The dictyostelids (Dictyostelia/Dictyostelea,
ICZN
The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its formal author, t ...
, Dictyosteliomycetes,
ICBN
The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN or ICNafp) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all tho ...
) or cellular slime molds are a group of
slime mold
Slime mold or slime mould is an informal name given to a polyphyletic assemblage of unrelated eukaryotic organisms in the Stramenopiles, Rhizaria, Discoba, Amoebozoa and Holomycota clades. Most are near-microscopic; those in the Myxogastria ...
s or social
amoeba
An amoeba (; less commonly spelled ameba or amœba; : amoebas (less commonly, amebas) or amoebae (amebae) ), often called an amoeboid, is a type of Cell (biology), cell or unicellular organism with the ability to alter its shape, primarily by ...
e.
Multicellular behavior

When food (normally bacteria) is readily available dictyostelids behave as individual amoebae, which feed and divide normally. However, when the food supply is exhausted, they aggregate to form a multicellular assembly, called a pseudoplasmodium,
grex, or slug (not to be confused with the
gastropod
Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, freshwater, and fro ...
mollusc
Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...
called a
slug
Slug, or land slug, is a common name for any apparently shell-less Terrestrial mollusc, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...
). The grex has a definite anterior and posterior, responds to light and temperature gradients, and has the ability to migrate. Under the correct circumstances the grex matures forming a
sorocarp
A sorocarp (from the Greek word ''soros'' "a heap" + ''karpos'' "fruit") is the fruiting body characteristic of certain cellular slime moulds (e.g., Dictyosteliida). Each sorocarp consists of both a sorophore (stalk) and a sorus.Lawrence, E. 2 ...
(fruiting body) with a stalk supporting one or more
sori (balls of spores). These spores are inactive cells protected by resistant cell walls, and become new amoebae once food is available.
In ''Acytostelium'', the
sorocarp
A sorocarp (from the Greek word ''soros'' "a heap" + ''karpos'' "fruit") is the fruiting body characteristic of certain cellular slime moulds (e.g., Dictyosteliida). Each sorocarp consists of both a sorophore (stalk) and a sorus.Lawrence, E. 2 ...
is supported by a stalk composed of
cellulose
Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...
, but in other dictyostelids the stalk is composed of cells, sometimes taking up the majority of the original amoebae. With a few exceptions, these cells die during stalk formation, and there is a definite correspondence between parts of the grex and parts of the fruiting body. Aggregation of amoebae generally takes place in converging streams. The amoebae move using filose
pseudopod
A pseudopod or pseudopodium (: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and ...
s, and are attracted to chemicals produced by other amoebae. In ''
Dictyostelium discoideum
''Dictyostelium discoideum'' is a species of soil-dwelling Amoeboid, amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly referred to as slime mold, ''D. discoideum'' is a eukaryote that transitions from a collection of unic ...
'', aggregation is signalled by
cAMP
Camp may refer to:
Areas of confinement, imprisonment, or for execution
* Concentration camp, an internment camp for political prisoners or politically targeted demographics, such as members of national or minority ethnic groups
* Extermination ...
, but others use different chemicals. In the species ''
Dictyostelium purpureum
''Dictyostelium purpureum'' is a species of ''Dictyostelium
''Dictyostelium'' is a genus of single- and multi-celled eukaryotic, phagotrophic bacterivores. Though they are Protista and in no way fungal, they traditionally are known as " ...
'', the grouping is by kinship, not just by proximity.
Uses as model organism
Dictyostelium has been used as a
model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Mo ...
in
molecular biology
Molecular biology is a branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, biomolecular synthesis, modification, mechanisms, and interactio ...
and
genetics
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinians, Augustinian ...
, and is studied as an example of
cell communication
In biology, cell signaling (cell signalling in British English) is the process by which a cell interacts with itself, other cells, and the environment. Cell signaling is a fundamental property of all cellular life in both prokaryotes and eukaryo ...
,
differentiation, and
programmed cell death
Programmed cell death (PCD) sometimes referred to as cell, or cellular suicide is the death of a cell (biology), cell as a result of events inside of a cell, such as apoptosis or autophagy. PCD is carried out in a biological process, which usual ...
