Abstract
Members of phylum Planctomycetes have been proposed to possess atypical cell organisation for the Bacteria, having a structure of sectioned cells consistent with internal compartments surrounded by membranes. Here via electron tomography we confirm the presence of compartments in the planctomycete Gemmata obscuriglobus cells. Resulting 3-D models for the most prominent structures, nuclear body and riboplasm, demonstrate their entirely membrane - enclosed nature. Immunogold localization of the FtsK protein also supports the internal organisation of G.obscuriglobus cells and their unique mechanism of cell division. We discuss how these new data expand our knowledge on bacterial cell biology and suggest evolutionary consequences of the findings.
Highlights
Past structural studies [1,2,3] have revealed unique cell organisation of the planctomycete bacteria, including the separation of their cytoplasm into compartments via internal membranes [4,5]
Any ribosome-containing cytoplasm in the pirellulosome region including that surrounding nucleoid has been called riboplasm, but here for convenience in distinguishing G. obscuriglobus compartments, this term will be confined to those regions containing ribosomes but not nucleoid
A possibility for rearrangements of riboplasm vesicles is demonstrated in Movie S3 and corresponding Figure S2 in File S1
Summary
Past structural studies [1,2,3] have revealed unique cell organisation of the planctomycete bacteria, including the separation of their cytoplasm into compartments via internal membranes [4,5]. In the planctomycete Gemmata obscuriglobus even a compartment bounded by an envelope, and enclosing the nucleoid DNA, and lying within the pirellulosome, has been suggested [1]. The functions of these structures are obscure due to lack of biochemical and molecular biology studies, so that almost all our current knowledge about the planctomycete cell organisation have been acquired via transmission electron microscopy (TEM) [1,2,3]. Our data on immunogold localisation of the cell division protein FtsK suggest a new mechanism of cell division, previously not described within Bacteria
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