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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 about 10–15% of insects.
Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in colour. The group includes the fluffy white woolly aphids. A typical life cycle involves flightless females giving living birth to female nymphs—who may also be already pregnant, an adaptation scientists call telescopic development—without the involvement of males. Maturing rapidly, females breed profusely so that the number of these insects multiplies quickly. Winged females may develop later in the season, allowing the insects to colonise new plants. In temperate regions, a phase of sexual reproduction occurs in the autumn, with the insects often overwintering as eggs.
The Hemiptera or true bugs are an order of insects comprising some 50,000 to 80,000 species of groups such as the cicadas, aphids, planthoppers, leafhoppers, bed bugs and shield bugs. They range in size from 1 mm (0.04 in) to around 15 cm (6 in), and share a common arrangement of sucking mouthparts. The name "true bugs" is often limited to the suborder Heteroptera. Many insects commonly known as "bugs", especially in American English, belong to other orders; for example, the lovebug is a fly and the May bug and ladybug are beetles.
Spiroplasma is a genus of Mollicutes, a group of small bacteria without cell walls. Spiroplasma shares the simple metabolism, parasitic lifestyle, fried-egg colony morphology and small genome of other Mollicutes, but has a distinctive helical morphology, unlike Mycoplasma. It has a spiral shape and moves in a corkscrew motion. Many Spiroplasma are found either in the gut or haemolymph of insects where they can act to manipulate host reproduction, or defend the host as endosymbionts. Spiroplasma are also disease-causing agents in the phloem of plants. Spiroplasmas are fastidious organisms, which require a rich culture medium. Typically they grow well at 30 °C, but not at 37 °C. A few species, notably Spiroplasma mirum, grow well at 37 °C, and cause cataracts and neurological damage in suckling mice. The best studied species of spiroplasmas are Spiroplasma poulsonii, a reproductive manipulator and defensive insect symbiont, Spiroplasma citri, the causative agent of citrus stubborn disease, and Spiroplasma kunkelii, the causative agent of corn stunt disease.
Carpenter ants are large ants indigenous to many forested parts of the world.
Gramine is a naturally occurring indole alkaloid present in several plant species. Gramine may play a defensive role in these plants, since it is toxic to many organisms.
Glucosinolates are natural components of many pungent plants such as mustard, cabbage, and horseradish. The pungency of those plants is due to mustard oils produced from glucosinolates when the plant material is chewed, cut, or otherwise damaged. These natural chemicals most likely contribute to plant defence against pests and diseases, and impart a characteristic bitter flavor property to cruciferous vegetables.
Buchnera aphidicola, a member of the Proteobacteria, 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.
A bacteriocyte, also known as a mycetocyte, is a specialized adipocyte found primarily in certain insect groups such as aphids, tsetse flies, German cockroaches, weevils. These cells contain endosymbiotic organisms such as bacteria and fungi, which provide essential amino acids and other chemicals to their host. Bacteriocytes may aggregate into a specialized organ called the bacteriome.
The Russian wheat aphid is an aphid that can cause significant losses in cereal crops. The species was introduced to the United States in 1986 and is considered an invasive species there. This aphid is pale green and up to 2 mm long. Cornicles are very short, rounded, and appear to be lacking. There is an appendage above the cauda giving the aphid the appearance of having two tails. The saliva of this aphid is toxic to the plant and causes whitish striping on cereal leaves. Feeding by this aphid will also cause the flag leaf to turn white and curl around the head causing incomplete head emergence. Host plants: cereal grain crops including wheat and barley and to a lesser extent, wild grasses such as wheatgrasses, brome-grasses, ryegrasses and anything in the grass family.
Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps (Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, sooner or later causing the death of these hosts. Different species specialise in hosts from different insect orders, most often Lepidoptera, though some select beetles, flies, or bugs; the spider wasps (Pompilidae) exclusively attack spiders.
Myzus persicae, known as the green peach aphid, greenfly, or the peach-potato aphid, is a small green aphid. It is the most significant aphid pest of peach trees, causing decreased growth, shrivelling of the leaves and the death of various tissues. It is also acts as a vector for the transport of plant viruses such as cucumber mosaic virus (CMV), potato virus Y (PVY) and tobacco etch virus (TEV). Potato virus Y and potato leafroll virus can be passed to members of the nightshade/potato family (Solanaceae), and various mosaic viruses to many other food crops.
