Abstract
BackgroundNeoantimycins are a group of 15-membered ring depsipeptides isolated from Streptomycetes with a broad-spectrum of anticancer activities. Neoantimycin biosynthesis is directed by the hybrid multimodular megaenzymes of non-ribosomal peptide synthetase and polyketide synthase. We previously discovered a new neoantimycin analogue unantimycin B, which was demonstrated to have selective anticancer activities and was produced from the neoantimycin biosynthetic pathway with a starter unit of 3-hydroxybenzoate, instead of the 3-formamidosalicylate unit that is common for neoantimycins. However, the low fermentation titre and tough isolation procedure have hindered in-depth pharmacological investigation of unantimycin B as an anticancer agent.ResultsIn this work, we genetically constructed two unantimycin B producer strains and inhibited neoantimycins production by removing natO and natJ-L genes essential for 3-formamidosalicylate biosynthesis, therefore facilitating chromatographic separation of unantimycin B from the complex fermentation extract. Based on the ΔnatO mutant, we improved unantimycin B production twofold, reaching approximately 12.8 mg/L, by feeding 3-hydroxybenzoate during fermentation. Furthermore, the production was improved more than sixfold, reaching approximately 40.0 mg/L, in the ΔnatO strain introduced with a chorismatase gene highly expressed under a strong promoter for endogenously over-producing 3-hydroxybenzoate.ConclusionThis work provides a case of targeting accumulation and significant production improvement of medicinally interesting natural products via genetic manipulation of precursor biosynthesis in Streptomycetes, the talented producers of pharmaceutical molecules.
Highlights
Streptomyces species are a family of Gram-positive bacteria renowned for their ability to produce a multitude of secondary metabolites with pharmaceuticalZhou et al Bioresour
We originally proposed that unantimycin B (UAT-B) titre would be higher than that from the parent strain since NAT non-ribosomal peptide synthetase (NRPS)-polyketide synthase (PKS) was exclusively utilized to synthesize UAT-B when 3-HBA
NAT biosynthesis is directed by a hybrid multimodular protein complex of non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) with the starting precursor of 3-formamidosalicylate (3-FAS) (Zhou et al 2018; Skyrud et al 2018)
Summary
Streptomyces species are a family of Gram-positive bacteria renowned for their ability to produce a multitude of secondary metabolites with pharmaceuticalZhou et al Bioresour. (2021) 8:43 previously discovered a new NAT derivative, unantimycin B (UAT-B), from the fermentation extract of terrestrial Streptomyces conglobatus and verified that the biosynthesis of UAT-B was directed by the NAT NRPSPKS with a starter unit of 3-hydroxybenzoate (3-HBA) (Shen et al 2020) (Fig. 1). The yield level of UAT-B increased relative to that of NAT-A in the heterologous expression host of S. albus J1074 (Shen et al 2020), the production titre of UAT-B (approximately 6.3 mg/L) remained at the same low level as that of the wild-type strain (Additional file 1: Fig. S1). The presence of the main product NAT-A seriously interrupted the chromatographic separation of UAT-B Owing to these challenges, UAT-B had to be prepared with a challenging isolation procedure from the complex fermentation extract, hindering in-depth pharmacological investigation of the compound as an anticancer agent. The low fermentation titre and tough isolation procedure have hindered in-depth pharmacological investigation of unantimycin B as an anticancer agent
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