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dc.contributor.advisorJeff Gore.en_US
dc.contributor.authorConwill, Arolyn.en_US
dc.contributor.otherMassachusetts Institute of Technology. Department of Physics.en_US
dc.date.accessioned2018-05-23T15:03:58Z
dc.date.available2018-05-23T15:03:58Z
dc.date.copyright2018en_US
dc.date.issued2018en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/115597
dc.descriptionThesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2018.en_US
dc.descriptionThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.en_US
dc.descriptionCataloged from student-submitted PDF version of thesis.en_US
dc.descriptionIncludes bibliographical references (pages 139-149).en_US
dc.description.abstractCooperation between microbes can enable microbial communities to survive in harsh environments. Enzymatic deactivation of antibiotics is a cooperative behavior that can allow resistant cells to protect sensitive cells from antibiotics. The prevalence of this mechanism of antibiotic resistance in clinical isolates and in soil bacteria makes it important both clinically and ecologically. Here, we show that two Escherichia coli strains can form a cross-protection mutualism, protecting each other in the presence of two antibiotics (ampicillin and chloramphenicol) so that the coculture can survive in antibiotic concentrations that inhibit growth of either strain alone. Moreover, we find that daily dilutions of the coculture lead to large oscillations in the relative abundance of the two strains, with the ratio of abundances varying by nearly four orders of magnitude over the course of the 3-day period of the oscillation. A simple mechanistic model is consistent with our experimental results. Next, we explore how this mutualism responds to a spatially structured environment where migration connects population patches. We find that intermediate migration rates maximize the probability of survival in harsh environments, whereas high migration rates lead to synchronization and thus risk simultaneous extinction. Interestingly, the increased stability is a result of the perturbed population dynamics that emerge in this regime, rather than ecological rescue. In addition, we explore the spatial expansion of the bacterial mutualism when subject to discrete space (a patchy environment) and discrete time (periodic growth cycles). Theoretical predictions suggest that range expansion of populations with an Allee effect (when average individual fitness increases with population size or density) in these conditions can exhibit pinning (inability to expand at low dispersal rates) and pulsed expansion (periodic or step-like expansion into new territory). Preliminary modeling and experimental results indicate that these phenomena can occur in our system. Our results may help elucidate the impact of migration on microbial population dynamics in spatially structured environments; more broadly, these studies may have implications on how migration influences large networks such as those studied in conservation biology and epidemiology.en_US
dc.description.statementofresponsibilityby Arolyn Conwill.en_US
dc.format.extent149 pagesen_US
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsMIT theses are protected by copyright. They may be viewed, downloaded, or printed from this source but further reproduction or distribution in any format is prohibited without written permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582en_US
dc.subjectPhysics.en_US
dc.titlePopulation oscillations, synchronization, and range expansion in a bacterial cross-protection mutualismen_US
dc.typeThesisen_US
dc.description.degreePh. D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Physics
dc.identifier.oclc1036985718en_US


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