title: Grappling archaea: ultrastructural analyses of an uncultivated, cold-loving archaeon, and its biofilm.
abstract: Similarly to Bacteria, Archaea are microorganisms that interact with their surrounding environment in a versatile manner. To date, interactions based on cellular structure and surface appendages have mainly been documented using model systems of cultivable archaea under laboratory conditions. Here, we report on the microbial interactions and ultrastructural features of the uncultivated SM1 Euryarchaeon, which is highly dominant in its biotope. Therefore, biofilm samples taken from the Sippenauer Moor, Germany, were investigated via transmission electron microscopy (TEM; negative staining, thin-sectioning) and scanning electron microscopy (SEM) in order to elucidate the fine structures of the microbial cells and the biofilm itself. The biofilm consisted of small archaeal cocci (0.6 μm diameter), arranged in a regular pattern (1.0-2.0 μm distance from cell to cell), whereas each archaeon was connected to 6 other archaea on average. Extracellular polymeric substances (EPS) were limited to the close vicinity of the archaeal cells, and specific cell surface appendages (hami, Moissl et al., 2005) protruded beyond the EPS matrix enabling microbial interaction by cell-cell contacts among the archaea and between archaea and bacteria. All analyzed hami revealed their previously described architecture of nano-grappling hooks and barb-wire basal structures. Considering the archaeal cell walls, the SM1 Euryarchaea exhibited a double-membrane, which has rarely been reported for members of this phylogenetic domain. Based on these findings, the current generalized picture on archaeal cell walls needs to be revisited, as archaeal cell structures are more complex and sophisticated than previously assumed, particularly when looking into the uncultivated majority.
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Alexandra K
authors.initials: AK
authors.lastname: Perras
authors.affiliation: Department of Biology I, Biozentrum Ludwig Maximilian University of Munich Planegg-Martinsried, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wanner
authors.affiliation: Department of Biology I, Biozentrum Ludwig Maximilian University of Munich Planegg-Martinsried, Germany ; Zellbiologie, Philipps-Universität Marburg Marburg, Germany ; LOEWE Research Centre for Synthetic Microbiology (Synmikro) Marbug, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Klingl
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Mora
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Anna K
authors.initials: AK
authors.lastname: Auerbach
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Veronika
authors.initials: V
authors.lastname: Heinz
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Probst
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Huber
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Rachel
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Meck
authors.affiliation: Department of Microbiology and Archaea Center, University of Regensburg Regensburg, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Moissl-Eichinger
keywords: EPS; SEM; TEM; archaea; biofilm; hami; microbial interaction; ultrastructure