Cell Division Dynamics in cell-walled Archaea

The Archaea, originally thought to be microorganisms only living in extreme environments have recently taken center stage as ubiquitous, ecologically and evolutionary important prokaryotes (organisms who lack a nucleus and other cell organelles). Moreover, methane- producing archaea live in the gastrointestinal tract of humans and other animals, but their role in the intestine is poorly understood. Even less is known about the way how archaea grow and divide, because most cell biology research has been focused on eukaryotes (organisms whose cells have a nucleus such as animals, plants and fungi) and bacteria. At first glance archaea are similar to bacteria, both are small single cell prokaryotes, but there are major differences, for example the mechanisms for genetic information transmission and their cell wall composition. The cell wall of bacteria is composed of peptidoglycan (PG), whereas archaea have more diverse cell walls that lack PG. Interestingly, only two orders of methane-producing archaea, Methanobacteriales and Methanopyrales have a cell wall made of pseudopepdidoglycan (pPG), which is structurally similar to that of bacteria but biochemically different In order to divide, archaea need to grow and then constrict their cell wall, and these processes need to be coordinated spatially and timewise. In bacteria, the main cell division protein is FtsZ, that forms a ring (Z-ring) at the division plane and interacts with several other proteins. The Z-ring is anchored to the membrane by either the FtsA, ZipA, or SepF protein and is placed at mid cell by the MinC and MinD proteins. With the exception of FtsZ, SepF and MinD, archaea lack most of of bacterial cell division proteins, suggesting the existence of a different cell division machinery in these microbes. Recently, it was demonstrated that in human- associated Methanobrevibacter smithii (Methanobacteriales) the Z-ring is anchored by SepF, but structural and fluorescence microscopy data revealed an FtsZ/SepF interaction and localization different from bacteria. Further, Methanopyrus kandleri (Methanopyrales) is the only archaeon known to have FtsA. The research hypothesis for this work is that the cell division machinery in archaea with a pPG cell wall is different compared to archaea without pPG. The main research questions are: How do SepF and/or FtsA influence the dynamics of FtsZ? Are the Min proteins responsible for Z- ring placement? What is the function and localization of SepF and FtsA during the cell cycle i n M. kandleri? To answer these questions a combination of cell biology and biophysical approaches, high-resolution microscopy and evolutionary analysis will be used. Ultimately, this project will provide fundamental information concerning cellular processes coordinating cell division in archaea with a pPG cell wall, that have adapted to inhabit a wide range of environments from hot springs to the human gut.