''Paramecium biaurelia'' is a species of unicellular ciliates under the genus ''

Paramecium '' ''Paramecium'' ( , ; also spelled ''Paramoecium'') is a genus of eukaryotic, unicellular ciliates, commonly studied as a representative of the ciliate group. ''Paramecia'' are widespread in freshwater, brackish, and marine environments and a ...

'', and one of the

cryptic species In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

of ''

Paramecium aurelia ''Paramecium aurelia'' are unicellular organisms belonging to the genus ''Paramecium'' of the phylum Ciliophora. They are covered in cilia which help in movement and feeding.''Paramecium'' can reproduce sexually, asexually, or by the process ...

''. It is a free-living

protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...

in water bodies and harbours several different bacteria as

endosymbionts An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within" ...

. Although the bacteria are parasites by definition, they also exhibit mutual relationship with the protist by providing survival benefits. It is used as an organism model in the study of the effects of gravitational forces in different environments. ''Paramecium biaurelia'' was described by Tracy Morton Sonneborn in 1975 while analysing the different cryptic species of ''P. aurelia''.

Biology

''Paramecium biaurelia'' is a unicellular protist with elongated body, which measures about 133 μm in length. The distinguishing feature from other species of ''P. aurelia'' is that it reproduces at below 21°C and specifically between 9 PM and 7 AM. It is also genetically distinct (

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

) without any indication of genetic mixing ( gene flow) with other cryptic species. The most important bacterial endosymbionts are ''Holospora caryophila,'' ''Caedibacter paraconjugatus'', and (''

Candidatus In prokaryote nomenclature, ''Candidatus'' (Latin for candidate of Roman office) is used to name prokaryotic phyla that are well characterized but yet-uncultured. Contemporary sequencing approaches, such as 16S sequencing or metagenomics, provide m ...

'') Bealeia paramacronuclearis, which are members of the family

Rickettsiaceae The Rickettsiaceae are a family of bacteria. The genus '' Rickettsia'' is the most prominent genus within the family. The bacteria that eventually formed the mitochondrion (an organelle in eukaryotic cells) is believed to have originated from ...

, and (''Candidatus'') Fokinia cryptica, which belongs to the family

Midichloriaceae "''Candidatus'' Midichloriaceae" is a family of bacteria, included in the order Rickettsiales. No member of this family has been cultured in the laboratory, so the entire family has been given the status ''candidatus In prokaryote nomenclature, ...

. The bacteria are gram-negative species. They are energy parasites as they depend on the host's ATP for their energetic functions, but they increase the growth rate of the protists in return. ''H. caryophila'' can infect ''P. biaurelia'' and '' P. caudatum'', and was reclassified into a new genus as ''Preeria caryophila'', based on detailed morphological analysis and phylogeny. ''P. caryophila'' are parasitic inside the nucleus of ''P. biaurelia.'' As with other species of ''Holospora,'' they rely on the protist for amino acids, energy metabolic pathways including glycolysis and the

citric acid cycle The citric acid cycle (CAC)—also known as the Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and protein ...

, as well as for

nucleotides Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules w ...

. In contrast, Bealeia paramacronuclearis and Fokinia cryptica are cytoplasmic parasites. Bealeia paramacronuclearis are spherical or oval shaped measuring about 1.8 to 2.4 μm long and 0.4 to 0.5 μm broad. Inside the protist, they are arranged in clusters of about 7 to 8 cells in parallel lines. They mostly lie close to the

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, ...

(the reason for the species name) and sometimes appear attached to the nuclear envelope. Fokinia cryptica are smaller with the diameter 0.35 to 0.40 μm. They are more randomly distributed in the cytoplasm.

Distribution

''Paramecium biaurelia'' is present in Europe, Asia, Australia, New Zealand, Tasmania, and North and South America. It is most abundant in cold to moderate climates but does not occur in the tropics.

References

{{Taxonbar, from=Q100348282 Species described in 1975 Oligohymenophorea Rickettsiales Endosymbiotic events