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Encyclopedia > Endosymbiont

An endosymbiont is any organism that lives within the body or cells of another organism, i.e. forming an endosymbiosis (Greek: endo = inner, sym = together and biosis = living). Examples are nitrogen-fixing bacteria (called rhizobia) which live in root nodules on legume roots, single-celled algae inside reef-building corals, and bacterial endosymbionts inside several insect species. Many other examples of endosymbiosis exist. It is estimated that beneficial endosymbionts provide essential nutrients to about 10%–15% of insects. In biology and ecology, an organism (in Greek organon = instrument) is a living complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole. ... Cells in culture, stained for keratin (red) and DNA (green). ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Rhizobia (from the Greek words Riza = Root and Bios = Life) are soil bacteria that fix nitrogen (diazotrophy) after becoming established inside root nodules of legumes (Fabaceae). ... Root nodules occur on the roots of plants that associate with symbiotic bacteria. ... Varieties of soybean seeds, a popular legume Pea pods The term legume has two closely related meanings in botany, a situation encountered with many botanical common names of useful plants, whereby an applied name can refer to either the plant itself, or to the edible fruit (or useful part). ... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... A coral reef can be an oasis of marine life. ... Classes & Orders See taxonomy Insects are invertebrate animals of the Class Insecta, the largest and (on land) most widely-distributed taxon within the phylum Arthropoda. ...

Many instances of endosymbiosis are obligate, that is neither the endosymbiont nor the host can survive without the other, such as gutless marine worms which get nutrition from their endosymbiotic bacteria. However, not all endosymbioses are obligate. Also, some endosymbioses can be harmful to either of the organisms involved. See symbiosis for further discussion of this issue. Common Clownfish (Amphiprion ocellaris) in their magnificent sea anemone (Heteractis magnifica) home. ...

It is generally agreed that certain organelles of the eukaryotic cell, especially mitochondria and chloroplasts, originated as bacterial endosymbionts. This theory is called the endosymbiotic theory, confirmed and popularized by Lynn Margulis. Schematic of typical animal cell, showing subcellular components. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (IPA: ), also spelled eucaryote, is an organism with a complex cell or cells, in which the genetic material is organized into membrane-bound nucleus/nuclei. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... The inside of a chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... The endosymbiotic theory, now generally accepted by biologists, concerns the origins of mitochondria and plastids (e. ... Lynn Margulis. ...


The endosymbiont theory and mitochondria and chloroplasts

Main article: Endosymbiotic theory

The endosymbiont theory explains the origins of organelles such as mitochondria and chloroplasts in eukaryotic cells. The theory proposes that chloroplasts and mitochondria evolved from certain types of bacteria that prokaryotic cells engulfed through endophagocytosis. These cells and the bacteria trapped inside them entered a symbiotic relationship, a close association between different types of organisms over an extended time. However, more specifically, the relationship was endosymbiotic, meaning that one of the organisms (the bacteria) lived within the other (the prokaryotic cells). The endosymbiotic theory, now generally accepted by biologists, concerns the origins of mitochondria and plastids (e. ... Schematic of typical animal cell, showing subcellular components. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (IPA: ), also spelled eucaryote, is an organism with a complex cell or cells, in which the genetic material is organized into membrane-bound nucleus/nuclei. ...

According to the endosymbiont theory, an anaerobic cell probably ingested an aerobic bacterium but failed to digest it. The aerobic bacterium flourished within the cell because the cell’s cytoplasm was abundant in half-digested food molecules. The bacterium digested these molecules with oxygen and gained great amounts of energy. Because the bacterium had so much energy, it probably leaked some of it as ATP into the cell’s cytoplasm. This benefited the anaerobic cell because it enabled it to digest food aerobically. Eventually, the aerobic bacterium could no longer live independently from the cell, and it therefore became a mitochondrion. The origin of the chloroplast is very similar to that of the mitochondrion. A cell must have captured a photosynthetic cyanobacterium and failed to digest it. The cyanobacterium thrived in the cell and eventually evolved into the first chloroplast. Other eukaryotic organelles may have also evolved through endosymbiosis. Scientists believe that cilia, flagella, centrioles, and microtubules may have come from a symbiosis between a spirilla-like bacterium and an early eukaryotic cell.

