Planctomycetes do possess a peptidoglycan cell wall
Planctomycetes are a phylum of aquatic bacteria and are found in samples of brackish, and marine and fresh water. They reproduce by budding. In structure, the organisms of this group are ovoid and have a holdfast, at the tip of a thin cylindrical extension from the cell body called the stalk, at the nonreproductive end that helps them to attach to each other during budding.
Cavalier-Smith has postulated that the Planctomycetes are within the clade Planctobacteria in the larger clade Gracilicutes, but this is not generally accepted.
Structure
For a long time bacteria belonging to this group were considered to lack peptidoglycan, (also called murein) in their cell walls, which is an important heteropolymer present in most bacterial cell walls that serves as a protective component. It was thought that instead their walls were made up of glycoprotein which is rich in glutamate. Recently, however, representatives of all three clades within the Planctomycetes were found to possess peptidoglycan containing cell walls.
Planctomycetes have a distinctive morphology with the appearance of membrane-bound internal compartments, often referred to as the paryphoplasm (ribosome-free space), pirellulosome (ribosome-containing space) and nucleoid (condensed nucleic acid region, in these species surrounded by a double membrane). Until the discovery of the Poribacteria, planctomycetes were the only bacteria known with these apparent internal compartments. Three-dimensional electron tomography reconstruction of a representative species, Gemmata obscuriglobus, has yielded varying interpretations of this observation. One 2013 study found the appearance of internal compartments to be due to a densely invaginated but continuous single membrane, concluding that only the two compartments typical of Gram-negative bacteria - the cytoplasm and periplasm - are present. However, the excess membrane triples the surface area of the cell relative to its volume, which may be related to Gemmata's sterol biosynthesis abilities. A 2014 study using similar methods reported confirmation of the earlier enclosed compartment hypothesis.
It has recently been shown that Gemmata obscuriglobus is able to take in large molecules via a process which in some ways resembles endocytosis, the process used by eukaryotic cells to engulf external items.
Molecular Signatures
Although the Planctomycetes are renowned for their unusual cellular characteristics, their distinctness from all other bacteria is additionally supported by the shared presence of two conserved signature indels (CSIs). These CSIs demarcate the group from neighboring phyla within the PVC group. An additional CSI has been found that is shared by all Planctomycetes species, with the exception of Kuenenia stuttgartiensis, which is in line with the observation that K. stuttgartiensis forms a deep branch within the phylum.
A conserved signature indel has also been found to be shared by the entire PVC group, including Planctomycetes. Planctomycetes also harbours an important conserved signature protein that has been characterized to play an important housekeeping function that is exclusive to members belonging to the PVC clade.
Life cycle
The life cycle of many planctomycetes involves alternation between sessile cells and flagellated swarmer cells. The sessile cells bud to form the flagellated swarmer cells which swim for a while before settling down to attach and begin reproduction.
Phylogeny
The phylogeny based on the work of the All-Species Living Tree Project.
Taxonomy
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LSPN) and the National Center for Biotechnology Information (NCBI).
Species Planctomicrobium piriforme Kulichevskaya et al. 2015
Genus Planctomyces Gimesi 1924
Species P. bekefii ♪ Gimesi 1924 (type sp.) ["Blastocaulis sphaerica" Henrici & Johnson 1935; "Acinothrix globulifera" Novácek 1938; "Planctomyces subulatus" Wawrik 1952; "Planctomyces crassus" Hortobágyi 1965]
Species P. guttaeformis ♪ (ex Hortobágyi 1965) Starr and Schmidt 1984
Species P. stranskae ♪ (ex Wawrik 1952) Starr and Schmidt 1984
Genus Planctopirus Scheuner et al. 2015
Species Planctopirus limnophila corrig. (Hirsch & Muller 1986) Scheuner et al. 2015 [Planctomyces limnophilus Hirsch and Müller 1986]
Genus Rhodopirellula Schlesner et al. 2004
Species R. baltica Schlesner et al. 2004 (type sp.)
Species R. caenicola Yoon et al. 2015
Species R. rosea Roh et al. 2014
Species R. rubra Bondoso et al. 2014
Species R. lusitana Bondoso et al. 2014
Species "R. europaea" ♠ Frank 2011
Species "R. islandica" ♠ Kizina et al. 2015
Species "R. maiorica" ♠ Frank 2011
Species "R. sallentina" ♠ Frank 2011
Genus Roseimaritima Bondoso et al. 2015
Species Roseimaritima ulvae Bondoso et al. 2015
Genus Rubinisphaera Scheuner et al. 2015
Species Rubinisphaera brasiliensis (Schlesner 1990) Scheuner et al. 2015 [Planctomyces brasiliensis Schlesner 1990]
Genus Rubripirellula Bondoso et al. 2015
Species Rubripirellula obstinata Bondoso et al. 2015
Genus Schlesneria Kulichevskaya et al. 2007
Species Schlesneria paludicola Kulichevskaya et al. 2007
Genus Singulisphaera Kulichevskaya et al. 2008 emend. Kulichevskaya et al. 2012
Species "S. mucilaginosa" ♠ Zaicnikova et al. 2011
Species S. acidiphila Kulichevskaya et al. 2008 (type sp.)
Species S. rosea Kulichevskaya et al. 2012
Genus Telmatocola Kulichevskaya et al. 2012
Species Telmatocola sphagniphila Kulichevskaya et al. 2012
Genus Thermogutta Slobodkina et al. 2015
Species T. hypogea Slobodkina et al. 2015
Species T. terrifontis Slobodkina et al. 2015
Genus Thermostilla Slobodkina et al. 2015
Species Thermostilla marina Slobodkina et al. 2015
Genus Zavarzinella Kulichevskaya et al. 2009
Species Zavarzinella formosa Kulichevskaya et al. 2009
Notes: ♠ Strains found at the National Center for Biotechnology Information (NCBI) but not listed in the List of Prokaryotic names with Standing in Nomenclature (LSPN) ♪ Prokaryotes where no pure (axenic) cultures are isolated or available, i. e. not cultivated or can not be sustained in culture for more than a few serial passages