Tailoring cyanobacteria for biofuel

Tailoring cyanobacteria for biofuel

Environmental as well as economic reasons call for a sustainable alternative for the use of fossil fuels. Light energy harnessed by photosynthetic organisms provides an attractive mean for biofuel production. Biofuels derived from sugars and oils found in arable crops have already been commercialized; however, these processes are not cost-effective. Additionally, the impact of these ‘first generation biofuels’ on food supply and price have raised ethical questions and encouraged a search for an alternative biomass source. Cyanobacteria offer an efficient mean for biofuel production that is not associated with the current problems of land-based-biofuel feedstock. They combine the benefits of fast growing simple microorganisms with a cost effective mode of growth based on light energy and mineral nutrients. We aim at establishing a simple process for bioethanol by yeast fermentation. We modify cyanobacteria to increase glycogen level as raw material for bioethanol. (Manuscript in preparation).

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Schematic presentation of glycogen metabolism.
ADP-glucose pyrophosphorylase (GlgC) catalyzes the first committed step in glycogen synthesis by converting glucose-1- phosphate (Glc-1-P) to ADP-Glucose (ADPG).  The next two sequential steps are catalyzed by glycogen synthase (GlgA), and branching enzyme (GlgB), respectively. Carbon skeletons are fed into this pathway, initially by the activity of Ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (RuBisCO) that catalyzes the CO2 fixation step of the Calvin-Benson-Bassham (CBB) cycle. The RuBisCO product, 3-phosphoglycerate (PGA), is stepwise converted into glyceraldehyde 3-phosphate (GAP) and further on by gluconeogenic enzymes (marked by an asterisk) to glucose and Glc-1-P. Glycogen catabolism is mediated by glycogen phosphorylase (GlgP) and debranching enzymes (The cyanobacterium used in the proposed study, Synechococcus elongatus possesses two homologs of debranching enzymes annotated, GlgX and DBE).  (This scheme is modified from Wilson et al. FEMS Microbiol Rev, 2010. 34(6): p. 952-85.)