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Oomycota or oomycetes () form a distinct
phylogenetic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

phylogenetic
lineage of
fungus A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungus
-like
eukaryotic Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
microorganisms A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...

microorganisms
. They are
filamentous The word filament, which is descended from Latin ''filum'' meaning "Thread (yarn), thread", is used in English for a variety of thread-like structures, including: In commerce * Fiber or, more loosely, yarn * Filament (textiles) In physics and en ...
and
heterotrophic A heterotroph (; from Ancient Greek "other" and "nutrition") is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are prim ...
, and can reproduce both sexually and asexually. Sexual reproduction of an
oospore An oospore is a thick-walled sexual spore In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular ...

oospore
is the result of contact between
hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by a ...

hyphae
of male
antheridia An antheridium is a haploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins cal ...

antheridia
and female
oogonia An oogonium (plural oogonia) is a small diploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal gen ...
; these spores can overwinter and are known as resting spores. Asexual reproduction involves the formation of
chlamydosporesA chlamydospore is the thick-walled large resting spore of several kinds of fungi A fungus (plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, gramm ...
and
sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a unicellular organism, single cell or can be multicellular organism, multicellular. All plants, fungus, fungi, and many other lineages for ...
, producing
motile Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with Sessility (motility), sessility, the ...
zoospores A zoospore is a motility, motile asexual spore that uses a flagellum for motion (physics), locomotion. Also called a swarm spore, these spores are created by some Protist, protists, bacteria, and fungi to propagate themselves. Diversity Flagella ty ...
. Oomycetes occupy both
saprophytic Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion Extracellular Phototropic Digestion is a process in which saprobionts feed by secreting enzymes through the cell membrane onto the food. ...
and
pathogenic In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory ...
lifestyles, and include some of the most notorious pathogens of plants, causing devastating diseases such as late blight of potato and
sudden oak death {{See Wiktionary, the fictional character named Sudden James Green aka "Sudden" is a fictional character created by an English author Oliver Strange in the early 1930s as the hero of a series, originally published by George Newnes Books Ltd, s ...
. One oomycete, the mycoparasite '''', is used for
biocontrol Biological control or biocontrol is a method of controlling pests such as insect Insects (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of commu ...
, attacking plant pathogenic fungi. The oomycetes are also often referred to as water molds (or water moulds), although the water-preferring nature which led to that name is not true of most species, which are terrestrial pathogens. Oomycetes were originally grouped with
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
due to similarities in morphology and lifestyle. However, molecular and phylogenetic studies revealed significant differences between fungi and oomycetes which means the latter are now grouped with the
stramenopiles Stramenopile is a clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - ...
(which include some types of
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Co ...

algae
). The Oomycota have a very sparse fossil record; a possible oomycete has been described from
Cretaceous The Cretaceous ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of division ...

Cretaceous
amber Amber is fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communi ...

amber
.


Etymology

Oomycota comes from the
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
ωόν (oon, 'egg') and μύκητας (mykitas, 'fungus'), referring to the large round
oogonia An oogonium (plural oogonia) is a small diploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal gen ...
, structures containing the female gametes, that are characteristic of the oomycetes. The name "water mold" refers to their earlier classification as fungi and their preference for conditions of high humidity and running surface water, which is characteristic for the basal taxa of the oomycetes.


Morphology

The oomycetes rarely have septa (see
hypha A hypha (; ) is a long, branching, filamentous structure of a fungus A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any ...
), and if they do, they are scarce, appearing at the bases of sporangia, and sometimes in older parts of the filaments. Some are unicellular, while others are filamentous and branching.


