Structural Studies of Planctomycete Gemmata obscuriglobus Support Cell Compartmentalisation in a Bacterium

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.