Enhanced amphotericin B production by genetically engineered Streptomyces nodosus

The antifungal agent amphotericin B (AmB) is a polyketide produced by Streptomyces nodosus. The synthetic precursors of amphotericin macrolactone skeleton are acetyl-CoAs, malonyl-CoAs and methylmalonyl-CoAs. The genome sequence of the wild type S. nodosus ATCC14899 revealed a type II PKS (PKS5) competing for malonyl-CoAs. The same competitive branch was sequenced and verified in a mutant named S. nodosus ZJB2016050 (S. nodosus N3) screened in our lab. The transcriptome of the secondary metabolic synthetic gene clusters comparisons suggested that PKS5 competition is a factor in low production. Deletion of the PKS5 led to the titer of AmB improved from 5.01 g/L to 6.32 g/L while the by-product amphotericin A (AmA) reduced from 0.51 g/L to 0.12 g/L. A sequence of genes includes PKS amphA, acc1, mme and mcm were overexpressed in ΔPKS5 mutant, resulting in improved production AmB from 5.01 g/L to 7.06 g/L in shake flask at 96 h.