Comparative Metabolomics
Reveals a Bifunctional Antibacterial
Conjugate from Combined-Culture of Streptomyces hygroscopicus HOK021 and Tsukamurella pulmonis TP-B0596
To investigate the potential for secondary metabolite
biosynthesis
by Streptomyces species, we employed a coculture
method to discover natural bioactive products and identified specific
antibacterial activity from a combined-culture of Streptomyces
hygroscopicus HOK021 and Tsukamurella
pulmonis TP-B0596. Molecular networking using ultrahigh
performance liquid chromatography-quadrupole time-of-flight tandem
mass spectrometry (UPLC-QTOF-MS/MS) data revealed a specific clade
of metabolites in this combined-culture that were not detected in
both monocultures. Using the chemical profiles, a previously unidentified
conjugate between FabF inhibitor and catechol-type siderophore was
successfully identified and named harundomycin A. Harundomycin A was
a conjugate between the 2,4-dihydroxy-3-aminobenzoate moiety of platensimycin
and N,N′-bis(2,3-dihydroxybenzoyl)-O-seryl-cysteine (bisDHBA-Ser-Cys) with a thioester linkage.
Along with the production of harundomycin A, platensimycin, its thiocarboxylic
acid form thioplatensimycin, enterobactin, and its degradation product N,N′-bis(2,3-dihydroxybenzoyl)-O-l-seryl-dehydroalanine (bisDHBA-Ser-Dha) were also induced
in the combined-culture. Genomic data of S. hygroscopicus HOK021 and T. pulmonis TP-B0596 indicated
that strain HOK021 possessed biosynthetic gene clusters for both platensimycin
and enterobactin, and thereby revealed that T. pulmonis stimulates HOK021 and acts as an inducer of both of these metabolites.
Although the harundomycin A was modified by bulky bisDHBA-Ser-Cys,
responsible for the binding to the target molecule FabF, it showed
a similar antibacterial spectrum to platensimycin, including against
methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci, suggesting that the pharmacophore
is platensimycin. Additionally, Chrome Azurol S assay showed that
harundomycin A possesses ferric iron-chelating activity comparable
to that of enterobactin. Our study demonstrated the transformation
of existing natural products to bifunctional molecules driven by bacterial
interaction