Planctomycetes
Encyclopedia
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.
Cavalier-Smith has postulated that the Planctomycetes are within the clade Planctobacteria
in the larger clade Gracilicutes
.
s belonging to this group lack murein
in their cell wall
. Murein is an important heteropolymer
present in most bacteria
l cell walls that serves as a protective component in the cell wall skeleton
. Instead their walls are made up of glycoprotein
rich in glutamate. Planctomycetes have internal structures that are more complex than would be typically expected in prokaryotes. While they do not have a nucleus
in the eukaryotic
sense, the nuclear material
can sometimes be enclosed in a double membrane
. In addition to this nucleoid
, there are two other membrane-separated compartments; the pirellulosome or riboplasm, which contains the ribosome
and related proteins, and the ribosome-free paryphoplasm. Only Epixenosomes
, a group of bacteria related to Verrucomicrobia
, have a more complex structure.
It has recently been shown that the planctomycete 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.
sequencing shows that the planctomycetes are related to the Verrucomicrobia
and possibly the Chlamydiae
. A number of essential pathways are not organised as operon
s, 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.
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.
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
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
of aquatic bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
and are found in samples of brackish
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
, and marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
and fresh
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. They reproduce by budding
Budding
Budding is a form of asexual reproduction in which a new organism grows on another one. The new organism remains attached as it grows, separating from the parent organism only when it is mature. Since the reproduction is asexual, the newly created organism is a clone and is genetically identical...
. In structure, the organisms of this group are ovoid
Oval (geometry)
In technical drawing, an oval is a figure constructed from two pairs of arcs, with two different radii . The arcs are joined at a point, in which lines tangential to both joining arcs lie on the same line, thus making the joint smooth...
and have a holdfast
Holdfast
A holdfast is a root-like structure that anchors aquatic sessile organisms, such as seaweed, other sessile algae, stalked crinoids, benthic cnidarians, and sponges, to the substrate. ...
, 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
Planctobacteria
Planctobacteria is a taxon created by Cavalier-Smith, specifically a division Historically bacteria were considered plants consequently the usage of "division" over "phylum" was brought over when the kindgom Monera was established. The bacteriological code has since imposed that the rank should be...
in the larger clade Gracilicutes
Gracilicutes
Gracilicutes is a controversial taxon in Bacterial taxonomy.Traditionally Gram staining results were most commonly used as a classification tool, consequently until the advent of molecular phylogeny, the Kingdom Prokaryotae was divided into four divisions,*...
.
Structure
The organismOrganism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s belonging to this group lack murein
Peptidoglycan
Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria , forming the cell wall. The sugar component consists of alternating residues of β- linked N-acetylglucosamine and N-acetylmuramic acid...
in their cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
. Murein is an important heteropolymer
Heteropolymer
A heteropolymer or copolymer is a polymer derived from two monomeric species, as opposed to a homopolymer where only one monomer is used...
present in most bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
l cell walls that serves as a protective component in the cell wall skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
. Instead their walls are made up of glycoprotein
Glycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...
rich in glutamate. Planctomycetes have internal structures that are more complex than would be typically expected in prokaryotes. While they do not have a nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
in the eukaryotic
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
sense, the nuclear material
Nuclear material
Nuclear material refers to the metals uranium, plutonium, and thorium, in any form, according to the IAEA. This is differentiated further into "source material", consisting of natural and depleted uranium, and "special fissionable material", consisting of enriched uranium , uranium-233, and...
can sometimes be enclosed in a double membrane
Biological membrane
A biological membrane or biomembrane is an enclosing or separatingmembrane that acts as a selective barrier, within or around a cell. It consists of a lipid bilayer with embedded proteins that may constitute close to 50% of membrane content...
. In addition to this nucleoid
Nucleoid
The nucleoid is an irregularly-shaped region within the cell of a prokaryote that contains all or most of the genetic material. In contrast to the nucleus of a eukaryotic cell, it is not surrounded by a nuclear membrane. The genome of prokaryotic organisms generally is a circular, double-stranded...
, there are two other membrane-separated compartments; the pirellulosome or riboplasm, which contains the ribosome
Ribosome
A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....
and related proteins, and the ribosome-free paryphoplasm. Only Epixenosomes
Epixenosomes
Epixenosomes are prokaryotes phylogenetically related to the bacterial division Verrucomicrobia.The generic name is derived by the episymbiotic adactation of the organisms , indeed they live on the dorsal surface of marine ciliated protozoa of Euplotidium genus...
, a group of bacteria related to Verrucomicrobia
Verrucomicrobia
Verrucomicrobia is a recently described phylum of bacteria. This phylum contains only a few described species . The species identified have been isolated from fresh water and soil environments and human feces...
, have a more complex structure.
It has recently been shown that the planctomycete Gemmata obscuriglobus is able to take in large molecules via a process which in some ways resembles endocytosis
Endocytosis
Endocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...
, the process used by eukaryotic cells to engulf external items.
Genome
RNARNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
sequencing shows that the planctomycetes are related to the Verrucomicrobia
Verrucomicrobia
Verrucomicrobia is a recently described phylum of bacteria. This phylum contains only a few described species . The species identified have been isolated from fresh water and soil environments and human feces...
and possibly the Chlamydiae
Chlamydiae
Chlamydiae is a bacterial phylum and class whose members are obligate intracellular pathogens. Many Chlamydiae coexist in an asymptomatic state within specific hosts, and it is widely believed that these hosts provide a natural reservoir for these species....
. A number of essential pathways are not organised as operon
Operon
In genetics, an operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create...
s, 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
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
to the integrin
Integrin
Integrins are receptors that mediate attachment between a cell and the tissues surrounding it, which may be other cells or the ECM. They also play a role in cell signaling and thereby regulate cellular shape, motility, and the cell cycle....
alpha-V, a protein that is important in transmembrane signal transduction in eukaryotes.
Life cycle
The life cycleBiological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
of many planctomycetes involves alternation between sessile
Sessility (zoology)
In zoology, sessility is a characteristic of animals which are not able to move about. They are usually permanently attached to a solid substrate of some kind, such as a part of a plant or dead tree trunk, a rock, or the hull of a ship in the case of barnacles. Corals lay down their own...
cells and flagellated
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...
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 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 106 by The All-Species Living Tree ProjectNotes:
♠ Strains found at the National Center for Biotechnology Information
National Center for Biotechnology Information
The National Center for Biotechnology Information is part of the United States National Library of Medicine , a branch of the National Institutes of Health. The NCBI is located in Bethesda, Maryland and was founded in 1988 through legislation sponsored by Senator Claude Pepper...
(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