Bacterial parasite of a plant nematode: morphology and ultrastructure

Abstract

The life cycle of a bacterial endoparasite of the plant-parasitic nematode Meloidogyne incognita was examined by scanning and transmission electron microscopy. The infective stage begins with the attachment of an endospore to the surface of the nematode. A germ tube then penetrates the cuticle, and mycelil colonies form in the pseudocoelom. Sporulation is initiated when terminal cells of the mycelium enlarge to form sporangia. A septum within each sporangium divides the forespore from the basal or parasporal portion of the cell. The forespore becomes enclosed by several laminar coats. The parasporal cell remains attached to the forespore and forms the parasporal microfibers. After the newly formed spores are released into the soil, these microfibers apparently enable a mature spore to attach to the nematode. These results indicate that the endoparasite is a procaryotic organism having structural features that are more common to members of Actinomycetales and to the bacterium Pasteuria ramosa than to the sporozoans or to the family Bacillaceae, as previous investigatios have concluded.

Observations on the pathogenicity of Pasteuria penetrans, a parasite of root‐knot nematodes

“…Bird (1986) was unable to demonstrate any effect of the parasite on the early stages of nematode development but the results presented here again indicate that this effect was density dependent. Sayre & Wergin (1977) estimated that only 20% of spores germinated whereas Stirling (1984) indicated that the proportion was nearer 30%. This suggests that on average between three and five spores on each juvenile are required to ensure infection.…”

“…A germ tube penetrates the cuticle to form a vegetative microcolony which then proliferates throughout the body of the developing nematode. The microcolonies fragment and eventually sporulate; the mature female is filled with spores and unable to reproduce (Sayre & Wergin, 1977).…”

Bacteria used in the biological control of plant-parasitic nematodes: populations, mechanisms of action, and future prospects

“…Persidis et al, (1991) showed that collagen may be responsible for the recognition process, because cuticle components involved in attachment are sensitive to trypsin and endoglycosidase F, and because gelatin (denatured collagen) itself can inhibit spore attachment (Persidis et al, 1991;Mohan et al, 2001). However, the incubation of second-stage juveniles in the presence of (Mankau et al, 1976;Sayre & Wergin, 1977;Morton et al, 2004;Huang et al, 2005).…”

“…These models of pathogenicity have been intensively studied, including the stages of attraction and attachment between bacteria and their hosts, entry into the host through nematode stoma or penetration of the nematode body wall, and parasitism or toxin-mediated host death ( Fig. 1) (Sayre & Wergin, 1977;Tan, 2002;Huang et al, 2005).…”

Cross-Species Infection Trials Reveal Cryptic Parasite Varieties and a Putative Polymorphism Shared Among Host Species

“…The host range of Pasteuria is currently unresolved. However, Pasteuria has been reported from field samples of D. magna, Daphnia longispina, Daphnia pulex (Stirnadel and Ebert 1997), Daphnia dentifera (Duffy et al 2010), Daphnia curvirostris (Goren and Ben-Ami 2012), and even cladocerans in other genera (Green 1974;Sayre and Wergin 1977;Goren and Ben-Ami 2012). These Daphnia species belong to different subgenera and are unlikely to have exchanged genes in the last 100 million years (Colbourne and Hebert 1996).…”