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Improved Photobiological H2 Production in Engineered Green Algal Cells

2005; Elsevier BV; Volume: 280; Issue: 40 Linguagem: Inglês

10.1074/jbc.m503840200

1083-351X

Olaf Kruse, Jens Rupprecht, K. P. Bader, Skye R. Thomas‐Hall, Peer M. Schenk, Giovanni Finazzi, Ben Hankamer,

Metalloenzymes and iron-sulfur proteins

Oxygenic photosynthetic organisms use solar energy to split water (H 2 O) 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 (H 2 ) production via the chloroplast hydrogenases HydA1 and A2 (H 2 ase). This process occurs under anaerobic conditions and provides a biological basis for solar-driven H 2 production. However, its relatively poor yield is a major limitation for the economic viability of this process. To improve H 2 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 H 2 ase. Selected strains were further screened for increased H 2 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 O 2 concentration (40% of the wild type (WT)), resulting in reduced inhibition of H 2 ase activation. The H 2 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 H 2 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 H 2 production systems.