Site-directed mutagenesis of the Anabaena sp. strain PCC 7120 nitrogenase active site to increase photobiological hydrogen production.
Cyanobacteria use sunlight and water to produce hydrogen gas (H₂), which is potentially useful as a clean and renewable biofuel. Photobiological H₂ arises primarily as an inevitable by-product of N₂ fixation by nitrogenase, an oxygen-labile enzyme typically containing an iron-molybdenum cofactor (FeMo-co) active site. In Anabaena sp. strain 7120, the enzyme is localized to the microaerobic environment of heterocysts, a highly differentiated subset of the filamentous cells. In an effort to increase H₂ production by this strain, six nitrogenase amino acid residues predicted to reside within 5 Å of the FeMo-co were mutated in an attempt to direct electron flow selectively toward proton reduction in the presence of N₂. Most of the 49 variants examined were deficient in N₂-fixing growth and exhibited decreases in their in vivo rates of acetylene reduction. Of greater interest, several variants examined under an N₂ atmosphere significantly increased their in vivo rates of H₂ production, approximating rates equivalent to those under an Ar atmosphere, and accumulated high levels of H₂ compared to the reference strains. These results demonstrate the feasibility of engineering cyanobacterial strains for enhanced photobiological production of H₂ in an aerobic, nitrogen-containing environment.
Masukawa
Hajime
H
DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA.
Inoue
Kazuhito
K
Sakurai
Hidehiro
H
Wolk
C Peter
CP
Hausinger
Robert P
RP
D000114:Acetylene / Q000378:metabolism; D017033:Anabaena / Q000201:enzymology* / Q000235:genetics; D020134:Catalytic Domain; D006859:Hydrogen / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D009591:Nitrogenase / Q000235:genetics* / Q000378:metabolism*; D010084:Oxidation-Reduction; D052817:Phototrophic Processes; D013472:Sunlight
D050505:Mutant Proteins; D006859:Hydrogen; D009591:Nitrogenase; D009584:Nitrogen; D000114:Acetylene