. It is also an interesting example of the evolution of cooperation and cheating. A large body of research data concerning ''
D. discoideum'' is available on-line at
DictyBase
dictyBase is an online bioinformatics database for the model organism ''Dictyostelium discoideum
''Dictyostelium discoideum'' is a species of soil-dwelling Amoeboid, amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly ref ...
.
Mechanism of aggregation in ''Dictyostelium discoideum''
The mechanism behind the aggregation of the amoebae relies on
cyclic adenosine monophosphate
Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger, or cellular signal occurring within cells, that is important in many biological processes. cAMP is a derivative of adenosine tri ...
(cAMP) as a signal molecule. One cell, the founder of the colony, begins to secrete cAMP in response to stress. Others detect this signal, and respond in two ways:
*The amoeba moves towards the signal.
*The amoeba secretes more cAMP to boost the signal.
The effect of this is to relay the signal throughout the nearby population of amoebae and cause inward movement to the area of highest cAMP concentration.
Within an individual cell, the mechanism is as follows:
#cAMP reception at the cell membrane activates a
G-protein
G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their ...
#G protein stimulates
Adenylate cyclase
Adenylate cyclase (EC 4.6.1.1, also commonly known as adenyl cyclase and adenylyl cyclase, abbreviated AC) is an enzyme with systematic name ATP diphosphate-lyase (cyclizing; 3′,5′-cyclic-AMP-forming). It catalyzes the following reaction:
:A ...
#cAMP diffuses out of cell into medium
#Internal cAMP inactivates the external cAMP receptor.
#A different g-protein stimulates
Phospholipase C
Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure). It is most commonly taken to be synonymous with the human forms of this enzyme, which play an important role i ...
#
IP3 induces calcium ion release
#Calcium ions act on the
cytoskeleton
The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compos ...
to induce the extension of
pseudopod
A pseudopod or pseudopodium (: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and ...
ia.
Because the internal cAMP concentration inactivates the receptor for external cAMP, an individual cell shows
oscillatory
Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...
behaviour. This behaviour produces beautiful spirals seen in converging colonies and is reminiscent of the
Belousov–Zhabotinsky reaction
A Belousov–Zhabotinsky reaction, or BZ reaction, is one of a class of reactions that serve as a classical example of non-equilibrium thermodynamics, resulting in the establishment of a nonlinear chemical oscillator. The only common element in ...
and two-dimensional
cyclic cellular automata.
Genome
The entire genome of ''
Dictyostelium discoideum
''Dictyostelium discoideum'' is a species of soil-dwelling Amoeboid, amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly referred to as slime mold, ''D. discoideum'' is a eukaryote that transitions from a collection of unic ...
'' was published in ''
Nature
Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...
'' in 2005 by geneticist
Ludwig Eichinger and coworkers.
The haploid genome contains approximately 12,500 genes on 6 chromosomes. For comparison, the diploid
human genome
The human genome is a complete set of nucleic acid sequences for humans, encoded as the DNA within each of the 23 distinct chromosomes in the cell nucleus. A small DNA molecule is found within individual Mitochondrial DNA, mitochondria. These ar ...
has 20,000-25,000 genes (represented twice) on 23 chromosome pairs. There is a high level of the nucleotides
adenosine
Adenosine (symbol A) is an organic compound that occurs widely in nature in the form of diverse derivatives. The molecule consists of an adenine attached to a ribose via a β-N9- glycosidic bond. Adenosine is one of the four nucleoside build ...
and
thymidine
Thymidine (nucleoside#List of nucleosides and corresponding nucleobases, symbol dT or dThd), also known as deoxythymidine, deoxyribosylthymine, or thymine deoxyriboside, is a pyrimidine nucleoside, deoxynucleoside. Deoxythymidine is the DNA nuc ...
(~77%) leading to a codon usage that favors more adenosines and thymidines in the third position. Tandem repeats of trinucleotides are abundant in Dictyostelium, which in humans cause
Trinucleotide repeat disorders
In genetics, trinucleotide repeat disorders, a subset of microsatellite expansion diseases (also known as repeat expansion disorders), are a set of over 30 genetic disorders caused by trinucleotide repeat expansion, a kind of mutation in which r ...
