{"689144":{"#nid":"689144","#data":{"type":"event","title":"PhD Defense by Hayley B. Hassler","body":[{"value":"\u003Cp\u003EIn partial fulfillment of the requirements for the degree of\u003C\/p\u003E\u003Cp\u003EDoctor of Philosophy in Quantitative Biosciences\u003Cbr\u003Ein the School of Biological Sciences\u003C\/p\u003E\u003Cp\u003EHayley B. Hassler\u003Cbr\u003E\u003Cbr\u003EDefends her thesis:\u003Cbr\u003EBacterial systems across scales: quantitative frameworks for within-host, ecological, and evolutionary dynamics\u003Cbr\u003E\u003Cbr\u003EFriday, April 3, 2026\u003Cbr\u003E1:00pm Eastern\u003Cbr\u003ELocation: IBB Suddath Seminar Room (1128)\u003Cbr\u003EZoom: \u0026nbsp;https:\/\/gatech.zoom.us\/j\/94408297865?pwd=OY25pGlaYyh8ul1Tw0nrBsh7eeYO9S.1\u003C\/p\u003E\u003Cp\u003EThesis Advisor:\u0026nbsp;\u003Cbr\u003EDr. Loren Dean Williams\u003Cbr\u003ESchool of Chemistry and Biochemistry\u003Cbr\u003EGeorgia Institute of Technology\u003Cbr\u003E\u003Cbr\u003ECommittee:\u0026nbsp;\u003Cbr\u003EDr. Gregory P. Fournier\u003Cbr\u003EEarth, Atmospheric, and Planetary Sciences\u003Cbr\u003EMassachusetts Institute of Technology\u003Cbr\u003E\u003Cbr\u003EDr. Eberhard O. Voit\u003Cbr\u003ESchool of Natural Sciences and Mathematics\u003Cbr\u003EUniversity of Texas, Dallas\u003Cbr\u003E\u003Cbr\u003EDr. William C. Ratcliff\u003Cbr\u003ESchool of Biological Sciences\u003Cbr\u003EGeorgia Institute of Technology\u003C\/p\u003E\u003Cp\u003EDr. Amit R. Reddi\u003Cbr\u003ESchool of Chemistry and Biochemistry\u003Cbr\u003EGeorgia Institute of Technology\u003C\/p\u003E\u003Cp\u003EDr. Claudia Alvarez-Carre\u00f1o\u003Cbr\u003EStructural and Molecular Biology\u003Cbr\u003EUniversity College London\u003Cbr\u003E\u003Cbr\u003EAbstract:\u003Cbr\u003EBacteria are shaped by forces operating across vastly different scales: within-host population dynamics, ecological pressures on trait maintenance, and evolutionary history that fixed core cellular machinery billions of years ago. This dissertation develops quantitative frameworks across all three scales, arguing that understanding bacterial behavior requires integrating all three together.\u0026nbsp;\u003Cbr\u003EA mathematical model of Clostridioides difficile infection, calibrated on murine microbiome data, reveals that susceptibility arises from a dual-insult mechanism: reduced commensal carrying capacity and increased commensal susceptibility to C. difficile inhibition. Neither perturbation alone causes infection, but together they create a permissive state. Spore formation allows C. difficile to persist through antibiotics and reestablish once commensals are suppressed, explaining why antibiotics alone fail. FMT following antibiotics breaks this cycle, accelerating commensal recovery threefold.\u0026nbsp;\u003Cbr\u003EReanalysis of Type VI Secretion System prevalence across 44,160 genomes revises the canonical estimate from 25% to approximately 40% of Gram-negative genera. The T6SS carries no detectable metabolic cost, so its highly patchy distribution at every taxonomic level implicates ecological context, specifically competitor identity and density, as the dominant selective force governing weapon maintenance.\u0026nbsp;\u003Cbr\u003EEvolutionary rate analysis across 528 Last Bacterial Common Ancestor genes reveals a continuous temporal gradient of peak evolutionary activity. Genetic Information Processing genes peak earliest, while Metabolic genes peak latest. Earlier-peaking genes are also significantly more likely to occupy central positions in the protein interaction network. This gradient is framed within Earth\u0027s geobiological record, consistent with environmental transitions having shaped when different cellular systems were free to diversify.\u003C\/p\u003E\u003Cp\u003EAcross all three chapters, bacterial behavior emerges as a product of immediate community context, the selective pressures that favor or disfavor particular traits, and the deep evolutionary history that constrains what options are available. Together, these chapters demonstrate how quantitative approaches can move bacterial research from description to mechanism, and from mechanism toward prediction.\u003C\/p\u003E\u003Cp\u003E\u0026nbsp;\u003C\/p\u003E","summary":"","format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003E\u003Cstrong\u003EBacterial systems across scales: quantitative frameworks for within-host, ecological, and evolutionary dynamics\u003C\/strong\u003E\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Bacterial systems across scales: quantitative frameworks for within-host, ecological, and evolutionary dynamics"}],"uid":"27707","created_gmt":"2026-03-23 19:44:08","changed_gmt":"2026-03-23 19:44:34","author":"Tatianna Richardson","boilerplate_text":"","field_publication":"","field_article_url":"","field_event_time":{"event_time_start":"2026-04-03T13:00:00-04:00","event_time_end":"2026-04-03T15:00:00-04:00","event_time_end_last":"2026-04-03T15:00:00-04:00","gmt_time_start":"2026-04-03 17:00:00","gmt_time_end":"2026-04-03 19:00:00","gmt_time_end_last":"2026-04-03 19:00:00","rrule":null,"timezone":"America\/New_York"},"location":"IBB Suddath Seminar Room (1128)","extras":[],"groups":[{"id":"221981","name":"Graduate Studies"}],"categories":[],"keywords":[{"id":"100811","name":"Phd Defense"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[{"id":"1788","name":"Other\/Miscellaneous"}],"invited_audience":[{"id":"78771","name":"Public"}],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[],"email":[],"slides":[],"orientation":[],"userdata":""}}}