= Slime mold =

======================================================================
= Slime mold =
======================================================================

Introduction
======================================================================
Slime mold or slime mould is an informal name given to several kinds
of unrelated eukaryotic organisms that can live freely as single
cells, but can aggregate together to form multicellular reproductive
structures. Slime molds were formerly classified as fungi but are no
longer considered part of that kingdom. Although not forming a single
monophyletic clade, they are grouped within the paraphyletic group
referred to as kingdom Protista.

More than 900 species of slime mold occur all over the world. Their
common name refers to part of some of these organisms' life cycles
where they can appear as gelatinous "slime". This is mostly seen with
the Myxogastria, which are the only macroscopic slime molds. Most
slime molds are smaller than a few centimeters, but some species may
reach sizes of up to several square meters and masses of up to 30
grams.

Many slime molds, mainly the "cellular" slime molds, do not spend most
of their time in this state. As long as food is abundant, these slime
molds exist as single-celled organisms. When food is in short supply,
many of these single-celled organisms will congregate and start moving
as a single body. In this state they are sensitive to airborne
chemicals and can detect food sources. They can readily change the
shape and function of parts and may form stalks that produce fruiting
bodies, releasing countless spores, light enough to be carried on the
wind or hitch a ride on passing animals.

They feed on microorganisms that live in any type of dead plant
material. They contribute to the decomposition of dead vegetation, and
feed on bacteria, yeasts, and fungi. For this reason, slime molds are
usually found in soil, lawns, and on the forest floor, commonly on
deciduous logs. However, in tropical areas they are also common on
inflorescences and fruits, and in aerial situations (e.g., in the
canopy of trees). In urban areas, they are found on mulch or even in
the leaf mold in rain gutters, and also grow in air conditioners,
especially when the drain is blocked.

Older classification
======================
Slime molds, as a group, are polyphyletic. They were originally
represented by the subkingdom Gymnomycota in the Fungi kingdom and
included the defunct phyla Myxomycota, Acrasiomycota, and
Labyrinthulomycota. Today, slime molds have been divided among several
supergroups, 'none' of which is included in the kingdom Fungi.

Slime molds can generally be divided into two main groups.
*A plasmodial slime mold is enclosed within a single membrane without
walls and is one large cell. This "supercell" (a syncytium) is
essentially a bag of cytoplasm containing thousands of individual
nuclei. See heterokaryosis.
*By contrast, cellular slime molds spend most of their lives as
individual unicellular protists, but when a chemical signal is
secreted, they assemble into a cluster that acts as one organism.

Modern classification
=======================
In more strict terms, slime molds comprise the mycetozoan group of the
amoebozoa. Mycetozoa include the following three groups:
*Myxogastria or myxomycetes: syncytial, plasmodial, or acellular slime
molds
*Dictyosteliida or dictyostelids: cellular slime molds
*Protosteloids: amoeboid slime-molds that form fruiting bodies

Even at this level of classification there are conflicts to be
resolved. Recent molecular evidence shows that, while the first two
groups are likely to be monophyletic, the protosteloids are likely to
be polyphyletic. For this reason, scientists are currently trying to
understand the relationships among these three groups.

The most commonly encountered are the Myxogastria. A common slime mold
that forms tiny brown tufts on rotting logs is 'Stemonitis'. Another
form, which lives in rotting logs and is often used in research, is
'Physarum polycephalum'. In logs, it has the appearance of a slimy
web-work of yellow threads, up to a few feet in size. 'Fuligo' forms
yellow crusts in mulch.

The 'Dictyosteliida', cellular slime molds, are distantly related to
the plasmodial slime molds and have a very different lifestyle. Their
amoebae do not form huge coenocytes, and remain individual. They live
in similar habitats and feed on microorganisms. When food runs out and
they are ready to form sporangia, they do something radically
different. They release signal molecules into their environment, by
which they find each other and create swarms. These amoeba then join
up into a tiny multicellular slug-like coordinated creature, which
crawls to an open lit place and grows into a fruiting body. Some of
the amoebae become spores to begin the next generation, but some of
the amoebae sacrifice themselves to become a dead stalk, lifting the
spores up into the air.

