2,3-butanediol production from starch by engineered Klebsiella pneumoniae G31-A.

2,3-Butanediol (2,3-BD) is an organic compound, which is widely used as a fuel and fuel additive and applied in chemical, food, and pharmaceutical industries. Contemporary strategies for its economic synthesis include the development of microbial technologies that use starch as cheap and renewable feedstock. The present work encompasses the metabolic engineering of the excellent 2,3-BD producer Klebsiella pneumoniae G31. In order to perform direct starch conversion into 2,3-BD, the amyL gene encoding quite active, liquefying α-amylase in Bacillus licheniformis was cloned under lac promoter control in the recombinant K. pneumoniae G31-A. The enhanced extracellular over-expression of amyL led to the highest extracellular amylase activity (68 U/ml) ever detected in Klebsiella. The recombinant strain was capable of simultaneous saccharification and fermentation (SSF) of potato starch to 2,3-BD. In SSF batch process by the use of 200 g/l starch, the amount of total diols produced was 60.9 g/l (53.8 g/l 2,3-BD and 7.1 g/l acetoin), corresponding to 0.31 g/g conversion rate. The presented results are the first to show successful starch conversion to 2,3-BD by K. pneumoniae in a one-step process.