Evolutionary ecology of antibiotics in soil communities

Antibiotics play significant roles in mediating microbial species interactions in the environment, yet the dynamics of selection for antibiotic inhibitory, signaling, and resistance phenotypes remain poorly understood.  Soil biological and environmental factors are often significantly correlated with antibiotic production capacities of Streptomyces populations in soil, likely because of their influences on nutrient competition.  We have characterized inhibitory, resistance, and signaling dynamics among sympatric (locally-coexisting) and allopatric Streptomyces populations in relation to isolate phylogeny and nutrient use capacities as a means of identifying factors that may be significant to selection.  Sympatric selection for both antibiotic inhibition and signaling phenotypes, and a significant correspondence of these phenotypes with niche overlap among interacting isolates support the hypothesis that antibiotics are important to mediating nutrient competition in soil. Consideration of complex networks of interactions among multiple sympatric populations shows that some patterns of inhibitory interaction among sets of 3 (or more) isolates are statistically more common than expected, suggesting that interactions between two populations can be mediated by interactions with a third population.  Identifying the environmental and community contexts which select for inhibitory and resistance phenotypes in soil Streptomyces populations has significant implications for both agricultural management and the search for novel antibiotics.