System biology approach to increase hydrogen production in C. reinhardtii
Jörg Toepel, Julia Beckmann, Anja Doebbe, Anh-Vu Nguyen and Olaf Kruse
Bielefeld University, Algae Biotechnology Group, Universitätsstrasse 27, 33615 Bielefeld, Germany
C. reinhardtii belongs to a selected group of organisms which have evolved the ability to use solar energy to recombine H+ and e- via the hydrogenase enzymes to produce hydrogen. The process of sulphur deprivation induces bio H2 production in C. reinhardtii and involve complex interactions between different metabolic pathways located both in the chloroplast and the mitochondria. When cells encounter anaerobic growth conditions, metabolic pathways are remodelled in response to oxygen and sulphur depletion. We used a system biology approach to analyze hydrogen production in C. reinhardtii in more detail. Therefore we analyzed the transcriptome, proteome and metabolome under anaerobic conditions for the wildtype CC406 and Stm6Glc4 cultures and created a model deduced of the data to find bottle necks and determine individual key transcripts and proteins necessary for Chlamydomonas hydrogen metabolism. This methodology allows to follow changes in transcript, protein and metabolome levels under different H2ase enzyme activity conditions during a time course experiment. In this way it provides complete sets of data before H2 production compared to high H2 producing phase but also direct comparison between wildtype CC-406 and high H2 producing mutant Stm6Glc4 over a wide time scale.
Our data showed an overall adaptation to anaerobis and sulphate depletion, e.g. a decreased photosynthetic activity, increased fermentation and reduced activity of the tricarbonacid cycle, pentose phosphate pathway and glycolysis. The cells accumulate ethanol, formate and lipids during the hydrogen production phase and used external added acetate for growth. Additionally, several new potential target genes and competitive electron sinks were detected.
The data can be used in follow up studies to increase electron flow towards the hydrogenases and to increase hydrogen production to lift it up to commercial usable level.
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