| Pasteuria penetrans is a naturally-occurring bacterial parasite of root-knot nematodes and a promising biocontrol agent. The endospores of this bacterium attach to the cuticle of second-stage juveniles and complete their life cycle within the infected female. Sequential steps required for the bacterium's propagation include: attachment, infection and germination, vegetative growth, sporulation and release. The hypothesis to be tested in these studies considers that molecular entities present on the surface of mature endospores, designated as spore adhesins, are synthesized at a certain time during the growth and sporulation of P. penetrans, and these allow the bacteria to attach to the nematode host. The objectives of this study were to: (1) determine the temporal relationship between adhesin epitope formation and sporulation of P. penetrans; (2) determine adhesin epitope distribution during spore development and association with nematode host and; (3) determine if the adhesin epitope is shared by different species of Pasteuria with different host specificities. ELISA and immunoblotting showed that only proteins extracted from P. penetrans-infected root-knot nematodes harvested 24 days after inoculation and growth at 35°C were recognized by the anti-P-20 IgM Mab that recognizes an adhesin epitope. Labeling, which was first observed in stage III of sporogenesis, identified the epitope distributed over the parasporal fibers, and over other structures, such as sporangium and exosporium, as the bacteria proceeded with the sporogenesis process. However, labeling was not observed on the basal rings, cortex, inner spore coat, outer spore coat, or protoplasm. Immunofluorescence revealed that the epitope does not occur uniformly on the surface of mature endospores. Immunocytochemistry and immunoblot analysis showed that the adhesin epitope is shared by other species of Pasteuria . The uniform distribution of the epitope over the thin sections of mature endospores of strains and species of Pasteuria support a role for the epitope in recognition of the nematode host as an early event in the attachment process. |
