''Trichomonas'' is a genus of
anaerobic
Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to:
* Anaerobic adhesive, a bonding a ...
excavate parasites of vertebrates. It was first discovered by
Alfred François Donné
Alfred François Donné (13 September 1801 – 7 March 1878) was a French bacteriologist and doctor. He was born in Noyon, France, and died in Paris. Donné was the discoverer of Trichomonas vaginalis. He was also the inventor of the photomicrogr ...
in 1836 when he found these parasites in the pus of a patient suffering from
vaginitis
Vaginitis, also known as vulvovaginitis, is inflammation of the vagina and vulva. Symptoms may include itching, burning, pain, discharge, and a bad smell. Certain types of vaginitis may result in complications during pregnancy.
The three main ...
, an inflammation of the vagina. Donné named the genus from its morphological characteristics. The prefix tricho- originates from the
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
word (thrix) meaning hair, describing ''Trichomonas''’s
flagella
A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
A microorganism may have f ...
. The suffix -monas ( – single unit), describes its similarity to unicellular organisms from the genus ''
Monas
The National Monument ( id, Monumen Nasional, abbreviated Monas) is a 132 m (433 ft) obelisk in the centre of Merdeka Square, Central Jakarta, symbolizing the fight for Indonesia. It is the national monument of the Republic of Indones ...
''.
Habitat and ecology
''Trichomonas'' is typically found in
anaerobic
Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to:
* Anaerobic adhesive, a bonding a ...
environments. It is a known parasite of many different animals including humans, birds, dogs, and cats.
In humans, it can be found in the
urogenital tract
The genitourinary system, or urogenital system, are the organs of the reproductive system and the urinary system. These are grouped together because of their proximity to each other, their common embryological origin and the use of common pathwa ...
and in the oral cavity. It is estimated that 276 million new cases of urogenital infections occur each year.
Depending on the ''Trichomonas'' species, it can either be transmitted through direct sexual contact or through contaminated water sources.
In birds, it can be found in the upper digestive tract and is transmitted when adult birds regurgitate food to feed their young, when a bird of prey feeds on an infected bird, and through contaminated food or water.
Morphology
''Trichomonas'' is around 10 µm in length and is normally pear-shaped. It has four
flagella
A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
A microorganism may have f ...
at its anterior end, distinguishing itself from closely related organisms that have different numbers of anterior flagella. At the base of these flagella are the parabasal bodies,
kinetosomes accompanied by Golgi stacks. The pelta is a sheet of
microtubules
Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm and have an inner diameter between 11 an ...
that curve around the flagellar bases. Posterior to the pelta is the
axostyle An axostyle is a sheet of microtubules found in certain protists. It arises from the bases of the flagella, sometimes projecting beyond the end of the cell, and is often flexible or contractile, and so may be involved in movement and provides suppo ...
, is a bundle of microtubules that extends from the anterior end of the organism all the way to the posterior end. The
nucleus
Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
*Atomic nucleus, the very dense central region of an atom
*Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucle ...
of ''Trichomonas'' is situated close to where the pelta and axostyle meet.
Another distinguishing feature of ''Trichomonas'' is the presence of an undulating membrane. The undulating membrane is a fin-like extension of the plasma membrane located on the side of the organism. A flagellum that extends to the posterior end of the organism is attached to the outer edge of the undulating membrane. At the base of the undulating membrane is a striated fiber called the costa which is thought to exist for structural support.
''Trichomonas'' has a very interesting
organelle
In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...
: the
hydrogenosome
A hydrogenosome is a membrane-enclosed organelle found in some anaerobic ciliates, flagellates, and fungi. Hydrogenosomes are highly variable organelles that have presumably evolved from protomitochondria to produce molecular hydrogen and ATP in ...
.
Hydrogenosomes are double-membraned organelles used by trichomonads, instead of
mitochondria
A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...
, to produce
ATP. They do not require oxygen and instead use
pyruvate
Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell.
Pyruvic aci ...
:
ferredoxin
Ferredoxins (from Latin ''ferrum'': iron + redox, often abbreviated "fd") are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied t ...
oxido-reductase and
hydrogenase A hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen (H2), as shown below:
Hydrogen uptake () is coupled to the reduction of electron acceptors such as oxygen, nitrate, sulfate, carbon dioxide (), and fumara ...
to produce ATP from pyruvate, generating
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
gas as a by-product.
Genetics
''
Trichomonas vaginalis
''Trichomonas vaginalis'' is an anaerobic, flagellated protozoan parasite and the causative agent of a sexually transmitted disease called trichomoniasis. It is the most common pathogenic protozoan that infects humans in industrialized countries ...
'', being the species that causes the most complications in humans, is the only fully sequenced ''Trichomonas'' species. Through whole-genome shotgun sequencing, the ''Trichomonas vaginalis'' genome is estimated to be around 160 Mb long, divided into six chromosomes. However, at least 65% of its genome was found to be redundant. The redundant genetic material is hypothesized to have emerged during ''Trichomonass transition from aerobic to anaerobic environments.
In addition to discovering the large proportion of
repetitive DNA
Repeated sequences (also known as repetitive elements, repeating units or repeats) are short or long patterns of nucleic acids (DNA or RNA) that occur in multiple copies throughout the genome. In many organisms, a significant fraction of the genom ...
in ''Trichomonas vaginalis'' genome, the sequenced genes were also characterized. Approximately 60,000
protein-coding gene
The human genome is a complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. These are usually treated separately as the n ...
s were found.
