Hydrogen production by Chlamydomonas reinhardtii revisited: Rubisco as a biotechnological target
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Hydrogen production by C. reinhardtii seems a promising alternative as a source of non-polluting biofuel. Hydrogen is generated as a result of combining free protons and electrons (supplied by ferredoxin) through the activity of an oxygen-sensitive hydrogenase. Thus, substantial hydrogen production is only observed in the light under anaerobic conditions. These require a reduced rate of photosynthetic oxygen evolution which is usually achieved by impairing photosystem II through sulphur starvation. Several approaches have been conducted to enhance and extend hydrogen production by addressing problems such as the mechanism of hydrogenase inhibition by oxygen, the stressing impact on the cells of the culture conditions, the use of starch as an alternate source of electrons under reduced photosynthetic activity, and the need of maintaining a balance between oxygen evolution and consumption. The photosynthetic enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) appears as suitable objective for biotechnological optimization of hydrogen production because of its relevance controlling the hydrogenase main competitor electron sink (the Calvin-Benson cycle), as well as starch accumulation and photorespiratory oxygen consumption. Possible strategies for increasing hydrogen generation based on alteration of Rubisco properties and/or catabolism through site-directed mutagenesis are discussed.
KeywordsBiofuel Chlamydomonas reinhardtii Chloroplast metabolism Hydrogen production Hydrogenase Rubisco
Work in the authors laboratories are supported by grants BIO2007-67708-C04-02 from MEC (Spain), BFU2009-11965 from MICINN (Spain) and PTDC/EBB-EBI/102728/2008 (Portugal).
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