title: Evidence for protection of nitrogenase from O(2) by colony structure in the aerobic diazotroph Gluconacetobacter diazotrophicus.
abstract: Gluconacetobacter diazotrophicus is an endophytic diazotroph of sugarcane which exhibits nitrogenase activity when growing in colonies on solid media. Nitrogenase activity of G. diazotrophicus colonies can adapt to changes in atmospheric partial pressure of oxygen (pO(2)). This paper investigates whether colony structure and the position of G. diazotrophicus cells in the colonies are components of the bacterium's ability to maintain nitrogenase activity at a variety of atmospheric pO(2) values. Colonies of G. diazotrophicus were grown on solid medium at atmospheric pO(2) of 2 and 20 kPa. Imaging of live, intact colonies by confocal laser scanning microscopy and of fixed, sectioned colonies by light microscopy revealed that at 2 kPa O(2) the uppermost bacteria in the colony were very near the upper surface of the colony, while the uppermost bacteria of colonies cultured at 20 kPa O(2) were positioned deeper in the mucilaginous matrix of the colony. Disruption of colony structure by physical manipulation or due to 'slumping' associated with colony development resulted in significant declines in nitrogenase activity. These results support the hypothesis that G. diazotrophicus utilizes the path-length of colony mucilage between the atmosphere and the bacteria to achieve a flux of O(2) that maintains aerobic respiration while not inhibiting nitrogenase activity.
authors.affiliation: Department of Biology, Carleton University, Ottawa, ON, CanadaK1S 5B61.
authors.forename: Z
authors.initials: Z
authors.lastname: Dong
authors.affiliation: Department of Plant Science, University of Manitoba, Winnipeg, MB, CanadaR3T 2N22.
authors.forename: C D
authors.initials: CD
authors.lastname: Zelmer
authors.affiliation: Department of Biology, Carleton University, Ottawa, ON, CanadaK1S 5B61.
authors.forename: M J
authors.initials: MJ
authors.lastname: Canny
authors.affiliation: Department of Biology, Carleton University, Ottawa, ON, CanadaK1S 5B61.
authors.forename: M E
authors.initials: ME
authors.lastname: McCully
authors.affiliation: Department of Plant Science, University of Manitoba, Winnipeg, MB, CanadaR3T 2N22.
authors.forename: B
authors.initials: B
authors.lastname: Luit
authors.affiliation: Department of Plant Science, University of Manitoba, Winnipeg, MB, CanadaR3T 2N22.
authors.forename: B
authors.initials: B
authors.lastname: Pan
authors.affiliation: Department of Physiology, University of Manitoba, Winnipeg, MB, CanadaR3E 3J73.
authors.forename: R S
authors.initials: RS
authors.lastname: Faustino
authors.affiliation: Department of Physiology, University of Manitoba, Winnipeg, MB, CanadaR3E 3J73.
authors.forename: G N
authors.initials: GN
authors.lastname: Pierce
authors.affiliation: Department of Plant Science, University of Manitoba, Winnipeg, MB, CanadaR3T 2N22.
authors.forename: J K
authors.initials: JK
authors.lastname: Vessey
mesh_terms: D016947:Acetobacteraceae / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology; D000222:Adaptation, Physiological; D001274:Atmospheric Pressure; D015169:Colony Count, Microbial; D003470:Culture Media; D018613:Microscopy, Confocal; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D010313:Partial Pressure
chemical_list: D003470:Culture Media; D009591:Nitrogenase; D010100:Oxygen