''Jakoba'' is a genus in the taxon

Excavata Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of free- ...

, and currently has a single described species, '' Jakoba libera'' described by

Patterson Patterson may refer to: People * Patterson (surname) Places ;Canada * Pattersons Corners, Ontario *Patterson Township, Ontario *Patterson, Calgary a neighbourhood in Calgary, Alberta. ;United States of America * Patterson, Arkansas *Patterson, C ...

in 1990, and named in honour of Dutch botanist (Algology, Myology and Lichenology) Jakoba Ruinen. (Previously described ''Jakoba incarcerata'' has been renamed ''

Andalucia incarcerata ''Andalucia incarcerata'' is a species of Excavata Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in ...

'', and '' Jakoba bahamensis'' /'' Jakoba bahamiensis'' is not formally described.) Jakoba libera atcc 50422 200

Appearance and characteristics

''Jakoba'' are small bacterivorous zooflagellates ( jakobids) found in marine and hypersaline environments. They are free swimming trophic cells with two

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 fro ...

and range between five and ten micrometers in length. Cells rotate along their longitudinal axis to allow for swimming in straight lines unless deformation and “squirming” occurs due to compression in debris. During feeding, bacteria are removed from the water column by a current created by the posterior

flagellum 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 ...

. This current causes the bacteria to collect in the groove on the right ventral side of the cell – aiding in ingestion and the creation of food

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 ...

Ultrastructure

Cellular components for ''Jakoba'' are not particularly unique. They contain a single

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 Nucl ...

found close to the flagellar bases, a single Golgi body, and the

mitochondrial A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used t ...

cristae A crista (; plural cristae) is a fold in the inner membrane of a mitochondrion. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a large amount of surface area fo ...

are flattened suggesting a relationship with other platicristate taxa. The

mitochondria A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...

of ''Jakoba'' are of particular interest evolutionarily due to their unique

bacterial Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...

-like

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...

s. It has been found that their

s contain considerably more functional

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

s than those of other

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

groups and it appears they have retained the ancestral eubacterial

RNA polymerase In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that synthesizes RNA from a DNA template. Using the enzyme helicase, RNAP locally opens th ...

, which has been replaced by viral type polymerase in all other mitochondriate eukaryotes. Overall, jakobid

genomes are primitively complex in that they resemble their proteobacterial ancestors more than any other

Life cycle

''Jakoba'' reproduce asexually by binary fission. The sexual reproduction or the formation of

cysts A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubble) ...

have not been observed.

Molecular sequence data

“The circular mitochondrial genome of ''Jakoba libera'' strain ATCC 50422 is 96.6 kbp in size. Sequencing is nearly completed. At present, 77 genes have been identified, none of them including an intron. Intergenic regions account for ~ 30% of the genome and contain clusters of tandem repeats whose unit length is ~20 bp. Transcribed genes are found on both DNA strands. The standard

genetic code The genetic code is the set of rules used by living cells to translate information encoded within genetic material ( DNA or RNA sequences of nucleotide triplets, or codons) into proteins. Translation is accomplished by the ribosome, which links ...

is used for

translation Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...

. Encoded genes include those commonly found in

mtDNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial DNA ...

, including the protein-coding genes nad1,2,3,4,4L,5,6, cob, cox1,2,3, and atp6,8,9, as well as large subunit (rnl) and small subunit (rns) rRNA genes and >22

tRNA 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 ...

genes. Also present are a number of protein genes typical of protist but not animal or fungal mtDNAs. These include nad7,9,11, atp1, rpl2,5,6,14,16, and rps2-4,11-14,19. A number of unique ORFs are also encoded by ''J. libera''

.” “A number of ''J. libera'' mitochondrial genes are rare or absent in other mitochondrial genomes but are present in

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

. Among these rare or unique

-encoded genes are dpo, rpoB,C, rrn5, rnpB, tufA, yejU-W, and several of the ribosomal protein genes.” “A comparison of gene order in the mtDNAs of ''J. libera''…” show “clusters that are otherwise not found in

but that evidently appeared during evolution of the mitochondrial genome after the divergence of the proto-mitochondrion from the bacterial lineage. Examples are the clusters sdh3 to nad5, (comprising 5 genes), atp8- rnrps4-atp9 and nad11-nad1-cox11-cox3-tufA.”

Cultures

There are currently three strains of ''Jakoba libera'' available for culture. They can not be grown axenically, but are easily raised in minimal media with added bacteria (''Klebsiella aerogenes'')

Similar genera

Jakobids ('' Jakobida'' or ''

Jakobea Jakobids are an order of free-living, heterotrophic, flagellar eukaryotes in the supergroup Excavata. They are small (less than 15 μm), and can be found in aerobic and anaerobic environments. The order Jakobida, believed to be monophyletic, cons ...

'') * '' Histiona'': 2-3 species * '' Reclinomonas'': 1 species '' Malawimonas'': 1 described species Retortamonads: * '' Retortamonas'' * '' Chilomastix'' Carpediemonas-like organisms: * ''

Carpediemonas ''Carpediemonas'' is genus of Metamonada, and belongs to the group Excavata. This organism is a unicellular flagellated eukaryote that was first discovered in substrate samples from the Great Barrier Reef. ''Carpediemonas'' can be found in ana ...

'' * '' Dysnectes'' * '' Hicanonectes'' * '' Ergobibamus'' * '' Kipferlia''

References

{{Taxonbar, from=Q6125390 Excavata genera Jakobids