PROGRESS IN PROTOZOOLOGY

240 A. T. SOLDO
vided the host with about 10% of their nutritional needs photosynthetically.
Foraminifera containing diatom symbionts were best adapted
for photosynthetic activity under conditions where they received 1-10%
of the incident light and were capable of effectively recycling nutrients
in an otherwise nutrient poor environment. At least one species, Heterostegina
depressa appeared to be totally dependent on its symbionts
to meet its nutritional needs.
D. S. W e i s studied the infectious process of algal symbionts of
Paramecium bursaria and found that infectivity was associated with
the ability of the algae to excrete maltose. He observed that, despite
a Poisson analysis that indicated a one-hit phenomenon, an average
of 1000 algae were required to infect a single ciliate. Because infection
frequency was greatly increased when ciliates were exposed to algae
intermittantly, rather than in a single dose, he proposed that susceptibility
to infection involved an inducible synthesis of receptors located
on the surface of the phagosomal membrane and that the inducer was
maltose, itself. In support of this hypothesis, the herbicide DCMU which
blocks algal maltose release, was found to prevent infection even when
present during an initial 30 min period of algal-ciliate contact. The frequency
of infection was also reduced when algae were exposed to the
lectin concanavalin A. W. R e i s s e r and K. Meier concurred with
Weis' finding that the algae excreted maltose and further suggested
that the sugar was digested by the ciliates and resulted in an increased
growth rate. These workers studied the uptake of algae during infection
and found them to be enclosed in perialgal vacuoles with closely attached
vacuolar membranes which facilitated nutrient exchange between
the partners. It was suggested that host-symbiont specificity may reside
in the ability of the host to "recognize" the symbionts. "Unsuitable"
algal led to the formation of food vacuoles around them and were
presumably digested by the protozoan. Freeze-fracture studies suggested
that perialgal and food vacuole membranes differed from each other
morphologically.
Bacterial Symbionts
K. Heckmann and R. den Hagen reported on their studies
with omikron, an infectious gram-negative bacterial endosymbiont found
in the fresh water ciliate Euplotes aediculatus. Destruction of the symbionts
by treatment with penicillin caused the ciliates to die unless
reinfected with omikron. All Euplotes with a 9-type 1 fronto-ventral
cirrus pattern were found to contain and be dependent upon symbionts
for cell division. E. crenosus and E. palustris, both characterized by
10 fronto-ventral cirri and E. musicola (9-type 2 pattern) did not contain
symbionts. Over 40 stocks representing 7 species were examined.
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