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{{Uncurated}} ==Classification== Domain: Bacteria; Phylum: Proteobacteria; Class: Gammaproteobacteria; Order: Enterobacterales; family: Enterbacteriaceae; Genus: ''Hamiltonella'' ===Species=== ''Hamiltonella defensa'' ==Description and Significance== Describe the appearance, habitat, etc. of the organism, and why you think it is important. ''H. defensa'' is a host-restricted, mutualist symbiont which is conditionally beneficial. This means that a couple of factors have to be present in order for ''Hamiltonella defensa'' to serve its purpose. Its main purpose is protecting aphids from braconid wasp parasitoids. It is an endosymbiont of aphids, so it lives inside these sap-sucking insects. This bacterium is important because it has the unique ability to defend its aphid host from these invasive parasitoids. ==Genome Structure== Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence? ''Hamiltonella defensa'' has an extremely dynamic genome. It is relatively small, only 2.1 Mb which consists of a 2,110,331-bp circular chromosome. It encodes 2,100 protein-coding genes, has a relatively large number of pseudogenes, and is littered with mobile DNA, insertion sequences, and phage remnants. Horizontal gene transfer plays a role in its dynamic genome. Additionally, approximately half of ''H. defensa's'' DNA comes from toxin-encoding bacteriophages called APSEs. APSEs are similar to lamda-like phages, which are bacterial viruses that infect ''E. coli''. It has other similarities to the ''E. coli'' bacterium, including a similar number of pseudogenes. Depending on which strain of APSE ''H. defensa'' obtains its DNA from, the development stage at which the parasitoid wasps are killed varies. ''H. defensa'' is auxotrophic for 8 of its 10 essential amino acids. It relies on ''Buchnera'', a primary endosymbiont of aphids, to synthesize these amino acids. However, despite ''H. defensa's'' limited biosynthetic capabilities, it has considerably more cell structural, DNA replication, recombination, and repair genes than do obligate endosymbionts. This is most likely due to its extremely varied sources of DNA. Additionally, its diverse genome allows for a wide variety of regulatory genes which help ''H. defensa'' to cope with changes to its environment, such as attack of hosts by parasitoids or an invasion of a new host species. ==Cell Structure, Metabolism and Life Cycle== Interesting features of cell structure; how it gains energy; what important molecules it produces. ''Hamiltonella defensa'' can be maternally transmitted of passed through horizontal gene transfer. It is found in approximately 34% of aphids. The reason it is not found in a higher percentage of aphids is because its presence can be costly to its host if there is no threat present. Specific costs to a host vary among aphid species, but generally, survivorship and life span were lower in aphids infected with ''H. defensa'' when no threat was present. Additionally, ''Hamiltonella defensa'' can conduct glycolysis on its own, which is a very unique ability for endosymbionts. This is important because it allows for energy production, even if ''H. defensa'' is living in oxygen-limited environments. ==Ecology and Pathogenesis== Habitat; symbiosis; biogeochemical significance; contributions to environment.<br> If relevant, how does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.<br><br> ==References== [https://academic.oup.com/gbe/article/10/3/786/4857210 Chevignon, Germain et al. "Culture-Facilitated Comparative Genomics of the Facultative Symbiont Hamiltonella defensa." ''Genome Biology and Evolution'' vol. 10,3 (2018): 786-802. doi.:10.1093/gbe/evy036] [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2690004/ Degnan, Patrick H et al. "Hamiltonella defensa, genome evolution of protective bacterial endosymbiont from pathogenic ancestors." ''Proceedings of the National Academy of Sciences of the United States of America'' vol. 106,22 (2009): 9063-8. doi:10.1073/pnas.0900194106] [https://aem.asm.org/content/80/18/5818/article-info#sec-2 Dykstra, Hannah R et al. "Factors Limiting the Spread of the Protective Symbiont Hamiltonella defensa in Aphis craccivora Aphids." ''Applied and Environmental Microbiology'', vol. 80,18 (2014): 5818-27. doi:10.1128/aem.01775-14.] [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1151865/ Moran, Nancy A et al. "Evolutionary relationships of three new species of Enterobacteriaceae living as symbionts of aphids and other insects." ''Applied and environmental microbiology'' vol. 71,6 (2005): 3302-10. doi:10.1128/AEM.71.6.3302-3310.2005] [https://www.pnas.org/content/102/36/12795 Oliver, K. M., et al. "Variation in Resistance to Parasitism in Aphids Is Due to Symbionts Not Host Genotype." ''Proceedings of the National Academy of Sciences,'' vol. 102,36 (2005): 12795-800. doi:10.1073/pnas.0506131102.] ==Author== Page authored by Isabella Valli, student of Prof. Jay Lennon at IndianaUniversity. <!-- Do not remove this line-->[[Category:Pages edited by students of Jay Lennon at Indiana University]]
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