''Chilodonella uncinata'' is a

single-celled A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

organism of the

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

class of alveoles. As a

, ''C. uncinata'' has

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

covering its body and a dual nuclear structure, the micronucleus and

macronucleus A macronucleus (formerly also meganucleus) is the larger type of nucleus in ciliates. Macronuclei are polyploid and undergo direct division without mitosis. It controls the non-reproductive cell functions, such as metabolism. During conjugation, t ...

. Unlike some other ciliates, ''C. uncinata'' contains millions of minichromosomes ( somatic chromosomes) in its macronucleus while its micronucleus is estimated to contain 3

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 ...

. ''Childonella uncinata'' is the causative agent of Chilodonelloza, a disease that affects the gills and skin of fresh water fish, and may act as a

facultative {{wiktionary, facultative Facultative means "optional" or "discretionary" (antonym '' obligate''), used mainly in biology in phrases such as: * Facultative (FAC), facultative wetland (FACW), or facultative upland (FACU): wetland indicator statuses ...

of mosquito larva.

Habitat

''Chilodonella uncinata'' has a cosmopolitan distribution. It is suspected to act as a

endoparasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

of the larvae of the '' Culex'', '' Aedes'', and '' Anopheles'' mosquito larva. It lives in fresh water ponds, lakes, creeks, and bayous where it feeds on bacteria and other microbes. Microscopic examination of cytological samples showed that mosquito larva containing subcutaneous encysted ''C. uncinata'' had a 25-100% mortality in the mosquito larva, but no viability examinations were conducted.

Biology and morphology

''Chilodonella uncinata'' has a broad thigmotactic zone that is two-thirds the length of the body width and has a pronounced anterior beak that is directed to the left. It can be maintained under laboratory conditions in a cereal wheat grass media inoculated with ''

Klebsiella ''Klebsiella'' is a genus of Gram-negative, oxidase-negative, rod-shaped bacteria with a prominent polysaccharide-based capsule. ''Klebsiella'' species are found everywhere in nature. This is thought to be due to distinct sublineages developin ...

sp''. Optimal growth occurs between 25 and 30 °C. ''C. uncinata'' is capable of sporulation and can resist environments with limited resources for a period of time.

Genome structure

All ciliates have two nuclei, but they differ in their structure of the somatic nucleus. All ciliates except

Karyorelictea Karyorelictea is a class of ciliates in the subphylum Postciliodesmatophora. Most species are members of the microbenthos community, that is, microscopic organisms found in the marine interstitial habitat, though one genus, ''Loxodes'', is foun ...

have a dividing macronucleus. ''C. uncinata'' also has a dividing macronucleus, but it modifies its macronuclear genome from the maternal micronuclear genome by producing macronuclear chromosomes that contain one or two

open reading frame In molecular biology, open reading frames (ORFs) are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible readin ...

(ORFs). The average size of these macronuclear chromosomes is 4 kbit/s. The macronuclear chromosomes are also amplified to produce a high variable copy number between the chromosomes. For example, chromosome A may have 500 copies while chromosome B only has 5 copies in the macronucleus. This leaves the macronuclear genome with millions of individual chromosomes, all containing

telomere A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Although there are different architectures, telomeres, in a broad sense, are a widespread genetic feature mos ...

ends, only one ORF, and little area for transcription factor binding for initiation of transcription.

Internally eliminated sequences

Internally eliminated sequences (IES) are noncoding regions of the

germ-line In biology and genetics, the germline is the population of a multicellular organism's cells that pass on their genetic material to the progeny (offspring). In other words, they are the cells that form the egg, sperm and the fertilised egg. Th ...

