Enhancement of nystatin production by redirecting precursor fluxes after disruption of the tetramycin gene from Streptomyces ahygroscopicus

Abstract

Complete and independent tetramycin and nystatin gene clusters containing varying lengths of type I polyketide synthase (PKS) genes were isolated from Streptomyces ahygroscopicus, a producer of tetramycin (a tetraene) in large amounts and nystatin A1 (a heptaene) in small amounts. Tetramycin was similar to pimaricin, and nystatin A1 was similar to amphotericin. All these polyene macrolide antibiotics possessed the same macrolactone ring biosynthesized from coenzyme A precursors by PKSs but had different number of atoms in the macrolactone ring and side groups. Because tetramycin and nystatin shared limited coenzyme A precursors in the same producer organism, blocking the consumption of precursors in tetramycin pathway may increase the coenzyme A pool. Thus, we genetically manipulated the tetramycin PKS to enhance nystatin production. The type I PKS ttmS1 gene mutant abolished production of tetramycin and had a beneficial effect on the production of nystatin A1. For the mutant, the yield of nystatin A1 was increased by 10-fold compared to that of the wild-type. Thus, deletion of the tetramycin pathway redirected precursor metabolic fluxes and provided an easy genetic approach to manipulate organisms and to increase production levels of a precise target.

Functional manipulations of the tetramycin positive regulatory gene ttmRIV to enhance the production of tetramycin A and nystatin A1 in Streptomyces ahygroscopicus

“…Nystatin A1 enhancement in the ΔttmRIV strain may have resulted from the redirection of precursor fluxes, such as was seen in the ttmS1 disruption [21]. This phenomenon also was observed in S. avermitilis mutants.…”

“…All Streptomyces strains were cultured through two-stage fermentation with shaking at 220 rpm and 28 °C. The components of seed and fermentation medium were as described by Ren et al [21]. After incubation at 28 °C for 24 h, seed cultures were used to inoculate fermentation medium to 10 % (v/v), and incubated for 96 h.…”

“…Nystatin A1 is the main component of nystatin produced by S. ahygroscopicus. Overall, tetramycin and nystatin share similar pathways and precursors [4,21].…”

“…The fermentation products of S. ahygroscopicus contain two kinds of polyene macrolide compounds: tetramycin and nystatin [21]. Tetramycin is a 26-member tetraene antibiotic with two components: tetramycin A and tetramycin B [8,20].…”

“…The tetramycin gene cluster had been reported from the genome of S. hygrospinosus var. beijingensis ACCC40068 [6] and S. ahygroscopicus CGMCC 4.7082 [21]. Nystatin is a 38-member tetraene antibiotic containing four components [10] used to treat fungal infections.…”