Natural argB plays essential roles for both polyoxin production and L-arginine biosynthesis. (A) PCR identification of CY22 mutant, the construction process is identical to that of CY7 mutant except that the CY21 mutant was used as start strain, and PCR product of CY22 mutant (1) was compared with that of CY21 mutant (2). (B) Growth phenotype of CY22 and its related complemented strains in minimal medium. CY7 mutant was used as positive control (1), and CY22 mutant (2) as well as its complemented strain (CY22/pJTU2170) with an empty vector (3) were selected as negative controls, CY22/pJTU4713 (argB) (4) and CY22/pJTU2870 (polP) (5) were detected as parallels. (C) Bioassay for the metabolites produced by CY22 and its related complemented strains. Samples of CY21 mutant (1), CY22 mutant (2), and CY22/pJTU2170 (3) were detected in parallel with those of CY22/pJTU4713 (argB) (4) and CY22/pJTU2870 (polP) (5). (D) HPLC analysis of the metabolites produced by the CY22 mutant and its related strains. Polyoxin authentic standard (ST) and metabolites produced by S. cacaoi wild type (WT) were used as positive controls, while the metabolites produced by CY21, CY22, CY22/pJTU2170 were utilized as negative controls; the samples of CY22/argB (pJTU4713) and CY22/polP (pJTU2870) were detected as parallels.