There are several examples of evidence that support the endosymbiont theory. Mitochondria and chloroplasts contain their own small supply of DNA, which may be remnants of the genome the organelles had when they were independent aerobic bacteria. The single most convincing evidence of the descent of organelles from bacteria is the position of mitochondria and plastid DNA sequences in phylogenetic trees of bacteria. Mitochondria have sequences that clearly indicate origin from a group of bacteria called the alpha-Proteobacteria. Plastids have DNA sequences that indicate origin from the cyanobacteria (blue-green algae). In addition, there are organisms alive today, called living intermediates, that are in a similar endosymbiotic condition to the prokaryotic cells and the aerobic bacteria. Living intermediates show that the evolution proposed by the endosymbiont theory is possible. For example, the giant amoeba Pelomyxa lacks mitochondria but has aerobic bacteria that carry out a similar role. A variety of corals, clams, snails, and one species of Paramecium permanently host algae in their cells. Many of the insect ensosymbionts have been shown to have ancient associations with their hosts, involving strictly vertical inheritance. In addition, these insect symbionts have similar patterns of genome evolution to those found in true organelles: genome reduction, rapid rates of gene evolution, and bias in nucleotide base composition favoring adenine and thymine, at the expense of guanine and cytosine. Pelomyxa are giant amoebae, usually 500-800 μm, but occasionally passing 3 mm in length. ... Paramecium is a well-known genus of ciliate protozoa, commonly studied as a representative of that group. ...

Further evidence of endosymbiosis are the prokaryotic ribosomes found within chloroplasts and mitochondria as well as the double membrane enclosing them. The inner membrane is thought to be the original membrane of the once independent prokaryote, while the outer one is thought to be the food vacuole it was enclosed in initially. Triple or quadruple membranes are found among certain algae, probably resulting from repeated endosymbiosis (although little else was retained of the engulfed cell).

These modern organisms with endosymbiotic relationships with aerobic bacteria have verified the endosymbiotic theory, which explains the origin of mitochondria and chloroplasts from bacteria. Researchers in molecular and evolutionary biology no longer question this theory, although some of the details, such as the mechanisms for loss of genes from organelles to host nuclear genomes, are still being worked out.

Bacterial endosymbionts in marine oligochaetes

Some marine oligochaetes (e.g Olavius or Inanidrillus) have obligate extracellular endosymbionts that fill the entire body of their host. These marine worms are nutritionally dependent on their symbiotic chemoautotrophic bacteria lacking any digestive or excretory system (no gut, mouth or nephridia). Orders Arhynchobdellida Haplotaxida Rhynchobdellida The Oligochaeta or few-bristled worms (singular Oligochaete, IPA /ˈɒlɪgoʊˌkit/) are well-segmented Annelids, most with a spacious coelom that is used as a hydroskeleton. ... Chemotrophs are organisms that obtain energy by the oxidation of electron donating molecules in their environments. ... A paired organ found in nearly all segments of the earthworms body; filters wastes from the coelomic fluid ...

Bacterial endosymbionts in other marine invertebrates

Extracellular endosymbionts are also represented in all 5 extant classes of Echinodermata (Crinoidea, Ophiuroidea, Asteroidea, Echinoidea, and Holothuroidea). Little is known of the nature of the association (mode of infection, transmission, metabolic requirements, etc.) but phylogenetic analysis indicates that these symbionts belong to the alpha group of the class Proteobacteria, relating them to Rhizobium and Thiobacillus. Other studies indicate that these subcuticular bacteria may be both abundant within their hosts and widely distributed among the Echinoderms in general. Classes Asteroidea Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea Echinoderms (Echinodermata) is a phylum of marine animals found in the ocean at all depths. ... Orders Articulata Cladida (extinct) Flexibilia (extinct) Camerada (extinct) Disparida (extinct) Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). ... Brittle stars are echinoderms, closely related to starfish. ... A database query syntax error has occurred. ... Slate pencil urchin (cidaroid) Group of black, long-spined Caribbean sea urchins, Diadema antillarum (Philippi) Sea urchin roe. ... Orders Subclass Apodacea  Apodida  Molpadiida Subclass Aspidochirotacea  Aspidochirotida  Elasipodida Subclass Dendrochirotacea  Dactylochirotida  Dendrochirotida The sea cucumber is an echinoderm of the class Holothuroidea, with an elongated body and leathery skin. ... A phylogeny (or phylogenesis) is the origin and evolution of a set of organisms, usually of a species. ... Orders Alpha Proteobacteria    Caulobacterales - e. ...

