Microbial Production of 2,3-Butanediol From Sugarcane Molasses Using Engineered Enterobacter Aerogenes

Development of renewable energy or bio-based chemicals is now receiving lots of attention. 2,3-Butanediol (2,3-BD) is an example of bulk chemicals produced by biotechnological routes. Through chemical reaction such as dehydration and esterification, 2,3-BD can be converted into various chemical compounds including 1,3-butadiene, PUMAs (Polyurethane-melamides), and methyl ethyl ketone (MEK; butan-2-one). Enterobacter aerogenes is a facultative anaerobe, which can produce significant amounts of 2,3-BD from a wide range of carbon sources and has high growth rate. Furthermore, the E. aerogenesgenome sequence has been revealed recently and the method of gene disruption was developed successfully.

  One of the biggest hindrances to be overcome in the biorefinery process is the price of the carbon source that accounts for a large portion of the cost of microbial 2,3-BD production. Sugarcane molasses is considered to be a suitable fermentative carbon source due to its low-price and high sugar content. However, sugarcane molasses was not efficiently utilized by E. aerogenes. To improve sucrose utilization in E. aerogenes, a transcriptional repressor (ScrR) of sucrose utilization operon in genomic DNA was disrupted by using the lambda red recombination method. In addition, we have conducted lactate dehydrogenase (ldhA) gene knockout because lactate is mostly produced as byproduct. The mutant strain showed significantly enhanced the sucrose utilization when sucrose or sugarcane molasses was used as a carbon source. In batch fermentation with sugarcane molasses, 2,3-BD production of mutant strain (ΔldhA ΔscrR) increased 60% compared to that of the wild type strain. Finally, 2,3-BD production reached 98.69 g/L at 36 h of cultivation in fed-batch fermentation. This result indicates that the metabolically engineered strain would be a promising 2,3-BD producer, employing an economic carbon source, sugarcane molasses.