Speaker
Description
When exposed to antibiotics, a population of bacteria may evolve resistance through the combination of random mutation and natural selection driving fixation of antibiotic resistance mutations. However, in a natural environment, a complex suite of stressors simultaneously drive natural selection and depending on their trade-offs and/ or interactions may impact adaptive evolution. Spatial structure in the environment is one such stressor that has the potential to drive a diverse range of molecular responses depending on the local interactions and small-scale variations in the environment. Local interactions and movement of cells can also have direct impacts on sensitivity to antibiotics, for example, bacteria been shown to vary in their sensitivity to antibiotics depending on their mode of motility (swimming, swarming, surfing etc.). To explore the importance of a spatially structured environment on the evolution of antibiotic resistance, we tracked populations of Pseudomonas aeruginosa exposed to a constant sub-lethal concentration of the antibiotic ciprofloxacin across four different environments that differed in their degree of spatial structure, manipulated by varying agar concentration. Whole genome sequencing of these populations after 100 generations of evolution showed that the number and frequency of evolved mutations differed depending on the presence/ absence antibiotic, the degree of spatial structure, and their interaction. The rate of adaptation was slower in structured environments regardless of the presence/ absence of antibiotic, evolved changes in dispersal rate depended on the interaction between spatial structure and presence/ absence of antibiotic. Our results suggest that the presence of antibiotics impacts the evolution of bacterial populations in a broad range of ways and the specifics of these adaptations can be significantly affected by the presence of spatial structure in the environment.