Transfer RNA
Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino ac ...
s for all 20
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
s and approximately 250
ribosomal RNA
Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...
were all found on the same
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
.
Life cycle
''Trichomonas'' has a
trophozoite A trophozoite (G. ''trope'', nourishment + ''zoon'', animal) is the activated, feeding stage in the life cycle of certain protozoa such as malaria-causing ''Plasmodium falciparum'' and those of the '' Giardia'' group. (The complement of the trophozo ...
form, its pear-shaped form, which is most commonly observed, and an
amoeboid
An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopo ...
form, which appears during host colonization.
It lacks a cyst form, but many studies have noted a unique form in which ''Trichomonas'' appears ovoidal rather than its typical pear-shaped form. In this ovoidal form, all its flagella are retracted in
endocytic
Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. E ...
vacuoles
A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
, giving the impression of a cystic form. However, due to the lack of a cystic wall surrounding the organism, many studies describe this form as a pseudocystic form.
In its trophozoite form, ''Trichomonas'' undergoes cell division through an interesting process called cryptopleuromitosis. There are three common forms of
mitosis
In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...
: open, closed, and semi-open. In open mitosis, the nuclear envelope disappears so that mitotic spindles can interact with the
chromosomes
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
. In closed mitosis, the nuclear envelope does not disappear but mitotic spindles appear within the nucleus to separate the chromosomes. In semi-open mitosis, the nuclear envelope remains intact but the mitotic spindles pierce through the nuclear envelope to divide the chromosomes. Cryptopleuromitosis is different from all the other more commonly known methods of cell division. In cryptopleuromitosis, the chromosomes divide without the breakdown of the nuclear envelope and without the entry of mitotic spindles into the nucleus.
Diseases
''Trichomonas'' causes disease in humans and in birds. In humans, the causative species is ''Trichomonas vaginalis'' and ''
Trichomonas tenax
''Trichomonas tenax'', or oral trichomonas, is a species of ''Trichomonas'' commonly found in the oral cavity of humans. Routine hygiene is generally not sufficient to eliminate the parasite, hence its Latin name, meaning "tenacious". The parasit ...
''.
In birds, the causative species are ''
Trichomonas gallinae
''Trichomonas gallinae'' is a cosmopolitan parasite of birds including finches, pigeons, doves, turkeys, chickens, parrots, raptors (hawks, golden eagle, etc.). The condition in birds of prey is called frounce.Kennedy, Murry J. "Trichomoniasis ...
'', ''Trichomonas gypactinii'', and ''Trichomonas stableri''.
In humans
''Trichomonas vaginalis'' is a sexually transmitted disease and causes
trichomoniasis
Trichomoniasis (trich) is an infectious disease caused by the parasite ''Trichomonas vaginalis''. About 70% of affected people do not have symptoms when infected. When symptoms occur, they typically begin 5 to 28 days after exposure. Symptoms ca ...
. It resides on squamous epithelium of the urogenital tract. Many carriers of ''Trichomonas vaginalis'', especially men, are asymptomatic. Complications for symptomatic women include vaginitis, endometritis, infertility, and cervical cancer. Complications for symptomatic men include urethritis, prostatitis, epididymitis, and infertility. It is also associated with increased risk of transmission and acquisition of HIV.
''Trichomonas tenax'' is transmitted through exchange of saliva and contaminated water sources. It is an opportunistic pathogen and may cause pulmonary trichomoniasis.
In birds
''Trichomonas'' in birds inhabit the upper digestive tract and also cause trichomoniasis. It creates lesions in the trachea and esophagus, occupying space and eventually causing emaciation and asphyxiation.
Species
* ''
Trichomonas brixi'' — inhabits the oral cavity of dogs and cats.
* ''
Trichomonas gallinae
''Trichomonas gallinae'' is a cosmopolitan parasite of birds including finches, pigeons, doves, turkeys, chickens, parrots, raptors (hawks, golden eagle, etc.). The condition in birds of prey is called frounce.Kennedy, Murry J. "Trichomoniasis ...
'' — inhabits the upper digestive tract of primarily pigeons and doves, but also other birds.
* ''
Trichomonas gypactinii'' — inhabits the upper digestive tract of scavenging birds of prey, such as vultures.
* ''
Trichomonas stableri
''Trichomonas'' is a genus of anaerobic excavate parasites of vertebrates. It was first discovered by Alfred François Donné in 1836 when he found these parasites in the pus of a patient suffering from vaginitis, an inflammation of the vagina. ...
'' — inhabits the upper digestive tract of pigeons.
* ''
Trichomonas tenax
''Trichomonas tenax'', or oral trichomonas, is a species of ''Trichomonas'' commonly found in the oral cavity of humans. Routine hygiene is generally not sufficient to eliminate the parasite, hence its Latin name, meaning "tenacious". The parasit ...
'' — inhabits the oral cavity of humans.
* ''
Trichomonas vaginalis
''Trichomonas vaginalis'' is an anaerobic, flagellated protozoan parasite and the causative agent of a sexually transmitted disease called trichomoniasis. It is the most common pathogenic protozoan that infects humans in industrialized countries ...
'' — inhabits the urogenital tract of humans.
References
*
{{Taxonbar, from=Q309497
Metamonads
Excavata genera