plant surface microbiology.pdf

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Robert Bauer and Franz Oberwinkler
in a greatly increased contact zone between the parasite and its host. This is
also the case in a third type of colacosome-arrangement. In Colacogloea bispora
(Oberwinkler et al. 1999), Colacogloea sp. (Fig. 6), Colacosiphon (Kirschner
et al. 2001a), Cryptomycocolax (Oberwinkler and Bauer 1990), Krieglsteinera,
and Heterogastridium, the appearance of colacosomes is associated with
curious interaction structures: filamentous outgrowths of the host cells are
intimately enclosed by galloid parasite cells. Numerous colacosomes are present
along the contact area between the host intrusion and the parasite cell
(Fig. 6). These host intrusions always terminate in the parasite cell. They are
unseptate, often branched and, astonishingly, lack cell walls, thus giving the
impression of haustoria (of the host into the parasite!!!). In Cryptomycocolax
a second type of colacosome was found along the cytoplasmic intrusions of
the host formed into the hyphae of the parasite (Fig. 7; Oberwinkler and
Bauer 1990). These colacosomes have a more electron-transparent core and
they fuse with the host cell via a pore of approximately 7–14 nm in diameter
(Figs. 7, 8). It is clear that the cellular interaction of Cryptomycocolax is complex
and currently misunderstood.
Colacosomes have also been found in Atractocolax, Leucosporidium,
Mastigobasidium, Rhodosporidium and Sporidiobolus, indicating a potential
for mycoparasitism in these genera that have been assumed to be saprobic
(Kreger van Rij and Veenhuis 1971; Bauer et al. 1997; Kirschner et al. 1999).
Fig. 8. Colacosome of Cryptomycocolax
abnorme in
contact with the host cytoplasm
(H) showing the
fusion pore (arrowhead) in
detail. Note that the pore
membranes are continuous
with both the host plasma
membrane and the membrane
surrounding the core
(c) of the colacosome
(arrow). Bar 0.1 µm