Symbiodinium dinoflagellate endosymbionts in marine metazoa and protists

Dinoflagellate endosymbionts of the genus Symbiodinium, commonly known as zooxanthellae, are found in corals, mollusks (esp. giant clams, the Tridacna), sponges, and foraminifera. These endosymbionts drive the amazing formation of coral reefs by capturing sunlight and providing their hosts with energy for carbonate deposition. Classes Dinophyceae Noctiluciphyceae Syndiniophyceae The dinoflagellates are a large group of flagellate protists. ... Zooxanthellae are golden-brown intracellular endosymbionts of various marine animals and protozoa, especially anthozoans. ... A coral reef can be an oasis of marine life. ... Classes Caudofoveata Aplacophora Polyplacophora Monoplacophora Bivalvia Scaphopoda Gastropoda Cephalopoda † Rostroconchia The mollusks or molluscs are the large and diverse phylum Mollusca, which includes a variety of familiar creatures well-known for their decorative shells or as seafood. ... Binomial name Tridacna gigas Linnaeus, 1758 The giant clam (Tridacna gigas) or traditionally, pa’ua, is the largest living bivalve mollusc. ... This article is about the animal. ... Orders Allogromiida Carterinida Fusulinida- extinct Globigerinida Involutinida- extinct Lagenida Miliolida Robertinida Rotaliida Silicoloculinida Spirillinida Textulariida incertae sedis    Xenophyophorea    Reticulomyxa The Foraminifera, or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands that branch and merge to form a dynamic net. ... Part of a coral reef. ... In inorganic chemistry, a carbonate is a salt of carbonic acid. ...

Previously thought to be a single species, molecular phylogenetic evidence over the past couple decades has shown there to be great diversity in Symbiodinium. In some cases there is specificity between host and Symbiodinium clade. More often, however, there is an ecological distribution of Symbiodinium, the symbionts switching between hosts with apparent ease. When reefs become environmentally stressed, this distribution of symbionts is related to the observed pattern of coral bleaching and recovery. Thus the distribution of Symbiodinium on coral reefs and its role in coral bleaching presents one of the most complex and interesting current problems in reef ecology. A phylogeny (or phylogenesis) is the origin and evolution of a set of organisms, usually of a species. ... Warm pink and yellow tones show where sea surface temperatures in the Great Barrier Reef were warm in the top image. ... The word ecology is often used in common parlance as a synonym for the natural environment or environmentalism. ...

Endosymbionts in protists

Mixotricha paradoxa is a protozoan that lacks mitochondria, however, spherical bacteria live inside the cell and serve the function of the mitochondria. Mixotricha also has three other species of symbionts that live on the surface of the cell. Binomial name Mixotricha paradoxa Sutherland, 1933 Mixotricha paradoxa is a species of protozoan that lives inside the termite species Mastotermes darwiniensis and has multiple bacterial symbionts. ...

Paramecium bursaria, a species of ciliate, has a mutualistic symbiotic relationship with green alga called Zoochlorella. The algae live inside the cell, in the cytoplasm. Binomial name Paramecium bursaria (Ehr. ... Classes Karyorelictea Heterotrichea Spirotrichea Litostomatea Phyllopharyngea Nassophorea Colpodea Prostomatea Oligohymenophorea Plagiopylea See text for subclasses. ...

Bacterial obligate endosymbionts in insects

Scientists classify insect endosymbionts in two broad categories, 'Primary' and 'Secondary'. Primary endosymbionts (sometimes referred to as P-endosymbionts) have been associated with their insect hosts for many millions of years (from 10 to several hundred million years in some cases), they form obligate associations (see below), and display cospeciation with their insect hosts. Secondary endosymbionts exhibit a more recently developed association, are sometimes horizontally trasnferred between hosts, live in the haemolymph of the insects (not specialized bacteriocytes, see below), are are not obligate.