The protosteloids have characters intermediate between the previous
two groups, but they are much smaller, the fruiting bodies only
forming one to a few spores.

Non-amoebozoan slime moulds include:
*Acrasids (Order Acrasida): slime molds which belong to the
Heterolobosea within the super group Excavata. They have a similar
life style to Dictyostelids, but their amoebae behave differently,
having eruptive pseudopodia. They used to belong to the defunct phylum
of Acrasiomycota.
*Plasmodiophorids (Order Plasmodiophorida): parasitic protists which
belong to the super group Rhizaria. They can cause cabbage club root
disease and powdery scab tuber disease. The Plasmodiophorids also form
coenocytes, but are internal parasites of plants (e.g., Club root
disease of cabbages).
*Labyrinthulomycota: slime nets, which belong to the superphylum
Heterokonta as the class Labyrinthulomycetes. They are marine and form
labyrinthine networks of tubes in which amoeba without pseudopods can
travel.
*'Fonticula' is a cellular slime mold that forms a fruiting body in a
volcano shape. 'Fonticula' is not closely related to either the
Dictyosteliida or the Acrasidae. A 2009 paper finds it to be related
to 'Nuclearia', which in turn is related to fungi.

Grouping Genera Morphology |rowspan=3|Amoebozoa > Conosa >
Mycetozoa Class Myxogastria: 'Cribraria', 'Lycogala', 'Tubifera',
'Echinostelium', 'Fuligo', 'Lepidoderma', 'Physarum', 'Comatricha',
'Stemonitis', 'Arcyria', 'Trichia' |Syncytial or plasmodial slime
molds Class Dictyostelia: 'Dictyostelium', 'Polysphondylium',
'Acytostelium' |Cellular slime molds Class Protostelia:
'Planoprotostelium', 'Protostelium', 'Ceratiomyxa' |Intermediate
between myxomycetes and dictyostelids, but they are much smaller, the
fruiting bodies only forming one to a few spores. Rhizaria >
Cercozoa > Endomyxa > Phytomyxea 'Lignieria', 'Membranosorus',
'Octomyxa', 'Phagomyxa', 'Plasmodiophora', 'Polymyxa', 'Sorodiscus',
'Sorosphaera', 'Spongospora', 'Tetramyxa', 'Woronina' Parasitic
protists that can cause cabbage club root disease and powdery scab
tuber disease. They form coenocytes, but are internal parasites of
plants. Excavata > Percolozoa > Heterolobosea > Acrasida
valign=top |'Acrasis' Chromalveolate > Heterokontophyta >
Labyrinthulomycetes Order Labyrinthulida: 'Labyrinthulids',
'Labyrinthula', 'Thraustochytrids', 'Aplanochytrium',
'Labyrinthuloides', 'Japonochytrium', 'Schizochytrium',
'Thraustochytrium', 'Ulkenia', 'Diplophryids', 'Diplophrys' Slime nets
that are marine and form labyrinthine networks of tubes in which
amoeba without pseudopods can travel. Opisthokonta > Holomycota
> Fonticulida 'Fonticula' Cellular slime mold that forms a fruitin
g
body in a volcano shape.

Life cycle
======================================================================
Slime molds begin life as amoeba-like cells. These unicellular amoebae
are commonly haploid and feed on bacteria. These amoebae can mate if
they encounter the correct mating type and form zygotes that then grow
into plasmodia. These contain many nuclei without cell membranes
between them, and can grow to be meters in size. The species 'Fuligo
septica' is often seen as a slimy yellow network in and on rotting
logs. The amoebae and the plasmodia engulf microorganisms. The
plasmodium grows into an interconnected network of protoplasmic
strands.

Within each protoplasmic strand, the cytoplasmic contents rapidly
stream. If one strand is carefully watched for about 50 seconds, the
cytoplasm can be seen to slow, stop, and then reverse direction. The
streaming protoplasm within a plasmodial strand can reach speeds of up
to 1.35 mm per second, which is the fastest rate recorded for any
microorganism. Migration of the plasmodium is accomplished when more
protoplasm streams to advancing areas and protoplasm is withdrawn from
rear areas. When the food supply wanes, the plasmodium will migrate to
the surface of its substrate and transform into rigid fruiting bodies.
The fruiting bodies or sporangia are what we commonly see; they
superficially look like fungi or molds but are not related to the true
fungi. These sporangia will then release spores which hatch into
amoebae to begin the life cycle again.

