Planctomycetes

Planctomycetes are a phylum of bacteria that exhibit several unusual characteristics, setting them apart from most other bacterial groups. They are typically found in aquatic environments, including freshwater, marine, and brackish waters, and some are also found in soil. A defining feature of many planctomycetes is their lack of a peptidoglycan cell wall, a common structural component in bacteria. Instead, their cell envelopes are more complex and can include proteinaceous S-layers.

Another remarkable trait is the presence of internal membrane-bound organelles within the cytoplasm of some species. These include structures like the nucleoid, which is enclosed by a membrane, and the planctomycetalian vacuoles (PVs), which are distinct compartments. This internal compartmentalization is highly unusual for prokaryotes, which generally lack membrane-bound organelles. Furthermore, some planctomycetes form complex multicellular communities called "rosettes," where individual cells attach to each other via specialized stalks. Reproduction in some species also involves a budding process, reminiscent of eukaryotic cell division. Their unique biology and ecological roles are subjects of ongoing research.