The Planctomycetes, Chlamydiae Verrucomicrobia/Lentisphaerae grouping is supported by 16S and 23S rRNA sequence analysis [12, 13]. Another study based on both phylogenetics of concatenated protein datasets and shared conserved inserts in proteins has supported

the link between the phyla Verrucomicrobia and Chlamydiae [14]. Other studies based on either 16S and 23S rRNA gene sequences [15], or individual or concatenated protein sequences [16, 17], have shown this website no specific relationships between the three phyla, Verrucomicrobia, Planctomycetes and Chlamydiae. However, for one of these studies [15] sequences from some superphylum lineages were not yet available and thus sequence selection may have influenced tree topology. In another of these studies [17], the inability to detect the PVC superphylum may have resulted from a loss of resolution due to editing concatenated sequence data to allow inclusion of a wide range of taxa including those of Eukaryotes. It is known that all members of the phylum Planctomycetes so far examined possess a characteristic cell plan involving compartmentalization of the cell cytoplasm by an intracytoplasmic membrane (ICM) separating the cytoplasm into two regions, the inner ribosome-containing pirellulosome and the less central ribosome-free paryphoplasm [18,

19]. The term “”pirellulosome”" was first introduced to describe a major nucleoid-containing cell compartment of planctomycetes bounded by an internal membrane, Mdivi1 concentration the intracytoplasmic Thalidomide membrane (ICM). A ribosome-free “”paryphoplasm”" region check details surrounds the pirellulosome and is separated from it by the ICM [18]. Based on the proposed relationships between the three lineages, we hypothesized that members of Planctomycetes and Verrucomicrobia might share

a similar ultrastructure plan. This is investigated in this study using transmission electron microscopy incorporating techniques such as high pressure freezing, cryosubstitution and freeze fracture, to examine four verrucomicrobia representing three of the six subdivisions. Results By applying high-pressure freezing, cryosubstitution and freeze-fracture techniques, internal compartmentalization of the cell has been observed in four representatives of the phylum Verrucomicrobia. The four species examined, Verrucomicrobium spinosum, Prosthecobacter dejongeii, Chthoniobacter flavus, and verrucomicrobia strain Ellin514, represent four genera and three distinct subdivisions (1, 2 and 3) of the phylum. Cells of all four species were examined after high-pressure freezing and cryosubstitution or after preparation of replicas of freeze-fractured cells. Cells of all four displayed features that are consistent with compartmentalization of the cell cytoplasm by internal membranes.