.
Sexual reproduction
Sexual development can occur when amoeboid cells are starved for their bacterial food supply and dark humid conditions are present.
Both heterothallic and homothallic strains of Dictostelium can undergo mating. Heterothallic sexual development has been most extensively studied in ''
D. discoideum'', and homothallic sexual development has been most well studied in ''D. mucoroides''.
Heterothallic matings are initiated by fusion of haploid cells (gametes) from two strains of opposite mating type. This contrasts with homothallic strains that appear to express both mating types.
Mating is initiated by gametogenesis that produces small, motile gametes that fuse to form a small
binucleate cell. The volume of the binucleate cell then increases to produce a giant binuclear cell. As growth proceeds, the nuclei swell, and then fuse forming a true diploid zygote giant cell. As this is occurring, amoebae have been undergoing cAMP-induced
chemotaxis
Chemotaxis (from ''chemical substance, chemo-'' + ''taxis'') is the movement of an organism or entity in response to a chemical stimulus. Somatic cells, bacteria, and other single-cell organism, single-cell or multicellular organisms direct thei ...
towards the giant cell surface. This forms a cellular aggregate and at the center of the aggregate the zygote giant cell ingests the surrounding amoebae. Phagocytosis is followed by digestion of the ingested amoebae. Next the zygote forms a macrocyst characterized by a surrounding extracellular cellulose sheath. After the macrocyst is formed it ordinarily remains dormant for a period before germination can occur. Within the macrocyst the diploid zygote undergoes meiosis followed by successive mitotic divisions. When the macrocyst germinates it releases many haploid amoeboid cells.
Taxonomy
Classification history
The Dictyostelium phylogeny tree has undergone multiple changes in the past decades. The first dictyostelid to be described was ''Dictyostelium mucoroides'' in 1869 by Osker Brefeld, and the original discovery of ''Dictyostelium discoideum'' occurred in 1935, with further discoveries from
Kenneth Raper
Kenneth Bryan Raper (July 11, 1908 – January 15, 1987) was an American mycologist.
Life
Kenneth B. Raper was born in 1908 as the seventh of eight children to William F. Raper and his wife Julia. The children all worked on the family farm in Wel ...
, followed by global efforts led by
James Cavender
James may refer to:
People
* James (given name)
* James (surname)
* James (musician), aka Faruq Mahfuz Anam James, (born 1964), Bollywood musician
* James, brother of Jesus
* King James (disambiguation), various kings named James
* Prince James ...
and collaborators. ''Dictyostelium discoideum'' was initially classified under ‘lower fungi,’ but the classification has since shifted the classification to under the Amoebozoa phylum where it is currently.
The groupings within the dictyostelid phylogeny tree has undergone frequent reordering due to availability new evidence. Most currently accepted phylogenies of dictyostelids utilize genome sequencing and
small subunit ribosomal DNA (ssu-rDNA). The dictyostelids can be further subdivided into four groups. In particular, group 4 contains the ''Dictyostelium discoideum'' species and differs from the other groups with its usage of cAMP as an attractant emitted during aggregation.
Evolution
Fossil calibrations indicate that dictyostelids class originally diverged into two major branches approximately 0.52 billion years ago. Current theories speculate that dictyostelid stalk and spore formation originally evolved as an adaption to global glacial formations. Further subdivision of dictyostelids species likely arose as most glacial formations melted. Most species in major groups 1, 2, and 3 display an encystment ability that allows individuals to survive low temperatures, but spores have shown an increased ability in resisting lower temperatures. Group 4 differs from other major groups in a general lacking ability to encyst, but its spores have shown better resistances against lower temperatures relative to spores from other groups.
The internal phylogeny of the Dictyostelids is shown in the
cladogram
A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
.
Taxonomy
Class Dictyostelia
Lister 1909 em. Olive 1970
* Genus ?''
Calospeira''
Arnaud 1949
* Genus ?''
Coenonia''
van Tieghem 1884 non Vandamme et al. 1999
* Genus ?''
