title: Microoxic Niches within the Thylakoid Stroma of Air-Grown Chlamydomonas reinhardtii Protect [FeFe]-Hydrogenase and Support Hydrogen Production under Fully Aerobic Environment.
abstract: Photosynthetic hydrogen production in the microalga Chlamydomonas reinhardtii is catalyzed by two [FeFe]-hydrogenase isoforms, HydA1 and HydA2, both irreversibly inactivated upon a few seconds exposure to atmospheric oxygen. Until recently, it was thought that hydrogenase is not active in air-grown microalgal cells. In contrast, we show that the entire pool of cellular [FeFe]-hydrogenase remains active in air-grown cells due to efficient scavenging of oxygen. Using membrane inlet mass spectrometry, (18)O2 isotope, and various inhibitors, we were able to dissect the various oxygen uptake mechanisms. We found that both chlororespiration, catalyzed by plastid terminal oxidase, and Mehler reactions, catalyzed by photosystem I and Flavodiiron proteins, significantly contribute to oxygen uptake rate. This rate is considerably enhanced with increasing light, thus forming local anaerobic niches at the proximity of the stromal face of the thylakoid membrane. Furthermore, we found that in transition to high light, the hydrogen production rate is significantly enhanced for a short duration (100 s), thus indicating that [FeFe]-hydrogenase functions as an immediate sink for surplus electrons in aerobic as well as in anaerobic environments. In summary, we show that an anaerobic locality in the chloroplast preserves [FeFe]-hydrogenase activity and supports continuous hydrogen production in air-grown microalgal cells.
authors.affiliation: Department of Molecular Biology and Ecology of Plants, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
authors.forename: Oded
authors.initials: O
authors.lastname: Liran
authors.affiliation: Department of Molecular Biology and Ecology of Plants, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
authors.forename: Rinat
authors.identifier: 0000-0002-6163-1469
authors.initials: R
authors.lastname: Semyatich
authors.affiliation: Department of Molecular Biology and Ecology of Plants, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
authors.forename: Yuval
authors.initials: Y
authors.lastname: Milrad
authors.affiliation: Department of Molecular Biology and Ecology of Plants, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
authors.forename: Haviva
authors.initials: H
authors.lastname: Eilenberg
authors.affiliation: Department of Molecular Biology and Ecology of Plants, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
authors.forename: Iddo
authors.initials: I
authors.lastname: Weiner
authors.affiliation: Department of Molecular Biology and Ecology of Plants, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel iftachy@tau.ac.il.
authors.forename: Iftach
authors.identifier: 0000-0003-0177-0624
authors.initials: I
authors.lastname: Yacoby
mesh_terms: D000332:Aerobiosis; D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism*; D000693:Anaerobiosis; D002478:Cells, Cultured; D016825:Chlamydomonas reinhardtii / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000201:enzymology / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000235:genetics / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D013058:Mass Spectrometry / Q000379:methods; D009154:Mutation; D010088:Oxidoreductases / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010103:Oxygen Isotopes / Q000378:metabolism; D045331:Photosystem I Protein Complex / Q000378:metabolism; D020524:Thylakoids / Q000378:metabolism*
chemical_list: D020418:Algal Proteins; D007506:Iron-Sulfur Proteins; D007527:Isoenzymes; D010103:Oxygen Isotopes; D045331:Photosystem I Protein Complex; D006859:Hydrogen; D010088:Oxidoreductases; C118830:iron hydrogenase; D006864:Hydrogenase; D010100:Oxygen