Elucidating the regulation and spread of an integrative and conjugative element from Streptococcus mutans in the oral microbiome

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Project Summary/Abstract Microbial evolution is dominated by horizontal gene transfer (HGT), which is prevalent in bacterial biofilms such as dental plaque. HGT is often mediated by conjugative elements, mobile genetic elements that encode machinery to transfer the element from a host (donor) cell to a recipient cell, thereby generating a new bacterial host. Integrative and conjugative elements (ICEs) appear to be the most prevalent type of conjugative element and some mediate genetic exchange between diverse bacterial species. ICEs play a critical role in the spread of virulence traits and antibiotic resistances within multidrug resistant pathogens. ICEs, or putative ICEs, are prevalent in oral bacteria. Streptococcus mutans, a major causative agent of dental caries, contains an uncharacterized ICE TnSmu1. This proposal undertakes the first characterization of TnSmu1 as a model of HGT within this critical oral pathogen. The data show that TnSmu1 is a functional ICE: It can excise from the host chromosome and transfer to recipient cells. The physiological function(s) of TnSmu1 and its ability to drive HGT in the oral cavity are unknown. This study tests the hypothesis that TnSmu1 activation is affected by host physiological signals and TnSmu1 presence in oral Streptococci allows increased survival in oral communities. This proposal will elucidate the regulation and fitness attributes of TnSmu1 and its ability to transfer to other members of the oral microbiome. Two transcription factors, CovR and SloR, encoded by S. mutans (i.e., not in TnSmu1), control many virulence genes involved in caries formation and bind the predicted regulatory region of TnSmu1. This study examines if these factors link the pathogenic attributes of S. mutans to its role in HGT. This proposal will investigate the role of CovR and SloR and the physiological conditions that regulate them on the excision and transfer of TnSmu1. This work tests the ability of TnSmu1 to spread within the diverse oral communities of dental plaque, transferring itself and other mobile genetic elements to different oral bacterial species. It will also define the cost/benefit of TnSmu1 to its host cells, as its presence may impact S. mutans fitness in the oral cavity. At the conclusion of these studies, this work will have created a new understanding of HGT, evolution, and pathogenesis of S. mutans within the oral microbiome. Additionally, this work will result in tools to genetically manipulate many oral microbes that lack robust genetic systems. The fellowship training plan provides the fellow with training in bacterial genetics while leveraging the fellow’s background with host pathogen interactions. Dr. Grossman (sponsor) is a renowned bacterial geneticist and molecular biologist that has >30 years of mentorship experience as a professor with many postdoctoral trainees obtaining independent research positions. The research environment in this lab and within the Massachusetts Institute of Technology serves to address the aims of the research proposed and to aid in the applicant’s development as an independent researcher and long term as an academic professor.