hamiltonella hamiltonella hamiltonella is a genus of enterobacteria in the gammaproteobacteria. hamiltonella defensa is a model organism for defensive symbiosis, protecting pea aphids from parasitoid wasps. hamiltonella has also been found as a nutritional mutualistic endosymbiont in whiteflies. hamiltonella scientific classification domain: bacteria phylum: pseudomonadota class: gammaproteobacteria order: enterobacterales family: enterobacteriaceae genus: candidatus hamiltonella