Antibiotic Resistance Mechanisms Inform Discovery: Identification and Characterization of a Novel Amycolatopsis Strain Producing Ristocetin.

Discovering new antibiotics is a major scientific challenge, made increasingly urgent by the continued development of resistance in bacterial pathogens. A fundamental understanding of the mechanisms of bacterial antibiotic resistance will be vital for the future discovery or design of new, more effective antibiotics. We have exploited our intimate knowledge of the molecular mechanism of glycopeptide antibiotic resistance in the harmless bacterium Streptomyces coelicolor to develop a new two-step cell wall bioactivity screen that efficiently identified a new actinomycete strain containing a previously uncharacterized glycopeptide synthetic gene cluster. The screen first identifies natural product extracts capable of triggering a generalized cell wall stress response mechanism, then subsequently specifically selects for glycopeptide antibacterials by assaying for induction of glycopeptide resistance genes. In this study, we have established a diverse natural product extract library from actinomycetes strains isolated from locations with widely varying climates and ecologies and screened them using the novel two-step bioassay system. The bioassay ultimately identified a single strain harboring the previously unidentified biosynthetic gene cluster for the glycopeptide ristocetin providing a proof-of-principle for the effectiveness of the screen. This is the first report of the ristocetin biosynthetic gene cluster which is predicted to include some interesting and previously uncharacterized enzymes. By focusing on screening libraries of microbial extracts this strategy provides the certainty that identified producer strains are competent for growth and the biosynthesis of the detected glycopeptide under laboratory conditions.