title: Metabolic pathways for photobiological hydrogen production by nitrogenase- and hydrogenase-containing unicellular cyanobacteria Cyanothece.
abstract: Current biotechnological interest in nitrogen-fixing cyanobacteria stems from their robust respiration and capacity to produce hydrogen. Here we quantify both dark- and light-induced H(2) effluxes by Cyanothece sp. Miami BG 043511 and establish their respective origins. Dark, anoxic H(2) production occurs via hydrogenase utilizing reductant from glycolytic catabolism of carbohydrates (autofermentation). Photo-H(2) is shown to occur via nitrogenase and requires illumination of PSI, whereas production of O(2) by co-illumination of PSII is inhibitory to nitrogenase above a threshold pO(2). Carbohydrate also serves as the major source of reductant for the PSI pathway mediated via nonphotochemical reduction of the plastoquinone pool by NADH dehydrogenases type-1 and type-2 (NDH-1 and NDH-2). Redirection of this reductant flux exclusively through the proton-coupled NDH-1 by inhibition of NDH-2 with flavone increases the photo-H(2) production rate by 2-fold (at the expense of the dark-H(2) rate), due to production of additional ATP (via the proton gradient). Comparison of photobiological hydrogen rates, yields, and energy conversion efficiencies reveals opportunities for improvement.
authors: Department of Chemistry and Chemical Biology, Waksman Institute of Microbiology, Rutgers University, Piscataway, New Jersey 08854, USA.
authors: Nicholas J
authors: NJ
authors: Skizim
authors: Gennady M
authors: GM
authors: Ananyev
authors: Anagha
authors: A
authors: Krishnan
authors: G Charles
authors: GC
authors: Dismukes
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D046889:Cyanothece / Q000235:genetics / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000235:genetics / Q000378:metabolism*; D009591:Nitrogenase / Q000235:genetics / Q000378:metabolism*; D045331:Photosystem I Protein Complex / Q000235:genetics / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D006859:Hydrogen; D006864:Hydrogenase; D009591:Nitrogenase