Hamiltonella defensa

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Domain: Bacteria; Phylum: Proteobacteria; Class: Gammaproteobacteria; Order: Enterobacterales; family: Enterbacteriaceae; Genus: Hamiltonella


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. 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 this invasive parasitoid.

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.

Cell Structure, Metabolism and Life Cycle

Interesting features of cell structure; how it gains energy; what important molecules it produces.

Ecology and Pathogenesis

Habitat; symbiosis; biogeochemical significance; contributions to environment.
If relevant, how does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.


[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

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

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

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.

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


Page authored by Isabella Valli, student of Prof. Jay Lennon at IndianaUniversity.