Classification

Previously the group was arranged into six orders. * The
Saprolegniales Saprolegniales is an order of freshwater mould. References Heterokont orders {{watermould-stub ...
are the most widespread. Many break down decaying matter; others are parasites. * The
Leptomitales Leptomitales are an order of water mould Oomycota or oomycetes () form a distinct phylogenetic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, ...
have wall thickenings that give their continuous cell body the appearance of septation. They bear chitin and often reproduce asexually. * The Rhipidiales use rhizoids to attach their thallus to the bed of stagnant or polluted water bodies. * The Albuginales are considered by some authors to be a family (Albuginaceae) within the Peronosporales, although it has been shown that they are phylogenetically distinct from this order. * The
Peronosporales The Peronosporales are an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or ...
too are mainly saprophytic or parasitic on plants, and have an aseptate, branching form. Many of the most damaging agricultural parasites belong to this order. * The
Lagenidiales Oomycota or oomycetes () form a distinct Phylogeny, phylogenetic lineage of Fungi, fungus-like eukaryotic microorganisms. They are Mycelia, filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oo ...
are the most primitive; some are filamentous, others unicellular; they are generally parasitic. However more recently this has been expanded considerably. * Anisolpidiales Dick 2001 ** Anisolpidiaceae Karling 1943 * Lagenismatales Dick 2001 ** Lagenismataceae Dick 1995 * Salilagenidiales Dick 2001 ** Salilagenidiaceae Dick 1995 * Rozellopsidales Dick 2001 ** Rozellopsidaceae Dick 1995 ** Pseudosphaeritaceae Dick 1995 * Ectrogellales ** Ectrogellaceae * Haptoglossales ** Haptoglossaceae * Eurychasmales ** Eurychasmataceae Petersen 1905 * Haliphthorales ** Haliphthoraceae Vishniac 1958 * Olpidiopsidales ** Sirolpidiaceae Cejp 1959 ** Pontismataceae Petersen 1909 ** Olpidiopsidaceae Cejp 1959 * Atkinsiellales ** Atkinisellaceae ** Crypticolaceae Dick 1995 *
Saprolegniales Saprolegniales is an order of freshwater mould. References Heterokont orders {{watermould-stub ...
** Achlyaceae ** Verrucalvaceae Dick 1984 **
Saprolegniaceae Saprolegniaceae is a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typica ...
Warm. 1884 eptolegniaceae*
Leptomitales Leptomitales are an order of water mould Oomycota or oomycetes () form a distinct phylogenetic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, ...
** Leptomitaceae Kuetz. 1843 podachlyellaceae Dick 1986** Leptolegniellaceae Dick 1971 ucellieriaceae Dick 1995* Rhipidiales ** Rhipidiaceae Cejp 1959 * Albuginales **
Albuginaceae Albuginaceae is a family of oomycetes. Genera and species Albuginaceae contains the following subtaxa: *''Albugo'' **''Albugo achyranthis'' **''Albugo aechmantherae'' **''Albugo arenosa'' **''Albugo austroafricana'' **''Albugo candida'' **''Al ...
Schroet. 1893 *
Peronosporales The Peronosporales are an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or ...
ythiales; Sclerosporales; Lagenidiales** Salisapiliaceae **
Pythiaceae Pythiaceae is a family (biology), family of water moulds. The family includes serious plant and animal pathogens in the genus ''Pythium''. The family was circumscribed by German mycologist Joseph Schröter in 1893. Lifecycle *Live on land (terres ...
Schroet. 1893 ythiogetonaceae; Lagenaceae Dick 1994; Lagenidiaceae; Peronophythoraceae; Myzocytiopsidaceae Dick 1995**
Peronosporaceae Peronosporaceae are a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typic ...
Warm. 1884 clerosporaceae Dick 1984


Phylogenetic relationships


Internal


External

This group was originally classified among the
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
(the name "oomycota" means "egg fungus") and later treated as
protists A protist () is any eukaryotic Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...
, based on general morphology and lifestyle. A
cladistic Cladistics (; ) is an approach to biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular ...
analysis based on modern discoveries about the biology of these organisms supports a relatively close relationship with some photosynthetic organisms, such as
brown alga The brown algae (singular: alga), comprising the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Cl ...
e and
diatom Diatoms (''diá-tom-os'' 'cut in half', from ''diá'', 'through' or 'apart', and the root of ''tém-n-ō'', 'I cut') are a major group of algae Algae (; singular alga ) is an informal term for a large and diverse group of s. It is a grou ...

diatom
s. A common
taxonomic classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...
based on these data, places the
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
Oomycota along with other classes such as Phaeophyceae (brown algae) within the
phylum In biology, a phylum (; plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken fr ...
Heterokonta Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which a ...
. This relationship is supported by a number of observed differences between the characteristics of oomycetes and fungi. For instance, the
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane cell membrane vs. Prokaryotes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to a ...
s of oomycetes are composed of
cellulose Cellulose is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

cellulose
rather than
chitin Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. The second most abundant polysaccharide in nature (behind only cellulose), it ...

chitin
and generally do not have . Also, in the vegetative state they have
diploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chromosomes refer to the number of mate ...
nuclei, whereas fungi have
haploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by ...
nuclei. Most oomycetes produce self-motile zoospores with two
flagella A flagellum (; ) is a hairlike appendage that protrudes from a wide range of microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and ...
. One flagellum has a "whiplash" morphology, and the other a branched "tinsel" morphology. The "tinsel" flagellum is unique to the Kingdom Heterokonta. Spores of the few fungal groups which retain flagella (such as the
Chytridiomycetes Chytridiomycetes () is a class (biology), class of fungi. Members are found in soil, fresh water, and saline estuaries. They are first known from the Rhynie chert. It has recently been redefined to exclude the taxa Neocallimastigomycota and Mon ...
) have only one whiplash flagellum. Oomycota and fungi have different metabolic pathways for synthesizing
lysine Lysine (symbol Lys or K) is an α-amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, ...

lysine
and have a number of enzymes that differ. The ultrastructure is also different, with oomycota having tubular mitochondrial
cristae A crista (; plural cristae) is a fold in the inner membrane of a mitochondrion A mitochondrion (; ) is a double-membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it al ...
and fungi having flattened cristae. In spite of this, many
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
of oomycetes are still described or listed as types of fungi and may sometimes be referred to as pseudofungi, or lower fungi.


