Characterization of the Self-Resistance Mechanism to Dityromycin in the Streptomyces Producer Strain

Dityromycin is a peptide antibiotic isolated from the culture broth of the soil microorganism Streptomyces sp. strain AM-2504. Recent structural studies have shown that dityromycin targets the ribosomal protein S12 in the 30S ribosomal subunit, inhibiting translocation. Herein, by using in vitro protein synthesis assays, we identified the resistance mechanism of the producer strain to the secondary metabolite dityromycin. The results show that the self-resistance mechanism of the Streptomyces sp. strain AM-2504 is due to a specific modification of the ribosome. In particular, two amino acid substitutions, located in a highly conserved region of the S12 protein corresponding to the binding site of the antibiotic, were found. These mutations cause a substantial loss of affinity of the dityromycin for the 30S ribosomal subunit, protecting the producer strain from the toxic effect of the antibiotic. In addition to providing a detailed description of the first mechanism of self-resistance based on a mutated ribosomal protein, this work demonstrates that the molecular determinants of the dityromycin resistance identified in Streptomyces can be transferred to Escherichia coli ribosomes, where they can trigger the same antibiotic resistance mechanism found in the producer strain.IMPORTANCE The World Health Organization has identified antimicrobial resistance as a substantial threat to human health. Because of the emergence of pathogenic bacteria resistant to multiple antibiotics worldwide, there is a need to identify the mode of action of antibiotics and to unravel the basic mechanisms responsible for drug resistance. Antibiotic producers' microorganisms can protect themselves from the toxic effect of the drug using different strategies; one of the most common involves the modification of the antibiotic's target site. In this work, we report a detailed analysis of the molecular mechanism, based on protein modification, devised by the soil microorganism Streptomyces sp. strain AM-2504 to protect itself from the activity of the peptide antibiotic dityromycin. Furthermore, we demonstrate that this mechanism can be reproduced in E. coli, thereby eliciting antibiotic resistance in this human commensal bacterium

Draft Genome Sequence of Streptomyces sp. Strain AM-2504, Identified by 16S rRNA Comparative Analysis as a Streptomyces kasugaensis Strain

We report here the draft genome sequence of Streptomyces sp. strain AM-2504, a microorganism producing a broad range of biotechnologically relevant molecules. The comparative analysis of its 16S rRNA sequence allowed the assignment of this strain to the Streptomyces kasugaensis species, thus fostering functional characterization of the secondary metabolites produced by this microorganism

Structural insights into Pseudomonas aeruginosa Type six secretion system exported effector 8

Recent reports indicate that the Type six secretion system exported effector 8 (Tse8) is a cytoactive effector secreted by the Type VI secretion system (T6SS) of the human pathogen Pseudomonas aeruginosa. The T6SS is a nanomachine that assembles inside of the bacteria and injects effectors/toxins into target cells, providing a fitness advantage over competing bacteria and facilitating host colonisation. Here we present the first crystal structure of Tse8 revealing that it conserves the architecture of the catalytic triad Lys84-transSer162-Ser186 that characterises members of the Amidase Signature superfamily. Furthermore, using binding affinity experiments, we show that the interaction of phenylmethylsulfonyl fluoride (PMSF) to Tse8 is dependent on the putative catalytic residue Ser186, providing support for its nucleophilic reactivity. This work thus demonstrates that Tse8 belongs to the Amidase Signature (AS) superfamily. Furthermore, it highlights Tse8 similarity to two family members: the Stenotrophomonas maltophilia Peptide Amidase and the Glutamyl-tRNAGln amidotransferase subunit A from Staphylococcus aureus.This work was supported by the Ministerio de Economía y Competitividad (MINECO) Contract CTQ2016-76941-R, the Fundación Biofísica Bizkaia, the Basque Excellence Research Centre (BERC) program of the Basque Government, and Fundación BBVA (to DAJ). MASP acknowledges support by the MINECO under the “Juan de la Cierva Postdoctoral program” (position FJCI-2015-25725). PF acknowledges support by the Marie Curie Action Career Integration Grant (PCIG14-GA-2013-632072), the Ministerio de Economía y Competitividad Grant (MINECO, CTQ2017-82222-R) and thanks MINECO for the Severo Ochoa Excellence Accreditation (SEV-2016-0644). We acknowledge Diamond Light Source, ALBA synchrotron beamline BL13-XALOC, their staff, and iNEXT (proposals 1618/2538) for providing access to synchrotron radiation facilities. Dr Laura M. Nolan and Prof. Alain Filloux are gratefully acknowledged for helpful discussions