title: Contrasted reactivity to oxygen tensions in Frankia sp. strain CcI3 throughout nitrogen fixation and assimilation.
abstract: Reconciling the irreconcilable is a primary struggle in aerobic nitrogen-fixing bacteria. Although nitrogenase is oxygen and reactive oxygen species-labile, oxygen tension is required to sustain respiration. In the nitrogen-fixing Frankia, various strategies have been developed through evolution to control the respiration and nitrogen-fixation balance. Here, we assessed the effect of different oxygen tensions on Frankia sp. strain CcI3 growth, vesicle production, and gene expression under different oxygen tensions. Both biomass and vesicle production were correlated with elevated oxygen levels under both nitrogen-replete and nitrogen-deficient conditions. The mRNA levels for the nitrogenase structural genes (nifHDK) were high under hypoxic and hyperoxic conditions compared to oxic conditions. The mRNA level for the hopanoid biosynthesis genes (sqhC and hpnC) was also elevated under hyperoxic conditions suggesting an increase in the vesicle envelope. Under nitrogen-deficient conditions, the hup2 mRNA levels increased with hyperoxic environment, while hup1 mRNA levels remained relatively constant. Taken together, these results indicate that Frankia protects nitrogenase by the use of multiple mechanisms including the vesicle-hopanoid barrier and increased respiratory protection.
authors.affiliation: Laboratoire Microorganismes et Biomolécules Actives, Université Tunis El Manar (FST) and Université Carthage (INSAT), Campus Universitaire, 2092 Tunis, Tunisia ; Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, 46 College Road, Durham, NH 03824-2617, USA.
authors.forename: Faten
authors.initials: F
authors.lastname: Ghodhbane-Gtari
authors.affiliation: Laboratoire Microorganismes et Biomolécules Actives, Université Tunis El Manar (FST) and Université Carthage (INSAT), Campus Universitaire, 2092 Tunis, Tunisia.
authors.forename: Karima
authors.initials: K
authors.lastname: Hezbri
authors.affiliation: Laboratoire Microorganismes et Biomolécules Actives, Université Tunis El Manar (FST) and Université Carthage (INSAT), Campus Universitaire, 2092 Tunis, Tunisia.
authors.forename: Amir
authors.initials: A
authors.lastname: Ktari
authors.affiliation: Laboratoire Microorganismes et Biomolécules Actives, Université Tunis El Manar (FST) and Université Carthage (INSAT), Campus Universitaire, 2092 Tunis, Tunisia.
authors.forename: Imed
authors.initials: I
authors.lastname: Sbissi
authors.affiliation: Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, 46 College Road, Durham, NH 03824-2617, USA.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Beauchemin
authors.affiliation: Laboratoire Microorganismes et Biomolécules Actives, Université Tunis El Manar (FST) and Université Carthage (INSAT), Campus Universitaire, 2092 Tunis, Tunisia ; Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, 46 College Road, Durham, NH 03824-2617, USA.
authors.forename: Maher
authors.initials: M
authors.lastname: Gtari
authors.affiliation: Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, 46 College Road, Durham, NH 03824-2617, USA.
authors.forename: Louis S
authors.initials: LS
authors.lastname: Tisa
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis; D040161:Frankia / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D009586:Nitrogen Fixation / Q000502:physiology*; D009591:Nitrogenase / Q000096:biosynthesis; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D012329:RNA, Bacterial / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis
chemical_list: D001426:Bacterial Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D009591:Nitrogenase; D010100:Oxygen