ERA-NET: Z-Fuels - A novel bacterial system with integrated micro-bubble distillation for the production of acetaldehyde

Butanol is a desirable biofuel as its characteristics most closely match gasoline and allows using current gasoline fuel infrastructure and vehicles. Its production, however, is limited by the energy requirements needed for its synthesis from ethanol and the poor yields. Existing microbial bioprocesses for the synthesis of butanol has low efficiency. A known intermediary in butanol production is acetaldehyde, the production of which involves high cost. Microorganisms exist which can produce acetaldehyde directly. The bacterium Zymomonas mobilis performs the most rapid ethanol synthesis and produces the highest ethanol yields among all known microorganisms. Acetaldehyde is the direct metabolic precursor of ethanol. Under vigorous aeration the respiratory chain of Z. mobilis can serve for acetaldehyde production, by draining reducing equivalents from the alcohol dehydrogenase reaction. However, the process yields and productivity are restricted by the metabolic inhibition caused by the produced acetaldehyde. Continuously and effective removal of acetaldehyde during the metabolic process will alleviate the inhibition and give higher yields The concept of the Z-Fuels project is to design, construct and operate a bacterial process, based on genetically engineered Z. mobilis with an integrated microbubble distillation system enabling continuous removal of the product.

Tekst kopiert fra egen sluttrapport: We have advanced basic Zymomonas biology (papers 5 and 6) and also generated new knowledge of intracellular physiological state at different conditions which is important for future metabolic engineering of Zymomonas mobilis as important biofuel cell factory (papers 1 and 2). Our approach with in-depth characterization of core metabolism is generic and can also be applied as template for metabolic engineering of other microbial cell factories. We have further refined our quantitative metabolomics technology and a large milestone for us was the establishment of a quantitative LC-MS/MS method using 13C-Isotope dilution strategy for NAD metabolites (paper 3) and validation of it on several important prokaryotic and eukaryotic biological model systems (paper 4).

Butanol is a desirable biofuel as its characteristics most closely match gasoline and allows using current gasoline fuel infrastruture and vehicles. Its production however is limited by the energy requirements needed for its synthesis from ethanol and the poor yields. A known intermediary in butanol production is acetaldehyde, the production of which involves high cost. Microorganisms exist which can produce acetaldehyde directly. The bacterium Zymomonas mobilis is the most prominent example, which bears a great potential for bioprocess improvement by metabolic engineering. However, the process yields and productivity are restricted by the metabolic inhibition caused by the produced acetaldehyde. The concept of the present project is to design, construct and operate a bacterial process, based on genetically engineered Z. mobilis with an integrated microbubble distillation system to convert complex sugary feedstocks and crude glycerol to acetaldehyde. Effective removal of acetaldehyde during the metabolic process will alleviate the inhibition and give higher yields. From the higher production quantities of acetaldehyde a more competitive and efficient route to butanol production can be obtained compared to current practise.