There is an increasing interest to commercially produce biofuels such as butanol for sustainable economic growth. Large amount of waste wood is produced daily being an environmental concern. Technology able to produce butanol from waste wood cost-effectively can pave the way for commercialization. Clostridium spp. such as C. acetobutylicum and C. beijerinckii are among the most promising microorganisms which can naturally produce butanol through anaerobic fermentation. As xylose is found to be the dominant fermentable sugar in waste wood, it is necessary to generate high butanol-yielding Clostridium spp. on xylose metabolism.
The current xylose utilization efficiency of Clostridium spp. is not industrially significant yet. Therefore there is considerable room for strain improvement. We are working to genetically modify the strain by over-expressing rate-limiting enzymes in xylose metabolism pathway. Three such enzymes are chosen: transaldolase (encoded by talA), b-hydroxybutyryl-CoA dehydrogenase (encoded by bhbd), and thiolase (encoded by thl). These genes of interest are PCR-amplified and inserted downstream of a constitutive promoter Pthl in Clostridium-Escherichia coli shuttle plasmids. The constructed plasmids are introduced into Clostridium spp. via electroporation. The butanol yields of the engineered strains are monitored by gas chromatography.
This work will present results to illustrate that pentose metabolism pathway has been enhanced in the metabolically engineered strains, which can potentially improve the butanol yield on xylose as sole carbon source.
* Research funded by Singapore A*STAR. Project Number: 0921390034.
* Correspondent author at t02210@tp.edu.sg.