Abstract
BackgroundHerbicidin F has an undecose tricyclic furano-pyrano-pyran structure with post-decorations. It was detected from Streptomyces mobaraensis US-43 fermentation broth as a trace component by HPLC–MS analysis. As herbicidins exhibit herbicidal, antibacterial, antifungal and antiparasitic activities, we are attracted to explore more analogues for further development.ResultsThe genome of S. mobaraensis US-43 was sequenced and a herbicidin biosynthetic gene cluster (hcd) was localized. The cluster contains structural genes, one transporter and three potential transcription regulatory genes. Overexpression of the three regulators respectively showed that only hcdR2 overexpression significantly improved the production of herbicidin F, and obviously increased the transcripts of 7 structural genes as well as the transporter gene. After performing homology searches using BLASTP in the GenBank database, 14 hcd-like clusters were found with a cluster-situated hcdR2 homologue. These HcdR2 orthologues showed overall structural similarity, especially in the C-terminal DNA binding domain. Based on bioinformatics analysis, a 21-bp consensus binding motif of HcdR2 was detected within 30 promoter regions in these genome-mined clusters. EMSA results verified that HcdR2 bound to the predicted consensus sequence. Additionally, we employed molecular networking to explore novel herbicidin analogues in hcdR2 overexpression strain. As a result, ten herbicidin analogues including six new compounds were identified based on MS/MS fragments. Herbicidin O was further purified and confirmed by 1H NMR spectrum.ConclusionsA herbicidin biosynthetic gene cluster (hcd) was identified in S. mobaraensis US-43. HcdR2, a member of LuxR family, was identified as the pathway-specific positive regulator, and the production of herbicidin F was dramatically increased by overexpression of hcdR2. Combined with molecular networking, ten herbicidin congeners including six novel herbicidin analogues were picked out from the secondary metabolites of hcdR2 overexpression strain. The orthologues of herbicidin F pathway-specific regulator HcdR2 were present in most of the genome-mined homologous biosynthetic gene clusters, which possessed at least one consensus binding motif with LuxR family characteristic. These results indicated that the combination of overexpression of hcdR2 orthologous regulator and molecular networking might be an effective way to exploit the “cryptic” herbicidin-related biosynthetic gene clusters for discovery of novel herbicidin analogues.
Highlights
Herbicidin F has an undecose tricyclic furano-pyrano-pyran structure with post-decorations
There’s one β-ketoacyl synthase that was first thought might be responsible for the biosynthesis of tiglyl moiety in herbicidin F
In this study, a herbicidin biosynthetic gene cluster was identified in S. mobaraensis US-43, a strain known for production of bleomycin analogues
Summary
Herbicidin F has an undecose tricyclic furano-pyrano-pyran structure with post-decorations. It was detected from Streptomyces mobaraensis US-43 fermentation broth as a trace component by HPLC–MS analysis. Herbicidins (Fig. 1) are adenosine-derived nucleoside antibiotics that have a characteristic tricyclic furano-pyrano-pyran structure with different decorations. They have been isolated from S. saganonensis [4,5,6,7], S. sp. At that time a Chinese patent by Tang’s group [11] has demonstrated the minimal gene cluster of aureonuclemycin (Fig. 1), the bare tricyclic core structure of herbicidins, produced by S. aureus var. The pathway-specific regulator was identified by overexpression of the potential regulators located near the hcd cluster, and hcdR2 exerted a significant positive role in the production of herbicidin F, which leads to the acquisition of enough amount of herbicidin F for structural determination by NMR spectra
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