title: Improved photobiological H2 production in engineered green algal cells.
abstract: Oxygenic photosynthetic organisms use solar energy to split water (H2O) into protons (H+), electrons (e-), and oxygen. A select group of photosynthetic microorganisms, including the green alga Chlamydomonas reinhardtii, has evolved the additional ability to redirect the derived H+ and e- to drive hydrogen (H2) production via the chloroplast hydrogenases HydA1 and A2 (H2 ase). This process occurs under anaerobic conditions and provides a biological basis for solar-driven H2 production. However, its relatively poor yield is a major limitation for the economic viability of this process. To improve H2 production in Chlamydomonas, we have developed a new approach to increase H+ and e- supply to the hydrogenases. In a first step, mutants blocked in the state 1 transition were selected. These mutants are inhibited in cyclic e- transfer around photosystem I, eliminating possible competition for e- with H2ase. Selected strains were further screened for increased H2 production rates, leading to the isolation of Stm6. This strain has a modified respiratory metabolism, providing it with two additional important properties as follows: large starch reserves (i.e. enhanced substrate availability), and a low dissolved O2 concentration (40% of the wild type (WT)), resulting in reduced inhibition of H2ase activation. The H2 production rates of Stm6 were 5-13 times that of the control WT strain over a range of conditions (light intensity, culture time, +/- uncoupler). Typically, approximately 540 ml of H2 liter(-1) culture (up to 98% pure) were produced over a 10-14-day period at a maximal rate of 4 ml h(-1) (efficiency = approximately 5 times the WT). Stm6 therefore represents an important step toward the development of future solar-powered H2 production systems.
authors.affiliation: Department of Biology VIII, Molecular Cell Physiology, University Bielefeld, 33501 Bielefeld, Germany. olaf.kruse@uni-bielefeld.de
authors.forename: Olaf
authors.initials: O
authors.lastname: Kruse
authors.forename: Jens
authors.initials: J
authors.lastname: Rupprecht
authors.forename: Klaus-Peter
authors.initials: KP
authors.lastname: Bader
authors.forename: Skye
authors.initials: S
authors.lastname: Thomas-Hall
authors.forename: Peer Martin
authors.initials: PM
authors.lastname: Schenk
authors.forename: Giovanni
authors.initials: G
authors.lastname: Finazzi
authors.forename: Ben
authors.initials: B
authors.lastname: Hankamer
mesh_terms: D000818:Animals; D001674:Bioelectric Energy Sources; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000502:physiology*; D005818:Genetic Engineering; D006859:Hydrogen; D006864:Hydrogenase / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D010100:Oxygen / Q000378:metabolism; D010641:Phenotype; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology
chemical_list: D006859:Hydrogen; D006864:Hydrogenase; D010100:Oxygen