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.
Nancy A. Moran is an American evolutionary biologist and entomologist, University of Texas Leslie Surginer Endowed Professor, and co-founder of the Yale Microbial Diversity Institute. Since 2005, she has been a member of the United States National Academy of Sciences. Her seminal research has focused on the pea aphid, Acyrthosiphon pisum and its bacterial symbionts including Buchnera (bacterium). In 2013, she returned to the University of Texas at Austin, where she continues to conduct research on bacterial symbionts in aphids, bees, and other insect species. She has also expanded the scale of her research to bacterial evolution as a whole. She believes that a good understanding of genetic drift and random chance could prevent misunderstandings surrounding evolution. Her current research goal focuses on complexity in life-histories and symbiosis between hosts and microbes, including the microbiota of insects.
Acyrthosiphon pisum, commonly known as the pea aphid, is a sap-sucking insect in the family Aphididae. It feeds on several species of legumes worldwide, including forage crops, such as pea, clover, alfalfa, and broad bean, and ranks among the aphid species of major agronomical importance. The pea aphid is a model organism for biological study whose genome has been sequenced and annotated.
The hologenome theory of evolution recasts the individual animal or plant as a community or a "holobiont" – the host plus all of its symbiotic microbes. Consequently, the collective genomes of the holobiont form a "hologenome". Holobionts and hologenomes are structural entities that replace misnomers in the context of host-microbiota symbioses such as superorganism, organ, and metagenome. Variation in the hologenome may encode phenotypic plasticity of the holobiont and can be subject to evolutionary changes caused by selection and drift, if portions of the hologenome are transmitted between generations with reasonable fidelity. One of the important outcomes of recasting the individual as a holobiont subject to evolutionary forces is that genetic variation in the hologenome can be brought about by changes in the host genome and also by changes in the microbiome, including new acquisitions of microbes, horizontal gene transfers, and changes in microbial abundance within hosts. Although there is a rich literature on binary host–microbe symbioses, the hologenome concept distinguishes itself by including the vast symbiotic complexity inherent in many multicellular hosts. For recent literature on holobionts and hologenomes published in an open access platform, see the following reference.
Serratia symbiotica is a species of bacteria that lives as a symbiont of aphids. In the aphid Cinara cedri, it coexists with Buchnera aphidicola, given the latter cannot produce tryptophan. It is also known to habitate in Aphis fabae. Together with other endosymbionts, it provides aphids protection against parasitoids.
Regiella insecticola is a species of bacteria, that lives as a symbiont of aphids. It shows a relationship with Photorhabdus species, together with Hamiltonella defensa. Together with other endosymbionts, it provides aphids protection against parasitoids.
Hamiltonella defensa is a species of bacteria. It is maternally or sexually transmitted and lives as an endosymbiont of whiteflies and aphids, meaning that it lives within a host, protecting its host from attack. It does this through bypassing the host's immune responses by protecting its host against parasitoid wasps. However, H. defensa is only defensive if infected by a virus. H. defensa shows a relationship with Photorhabdus species, together with Regiella insecticola. Together with other endosymbionts, it provides aphids protection against parasitoids. It is known to habitate Bemisia tabaci.
"Procabacteriaceae" is a Candidatus family of uncultivated Gram-negative Betaproteobacteria. The sole genus, "Procabacter", was identified as an obligate endosymbiont of Acanthamoeba.
References
- ↑ "Oliver K.M., Campos J., Moran N.A., and Hunter M.S. 2008. "Population dynamics of defensive symbionts in aphids." Proc. R Soc. B, 275(1632): 293-299
- ↑ Qi Su, Wen Xie, Shaoli Wang, Qingjun Wu, Baiming Liu, Yong Fang, Baoyun Xu, Youjun Zhang. 2014. "The Endosymbiont Hamiltonella Increases the Growth Rate of Its Host Bemisia tabaci during Periods of Nutritional Stress." PLoS ONE. doi : 10.1371/journal.pone.0089002
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