Morphology and ultrastructure of a Pasteuria form parasitic in Tylenchorhynchus cylindricus (Nematoda)

A new form of the nematode parasitic bacterium Pasteuria was discovered and studied in a population of Tylenchorhynchus cylindricus from Spain. The ultrastructural study revealed peculiar characters in the organization of the bacterium endospore, concernings the cortex layers and core general morphology. The endospore developmental process was studies. Observations are reported on the occurrence during sporulation and core maturation of stranded materials remaining within the endospore sporangium. Unusual parasporal fibers were also observed in this bacterial population. The bacterium and the host-parasite association represent a suitable model system to study factors influencing coevolution and divergence of species of interest for biological control applications.