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Pasteuria spp.
[ Life Cycle ] [ Pasteuria species and their hosts ]
Pasteuria spp. are endospore-forming actinomycetes that are parasites of invertebrates, including nematodes. The bacterium is an obligate parasite and cannot be cultured outside the body of the invertebrate host. Spores of nematophagous species adhere to the cuticle of host nematodes that encounter them while moving through soil.
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Pasteuria sp. spores adhering to the cuticle of Hoplolaimus
galeatus.
Photo by B. A. Jaffee |
The spores form a germ tube and penetrate the cuticle of the nematode.
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Infection of a root-knot nematode by Pasteuria penetrans.
Photo shows spore and penetration tube.
Photo by R. M. Sayre |
The germ tube then forms vegetative microcolonies of lobed, septate mycelium. As the infection progress, the microcolonies break up into daughter colonies that contain fewer, but larger vegetative cells. These large-celled colonies are referred to as quartets and doublets. Doublets separate and form single sporangia which give rise to single endospores. See Life Cycle for a diagram of the different stages in root-knot nematodes.
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Pasteuria sp. in the body cavity of Xiphinema
americanum. Three stages in the life cycle of Pasteuria can be seen:
microcolonies, separated quartets or doublets, and single sporangia. Photo by B. A. Jaffee |
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A female of Pratylenchus penetrans filled with endospores
of Pasteuria brachyurus. The nematode was still alive at time of photo.
Photo by P. Timper |
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Pasteuria spores from ruptured nematode.
Photo by B. A. Jaffee |
These endospores are resistant to environmental extremes and can persist in the soil for several years.
Pasteuria species are very host specific. Generally, populations of this bacterium are only efficient parasites of the nematode species from which they originated. There are four described species of Pasteuria and several undescribed species.