genome found in

Ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

s. They are defined as sections of DNA removed from the diploid micronuclear genome during which a copy of the micronuclear genome is converted to the macronuclear genome even though errors occur in which an IES sequence may not be deleted. There is little conservation of motifs between Ciliate species; however, ''C. uncinata'', like other ciliate species, show a conserved IES sequence motif within a species. It is unknown if IES sequences have a function in the genome, but in the ciliate '' Paramecium'', an IES sequence is used to determine the mating type of an individual. When a specific IES sequence is not deleted from the developing somatic nucleus, then it is type O mating type. However, if that IES is deleted from the developing macronucleus, it is type E mating type. ''Paramecium'' can only mate with individual of opposite mating type. Unlike '' Tetrahymena'' or '' Paramecium'', it has been observed that ''C. uncinata'' has a larger number of IES sequences within a single protein-coding gene than in other ciliates . Also there exists populations of ''C. uncinata'' that contain an IES sequence that other populations do not carry.

Reproduction and division

''Chilodonella uncinata'' has sexual conjugation for recombination, and replication of the cell occurs by asexual division

Sexual conjugation

Sex and reproduction are separate in ciliates. ''C. uncinata'' is capable of mating with other ''C. uncinata'' cells that have the same

mating type Mating types are the microorganism equivalent to sexes in multicellular lifeforms and are thought to be the ancestor to distinct Sex, sexes. They also occur in macro-organisms such as fungi. Definition Mating types are the microorganism equivalent ...

. After

complementary, the germ-line nucleus undergoes meiosis to produce

zygotic A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...

nuclei. Each conjugated cell transfers one zygotic nucleus to the other cell where the zygotic nuclei fuse. The diploid germ-line nucleus undergoes mitosis which creates a duplicated germ-line nucleus. At this point the somatic nucleus is being degraded. The duplicated germ-line nucleus then develops into the new somatic nucleus. The genomic structure of the somatic nucleus is being created by chromosomal fragmentation with single-gene chromosomes and amplification of these somatic chromosomes. It is unknown what determines the copy number of each chromosome or if the copy number of the somatic chromosomes are heritable between sexual conjugations.

Asexual reproduction

''C. uncinata'' goes through asexual reproduction for cell division and duplication called

amitosis Amitosis ('' a-'' + ''mitosis''), also called karyostenosis or direct cell division or binary fission, is cell proliferation that does not occur by mitosis, the mechanism usually identified as essential for cell division in eukaryotes. The polyploi ...

. As ''C. uncinata'' has two nuclei, it goes through two different styles of division of the nuclei. The germ-line nucleus goes through

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 ...

during asexual division while the somatic nucleus undergoes

. Amitosis is a stochastic process where unlike in mitosis, there is no spindle formation to segregate chromosomes during nuclear division. Instead, the chromosomes within the somatic nucleus are duplicated, and the nucleus goes through binary division. The precise mechanism is unknown, but it is believed that somatic chromosomes that are located on one side of the dividing somatic nucleus are distributed to one daughter cell, and the somatic chromosomes on the other side of the nucleus are distributed to the other daughter cell. This amitotic process causes the two daughter cells to potentially have identical germ-line nucleus but a different somatic nucleus in regards to the copy numbers of the chromosomes. As the somatic nucleus is the nucleus that is transcriptionally active, this somatic copy number mutation derived by the amitotic process could have fitness consequences for the individual cell.

Use in genomic research

''Childonella uncinata'' is easily cultured in the laboratory, has a fast generation time, and has a complex genomic structure that allows ''C. uncinata'' to be a

model organism A model organism (often shortened to model) 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 workin ...

for genomic architecture, genomic networks, and

genome evolution Genome evolution is the process by which a genome changes in structure (sequence) or size over time. The study of genome evolution involves multiple fields such as structural analysis of the genome, the study of genomic parasites, gene and ancient ...

research. Specifically, ''C. uncinata'' along with other closely related Ciliates has been used to determine the evolution of duplication of the alpha-tubulin gene. It was found that ''C. uncinata'' contains two paralogs of alpha-tubulin where the variation between the paralogs is highly concentrated within three small areas of the gene.

References

External links

* {{Taxonbar, from=Q5099150 Phyllopharyngea Animals described in 1838 Parasitic alveolates