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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. (The term endosymbiosis is from the Greek: ἔνδον endon "within", σύν syn "together" and βίωσις biosis "living".) 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.
Tsetse are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus Glossina, which are placed in their own family, Glossinidae. The tsetse is an obligate parasite, which lives by feeding on the blood of vertebrate animals. Tsetse has been extensively studied, because of their role in transmitting disease. They have a prominent economic impact in sub-Saharan Africa, as the biological vectors of trypanosomes, causing human and animal trypanosomiasis.
Pseudogenes are nonfunctional segments of DNA that resemble functional genes. Most arise as superfluous copies of functional genes, either directly by gene duplication or indirectly by reverse transcription of an mRNA transcript. Pseudogenes are usually identified when genome sequence analysis finds gene-like sequences that lack regulatory sequences needed for transcription or translation, or whose coding sequences are obviously defective due to frameshifts or premature stop codons. Pseudogenes are a type of junk DNA.
Wolbachia is a genus of intracellular bacteria that infects mainly arthropod species, including a high proportion of insects, and also some nematodes. It is one of the most common parasitic microbes, and is possibly the most common reproductive parasite in the biosphere. Its interactions with its hosts are often complex, and in some cases have evolved to be mutualistic rather than parasitic. Some host species cannot reproduce, or even survive, without Wolbachia colonisation. One study concluded that more than 16% of neotropical insect species carry bacteria of this genus, and as many as 25 to 70% of all insect species are estimated to be potential hosts.
Ensifer meliloti are an aerobic, Gram-negative, and diazotrophic species of bacteria. S. meliloti are motile and possess a cluster of peritrichous flagella. S. meliloti fix atmospheric nitrogen into ammonia for their legume symbionts, such as alfalfa. S. meliloti forms a symbiotic relationship with legumes from the genera Medicago, Melilotus and Trigonella, including the model legume Medicago truncatula. This symbiosis promotes the development of a plant organ, termed a root nodule. Because soil often contains a limited amount of nitrogen for plant use, the symbiotic relationship between S. meliloti and their legume hosts has agricultural applications. These techniques reduce the need for inorganic nitrogenous fertilizers.
Buchnera aphidicola, a member of the Pseudomonadota and the only species in the genus Buchnera, is the primary endosymbiont of aphids, and has been studied in the pea aphid, Acyrthosiphon pisum. Buchnera is believed to have had a free-living, Gram-negative ancestor similar to a modern Enterobacterales, such as Escherichia coli. Buchnera is 3 µm in diameter and has some of the key characteristics of their Enterobacterales relatives, such as a Gram-negative cell wall. However, unlike most other Gram-negative bacteria, Buchnera lacks the genes to produce lipopolysaccharides for its outer membrane. The long association with aphids and the limitation of crossover events due to strictly vertical transmission has seen the deletion of genes required for anaerobic respiration, the synthesis of amino sugars, fatty acids, phospholipids, and complex carbohydrates. This has resulted not only in one of the smallest known genomes of any living organism, but also one of the most genetically stable.
Wigglesworthia glossinidia is a species of gram-negative bacteria which was isolated from the gut of the tsetse fly. W. glossinidia is a bacterial endosymbiont of the tsetse fly. Because of this relationship, Wigglesworthia has lost a large part of its genome and has one of the smallest known genomes of any living organism, consisting of a single chromosome of 700,000 bp and a plasmid of 5,200. Together with Buchnera aphidicola, Wigglesworthia has been the subject of genetic research into the minimal genome necessary for any living organism. Wigglesworthia also synthesizes key B-complex vitamins which the tsetse fly does not get from its diet of blood. Without the vitamins Wigglesworthia produces, the tsetse fly has greatly reduced growth and reproduction. Since the tsetse fly is the primary vector of Trypanosoma brucei, the pathogen that causes African trypanosomiasis, it has been suggested that W. glossinidia may one day be used to help control the spread of this disease.
Paratransgenesis is a technique that attempts to eliminate a pathogen from vector populations through transgenesis of a symbiont of the vector. The goal of this technique is to control vector-borne diseases. The first step is to identify proteins that prevent the vector species from transmitting the pathogen. The genes coding for these proteins are then introduced into the symbiont, so that they can be expressed in the vector. The final step in the strategy is to introduce these transgenic symbionts into vector populations in the wild. One use of this technique is to prevent mortality for humans from insect-borne diseases. Preventive methods and current controls against vector-borne diseases depend on insecticides, even though some mosquito breeds may be resistant to them. There are other ways to fully eliminate them. “Paratransgenesis focuses on utilizing genetically modified insect symbionts to express molecules within the vector that are deleterious to pathogens they transmit.” The acidic bacteria Asaia symbionts are beneficial in the normal development of mosquito larvae; however, it is unknown what Asais symbionts do to adult mosquitoes.
Gammaproteobacteria is a class of bacteria in the phylum Pseudomonadota. It contains about 250 genera, which makes it the most genus-rich taxon of the Prokaryotes. Several medically, ecologically, and scientifically important groups of bacteria belong to this class. It is composed by all Gram-negative microbes and is the most phylogenetically and physiologically diverse class of Proteobacteria.
Blattabacterium is a genus of obligate mutualistic endosymbiont bacteria that are believed to inhabit all species of cockroach studied to date, with the exception of the genus Nocticola. The genus' presence in the termite Mastotermes darwiniensis led to speculation, later confirmed, that termites and cockroaches are evolutionarily linked.
