초록
<P>Astragalin (kaempferol 3-<I>O</I>-glucoside) is used as a standard to assess the quality of <I>Radix astragali</I> and has exhibited a number of biological properties. In this work, we screened several UDP-dependent glycosyltransferases (UGT) for their potential as efficient biocatalysts for astragalin synthesis. The highest astragalin production with 285 mg/L was detected in the recombinant strain expressing UGT from <I>Arabidopis thaliana</I> (AtUGT78D2). To further improve astragalin production, an efficient UDP-glucose synthesis pathway was reconstructed in the recombinant strain by introducing sucrose permease, sucrose phosphorylase, and uridylyltransferase. On the basis of those results, a recombinant strain, BL21-II, was constructed to produce astragalin. By optimizing conversion conditions, astragalin production was increased from 570 to 1708 mg/L. The production was scaled up using a fed-batch fermentation, and maximal astragalin production was 3600 mg/L, with a specific productivity of 150 mg/L/h after 24 h incubation and a corresponding molar conversion of 91.9%, the highest yield reported to date.</P><P><B>Graphic Abstract</B><BR><IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jafcau/2016/jafcau.2016.64.issue-42/acs.jafc.6b03447/production/images/medium/jf-2016-034478_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jf6b03447'>ACS Electronic Supporting Info</A></P>