Among primary endosymbionts of insects, the best studied are the pea aphid Acyrthosiphon pisum and its endosymbiont Buchnera sp. APS, and the tsetse fly Glossina morsitans morsitans and its endosymbiont Wigglesworthia glossinidia brevipalpis. As with endosymbiosis in other insects, the symbiosis is obligate in that neither the bacteria nor the insect is viable without the other. Scientists have been unable to cultivate the bacteria in lab conditions outside of the insect. With special nutritionally-enhanced diets, the insects can survive, but are unhealthy, and at best survive only a few generations. Families There are 10 families: Adelgidae - adelgids, conifer aphids Anoeciidae Aphididae Drepanosiphidae Homomasagymibutae Greenideidae Hormaphididae Lachnidae Mindaridae Pemphigidae Phloeomyzidae Phylloxeridae Thelaxidae Aphids, also known as greenfly/blackfly or plantlice, are minute plant-feeding insects in the superfamily Aphidoidea in the homopterous division of the order Hemiptera. ... Bruchnera aphidicola, a member of the Proteobacteria, is the primary symbiont of A. psium. ... Binomial name Glossina morsitans The tsetse fly, Glossina morsitans, is a fly (order Diptera) that eats blood from animals, including humans. ... Binomial name Wigglesworthia glossinidia Wigglesworthia glossinidia brevipalpis is a gram negative bacterium in the enterobacteriaceae family, related to E. coli, which lives in the gut of the tsetse fly. ...

These endosymbionts live in specialized insect cells called bacteriocytes (also called mycetocytes), and are maternally-transmitted, i.e. the mother transmits her endosymbionts to her offspring. In some cases, the bacteria are transmitted in the egg, as in Buchnera; in others like Wigglesworthia, they are transmitted via milk to the developing insect embryo. A bacteriocyte (Greek: bacteria cell), also called a mycetocyte, is a specialized adipocyte found in some insect groups such as aphids, german cockroaches, and many others. ...

The primary endosymbionts are thought to help the host by either synthesizing nutrients that the host cannot make itself, or by metabolizing insect waste products into safer forms. For example, the primary role of Buchnera is thought to be to synthesize essential amino acids that the aphid cannot acquire from its natural diet of plant sap. The evidence is (1) when aphids' endosymbionts are killed using antibiotics, they appear healthier when their plant sap diet is supplemented with the appropriate amino acids, and (2) after the Buchnera genome was sequenced, analysis uncovered a large number of genes that likely code for amino acid biosynthesis genes; most bacteria that live inside other organisms do not have such genes, so their existence in Buchnera is noteworthy. Similarly, the primary role of Wigglesworthia is probably to synthesize vitamins that the tsetse fly does not get from the blood that it eats. ‹ The template below has been proposed for deletion. ... An amino acid residue is what is left of an amino acid once a molecule of water has been lost (an H+ from the nitrogenous side and an OH- from the carboxylic side) in the formation of a peptide bond. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... A vitamin is an organic molecule required by a living organism in minute amounts for proper health. ...

Bacteria benefit from the reduced exposure to predators, the ample supply of nutrients and relative environmental stability inside the host.

Genome sequencing reveals that obligate bacterial endosymbionts of insects have among the smallest of known bacterial genomes and have lost many genes that are commonly found in closely related bacteria. Several theories have been put forth to explain the loss of genes. Presumably some of these genes are not needed in the environment of the host insect cell. A complementary theory suggests that the relatively small numbers of bacteria inside each insect decrease the efficiency of natural selection in 'purging' deleterious mutations and small mutations from the population, resulting in a loss of genes over many millions of years. Research in which a parallel phylogeny of bacteria and insects was inferred supports the belief that the primary endosymbionts are transferred only vertically (i.e. from the mother), and not horizontally (i.e. by escaping the host and entering a new host). it has a lover, usually by the name us jeb deb.* Genome reduction (Genome degradation) is the process by which a genome shrinks relative to its ancestor. ... In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ...

Attacking obligate bacterial endosymbionts may present a way to control their insect hosts, many of which are pests or carriers of human disease. For example aphids are crop pests and the tsetse fly carries the organism (trypanosome protozoa) that causes African sleeping sickness. Other motivations for their study is to understand symbiosis, and to understand how bacteria with severely depleted genomes are able to survive, thus improving our knowledge of genetics and molecular biology. Genera Blastocrithidia Crithidia Endotrypanum Herpetomonas Leishmania Leptomonas Phytomonas Trypanosoma Wallaceina Trypanosomes are a group of kinetoplastid protozoa distinguished by having only a single flagellum. ... Wikisource has an original article from the 1911 Encyclopædia Britannica about: Protozoa Protozoa (in Greek proto = first and zoa = animal) are single-celled eukaryotes (organisms whose cells have nuclei) that show some characteristics usually associated with animals, most notably mobility and heterotrophy. ... Sleeping sickness or African trypanosomiasis is a parasitic disease in people and in animals. ...

