Heterologous expression of the pJTU4620 derivatives (with individual mutation of polN , polM and polL ) in S. lividans TK24. (A) Schematic representation for the construction of pJTU4620 derivatives, the genes polL-N were independently in-frame-deleted in pJTU4620. (B) Bioassay for the related S. lividans TK24 recombinants, the sample of pJTU4620 (TK24 containing pJTU4620), pJTU4620/ΔpolN, pJTU4620/ΔpolM and pJTU4620/ ΔpolL were correspondingly spotted as 1-4; TK24 containing pSET152 (spot 5) was used as negative control. (C) HPLC analysis of the metabolites individually produced by the S. lividans TK24 recombinants. The authentic polyoxin standards (ST) and the sample of TK24 containing pJTU620 (4620) were used as positive controls, and TK24 containing pSET252 was used as negative control. The samples of TK24 bearing 4620 derivatives were individually indicated as 4620/ΔpolN, pJTU4620/ΔpolM and 4620/ΔpolL. POL: polyoxin.