Phase Transitions in Bacterial Populations

Phase transitions have been observed in a number of different biological systems and processes from bird flocks to neuronal firing. Recently, we have identified non-equilibrium phase transitions in microbial populations undergoing population extinction in response to specific environmental stressors such as temperature and antibiotics. These observed phase transitions during population collapse broadly correspond to previous computational models of evolutionary dynamics. Surprisingly, in our experiments there was a diverse pattern of population collapse within and between different classes of antibiotics with no obvious explanation for this difference. Even within classes of chemically related antibiotics some exhibit critical phase transition like behavior with sharp declines in growth and high standard deviations between bacterial populationsm, whereas others show much more gradual declines with very little difference between populations. Preliminary evidence from our lab suggests that these differences in phase-transition behavior may be in part driven by resistance evolution. We are currently using experimental evolution and next generation sequencing to investigate if the frequency and spectrum of possible resistance mutations determine the emergence of critical phase transitions during antibiotic treatment. This work will not only inform how and when antibiotic resistance mutations are likely to evolve but will more broadly investigate evolutionary rescue during critical phase transition population collapse.