Enhancing the unexplored chemical diversity of Streptomyces sp. to produce new antibiotics active against multidrug resistant Acinetobacter baumannii

Streptomyces species are a major source of antibiotics but are often grown under restrictive conditions that limit biosynthetic gene expression. As a result, the vast majority of secondary metabolites within a single species remain unexpressed in the lab along with the huge variety in chemical structures and bioactivities. The overarching aim of this project was to identify conditions that produce novel antibiotics, specifically against Gram-negative pathogens. The culture collection NCIMB contains hundreds of Streptomyces isolated from around the world. Strains were selected from the collection guided by preliminary bioactivity studies and available literature. These were then grown in an extensive variety of conditions designed to stimulate production of a wide variety of secondary metabolites, detected by UPLC-MS and analysed using the freely available metabolomic tools MZmine, MetaboAnalyst, and GNPS. Conditions included various carbon and nitrogen sources, temperatures, stresses, epigenetic inhibitors, and other microbes. Compounds active against the Gram negative multidrug resistant pathogen Acinetobacter baumannii were detected in the scaleup culture supernatant fractions. Metabolite identification through GNPS did not detect any previously discovered compounds active against A. baumannii, indicating a potentially novel antibiotic against one of the WHO’s priority pathogens.