[2] Daphnia is a genus of small planktonic crustaceans including D. magna, P. ramosa's most popular host target.

An established and widely used coevolutionary model of host-pathogen interactions exists with P. ramosa and D.

[2] These endospores are highly resistant to different environmental stresses, including freezing temperatures, and can remain in the environment for decades without any deleterious effects.

The spores are shed into the environment from the dead host and can remain in the sediment for decades while maintaining their infectivity.

[6] The infection success of P. ramosa depends on its ability to attach to the host esophagus and to spread into its body cavity where the propagation of the pathogen takes place.

[5][8] Although the process through which the genotypic interactions occur is unclear, environmental factors, such as temperature, play a large role in the castration of Daphnia.

[3][4][10] A culture established by James T. Staley, ATCC 27377T, was previously considered to be the neotype for this species, but has been reassigned to Pirellula staleyi Schlesner and Hirsch, 1987[11] because it did not conform to Metchnikoff's original description of Pasteuria ramosa.