Bacterial interspecies interactions modulate pH-mediated antibiotic tolerance.

Predicting antibiotic efficacy within microbial communities remains highly challenging. Interspecies interactions can impact antibiotic activity through many mechanisms, including alterations to bacterial physiology. Here, we studied synthetic communities constructed from the core members of the fruit fly gut microbiota. Co-culturing of with species altered its tolerance to the transcriptional inhibitor rifampin. By measuring key metabolites and environmental pH, we determined that species counter the acidification driven by production of lactate. Shifts in pH were sufficient to modulate tolerance to rifampin and the translational inhibitor erythromycin. A reduction in lag time exiting stationary phase was linked to tolerance to rifampicin, opposite to a previously identified mode of tolerance to ampicillin in . This mechanistic understanding of the coupling among interspecies interactions, environmental pH, and antibiotic tolerance enables future predictions of growth and the effects of antibiotics in more complex communities.