Engineering carbon-conserving synthetic pathways for assimilation and conversion of C5/C6 carbon sources into added value chemicals

Présenté au: 3. International Conference on Enzymology and Molecular BiologyDate: 05-06 Mars 2018 Lieu: LondresThe development of carbon efficient pathways for added value (bio)chemicals production is the essence of White Biotechnology. The limit of carbon conservation in all (bio)chemical syntheses is determined by the electron balance in substrate(s) and product(s). Natural pathways do not have often the stoichiometric capacity to produce a value-added compound at yields that correspond to the thermodynamic maximum. A good example of this lack of stoichiometric efficiency is the bioproduction of glycolic acid (GA), a two carbon compound of considerable industrial interest notably in cosmetics and biodegradable polymers. We addressed this objective by employing the following strategies. Firstly, we reconsider a new pathway for C5 assimilation that relies on the carbon-conserving aldolytic cleavage of X1P or R1P to yield the C2 compound glycolaldehyde and the C3 DHAP compound by expression of a ketohexo-1-kinase (Khk-C) and aldolase (Aldo-B). Glycoaldehyde is then either reduced into ethylene glycol or oxidized into glycolic acid usingh endogenous reductase/dehydrogenase. With this approach, EG and GA at yield close to maximal of 1 mol/mol sugar have been obtained. This synthetic pathway was then coimbined with the natural glyoxylate shunt, to yield a production of GA ∼30% from a xylose/glucose mixture (66%/33%) 30% higher than using the sole natural pathway. Yet, as this strategy does not avoid a loss of carbon at the level of pyruvate, we created a cycling route that overcome this loss and which allowed both hexoses and pentoses to be converted into glycolic acid at their highest theoretical yiel