Combinatorial metabolic engineering modifications to improve the yield of the bioherbicide thaxtomin A
Streptomyces acidscabies S8,a thaxtomin A-producing strain,was used as the starting strain.By increasing the gene copy number of S-adenosine methionine reductase MetK and positive regulatory factor TxtR,using the constitutive promoter element kasOp* and ribosome binding site(RBS),respectively,the combinational metabolic engineering method was applied to construct the recombinant plasmides of txtR,metK and their co-expression.The plasmids were integrated into the genome of the strain by conjugation transfer,and the positive genetically engineered bacteria were screened.The fermentation products were analyzed by HPLC,and the results showed that the fermentation units of thaxtomin A were increased by 105％,38％and 154％,respectively.The combination of gene expression regulatory elements and the genetic modification of txtR and(or)metK could significantly improve the biosynthesis of thaxtomin A.
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