초록
<P>Propionic acid (PA) is an important chemical building block widely used in the food, pharmaceutical, and chemical industries. In our previous study, a shuttle vector was developed as a useful tool for engineering <I>Propionibacterium jensenii</I>, and two key enzymes—glycerol dehydrogenase and malate dehydrogenase—were overexpressed to improve PA titer. Here, we aimed to improve PA production further via the pathway engineering of <I>P. jensenii</I>. First, the phosphoenolpyruvate carboxylase gene (<I>ppc</I>) from <I>Klebsiella pneumoniae</I> was overexpressed to access the one-step synthesis of oxaloacetate directly from phosphoenolpyruvate without pyruvate as intermediate. Next, genes encoding lactate dehydrogenase (<I>ldh</I>) and pyruvate oxidase (<I>poxB</I>) were deleted to block the synthesis of the by-products lactic acid and acetic acid, respectively. Overexpression of <I>ppc</I> and deleting <I>ldh</I> improved PA titer from 26.95 ± 1.21 g·L<SUP>−1</SUP> to 33.21 ± 1.92 g·L<SUP>−1</SUP> and 30.50 ± 1.63 g·L<SUP>−1</SUP>, whereas <I>poxB</I> deletion decreased it. The influence of this pathway engineering on gene transcription, enzyme expression, NADH/NAD<SUP>+</SUP> ratio, and metabolite concentration was also investigated. Finally, PA production in <I>P. jensenii</I> with <I>ppc</I> overexpression as well as <I>ldh</I> deletion was investigated, which resulted in further increases in PA titer to 34.93 ± 2.99 g·L<SUP>−1</SUP> in a fed-batch culture.</P>