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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. This phenomenon is known as endosymbiosis. Examples are nitrogen-fixing bacteria, which live in the root nodules of legumes, single-cell algae inside reef-building corals and bacterial endosymbionts that provide essential nutrients to insects.
Nanoarchaeota is a proposed phylum in the domain Archaea that currently has only one representative, Nanoarchaeum equitans, which was discovered in a submarine hydrothermal vent and first described in 2002.
The Chlamydiota are a bacterial phylum and class whose members are remarkably diverse, including pathogens of humans and animals, symbionts of ubiquitous protozoa, and marine sediment forms not yet well understood. All of the Chlamydiota that humans have known about for many decades are obligate intracellular bacteria; in 2020 many additional Chlamydiota were discovered in ocean-floor environments, and it is not yet known whether they all have hosts. Historically it was believed that all Chlamydiota had a peptidoglycan-free cell wall, but studies in the 2010s demonstrated a detectable presence of peptidoglycan, as well as other important proteins.
Parachlamydiaceae is a family of bacteria in the order Chlamydiales. Species in this family have a Chlamydia–like cycle of replication and their ribosomal RNA genes are 80–90% identical to ribosomal genes in the Chlamydiaceae. The Parachlamydiaceae naturally infect amoebae and can be grown in cultured Vero cells. The Parachlamydiaceae are not recognized by monoclonal antibodies that detect Chlamydiaceae lipopolysaccharide.
Betaproteobacteria are a class of Gram-negative bacteria, and one of the eight classes of the phylum Pseudomonadota.
Alphaproteobacteria is a class of bacteria in the phylum Pseudomonadota. The Magnetococcales and Mariprofundales are considered basal or sister to the Alphaproteobacteria. The Alphaproteobacteria are highly diverse and possess few commonalities, but nevertheless share a common ancestor. Like all Proteobacteria, its members are gram-negative, although some of its intracellular parasitic members lack peptidoglycan and are consequently gram variable.
"Candidatus Carsonella ruddii" is an obligate endosymbiotic Gammaproteobacterium with one of the smallest genomes of any characterised bacteria.
The PVC superphylum is a superphylum of bacteria named after its three important members, Planctomycetota, Verrucomicrobiota, and Chlamydiota. Cavalier-Smith postulated that the PVC bacteria probably lost or reduced their peptidoglycan cell wall twice. It has been hypothesised that a member of the PVC clade might have been the host cell in the endosymbiotic event that gave rise to the first proto-eukaryotic cell.
The Chloroflexota are a phylum of bacteria containing isolates with a diversity of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for photosynthesis ; and anaerobic halorespirers, which uses halogenated organics as electron acceptors.
The Nitrososphaerota are a phylum of the Archaea proposed in 2008 after the genome of Cenarchaeum symbiosum was sequenced and found to differ significantly from other members of the hyperthermophilic phylum Thermoproteota. Three described species in addition to C. symbiosum are Nitrosopumilus maritimus, Nitrososphaera viennensis, and Nitrososphaera gargensis. The phylum was proposed in 2008 based on phylogenetic data, such as the sequences of these organisms' ribosomal RNA genes, and the presence of a form of type I topoisomerase that was previously thought to be unique to the eukaryotes. This assignment was confirmed by further analysis published in 2010 that examined the genomes of the ammonia-oxidizing archaea Nitrosopumilus maritimus and Nitrososphaera gargensis, concluding that these species form a distinct lineage that includes Cenarchaeum symbiosum. The lipid crenarchaeol has been found only in Nitrososphaerota, making it a potential biomarker for the phylum. Most organisms of this lineage thus far identified are chemolithoautotrophic ammonia-oxidizers and may play important roles in biogeochemical cycles, such as the nitrogen cycle and the carbon cycle. Metagenomic sequencing indicates that they constitute ~1% of the sea surface metagenome across many sites.
