Novel roles for antibiotic metabolites localized at the cell surface during inter-species bacterial competition

The predominant descriptions of natural products during microbial competition are as growth-inhibiting antibiotics. However, while many natural products are known to possess antibiotic activity, they localize in patterns that suggest they are functional for the producing organism in ways that extend past growth-inhibition of neighboring organisms. Using newly available tools such as imaging mass spectrometry (IMS), we are able to monitor metabolite localization during competition between two genetically tractable organisms, Bacillus subtilis and Streptomyces sp. Mg1. The linear polyene metabolite Mg1-pk1, when purified and applied in vitro, is bactericidal toward B. subtilis, an activity not commonly associated with polyenes. In IMS experiments, Mg1-pk1 is found associated with the cell surface of S. Mg1. This localization pattern, in stark contrast to the more diffuse localization patterns of metabolites such as chalcomycin A, suggests Mg1-pk1 may have additional non-antibiotic roles in S. Mg1. When we delete the biosynthetic genes of Mg1-pk1, S. Mg1 becomes more susceptible to the antibiotic bacillaene produced by competing B. subtilis. This observed hypersensitivity suggests a defensive role for Mg1-pk1 during bacterial competition, the mechanism of which we are currently investigating. Localization of antibiotics at the cell surface of their producing organisms is commonly observed, for example in the antifungal metabolites amphotericin B and ECO-02301. By considering critical information such as localization in the producing organisms, we aim to uncover previously undescribed functions for antibiotics during bacterial competition, which may lead to the identification of new targets for therapeutic discovery.