The minimal genome is a concept which can be defined as the set of genes sufficient for life to exist and propagate under nutrient-rich and stress-free conditions. Alternatively, it can also be defined as the gene set supporting life on an axenic cell culture in rich media, and it is thought what makes up the minimal genome will depend on the environmental conditions that the organism inhabits. By one early investigation, the minimal genome of a bacterium should include a virtually complete set of proteins for replication and translation, a transcription apparatus including four subunits of RNA polymerase including the sigma factor rudimentary proteins sufficient for recombination and repair, several chaperone proteins, the capacity for anaerobic metabolism through glycolysis and substrate-level phosphorylation, transamination of glutamyl-tRNA to glutaminyl-tRNA, lipid biosynthesis, eight cofactor enzymes, protein export machinery, and a limited metabolite transport network including membrane ATPases. Proteins involved in the minimum bacterial genome tend to be substantially more related to proteins found in archaea and eukaryotes compared to the average gene in the bacterial genome more generally indicating a substantial number of universally conserved proteins. The minimal genomes reconstructed on the basis of existing genes does not preclude simpler systems in more primitive cells, such as an RNA world genome which does not have the need for DNA replication machinery, which is otherwise part of the minimal genome of current cells.
Arsenophonus is a genus of Morganellaceae, of the Gammaproteobacteria. Members of the Arsenophonus genus are increasingly discovered bacterial symbionts of arthropods that are estimated to infect over 5% of arthropod species globally and form a variety of relationships with hosts across the mutualism parasitism continuum. Arsenophonus bacteria have been identified in a diversity of insect taxa, including economically important species such as the Western honey bee and the rice pest Nilaparvata lugens.
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 Karelsulcia muelleri" is an aerobic, gram-negative, bacillus bacterium that is a part of the phylum Bacteroidota. "Ca. K. muelleri" is an obligate and mutualistic symbiotic microbe commonly found occupying specialized cell compartments of sap-feeding insects called bacteriocytes. A majority of the research done on "Ca. K. muelleri" has detailed its relationship with the host Homalodisca vitripennis. Other studies have documented the nature of its residency in other insects like the maize leafhopper (Cicadulina) or the spittlebug (Cercopoidea). "Ca. K. muelleri" is noted for its exceptionally minimal genome and it is currently identified as having the smallest known sequenced Bacteroidota genome at only 245 kilobases.
Glossina fuscipes is a riverine fly species in the genus Glossina, which are commonly known as tsetse flies. Typically found in sub-Saharan Africa but with a small Arabian range, G. fuscipes is a regional vector of African trypanosomiasis, commonly known as sleeping sickness, that causes significant rates of morbidity and mortality among humans and livestock. Consequently, the species is among several being targeted by researchers for population control as a method for controlling the disease.
Candidatus Arsenophonus arthropodicus is a Gram-negative and intracellular secondary (S) endosymbiont that belongs to the genus Arsenophonus. This bacterium is found in the Hippoboscid louse fly, Pseudolynchia canariensis. S-endosymbionts are commonly found in distinct tissues. Strains of recovered Arsenophonus found in arthropods share 99% sequence identification in the 16S rRNA gene across all species. Arsenophonus-host interactions involve parasitism and mutualism, including a popular mechanism of "male-killing" found commonly in a related species, Arsenophonus nasoniae. This species is considered "Ca. A. arthropodicus" due it being as of yet uncultured.
Glossina morsitans is a species of tsetse fly in the genus Glossina. It is one of the major vectors of Trypanosoma brucei rhodesiense in African savannas.
Fatma Serap Aksoy is a Turkish–American medical entomologist.
Alan Christoffels is a bioinformatics scientist, academic, and an author. He is Professor of Bioinformatics, and the director of the South African National Bioinformatics Institute at the University of the Western Cape. He has been serving as a senior advisor to the Africa Centres for Disease Control and Prevention Pathogen genomics & Partnerships and DSI/NRF Research Chair in Bioinformatics and Public Health Genomics.
References
- ↑ Dale C, Maudlin I (January 1999). "Sodalis gen. nov. and Sodalis glossinidius sp. nov., a microaerophilic secondary endosymbiont of the tsetse fly Glossina morsitans morsitans". International Journal of Systematic Bacteriology. 49 Pt 1 (1): 267–75. doi: 10.1099/00207713-49-1-267 . PMID 10028272.
- ↑ Darby AC, Lagnel J, Matthew CZ, Bourtzis K, Maudlin I, Welburn SC (July 2005). "Extrachromosomal DNA of the symbiont Sodalis glossinidius". Journal of Bacteriology . 187 (14): 5003–7. doi:10.1128/JB.187.14.5003-5007.2005. PMC 1169519 . PMID 15995217.
- ↑ Toh H, Weiss BL, Perkin SA, Yamashita A, Oshima K, Hattori M, Aksoy S (February 2006). "Massive genome erosion and functional adaptations provide insights into the symbiotic lifestyle of Sodalis glossinidius in the tsetse host". Genome Research. 16 (2): 149–56. doi:10.1101/gr.4106106. PMC 1361709 . PMID 16365377.
- ↑ Goodhead I, Blow F, Brownridge P, Hughes M, Kenny J, Krishna R, et al. (January 2020). "Large-scale and significant expression from pseudogenes in Sodalis glossinidius - a facultative bacterial endosymbiont". Microbial Genomics. 6 (1). doi:10.1099/mgen.0.000285. PMC 7067036 . PMID 31922467.
- ↑ Kirsch, Joshua M.; Brzozowski, Robert S.; Faith, Dominick; Round, June L.; Secor, Patrick R.; Duerkop, Breck A. (2021-09-29). "Bacteriophage-Bacteria Interactions in the Gut: From Invertebrates to Mammals". Annual Review of Virology . Annual Reviews. 8 (1): 95–113. doi:10.1146/annurev-virology-091919-101238. ISSN 2327-056X. PMC 8484061 . PMID 34255542.
