The Pasteuria group of Gram-positive, endospore-forming bacteria are parasites of invertebrates and exhibit differences in host specificity. We describe a cross-infection study between an isolate of Pasteuria from pigeon pea cyst nematode, Heterodera cajani, which also infects the potato cyst nematode, Globodera pallida, from the United Kingdom. A proportion of the attached endospores, 13% on H. cajani and 22% on G. pallida adhere to the cuticle in an inverted orientation. Inverted and conventionally attached endospores germinated and produced bacillus-like rods that completed their life cycle in < 15 weeks within females of G. pallida. This is the first example in which the life cycle of a Pasteuria population was systematically followed in two different nematode genera. A 1430-base pair fragment of the 16S rRNA gene sequence of the Pasteuria isolate from H. cajani revealed 98.6% similarity to the orthologous gene in Pasteuria nishizawae. Additionally, their respective endospore sizes were not significantly different, in contrast their host ranges are. Potential reasons for this remain unclear and are discussed.