Elucidating mechanisms of archaeal adaptation to changing environments through cell shape and biofilm studies

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Doctor of Philosophy (PhD)
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cell shape
Haloferax volcanii
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Schiller, Heather

Microorganisms encounter diverse environments, whether favorable or hostile. Responding appropriately to such dynamic environments is crucial to ensure cell survival, including cells of species within the domain Archaea. Archaea, while considered prokaryotes like bacteria, are closely related evolutionarily to eukaryotes, and their ubiquity in the environment and as part of the human microbiome poses them as crucial players in various microbial processes. Yet, comparatively little is known about archaea and the ways in which they respond to their environments. Examples of such responses include cell-shape transition and biofilm formation, both of which can be observed in the model archaeon Haloferax volcanii. Hfx. volcanii can form elongated rods in early-log growth phase and when swimming, while irregularly shaped disks occur in mid- and late-log growth phases and are hypothesized to be important for nutrient uptake and surface adhesion. However, few components are known to be important for shape, and the functions of shape are not well-studied. In addition to morphological transitions, planktonic Hfx. volcanii can transition into two types of biofilms: surface-attached and immersed liquid biofilms. Some proteins important for static surface-attached biofilms have been elucidated, but assessment of these biofilms under shear-force conditions is lacking; conversely, the proteins important for immersed liquid biofilms have not been identified. In this work, I identified and characterized regulatory and cytoskeletal components important for cell shape, including a novel actin homolog. I also reported phenotypic differences in surface-attached biofilms formed under static versus shear-force conditions and determined that the components required for immersed liquid biofilms are completely distinct from those of surface-attached biofilms. Lastly, I began to assess the function of cell shape in the context of biofilms through identifying the shape of cells within wild-type biofilms and proposing a model for adhesion and biofilm formation on the basis of shape. Insights into these processes allow us to gain a more comprehensive understanding of cell biological processes within archaea as well as potentially uncover similar mechanisms of regulation in bacteria and eukaryotes.

Pohlschroder, Mechthild
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