub>2</jats:sub> , CO <jats:sub>2</jats:sub> , N <jats:sub>2</jats:sub> , and H <jats:sub>2</jats:sub> was followed simultaneously with a mass spectrometer in cultures grown under nitrogen-fixing conditions. Isotopic tracing was used to separate evolution and uptake of CO <jats:sub>2</jats:sub> and O <jats:sub>2</jats:sub> . The amount of H <jats:sub>2</jats:sub> produced per molecule of N <jats:sub>2</jats:sub> fixed was found to vary with light conditions, high light giving a greater increase in H <jats:sub>2</jats:sub> production than N <jats:sub>2</jats:sub> fixation. The ratio under low light and high light was approximately 1.4 and 6.1 molecules of H <jats:sub>2</jats:sub> produced per molecule of N <jats:sub>2</jats:sub> fixed, respectively. Incubation under high light for a longer time, until the culture was depleted of CO <jats:sub>2</jats:sub> , caused a decrease in the nitrogen fixation rate. At the same time, hydrogen production in the hydrogenase-deficient strain was increased from an initial rate of approximately 6 μmol (mg of chlorophyll <jats:italic>a</jats:italic> ) <jats:sup>−1</jats:sup> h <jats:sup>−1</jats:sup> to 9 μmol (mg of chlorophyll <jats:italic>a</jats:italic> ) <jats:sup>−1</jats:sup> h <jats:sup>−1</jats:sup> after about 50 min. A light-stimulated hydrogen-deuterium exchange activity stemming from the nitrogenase was observed in the two strains. The present findings are important for understanding this nitrogenase-based system, aiming at photobiological hydrogen production, as we have identified the conditions under which the energy flow through the nitrogenase can be directed towards hydrogen production rather than nitrogen fixation. </jats:p>

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