title: Protons and pleomorphs: aerobic hydrogen production in Azotobacters.
abstract: As obligate aerobic soil organisms, the ability of Azotobacter species to fix nitrogen is unusual given that the nitrogenase complex requires a reduced cellular environment. Molecular hydrogen is an unavoidable byproduct of the reduction of dinitrogen; at least one molecule of H2 is produced for each molecule of N2 fixed. This could be considered a fault in nitrogenase efficiency, essentially a waste of energy and reducing equivalents. Wild-type Azotobacter captures this hydrogen and oxidizes it with its membrane-bound uptake hydrogenase complex. Strains lacking an active hydrogenase complex have been investigated for their hydrogen production capacities. What is the role of H2 in the energy metabolism of nitrogen-fixing Azotobacter? Is hydrogen production involved in Azotobacter species' protection from or tolerance to oxygen, or vice versa? What yields of hydrogen can be expected from hydrogen-evolving strains? Can the yield of hydrogen be controlled or increased by changing genetic, environmental, or physiological conditions? We will address these questions in the following mini-review.
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, 4554 Thomas Hall, Campus Box 7615, Raleigh, NC, 27695, USA.
authors.forename: Jesse D
authors.initials: JD
authors.lastname: Noar
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, 4554 Thomas Hall, Campus Box 7615, Raleigh, NC, 27695, USA. jbbarcen@ncsu.edu.
authors.forename: José M
authors.initials: JM
authors.lastname: Bruno-Bárcena
mesh_terms: D001395:Azotobacter / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D052836:Heterotrophic Processes; D006859:Hydrogen / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D011522:Protons; D012988:Soil Microbiology
chemical_list: D011522:Protons; D006859:Hydrogen
keywords: Aerobe; Azotobacter; Heterotroph; Hydrogen; Nitrogenase