Institute for the Physics of Living Systems


New publication in Current Biology for Baum and Henriques Labs

4 June 2020

Live Imaging of a Hyperthermophilic Archaeon Reveals Distinct Roles for Two ESCRT-III Homologs in Ensuring a Robust and Symmetric Division.

Baum CB

Why try to image live cell divisions in the hyperthermophile Sulfolobus at 75°C? There are several reasons for wanting to do so. First, many cell biological processes previously thought to be unique to eukaryotes are present in a simplified form in TACK archaea (which include the archaeon Sulfolobus) – making this an excellent system in which to study how they work. This includes ESCRT-III and Vps4, which play similar roles in membrane remodelling and cell division in these archaea and in eukaryotes. Second, eukaryotes are known to have arisen from a merger between an archaeal host from the TACK/Asgard family and a bacterial cell that gave rise to the mitochondria. Thus, studying Sulfolobus cell biology promises to give us insights into the origins and evolution of the eukaryotic cell. In a new publication in Current Biology, the Baum and Henriques labs describe the ‘‘Sulfoscope,’’ a microscopy platform that allows live imaging of hyperthermophiles. By imaging cell division in the archaeon Sulfolobus, they observe tight coupling between DNA reorganization and cell division, and complementary roles for two ESCRT-III homologs in ensuring robust and symmetric cytokinesis.


Live-cell imaging has revolutionized our understanding of dynamic cellular processes in bacteria and eukaryotes. Although similar techniques have been applied to the study of halophilic archaea, our ability to explore the cell biology of thermophilic archaea has been limited by the technical challenges of imaging at high temperatures. Sulfolobus are the most intensively studied members of TACK archaea and have well-established molecular genetics. Additionally, studies using Sulfolobus were among the first to reveal striking similarities between the cell biology of eukaryotes and archaea. However, to date, it has not been possible to image Sulfolobus cells as they grow and divide. Here, we report the construction of the Sulfoscope, a heated chamber on an inverted fluorescent microscope that enables live-cell imaging of thermophiles. By using thermostable fluorescent probes together with this system, we were able to image Sulfolobus acidocaldarius cells live to reveal tight coupling between changes in DNA condensation, segregation, and cell division. Furthermore, by imaging deletion mutants, we observed functional differences between the two ESCRT-III proteins implicated in cytokinesis, CdvB1 and CdvB2. The deletion of cdvB1 compromised cell division, causing occasional division failures, whereas the ΔcdvB2 exhibited a profound loss of division symmetry, generating daughter cells that vary widely in size and eventually generating ghost cells. These data indicate that DNA separation and cytokinesis are coordinated in Sulfolobus, as is the case in eukaryotes, and that two contractile ESCRT-III polymers perform distinct roles to ensure that Sulfolobus cells undergo a robust and symmetrical division.