초록
<P><B>Abstract</B></P> <P>L-serine is a promising building block biochemical with a high theoretical production yield from glucose. Toxicity of L-serine is however prohibitive for high-titer production in <I>E. coli</I>. Here, <I>E. coli</I> lacking L-serine degradation pathways was evolved for improved tolerance by gradually increasing L-serine concentration from 3 to 100g/L using adaptive laboratory evolution (ALE). Genome sequencing of isolated clones revealed multiplication of genetic regions, as well as mutations in <I>thrA</I>, thereby showing a potential mechanism of serine inhibition. Additional mutations were evaluated by MAGE combined with amplicon sequencing, revealing role of <I>rho</I>, <I>lrp</I>, <I>pykF</I>, <I>eno</I>, and <I>rpoB</I> on tolerance and fitness in minimal medium. Production using the tolerant strains resulted in 37g/L of L-serine with a 24% mass yield. The resulting titer is similar to the highest production reported for any organism thereby highlighting the potential of ALE for industrial biotechnology.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Adaptive laboratory evolution enhanced tolerance towards L-serine from 3 to 100g/L. </LI> <LI> Potential site of L-serine inhibition identified on homoserine dehydrogenase, ThrA. </LI> <LI> Gene clusters encoding potential serine exporters duplicated in evolved strains. </LI> <LI> Combined MAGE and amplicon sequencing enables identification of causative mutations. </LI> <LI> Evolved strain produced 37g/L of L-serine with a 24% mass yield from glucose. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>