Determinants underlying horizontal gene transfer-mediated pathogen success

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Project Summary Horizontal gene transfer (HGT), specifically plasmid conjugation, is a driving force in microbial evolution and pathogenesis. The process of conjugation appears deceptively simple: a donor cell transfers a copy of a plasmid to a compatible recipient cell through a physical mating bridge. In doing so, diverse traits, such as metabolic, virulence, and antibiotic resistance genes, can be spread. As such, HGT has been implicated in a variety of human health and industrial applications, ranging from multi-drug resistance to bioremediation. Advances in microbiome studies have revealed that HGT occurs between both closely and distantly related strains, yielding a wide diversity of potential strain/plasmid combinations; despite this, epidemiological surveillance clearly demonstrates that only a small minority of clones and their associated plasmids persist in situ and are highly conserved across different ecological, geographical, and clinical contexts. Thus, it is widely believed that the overall fitness of individual strain-plasmid pairs is a key feature of successful pathogens. Fundamentally, this success is driven by a dynamic interaction between a plasmid-carrying donor and suitable recipient strain in a favorable environment, resulting in the formation of new strain-plasmid pairs (e.g., transconjugants). However, research to date has primarily focused on established strain-plasmid combinations (e.g., donor capabilities and/or plasmid fitness costs); in contrast, the dynamics and factors favoring the initial formation of these combinations are entirely unknown. Yet, such information is critical to both predict new pathogen emergence and develop strategies that intervene in plasmid acquisition before they become established in a population. To address this gap, my research program leverages our unique interdisciplinary expertise in computational modeling, bioinformatics, and mechanistic experiments to investigate the molecular factors favoring the formation of new strain-plasmid combinations. Our proposed themes approach this problem from three complementary perspectives: (1) What genetic features make certain plasmids harder/easier to acquire? (2) What determines a strain’s potential to act as a good HGT recipient? (3) How does environmental selection impact plasmid acquisition capabilities? Combined, these parallel objectives work towards a unified framework that integrates insights across multiple levels of complexity (i.e., molecular to ecological/evolutionary). These research directions contribute to our long-term goal, one that is central to the NIGMS mission, of reliably predicting (and ultimately controlling) clinically relevant strain/plasmid prevalence, and will eventually enable us to anticipate pathogen emergence a priori and explore downstream applications, e.g., novel antibiotic treatment strategies.