Engineered Serratia Macescens MG-1 For (3R)-acetoin Production

Chiral acetoin is an important platform compound, it can be used as pharmaceutical intermediate or to synthesize novel optically active ?-hydroxyketone derivatives and liquid crystal composites. In this study, genetic motification protocols were used for the transformation of Serratia marcescens MG1 to construct a (3R)-acetoin producing strain. The fermentation process was also optimized to improve the production of (3R)-acetoin. The main contents and res?lts include:1. The meso-2,3-butanediol dehydrogenase (meso-2,3-BDH) encoded by slaC encoding and glycerol dehydrogenase (GDH) encoded by gldA which were responsible for transforming acetoin to 2,3-butanediol were blocked in MG1. The res?lting strain MG14 was found to produce single configuration of (3R)-acetoin with a production of 21.04 g/L. A slight amount of 2,3-butanediol was also detected in the double mutant strain which suggested that there was another enzyme responsible for the synthesis of 2,3-butanediol except meso-2,3BDH and GDH.2. Three SlaR expression plasmids using promoter PC, PA and PR were constructed and transformed to MG14. Three recombinant strain MG15, MG16 and MG17 were obtained. After the fermentation process,27.72 g/L of (3R)-acetoin was produced in MG15, which was 29.91% higher than MG14.3. The fermentation conditions of MG15 were optimized through single factor experiment. The suitable condition included temperature of 30?,20 ml liquid volume in 250-ml flask, initial pH of 7.0 and inoculation size of 5%. The fermentation medium components were optimized using Plackett-Burman design and response surface methodology. The optimized fermentation components included 105 g/L sucrose,35 g/L yeast extract,25 g/L sodium citrate and 1 g/L acetic acid,0.5 g/L NH4H2PO4,0.2 g/L MgSO4,0.02 g/L MnSO4. The (3R)-acetoin production was improved from 27.72 g/L to 39.91 g/L using the optimized medium.