Pasteuria

Pasteuria is a genus of mycelial and endospore-forming, nonmotile gram-positive bacteria that are obligate parasites of some nematodes and crustaceans. The genus of Pasteuria was previously classified within the family Alicyclobacillaceae, but has since been moved to the family Pasteuriaceae.

== Steps of infection == Animals that are susceptible to Pasteuria become infected when they are exposed to endospores in soil or water. Therefore, Pasteuria are transmitted horizontally between hosts and when an infected host dies, it releases spores to the soil or sediment. The likelihood of infections is related to the endospore density in the environment and can be affected by temperature. However, the ability of an endospore to attach to and infect a host is highly specific and following contact with a compatible host, the Pasteuria endospores are activated, penetrate the host's cuticle, proliferate within the host thereby restricting it from reproducing and ultimately the host dies. In water fleas, the ability of the endospore to successfully attach during the infection process is related to the genotype of the host and the parasite. However, in phytonematodes there was no direct relationship between cuticle heterogeneity as exhibited by endospore attachment and the phylogeny of the nematode. Furthermore, in phytonematodes the cues which initiate germination differ between different endospore isolates. For example, in Pasteuria penetrans that infects root-knot nematodes (Meloidogyne spp.) endospore germination usually occurs sometime between the nematode entering the root, setting up the feeding site and the first molt as currently there are no reports of second-stage juveniles (J2) of Meloidogyne spp. containing either developmental stages or endospores of P. penetrans. However, developmental stages and endospores of a field population of Pasteuria have been observed in J2s of Heterodera avenae. An infected root-knot female can contain up to two million endospores, while an infected J2 of H. avenae will contain less than a thousand endospores''. Interestingly, endospores that do not infect water fleas and pass through a resistant host can still remain viable and infectious. This suggests that different species or strains of the bacterium have evolved different life-cycle strategies.