Synthetic biology of photosynthesis: redirecting carbon flows towards sustainable bioproduction

In order to develop a strategy to engineer a metabolic module of a microbial species such that it produces a compound of interest, detailed knowledge and understanding of the organisms’ genetic, metabolic and regulatory networks as well as of the interactions between these networks is needed. Efficient and robust production is rarely, if ever, the result of a straightforward transfer of gene(s) for the very reason that the activity of new enzymes disturbs the delicate balance between intracellular metabolites, enzyme activities and regulatory devices that have evolved to optimize the cell's ultimate function: to survive and proliferate. The Photanol technology is based on the capacity of a phototrophic prokaryote to capture and reduce CO2 to (phosphorylated) sugars by (sun)light energy dependent mechanisms with the capacity of chemotrophic bacteria to ferment these sugars to a wide range of useful compounds. Essentially, a fermentative pathway is (chromosomally) introduced in the photosynthetic organism and the substrate for that pathway is provided by the cell's CO2 fixing and subsequent Calvin cycle activity. Proof of principle for the concept has been provided for three compounds. However, production affects the cell's physiology often adversely and in an unpredicted manner. We will demonstrate how further analysis of the genetic, metabolic and physiological effects (i.e. how Synthetic Systems Biology) may lead the way to design a properly and robustly performing production system that satisfies the demands for stability, economic feasibility and sustainability.