Streptomyces from traditional medicine: sources of new innovations in antibiotic discovery

Abstract

Given the increased reporting of multi-resistant bacteria and the shortage of newly approved medicines, researchers have been looking towards extreme and unusual environments as a new source of antibiotics. Streptomyces currently provides many of the world's clinical antibiotics, so it comes as no surprise that these bacteria have recently been isolated from traditional medicine. Given the wide array of traditional medicines, it is hoped that these discoveries can provide the much sought after core structure diversity that will be required of a new generation of antibiotics. This review discusses the contribution of Streptomyces to antibiotics and the potential of newly discovered species in traditional medicine. We also explore how knowledge of traditional medicines can aid current initiatives in sourcing new and chemically diverse antibiotics.

Keywords: endophytes; ethnopharmacology; extreme environments; pathogens; secondary metabolites; silent gene clusters.

Fig. 1.

Oxytetacyline synthesis by the PKS type II system: consecutive modules of the PKS type II enzyme catalyse the successive decarboxylative condensations of malonyl CoA, followed by modifications by transferases, oxygenases and cyclases, and additional modifications to produce oxytetracycline. Figure adapted from that of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (NC-IUBMB) in consultation with the IUPAC-IUBMB Joint Commission on Biochemical Nomenclature (JCBN) [91].

Fig. 2.

NRPS system for polymyxin from Paenibacillus polymyxa . The NRPS enzyme is composed of many modules that contain subunits (boxes) that help to attach amino acids. The thioesterase domain (TE) is responsible for cyclizing and releasing the peptide at the end of synthesis. Figure reproduced by kind permission of Dr T. Velkov [92].

Fig. 3.

A leafcutter ant (Acromyrmex) covered in Pseudonocardia . Photograph by João Pedro Sá Medeiros (Antwiki – https://www.antwiki.org/wiki/Acromyrmex) [40].

Fig. 4.

Formicamycin E. Adapted from [38].

Fig. 5.

Streptomyces from a traditional soil cure in the West Fermanagh Scarplands (a) was cultivated on selective isolation agar (b) yielding Streptomyces sp. myrophorea (c), which inhibited MRSA, as evidenced by a clear zone of inhibition (d).