title: Ecological rationale for H2metabolism during aquatic blooms of the cyanobacterium Anabaena.
abstract: Nitrogenase-produced H2serves to remove excess intracellular O2during vigorous growth periods (blooms) of the nuisance cyanobacterium Anabaena. In two naturally-occurring species, A. oscillarioides and A. spiroides, nitrogen fixation (acetylene reduction) showed a high degree of resistance to O2inactivation. Under the influence of supersaturated O2concentrations, commonly encountered in lake blooms, elevated cellular ATP levels and enhanced uptake hydrogenase and nitrogenase activities were observed in actively growing filaments. Oxygen enhancement of nitrogenase activity appears mediated through localized uptake hydrogenase reactions. Hydrogen assimilated by hydrogenase is combined with O2in a "Knallgas" reaction, leading to the formation of H2O and ATP via a respiratory chain. This combination of activities appears poised at O2removal and allows Anabaena to dominate O2supersaturated surface waters while maintaining optimal nitrogenase activity. Hence, instead of being a wasteful dissipation of reducing power, H2evolution via nitrogenase ultimately affords protection from O2while constituting a source of ATP through subsequent H2metabolism.
authors.affiliation: Institute of Marine Sciences, University of North Carolina, 28557, Morehead City, North Carolina, USA.
authors.forename: Hans W
authors.initials: HW
authors.lastname: Paerl