Biology


Reproduction

Most of the oomycetes produce two distinct types of spores. The main dispersive spores are asexual, self-motile
spore In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...
s called
zoospore A zoospore is a motile Motility is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of li ...
s, which are capable of chemotaxis (movement toward or away from a chemical signal, such as those released by potential food sources) in surface water (including precipitation on plant surfaces). A few oomycetes produce aerial asexual spores that are distributed by wind. They also produce sexual spores, called
oospore An oospore is a thick-walled sexual spore In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular ...

oospore
s, that are translucent, double-walled, spherical structures used to survive adverse environmental conditions.


Ecology and pathogenicity

Many oomycetes species are economically important, aggressive algae and plant pathogens. Some species can cause disease in fish, and at least one is a pathogen of mammals. The majority of the plant pathogenic species can be classified into four groups, although more exist. * The ''
Phytophthora ''Phytophthora'' (from Greek language, Greek (''phytón''), "plant" and (), "destruction"; "the plant-destroyer") is a genus of plant-damaging oomycetes (water molds), whose member species are capable of causing enormous economic losses on cro ...
'' group is a
paraphyletic In taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only ...

paraphyletic
genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
that causes diseases such as dieback,
late blight ''Phytophthora infestans'' is an oomycete or Oomycete, water mold, a fungus-like microorganism that causes the serious potato and tomato disease known as late blight or potato blight. Early blight, caused by ''Alternaria solani'', is also often c ...
in
potato The potato is a starch#Food, starchy tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial plant, perennial in the nightshade family Solanaceae. Wild potato species can be found thro ...

potato
es (the cause of the Great Famine of the 1840s that ravaged
Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic. It is separated from Great Britain to its east by the North Channel (Great Britain and Ireland), North Channel, the Irish Sea ...

Ireland
and other parts of Europe),
sudden oak death {{See Wiktionary, the fictional character named Sudden James Green aka "Sudden" is a fictional character created by an English author Oliver Strange in the early 1930s as the hero of a series, originally published by George Newnes Books Ltd, s ...
,
rhododendron root rot ''Phytophthora cactorum'' is a fungus-like plant pathogen that causes root rot on rhododendron and many other species, as well as leather rot on Strawberry, strawberries. . Hosts, symptoms, and diagnosis ''Phytophthora cactorum'' has an extremel ...
, and ink disease in the * The
paraphyletic In taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only ...

paraphyletic
''
Pythium ''Pythium'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circums ...
'' group is more prevalent than ''Phytophthora'' and individual species have larger host ranges, although usually causing less damage. ''Pythium''
damping off Damping off (or damping-off) is a horticultural disease or condition, caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate Germination is the process by which an organism In ...
is a very common problem in greenhouses, where the organism kills newly emerged seedlings. Mycoparasitic members of this group (e.g. '''') parasitize other oomycetes and fungi, and have been employed as biocontrol agents. One ''Pythium'' species, ''Pythium insidiosum'', also causes
Pythiosis Image:Pythiosis hyphae.jpg, ''Pythium'' hyphae Pythiosis is a rare and deadly tropical disease caused by the oomycete ''Pythium insidiosum''. Long regarded as being caused by a fungus, the causative agent was not discovered until 1987. It occurs mos ...
in mammals. * The third group are the
downy mildew Downy mildew refers to any of several types of oomycete microbes that are obligate parasites of plants. Downy mildews exclusively belong to Peronosporaceae. In commerce, commercial agriculture, they are a particular problem for growers of Crucife ...
s, which are easily identifiable by the appearance of white, brownish or olive "mildew" on the leaf undersides (although this group can be confused with the unrelated fungal
powdery mildew Powdery mildew is a fungus, fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as it ...

powdery mildew
s). * The fourth group are the white blister rusts, Albuginales, which cause white blister disease on a variety of flowering plants. White blister rusts sporulate beneath the
epidermis The epidermis is the outermost of the three layers that comprise the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of animal Animals (also calle ...
of their hosts, causing spore-filled blisters on stems, leaves and the
inflorescence An inflorescence is a group or cluster of flower A flower, sometimes known as a bloom or blossom Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some ...
. The Albuginales are currently divided into three genera, ''
Albugo ''Albugo'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscr ...
'' parasitic predominantly to
Brassicales The Brassicales (or Cruciales) are an order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associ ...
, ''
Pustula ''Pustula'' is a genus of plant-parasitic oomycetes segregated from ''Albugo''. The name is derived from Latin's ''pustula'' meaning "blister". References

{{reflist Water mould genera Albuginaceae ru:Albuginaceae ...
'', parasitic predominantly to Asterales, and ''Wilsoniana'', predominantly parasitic to Caryophyllales. Like the downy mildews, the white blister rusts are obligate biotrophic, biotrophs, which means that they are unable to survive without the presence of a living host.


References


External links


Description of The Phylum Oomycota
– Systematic Biology

– University of California Museum of Paleontology (UCMP)

{{Taxonbar, from1=Q223597, from2=Q61997516 Water moulds,