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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/12/29 23:14:33」(JST)

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Dictyostelium are Dictyostelid single- and multi-celled eukaryotic, phagotrophic bacterivores usually present and often abundant in terrestrial ecosystems and are a normal component of the microflora that help in soil balance between bacteria and soils.^[1] The amoeba are often grouped as slime molds. The order is the Dictyosteliida (Dictyostelid cellular slime molds or social amoebae. ) Dictyosteliida contains organisms that hover on the borderline between uni- and multicellularity. The protists are often found on organic matter or in soils and caves. Typically, cells grow separately and independently but interact to form multi-cellular structures when challenged by adverse conditions such as starvation. Up to 1,000,000 cells signal each other by releasing chemoattractants such as cyclic AMP (cAMP) or glorin, and coalesce by chemotaxis to form an aggregate that becomes surrounded by an extracellular matrix and may move collectively before differentiating into a fruiting body.^[2] Basic processes of development such as differential cell sorting, pattern formation, stimulus-induced gene expression, and cell-type regulation are common to Dictyostelium and metazoans. For further detail see family Dictyostelid.

Discovery

The cellular slime molds were formerly considered to be fungi following their discovery in 1869 by Brefeld. Although they resemble fungi in some respects, they have been included in the Protista kingdom.^[3] Individual cells resemble small amoebae in their movement and feeding, and so are referred to as myxamoebae. D. discoideum is the most studied of the genus.

Importance

Schematic of Dictyostelium life cycle

Most of its life, this haploid social amoeba undergoes a vegetative cycle, preying upon bacteria in the soil, and periodically dividing mitotically. When food is scarce, either the sexual cycle or the social cycle begins. Under the social cycle, amoebae aggregate in response to cAMP by the thousands, and form a motile slug, which moves towards light. Ultimately the slug forms a fruiting body in which about 20% of the cells die to lift the remaining cells up to a better place for sporulation and dispersal.

When starved for their bacterial food supply and exposed to dark, moist conditions, heterothallic or homothallic strains can undergo sexual development that results in the formation of a diploid zygote.^[4] Heterothallic mating has been best studied in Dictyostelium discoideum and homothallic mating has been best studied in Dictyostelium mucoroides (strain DM7). In the heterothallic sexual cycle, amoebae aggregate in response to cAMP and sex pheromones, and two cells of opposite mating types fuse, and then begin consuming the other attracted cells. Before they are consumed, some of the prey cells form a cellulose wall around the entire group. When cannibalism is complete, the giant diploid cell is a hardy macrocyst which eventually undergoes recombination and meiosis, and hatches hundreds of recombinants.^[5]^[6] In D. mucoroides (DM7) homothallic mating, cells are directed towards sexual development by ethylene.^[4]

Professor John Tyler Bonner has spent a lifetime researching the slime molds and created a number of fascinating videos in the 1940s to show the life cycle; he has mostly studied D. discoideum. In the videos, intelligence appears to be observed as the single cells, after separation, regroup into a cellular mass. The time-lapse film captivated audiences; indeed, Bonner when giving conferences has stated that the film “always stole the show”.^[7] The video is available on YouTube.^[8]

Species

Taxonomy of D.sp is complicated. It has also been confused by the different forms in the life cycle stages and by the similar Polysphondylium spp. Below are some reported examples.

Dictyostelium caveatum (Wadell 1982)
Dictyostelium discoideum
Dictyostelium iregularis (Olive, Nelson and Stoianovitch 1967)
Dictyostelium lacteum
Dictyostelium minutum
Dictyostelium mucoroides
Dictyostelium polycephalum
Dictyostelium purpureum
Dictyostelium rosarium

References

^ Landolt. C. (2006) Dictyostelid Cellular Slime Molds from Caves. Journal of Cave and Karst studies v. 68 no. 1 pp. 22-26.
^ http://dictybase.org/tutorial/about_dictyostelium.htm
^ Kessin, R (1944). ISBN 0-521-58364-0.
^ ^a ^b O'Day DH, Keszei A (May 2012). "Signalling and sex in the social amoebozoans". Biol Rev Camb Philos Soc 87 (2): 313–29. doi:10.1111/j.1469-185X.2011.00200.x. PMID 21929567.
^ http://www.ruf.rice.edu/~bioslabs/studies/invertebrates/dicty.html
^ http://dictybase.org/
^ http://embryo.asu.edu/view/embryo:125124
^ http://www.youtube.com/watch?v=bkVhLJLG7ug

English Journal

Two distinct sensing pathways allow recognition of Klebsiella pneumoniae by Dictyostelium amoebae.

