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Currently, a bulk amount of raw glycerol is formed as the main by-product during biodiesel production, which is as high as 10% (w/w) of biodiesel generated. The surplus of raw glycerol has not only greatly disturbed the market of traditional glycerol in the preparation and price, but also brought a significant environmental problem since it cannot be discharged direct into the environment without any treatment. As a result of these issues, a large research effort has been devoted to developing methods to refine glycerol as a low-cost feedstock into industrially
valuable materials such as fuels, building blocks, and bioactive substances. 1,3-Propanediol (1,3-PD) is a valuable chemical that is used mainly for the synthesis of polymethylene terephalates by polymerization with terephthalates. Use of this polymer in the manufacturing of textile fiber, film, plastic, etc. is rapidly expanding. Klebsiella pneumoniae is a typical microbial strain capable of producing 1,3-PD, in which the metabolic pathway responsible for the production of 1,3-PD has been well studied. The microbial production of 1,3-PD by K. pneumoniae involves the formation of various by-products. 2,3-Butanediol, one of the main by-products, may serve as an obstacle for obtaining a high purity of 1,3-PD in downstream processes because of its similar boiling point. To eliminate the by-products synthesis, glycerol
metabolic pathway was engineered by deleting from the chromosomal DNA the genes involved in the synthesis of by-products. The by-product formation except for acetate was eliminated in the resultant strains. Additionally, 3-hydroxypropionic acid (3-HP) that is one of the most interest among alternative chemicals derived from biomass as precursor of acryl derivatives, could be produced from glycerol by the native and engineered strains of K. pneumoniae. The recombinant strains would be valuable as a platform strain for development of industrial process of production of 1,3-PD or 3-HP from glycerol.