|Families & Genera|
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, called the stalk, at the nonreproductive end that helps them to attach to each other during budding.
The bacteria belonging to this group 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. Instead their walls are made up of glycoprotein which is rich in glutamate. For a long time Planctomycetes were thought to be unique in that, unlike other prokaryotes, they contained intracellular compartments separated by membranes. Compartments that were often quoted in literature were paryphoplasm (ribosome-free space), pirellulosome (ribosome-containing space) and even a nucleoid surrounded by a double membrane. However, Santarella-Mellwig et al have recently shown (2013), that the apparent internal compartments seen in microscope images of Gemmata obscuriglobus (a Planctomycetes species) are in fact interconnected and are surrounded by only a single highly convoluted membrane. Therefore, like other gram-negative bacteria Gemmata has only 2 compartments present, namely cytoplasm and periplasm. The authors calculated that excess of membrane triplicates the surface area of the cell relative to its volume and they suggest that this might have enabled Gemmata to retain an ancient pathway of sterol synthesis.
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.
RNA sequencing shows that the planctomycetes are related to the Verrucomicrobia and possibly the Chlamydiae. A number of essential pathways are not organised as operons, which is unusual for bacteria. A number of genes have been found (through sequence comparisons) that are similar to genes found in eukaryotes. One such example is a gene sequence (in Gemmata obscuriglobus) that was found to have significant homology to the integrin alpha-V, a protein that is important in transmembrane signal transduction in eukaryotes.
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.
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LSPN)  and the phylogeny is based on 16S rRNA-based LTP release 111 by The All-Species Living Tree Project 
♠ 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
- Beyond Prokaryotes and Eukaryotes : Planctomycetes and Cell Organization.
- Gemmata at Microbewiki