Lima WC, Balestrino D, Forestier C, Cosson P.Author information Department for Cell Physiology and Metabolism, Centre Medical Universitaire, University of Geneva, 1 rue Michel Servet, 1211, Geneva 4, Switzerland.AbstractRecognition of bacteria by metazoans is mediated by receptors that recognize different types of microorganisms and elicit specific cellular responses. The soil amoebae Dictyostelium discoideum feeds upon a variable mixture of environmental bacteria, and it is expected to recognize and adapt to various food sources. To date, however, no bacteria-sensing mechanisms have been described. In this study, we isolated a Dictyostelium mutant (fspA KO) unable to grow in the presence of non-capsulated Klebsiella pneumoniae bacteria, but growing as efficiently as wild-type cells in the presence of other bacteria, such as Bacillus subtilis. fspA KO cells were also unable to respond to K. pneumoniae and more specifically to bacterially secreted folate in a chemokinetic assay, while they responded readily to B. subtilis. Remarkably, both WT and fspA KO cells were able to grow in the presence of capsulated LM21 K. pneumoniae, and responded to purified capsule, indicating that capsule recognition may represent an alternative, FspA-independent mechanism for K. pneumoniae sensing. When LM21 capsule synthesis genes were deleted, growth and chemokinetic response were lost for fspA KO cells, but not for WT cells. Altogether, these results indicate that Dictyostelium amoebae use specific recognition mechanisms to respond to different K. pneumoniae elements.
Cellular microbiology.Cell Microbiol.2014 Mar;16(3):311-23. doi: 10.1111/cmi.12226. Epub 2013 Nov 6.
Recognition of bacteria by metazoans is mediated by receptors that recognize different types of microorganisms and elicit specific cellular responses. The soil amoebae Dictyostelium discoideum feeds upon a variable mixture of environmental bacteria, and it is expected to recognize and adapt to vario
PMID 24128258

Analysis of Rheb in the cellular slime mold Dictyostelium discoideum: Cellular localization, spatial expression and overexpression.

Swer PB, Bhadoriya P, Saran S.Author information School of Life Science, Jawaharlal Nehru University, New Delhi 110 067, India.AbstractDictyostelium discoideum encodes a single Rheb protein showing sequence similarity to human homologues of Rheb. The DdRheb protein shares 52 percent identity and 100 percent similarity with the human Rheb1 protein. Fluorescence of Rheb yellow fluorescent protein fusion was detected in the D. discoideum cytoplasm. Reverse transcription-polymerase chain reaction and whole-mount in situ hybridization analyses showed that rheb is expressed at all stages of development and in prestalk cells in the multicellular structures developed. When the expression of rheb as a fusion with lacZ was driven under its own promoter, the beta-galactosidase activity was seen in the prestalk cells. D. discoideum overexpressing Rheb shows an increase in the size of the cell. Treatment of the overexpressing Rheb cells with rapamycin confirms its involvement in the TOR signalling pathway.
Journal of biosciences.J Biosci.2014 Mar;39(1):75-84.
Dictyostelium discoideum encodes a single Rheb protein showing sequence similarity to human homologues of Rheb. The DdRheb protein shares 52 percent identity and 100 percent similarity with the human Rheb1 protein. Fluorescence of Rheb yellow fluorescent protein fusion was detected in the D. discoid
PMID 24499792

Japanese Journal

Steely Enzymes Are Involved in Prestalk and Prespore Pattern Formation

SATO Yukie G.,KAGAMI Haruna N.,NARITA Takaaki B. [他]
Bioscience, Biotechnology, and Biochemistry 77(10), 2008-2012, 2013-10
NAID 40019850815

Glycogen Synthase Kinase 3 influences cell motility and chemotaxis by regulating PI3K membrane localization in Dictyostelium

Sun Tong,Kim Bohye,Kim Lou W.
Development, growth & differentiation 55(8), 723-734, 2013-10
NAID 40019848547

Related Pictures

★リンクテーブル★

リンク元	「タマホコリカビ属」「Dictyosteliida」「タマホコリカビ類」「ディクチオステリウム属」「cellular slime mold」
拡張検索	「Dictyostelium属」「Dictyostelium discoideum」

「タマホコリカビ属」

Dictyostelium
Scientific classification
Domain:	Eukarya
Kingdom:	Amoebozoa
Phylum:	Mycetozoa
Class:	Dictyostelia
Order:	Dictyosteliida
Family:	Dictyosteliidae
Genus:	Dictyostelium