AUTHOR=Klingl Andreas 

TITLE=S-layer and cytoplasmic membrane – exceptions from the typical archaeal cell wall with a focus on double membranes

JOURNAL=Frontiers in Microbiology

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2014.00624

DOI=10.3389/fmicb.2014.00624

ISSN=1664-302X

ABSTRACT=<p>The common idea of typical cell wall architecture in archaea consists of a pseudo-crystalline proteinaceous surface layer (S-layer), situated upon the cytoplasmic membrane. This is true for the majority of described archaea, hitherto. Within the crenarchaea, the S-layer often represents the only cell wall component, but there are various exceptions from this wall architecture. Beside (glycosylated) S-layers in (hyper)thermophilic cren- and euryarchaea as well as halophilic archaea, one can find a great variety of other cell wall structures like proteoglycan-like S-layers (Halobacteria), glutaminylglycan (Natronococci), methanochondroitin (<italic>Methanosarcina</italic>) or double layered cell walls with pseudomurein (<italic>Methanothermus</italic> and <italic>Methanopyrus</italic>). The presence of an outermost cellular membrane in the crenarchaeal species <italic>Ignicoccus hospitalis</italic> already gave indications for an outer membrane similar to Gram-negative bacteria. Although there is just limited data concerning their biochemistry and ultrastructure, recent studies on the euryarchaeal methanogen <italic>Methanomassiliicoccus luminyensis</italic>, cells of the ARMAN group, and the SM1 euryarchaeon delivered further examples for this exceptional cell envelope type consisting of two membranes.</p>