title: Metabolic adaptations in a H2 producing heterocyst-forming cyanobacterium: potentials and implications for biological engineering.
abstract: Nostoc punctiforme ATCC 29133 is a photoautotrophic cyanobacterium with the ability to fix atmospheric nitrogen and photoproduce hydrogen through the enzyme nitrogenase. The H(2) produced is reoxidized by an uptake hydrogenase. Inactivation of the uptake hydrogenase in N. punctiforme leads to increased H(2) release but unchanged rates of N(2) fixation, indicating redirected metabolism. System-wide understanding of the mechanisms of this metabolic redirection was obtained using complementary quantitative proteomic approaches, at both the filament and the heterocyst level. Of the total 1070 identified and quantified proteins, 239 were differentially expressed in the uptake hydrogenase mutant (NHM5) as compared to wild type. Our results indicate that the inactivation of uptake hydrogenase in N. punctiforme changes the overall metabolic equilibrium, affecting both oxygen reduction mechanisms in heterocysts as well as processes providing reducing equivalents for metabolic functions such as N(2) fixation. We identify specific metabolic processes used by NHM5 to maintain a high rate of N(2) fixation, and thereby potential targets for further improvement of nitrogenase based H(2) photogeneration. These targets include, but are not limited to, components of the oxygen scavenging capacity and cell envelope of heterocysts and proteins directly or indirectly involved in reduced carbon transport from vegetative cells to heterocysts.
authors.affiliation: Department of Photochemistry and Molecular Science, The Ångström Laboratories, Uppsala University, SE-751 20 Uppsala, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Ekman
authors.forename: Saw Yen
authors.initials: SY
authors.lastname: Ow
authors.forename: Marie
authors.initials: M
authors.lastname: Holmqvist
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Zhang
authors.forename: Jon
authors.initials: J
authors.lastname: van Wagenen
authors.forename: Phillip C
authors.initials: PC
authors.lastname: Wright
authors.forename: Karin
authors.initials: K
authors.lastname: Stensjö
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D057005:Bioengineering / Q000379:methods*; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism; D002853:Chromatography, Liquid / Q000379:methods; D000458:Cyanobacteria / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D004734:Energy Metabolism; D006859:Hydrogen / Q000378:metabolism*; D013058:Mass Spectrometry / Q000379:methods; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation / Q000502:physiology; D009591:Nitrogenase / Q000235:genetics / Q000378:metabolism; D046937:Nostoc / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D040901:Proteomics / Q000379:methods
chemical_list: D001426:Bacterial Proteins; D002244:Carbon; D006859:Hydrogen; D009591:Nitrogenase; D009584:Nitrogen