Synstelium''
Baldauf, Sheikh & Thulin 2017
* Order
Actyosteliales Baldauf, Sheikh & Thulin 2017
** Family
Cavenderiaceae Baldauf, Sheikh & Thulin 2017
*** Genus ''
Cavenderia''
Baldauf, Sheikh & Thulin 2017
** Family
Acytosteliidae Raper ex Raper & Quinlan 1958
*** Genus ''
Acytostelium
''Acytostelium'' is a genus of dictyostelid.
The genus ''Acytostelium'' inhabit surface humus and leaf mold of forest soils and are widely distributed in different forests of the world.
Species include:
* '' Acytostelium aggregatum'' Cavender ...
''
Raper 1956
*** Genus ''
Heterostelium''
Baldauf, Sheikh & Thulin 2017
*** Genus ''
Rostrostelium''
Baldauf, Sheikh & Thulin 2017
* Order
Dictyosteliales
The dictyostelids (Dictyostelia/Dictyostelea, ICZN, Dictyosteliomycetes, ICBN) or cellular slime molds are a group of slime molds or social amoebae.
Multicellular behavior
When food (normally bacteria) is readily available dictyostelids behave ...
Olive ex Kirk, Cannon & David 2001
** Genus ?''
Coremiostelium''
Baldauf, Sheikh & Thulin 2017
** Genus ?''
Heliomycopsis''
Arnaud 1949
** Genus ?''
Pygmomyces''
Arnaud 1949
** Genus †?''
Myxomitodes''
Bengtson et al. 2007
** Genus ?''
Rhabdocystis''
Arnaud 1949
** Family
Dictyosteliidae Rostafinski 1875 ex Cooke 1877
*** ''
Dictyostelium
''Dictyostelium'' is a genus of single- and multi-celled eukaryotic, phagotrophic bacterivores. Though they are Protista and in no way fungal, they traditionally are known as "slime molds". They are present in most terrestrial ecosystems a ...
''
Brefeld 1870
*** ''
Polysphondylium
''Polysphondylium'' is a genus of cellular slime mold, including the species ''Polysphondylium pallidum''. The genus was circumscribed by German mycologist Julius Oscar Brefeld in 1884.
Species
*'' Polysphondylium acuminatum'' Vadell & Cavender ...
''
Brefeld 1884
** Family
Raperosteliaceae Baldauf, Sheikh & Thulin 2017
*** Genus ''
Hagiwaraea''
Baldauf, Sheikh & Thulin 2017
*** Genus ''
Raperostelium''
Baldauf, Sheikh & Thulin 2017
*** Genus ''
Speleostelium''
Baldauf, Sheikh & Thulin 2017
*** Genus ''
Tieghemostelium''
Baldauf, Sheikh & Thulin 2017
Model host organism for ''Legionella''
''Dictyostelium'' shares many molecular features with
macrophages
Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...
, the human host of ''
Legionella
''Legionella'' is a genus of gram-negative bacteria, gram-negative bacteria that can be seen using a silver stain or grown in a special media that contains cysteine, an amino acid. It is known to cause legionellosis (all illnesses caused by ''Legi ...
''. The cytoskeletal composition of ''D. discoideum'' is similar to that of mammalian cells as are the processes driven by these components, such as phagocytosis, membrane trafficking, endocytic transit and vesicle sorting. Like leukocytes, ''D. discoideum'' possess chemotactic capacity. Hence, ''D. discoideum'' represents a suitable model system to ascertain the influence of a variety of host cell factors during ''
Legionella
''Legionella'' is a genus of gram-negative bacteria, gram-negative bacteria that can be seen using a silver stain or grown in a special media that contains cysteine, an amino acid. It is known to cause legionellosis (all illnesses caused by ''Legi ...
'' infections.
References
External links
''Dictyostelium'' (2007)dictyBaseOnline Informatics Resource for ''Dictyostelium''
dictyBase wikiofficial wiki site for dictyBase
''Dictyostelium discoideum'' Genome Project''Dictyostelium discoideum'' description, life cycle
{{Taxonbar, from=Q17583501, from2=Q310364, from3=Q33225272, from4=Q33225355, from5=Q33225219
Eumycetozoa