Identifying the Rules Governing Host-Microbiome Composition and Function

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Project Summary/Abstract All eukaryotes harbor host-associated microbiomes. Determining what regulates host-microbiome function has the potential to revolutionize our approaches towards maintenance of host health. Host genetics and the environment are two key factors that contribute towards host-microbiome composition and function. We aim to advance our understanding of the relative roles of these two factors in regulating assembly of microbial communities, short-term changes in these communities through ecological succession, and long-term changes through evolutionary processes. Further, microbiomes are complex biological networks. Understanding the underlying structure of ecological interactions within these networks can improve predictions for when and how microbiomes might confer beneficial versus deleterious functions associated with disease. Our lab aims to advance fundamental understanding of host-microbiomes by leveraging the microbiomes of microbes. Specifically we employ single-celled eukaryotic phytoplankton as a highly-tractable experimental system. To further these goals we will focus on the following three themes over the next five years. (1) We will couple the unparalleled diversity of phytoplankton with bacterial –omics approaches to test how microbiomes assemble in response to host genetics. By assessing bacterial gene expression responses to host genetics, in tandem with fluctuating environmental conditions, this work will lend insights in to the host genetic x environmental forces that drive microbiome assembly of eukaryotic microbiomes. (2) We will evaluate mechanisms of microbiome change for maintenance of host homeostasis in fluctuating environments, including ecological shifts in bacterial taxonomic composition, shifts in bacterial gene expression, and bacterial strain evolution. It is important to understand the relative roles of these mechanisms because each occurs over different timescales and their effects can have varying degrees of permanence on their host. (3) We will leverage classical community ecology theory in biological networks with recent advances in flow cytometry bacterial fingerprinting to characterize traits of transient versus stable microbiome networks. We will quantify bacteria-bacteria interaction strengths within naturally assembled and engineered microbiomes to understand how network structure contributes to transitions between host health and disease states. Additionally, our research program will elucidate the implications of declining microbial diversity on eukaryotic host health. We will study host- microbiome co-evolutionary mismatches, such as those caused by humans consuming processed diets and living in human-built environments that differ from those of our evolutionary history. Ultimately, our work will leverage a highly tractable experimental system to advance our understanding of the microbiomes that modulate human health.