초록
<P><B>Abstract</B></P> <P>The introduction of a synthetic metabolic pathway consisting of multiple genes derived from various organisms enables cyanobacteria to directly produce valuable chemicals from carbon dioxide. We previously constructed a synthetic metabolic pathway composed of genes from <I>Escherichia coli, Saccharomyces cerevisiae,</I> and <I>Klebsiella pneumoniae</I>. This pathway enabled 1,3-propanediol (1,3-PDO) production from cellular DHAP via glycerol in the cyanobacterium, <I>Synechococcus elongatus</I> PCC 7942. The production of 1,3-PDO (3.79mM, 0.29g/l) directly from carbon dioxide by engineered <I>S. elongatus</I> PCC 7942 was successfully accomplished. However, the constructed strain accumulated a remarkable amount of glycerol (12.6mM, 1.16g/l), an intermediate metabolite in 1,3-PDO production. Notably, enhancement of latter reactions of synthetic metabolic pathway for conversion of glycerol to 1,3-PDO increases 1,3-PDO production. In this study, we aimed to increase the observed 1,3-PDO production titer. First, the weaker <I>S. elongatus</I> PCC 7942 promoter, <I>P</I> <SUB>L</SUB>lacO1, was replaced with a stronger promoter (<I>P</I>trc) to regulate genes involved in the conversion of glycerol to 1,3-PDO. Second, the induction timing for gene expression and medium composition were optimized. Promoter replacement resulted in higher 1,3-PDO production than glycerol accumulation, and the amount of products (1,3-PDO and glycerol) generated via the synthetic metabolic pathway increased with optimization of medium composition. Accordingly, we achieved the highest titer of 1,3-PDO (16.1mM, 1.22g/l) and this was higher than glycerol accumulation (9.46mM, 0.87g/l). The improved titer was over 4-fold higher than that of our previous study.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The highest titer of 1,3-PDO (16.1mM, 1.22g/l) was achieved by cyanobacteria. </LI> <LI> The sum of products (1,3-PDO and glycerol) derived from carbon dioxide reached 25.5mM. </LI> <LI> Promoter replacement increased the conversion rate of glycerol into 1,3-PDO. </LI> <LI> The titer of 1,3-PDO was increased by growth phase elongation. </LI> </UL> </P>