Nitrospirota is a phylum of bacteria. It includes multiple genera, such as Nitrospira, the largest. The first member of this phylum, Nitrospira marina, was discovered in 1985. The second member, Nitrospira moscoviensis, was discovered in 1995.
"Candidatus Caballeronia calva" is a bacterium from the genus Caballeronia and the family Burkholderiaceae. "Candidatus Caballeronia calva" is an endosymbiont of Psychotria calva.
Sodalis is a genus of bacteria within the family Pectobacteriaceae. This genus contains several insect endosymbionts and also a free-living group. It is studied due to its potential use in the biological control of the tsetse fly. Sodalis is an important model for evolutionary biologists because of its nascent endosymbiosis with insects.
"Candidatus Caballeronia hispidae" is a bacterium from the genus Caballeronia and the family Burkholderiaceae.>
Candidatus Caballeronia kirkii is a Gram-negative, non-fermenting bacterium from the genus Caballeronia and the family Burkholderiaceae. Ca. C. kirkii is an endosymbiont of the plant Psychotria kirkii, also known as Rubiaceae, and exists inside leaf and stem nodules.
"Candidatus Caballeronia rigidae" is a bacterium from the genus Caballeronia and the family Burkholderiaceae. Candidatus Burkholderia rigidae is an endosymbiont.
"Candidatus Burkholderia schumannianae" is a bacterium from the genus Caballeronia and the family Burkholderiaceae. "Candidatus Caballeronia schumannianae" is an endosymbiont.
Paramecium biaurelia is a species of unicellular ciliates under the genus Paramecium, and one of the cryptic species of Paramecium aurelia. It is a free-living protist in water bodies and harbours several different bacteria as endosymbionts. 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.
Candidatus "Glomeribacter gigasporarum" is a gram-negative β-proteobacteria. The bacterium is rod-shaped, and has a obligate endosymbiotic relationship with the arbuscular-mycorrhizal fungi Gigaspora margarita. Sequencing of the16S rRNA gene places Ca. "G. gigasporarum" within the Burkholderia genus. Ca. "G. gigasporarum is unculturable as of yet, but can stay alive in enrichment for up to 4 weeks. The candidate bacteria is considered "the smallest beta-proteobacterium" with a genome size of 1.4 Mb. The chromosome is 750 kb long and a plasmid is 600 to 650 kb. The genome size was determined using gel-electrophoresis.
Amoebozoa of the free living genus Acanthamoeba and the social amoeba genus Dictyostelium are single celled eukaryotic organisms that feed on bacteria, fungi, and algae through phagocytosis, with digestion occurring in phagolysosomes. Amoebozoa are present in most terrestrial ecosystems including soil and freshwater. Amoebozoa contain a vast array of symbionts that range from transient to permanent infections, confer a range of effects from mutualistic to pathogenic, and can act as environmental reservoirs for animal pathogenic bacteria. As single celled phagocytic organisms, amoebas simulate the function and environment of immune cells like macrophages, and as such their interactions with bacteria and other microbes are of great importance in understanding functions of the human immune system, as well as understanding how microbiomes can originate in eukaryotic organisms.
References
- ↑ Horn, M; Fritsche, TR; Linner, T; Gautom, RK; Harzenetter, MD; Wagner, M (March 2002). "Obligate bacterial endosymbionts of Acanthamoeba spp. related to the beta-Proteobacteria: proposal of 'Candidatus Procabacter acanthamoebae' gen. nov., sp. nov". International Journal of Systematic and Evolutionary Microbiology. 52 (Pt 2): 599–605. doi: 10.1099/00207713-52-2-599 . PMID 11931173.
- ↑ Heinz, E; Kolarov, I; Kästner, C; Toenshoff, ER; Wagner, M; Horn, M (June 2007). "An Acanthamoeba sp. containing two phylogenetically different bacterial endosymbionts". Environmental Microbiology. 9 (6): 1604–1609. doi:10.1111/j.1462-2920.2007.01268.x. PMC 1974821 . PMID 17504498.
