| Fimbriae not only consume a lot of energy and material,but also play an essential role in biofilm biosynthesis.Blocking fimbria biosynthesis should benefit the growth of E.coli TWF001 and biosynthesis of target products by saving substrate and energy during fermentation.Escherichia coli contains 12 chaperone-usher operons used for fimbria biosynthesis and assembly.This study started from a L-threonine-producing strain TWF001.By deleting 12 CU system gene clusters,blocking synthesis of fimbria,L-threonine production was further increased.（1）E.coli mutants TWK001-TWK012 were constructed from TWF001 by deleting Ycb,Yad,Yde,Yeh,Yqi,Yra,Yfc,Type 1,Yhc,Sfm,Mat and Ybg CU operons,respectively,and L-threonine yield in these mutants were improved in varying degrees.TWK012 produced 12.4g·L-1 L-threonine after 36 h.（2）In Escherichia coli TWK001,multiple CU gene clusters were knocked out simultaneously,and TWK021 with the highest production of L-threonine was obtained.After36 h fermentation,L-threonine yield in TWK021 reached 15.75 g·L-1,with the production efficiency at 0.438 g·L-1·h-1,and the conversion rate of glucose to L-threonine reached 0.298g·g-1,which was a 27%increase to TWK021.（3）Optimization of fermentation medium of E.coli mutant TWF021 further increased L-threonine production to 17 g·L-1,with the production efficiency at 0.472 g·L-1·h-1.After 48 h fed-fermentation,L-threonine yield in TWK021 reached 62.7 g·L-1,with the production efficiency at 1.493 g·L-1·h-1,and the conversion rate of glucose to L-threonine reached 0.427g·g-1,which was a 17.1%increase to TWF001.（5）In E.coli TWF001,nlp E,csr B and qse BC related to motivity and biofilm formation were knocked out,and L-threonine production reached 17.9 g·L-1,with the production efficiency at 0.497 g·L-1·h-1,and the conversion rate of glucose to L-threonine reached 0.445g·g-1,which was a 55.7%increase to TWF001.But as nlp E,csr B and qse BC were deleted in TWK021,the production of L-threonine was not improved obviously. |
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