Less is known about secondary endosymbionts. The pea aphid (Acyrthosiphon pisum) is known to contain at least three secondary endosymbionts, Hamiltonella defensa, Regiella insecticola, and Serratia symbiotica. H. defensa aids in defending the insect from parasitoids.

References and external links

Obligate bacterial endosymbiosis in marine oligochaetes:

  • Endosymbiotic sulphate-reducing and sulphide-oxidizing bacteria in an oligochaete worm. Dubilier N., Mülders C.,Ferdelman T., De Beer D.,Pernthaler A.,Klein M., Wagner M., Erseus C., Thiermann F., Krieger J., Giere O & Amann R. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11357130

Bacterial endosymbionts in echinoderms:

Symbiodinium dinoflagellate endosymbionts in marine metazoa and protists

Viral endosymbionts,endovirus

During pregnacy in mammals ,a endovirus is activated during the implantation of the embrio.Because of this it'is theories that a viral infection contributed in the evolution of mammals.

Obligate bacterial endosymbionts in insects:

  • PLOS Biology Primer- Endosymbiosis: lessons in conflict resolution http://www.plosbiology.org/plosonline/?request=get-document&doi=10.1371/journal.pbio.0020068
  • A general review of bacterial endosymbionts in insects. P. Baumann, N. A. Moran and L. Baumann, Bacteriocyte-associated endosymbionts of insects in M. Dworkin, ed., The prokaryotes, Springer, New York, 2000. http://link.springer.de/link/service/books/10125/
  • An excellent review of insect endosymbionts that focuses on genetic issues. Jennifer J. Wernegreen (2002), Genome evolution in bacterial endosymbionts of insects, Nature Reviews Genetics, 3, pp. 850-861. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12415315&dopt=Abstract
  • A review article on aphids and their bacterial endosymbionts. A. E. Douglas (1998), Nutritional interactions in insect-microbial symbioses: Aphids and Their Symbiotic Bacteria Buchnera, Annual Reviews of Entomology, 43, pp. 17-37.
  • Describes possible methods to control the human pathogen causing African sleeping sickness, which is transmitted by tsetse flies. Focuses on methods using the primary and secondary endosymbionts of the tsetse fly. Serap Aksoy, Ian Maudlin, Colin Dale, Alan S. Robinsonand and Scott L. O’Neill (2001), Prospects for control of African trypanosomiasis by tsetse vector, TRENDS in Parasitology, 17 (1), pp. 29-35. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11137738&dopt=Abstract
  • Announces and analyzes the full genome sequence of Buchnera sp. APS, the endosymbiont of the pea aphid, and the first endosymbiont to have its genome sequenced. S. Shigenobu, H. Watanabe, M. Hattori, Y. Sakaki and H. Ishikawa (2000), Genome sequence of the endocellular bacterial symbiont of aphids Buchnera sp. APS, Nature, 407, pp. 81-86. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10993077&dopt=Abstract
  • An article that presents for the first time a theory on how obligate endosymbionts may have their genomes degraded, in a freely-available journal. Nancy A. Moran (1996), Accelerated evolution and Muller’s ratchet in endosymbiotic bacteria, Proceedings of the National Academy of Sciences of the USA, 93, pp. 2873-2878. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8610134&dopt=Abstract

  Results from FactBites:
Endosymbiont - Wikipedia, the free encyclopedia (2117 words)
The endosymbiont theory explains the origins of organelles such as mitochondria and chloroplasts in eukaryotic cells.
Dinoflagellate endosymbionts of the genus Symbiodinium, commonly known as zooxanthellae, are found in corals, mollusks (esp. giant clams, the Tridacna), sponges, and foraminifera.
Genome sequencing reveals that obligate bacterial endosymbionts of insects have among the smallest of known bacterial genomes and have lost many genes that are commonly found in closely related bacteria.
Endosymbiont - definition of Endosymbiont in Encyclopedia (763 words)
An endosymbiont (also known as intracellular symbiont) is any organism that lives within cells of another organism, i.e.
Among bacterial endosymbionts of insects, the best studied are the pea aphid Acyrthosiphon pisum and its endosymbiont Buchnera sp.
Genome sequencing reveals that obligate bacterial endosymbionts of insects have among the smallest of known bacterial genomes and have lost many genes that are commonly found in other bacteria.
  More results at FactBites »



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