초록
<P><B>Abstract</B></P> <P>Biotechnological production of biofuels is restricted by toxicity of the products such as ethanol and butanol. As its low toxicity to microbes, 2,3-butanediol (2,3-BD), a fuel and platform bio-chemical, could be a promising alternative for biofuel production from renewable bioresources. In addition, no bacterial strains have been reported to produce enantiopure 2,3-BD using lignocellulosic hydrolysates. In this study, <I>Enterobacter cloacae</I> strain SDM was systematically and metabolically engineered to construct an efficient biocatalyst for production of the fuel and enantiopure bio-chemical—(2<I>R</I>,3<I>R</I>)-2,3-BD. First, the various (2<I>R</I>,3<I>R</I>)-2,3-BD dehydrogenase encoding genes were expressed in a <I>meso</I>-2,3-BD dehydrogenase encoding gene disrupted <I>E. cloacae</I> strain under native promoter <I>P</I> <SUB> <I>b</I> </SUB> of the 2,3-BD biosynthetic gene cluster of <I>E. cloacae</I>. Then, carbon catabolite repression was eliminated via inactivation of the glucose transporter encoding gene <I>ptsG</I> and overexpression of a galactose permease encoding gene <I>galP.</I> The resultant strain could utilize glucose and xylose simultaneously. To improve the efficiency of (2<I>R</I>,3<I>R</I>)-2,3-BD production, the byproduct-producing genes (<I>ldh</I> and <I>frdA</I>) were knocked out, thereby enhancing the yield of (2<I>R</I>,3<I>R</I>)-2,3-BD by 16.5% in 500-mL Erlenmeyer flasks. By using fed-batch fermentation in a 5-L bioreactor, 152.0g/L (2<I>R</I>,3<I>R</I>)-2,3-BD (purity>97.5%) was produced within 44h with a specific productivity of 3.5g/[Lh] and a yield of 97.7% from a mixture of glucose and xylose, two major carbohydrate components in lignocellulosic hydrolysates. In addition, when a lignocellulosic hydrolysate was used as the substrate, 119.4g/L (2<I>R</I>,3<I>R</I>)-2,3-BD (purity>96.0%) was produced within 51h with a productivity of 2.3g/[Lh] and a yield of 95.0%. These results show that the highest records have been acquired for enantiopure (2<I>R</I>,3<I>R</I>)-2,3-BD production by a native or engineered strain from biomass-derived sugars. In addition to producing the 2,3-BD, our systematic approach might also be used in the production of other important chemicals by using lignocellulose-derived sugars.</P> <P><B>Highlights</B></P> <P> <UL> <LI> (2<I>R</I>,3<I>R</I>)-2,3-BD producers were constructed from a native 2,3-BD producer. </LI> <LI> The engineered strain enabled efficient co-utilization of glucose and xylose for BD production. </LI> <LI> The highest records were acquired for the BD production by an engineered strain. </LI> </UL> </P>