Plasmodia
======================================================================
In 'Myxogastria', the plasmodial portion of the life cycle only occurs
after syngamy, which is the fusion of cytoplasm and nuclei of
myxoamoebae or swarm cells. The diploid zygote becomes a
multinucleated plasmodium through multiple nuclear divisions without
further cell division. Myxomycete plasmodia are multinucleate masses
of protoplasm that move by cytoplasmic streaming. In order for the
plasmodium to move, cytoplasm must be diverted towards the leading
edge from the lagging end. This process results in the plasmodium
advancing in fan-like fronts. As it moves, plasmodium also gains
nutrients through the phagocytosis of bacteria and small pieces of
organic matter.

The plasmodium also has the ability to subdivide and establish
separate plasmodia. Conversely, separate plasmodia that are
genetically similar and compatible can fuse together to create a
larger plasmodium. In the event that conditions become dry, the
plasmodium will form a sclerotium, essentially a dry and dormant
state. In the event that conditions become moist again the sclerotium
absorbs water and an active plasmodium is restored. When the food
supply wanes, the Myxomycete plasmodium will enter the next stage of
its life cycle forming haploid spores, often in a well-defined
sporangium or other spore-bearing structure.

Behavior
======================================================================
When a slime mold mass or mound is physically separated, the cells
find their way back to re-unite. Studies on 'Physarum polycephalum'
have even shown an ability to learn and predict periodic unfavorable
conditions in laboratory experiments. John Tyler Bonner, a professor
of ecology known for his studies of slime molds, argues that they are
"no more than a bag of amoebae encased in a thin slime sheath, yet
they manage to have various behaviours that are equal to those of
animals who possess muscles and nerves with ganglia - that is, simple
brains."

Atsushi Tero of Hokkaido University grew 'Physarum' in a flat wet
dish, placing the mold in a central position representing Tokyo and
oat flakes surrounding it corresponding to the locations of other
major cities in the Greater Tokyo Area. As 'Physarum' avoids bright
light, light was used to simulate mountains, water and other obstacles
in the dish. The mold first densely filled the space with plasmodia,
and then thinned the network to focus on efficiently connected
branches. The network strikingly resembled Tokyo's rail system.

Slime mould 'Physarum polycephalum' was also used by Andrew Adamatzky
from the University of the West of England and his colleagues
world-wide in experimental laboratory approximations of motorway
networks of 14 geographical areas: Australia, Africa, Belgium, Brazil,
Canada, China, Germany, Iberia, Italy, Malaysia, Mexico, the
Netherlands, UK and USA.

See also
======================================================================
*Dictyostelium
*Mold, a kind of fungus
*Mycetozoa
*Sorocarp
*Swarming motility
*Water mold, or Oomycete, a kind of protist

External links
======================================================================
*[http://www.abc.net.au/science/articles/2000/09/28/189608.htm?site=galileo&
topic=latest
Slime Mould Solves Maze Puzzle] from abc.net.au
*[http://www.economist.com/sciencetechnology/displaystory.cfm?story_id=15328524
Slime Mould duplicates Rail Networks] from The Economist
*[https://www.newscientist.com/article/mg20527426-300-designing-highways-the-sli
me-mould-way/
Designing highways the slime mould way] from 'New Scientist'
*[https://www.smithsonianmag.com/science-nature/hunting-slime-molds-38805499/
Hunting Slime Molds] from 'Smithsonian Magazine'
*[http://myxomycetes.net Myxomycetes.net] Myxomycetes photo gallery

License
=========
All content on Gopherpedia comes from Wikipedia, and is licensed under CC-BY-SA
License URL: http://creativecommons.org/licenses/by-sa/3.0/
Original Article: http://en.wikipedia.org/wiki/Slime_mold