Improved Photobiological H2 Production in Engineered Green Algal Cells*
- Olaf Kruse‡1,
- Jens Rupprecht§,
- Klaus-Peter Bader‡,
- Skye Thomas-Hall¶,
- Peer Martin Schenk¶,
- Giovanni Finazzi∥ and
- Ben Hankamer§
- ‡Department of Biology VIII, Molecular Cell Physiology, University Bielefeld, 33501 Bielefeld, Germany, ∥UPR 1261-CNRS Institut de Biologie Physico-Chimique, 75005 Paris, France, §Institute for Molecular Bioscience, University of Queensland, St. Lucia Campus, Queensland 4072, Australia, and ¶Faculty of Biological and Chemical Sciences, University of Queensland, Queensland 4072, Australia
- ↵1 To whom correspondence should be addressed. Tel.: 49-521-1065611; Fax: 49-521-1066410; E-mail: olaf.kruse{at}uni-bielefeld.de.
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, ∼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 = ∼5 times the WT). Stm6 therefore represents an important step toward the development of future solar-powered H2 production systems.
- Received April 8, 2005.
- Revision received August 12, 2005.
- The American Society for Biochemistry and Molecular Biology, Inc.











