PROGRESS IN PROTOZOOLOGY

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Only those with 9-type 1 fronto-ventral cirri contained symbionts.
J. A. Kloetzel exposed omi/cron-containing Euplotes aediculatus to
gamma irradiation in an attempt to produce amieronucleate strains and
found the greatest effect to be on the symbionts. Animals exposed to
40 Krad usually died by day 17 whereas cells exposed to 23 Krad
survived and divided after a lag of several days. Survival was attributed
to the re-establishment of normal-appearing symbiont populations,
a result consistent with Heckmann's finding that omikron was
essential for the growth and division of E. aediculatus. A. T. Soldo
studied bacterial-like symbionts, termed xenosomes, of the marine ciliate
Parauronema acutum. Xenosomes, found in 12 strains of the protozoan,
were gram-negative, contained RNA, DNA and protein, divided
in synchronism with the host and were susceptible to the action of
a number of antibiotics. Unlike omikron particles, xenosomes were not
essential for the growth of the protozoan. Rather, they appeared to be
dependent upon the protozoans for growth. Xenosomes were found to
infect homologous as well as heterologous Parauronema cells. Some
strains were capable of killing certain species of the genus Uronema.
The structure and size of chromosomal xenosomal DNA was unusual for
a bacterium. There were 8 copies of a circularly permuted DNA molecule
of MW = 0.34 X 10 9 ; most free-living bacteria contain one (or at
most two) copies of the genome and are much larger with respect to
molecular weight. H-D. G o r t z described a symbiotic bacterium, Holospora
elegans that multiplied exclusively in the micronucleus of Paramecium
caudatum. After being taken up in the food vacuole together
with prey organisms, the infectious form of the symbiont underwent
a series of morphological changes and was carried in a "transport vessel"
to the micronucleus. The tip of the symbiont, which may be seen with
thin fibrils projecting from it, entered the micronucleus and established
the infection. In other work with P. caudatum, J. Dieckmann
described gram-negative bacterium-like symbionts, 4-10 |im long and
1-2.5 |iim wide, which were present in the cytoplasm. The symbionts
contained refractile inclusion bodies that differed in appearance from
the R-bodies of kappa and were motile, propelled by flagella, when released
from the ciliate. The symbionts were capable of infecting syngens
1, 3, 12 and 13 of P. caudatum but not other ciliate species. Unless
the paramecia were grown at 2-3 fissions per day the symbionts multiplied
and killed the host. A. I. Radchenko reported on the presence
of gram-negative bacterial symbionts in the nucleus of the euglenoid
flagellate Peranema trichophorum. The symbionts were 1-2 jjm
long and 0-3 fim wide. The cell wall was 20-30 nm thick. Nucleoids
resembling DNA of bacteria were observed; ribosomes, 17 nm in diameter,
were also present. The symbionts were non-motile and did not
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