Introduction to Fungi, Third Edition

206 ZYGOMYCOTA
Fig 7.36 Basidiobolusranarum. (a) Stages in the
development of endospores by primary
ballistoconidia. Above: cytoplasmic contents cleaving
to form two protoplasts.Centre: sporangium
containing over a dozen sporangiospores. Below:
sporangium showing breakdown of sporangium wall
(traced from Dykstra,1994). (b) Successive cleavage
of protoplasts from a primary ballistosporic conidium
placed on a rich agar medium to form the‘Palmella’
stage. (c) Germination of a primary ballistoconidium
to form a uninucleate secondary capilliconidium with
a terminal beak which has extruded a sticky haptor.
(d) Capilliconidium which has divided to produce
several endospores, some of which have been
released following breakdown of its wall.One of the
endospores is germinating. Scale bars: (a,b) ¼ 20 mm,
(c,d) ¼ 12.5 mm.
Malloch, 1989). Mites are ingested by beetles, the
main vectors of B. ranarum, but other insects,
spiders, millipedes, woodlice, worms and snails
may also acquire conidia. These are ingested by
vertebrate insectivores. Within the vertebrate
gut, endospores are released from ballistosporic
conidia and capilliconidia.
Endospores germinate in the vertebrate gut
to form spherical, large, uninucleate, hyaline
cells up to 20 mm. These were called the ‘Darm-
Form’ (gut-stage) of B. ranarum by Levisohn (1927)
who showed that a single ingested primary
conidium can give rise to 50 60 division
products (meristospores) forming gut-stage cells
(Fig. 7.34a). The concentration of Basidiobolus
propagules builds up in the guts of the vertebrate
vectors, and the fungus can be isolated
from faeces of lizards up to 18 days after the
animals are deprived of infected prey (Coremans-
Pelseneer, 1973; Okafor et al., 1984). The gut-stage
cells are voided with the faeces and can survive
for several months under dry conditions. Under
moist warm conditions they germinate to form a
mycelium from which ballistosporic conidiophores
develop, whereas on certain media they
enlarge and their contents undergo successive
binary fission to form globose thick-walled cells.
This state is sometimes termed the ‘Palmella’
state (Fig. 7.36b) because of its superficial
resemblance of a genus of green algae.