CONTENT - International Society of Zoological Sciences

S7 ICZ2008 - Abstracts
S8 - Biodiversity and ecology of Protists S9 – Genomics and cell biology of Protists
A global perspective of the biodiversity of heterotrophic
nanoflagellates as the most abundant heterotrophic eukaryotes
Harmut Arndt 1* , Frank Nitsche 1 , Frank Scheckenbach 1 and Claudia
Wylezich 1,2
1 Department of General Ecology, Zoological Institute, University of
Cologne, D-50968 Koeln (Cologne), Germany
2 Institute for Baltic Sea Research, D-18119 Rostock, Germany
Protist diversity is still controversially discussed. One group of
protistologists assumes a relatively low number of protistan species
compared to their low size due to assumed high rates of dispersal
and low speciation rates. Another group of protistologists assumes
high protistan diversity similar to other groups of eukaryotes claiming
a high number of cryptic species behind each nominal species. We
will summarise investigations of heterotrophic nanoflagellates
regarding their diversity and distribution patterns. We will include
samples from the largest, though seldom investigated parts of the
biosphere, deep sea, groundwater and polar regions. There seems
to exist biogeographies in nanoflagellates. The endemic and
cosmopolitan distribution of certain taxa will be discussed. Regarding
the knowledge of nanoflagellate biodiversity, we are still at the
beginning and we will point to several problems associated with a
current estimate of biodiversity patterns. According to our recent
estimates, protists as the most abundant eukaryotic key players in
most ecosystems and as the evolutionary oldest and
phylogenetically most diverse eukaryotes should account for a large
proportion of Earth’s eukaryotic diversity. The knowledge of
biogeographic characteristics of nanoprotists is also important from
the viewpoint of overall biological theory. Are small organisms
different from large organisms? At least regarding their importance
for the matter transfer in both aquatic and terrestrial ecosystems
protists are much more important than larger eukaryotes. The
knowledge of diversity patterns of nanoprotists seems to be
fundamental for understanding the Earth’s biodiversity patterns and
ecosystem functioning and may give us also a hint for a better
understanding of evolutionary processes.
The genome of Paramecium
Jean Cohen
Centre de Génétique Moléculaire, CNRS, 91198 Gif-sur-Yvette
cedex.
Ciliates such as Paramecium are the only unicellular eukaryotes
known to separate germinal and somatic functions. Diploid but silent
micronuclei transmit the genetic information to the next sexual
generation. Polyploid macronuclei express the genetic information
from a streamlined version of the genome but are replaced at each
sexual generation through reproducible rearrangements of the
zygotic genome involving elimination of repeated sequences, precise
excision of unique-copy internal eliminated sequences (IES), and
amplification of the cellular genes to high copy number. The
macronuclear genome of Paramecium tetraurelia was recently
sequenced by a shotgun approach, providing access to the gene
repertoire. The 72-Mb assembly represents a consensus sequence
for the somatic DNA which revealed the presence of nearly 40,000
genes, most of them arising through at least three successive wholegenome
duplications, which is produced after sexual. An overview of
genomic and postgenomic data obtained with the Paramecium
genome will be presented.
Aury et al. 2006. Global trends of whole-genome duplications
revealed by the ciliate Paramecium tetraurelia. Nature 444, 171-178.
Duret et al. 2008. Analysis of sequence variability in the
macronuclear DNA of Paramecium tetraurelia: a somatic view of the
germ line. Genome Research, 18, 585-596.
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Bacterial Endocytobionts Variety in Ciliophora
Sergei I. Fokin
Department of Invertebrate Zoology, St. Petersburg State University,
199034, Russia
Different bacteria, which could be considered facultative or,
sometimes, permanent endocytobionts (Eb) can occupy ciliate’s cell.
Till now over 230 ciliate species were recorded as hosts of different
intracellular bacteria. However, approximate number of species of
free-living ciliated protists is about 9000-20000. Thus the number of
recorded Eb is, apparently, just a small part of the real biodiversity of
this mostly undiscovered world. In the presentation is mentioned
some new material concerning Eb variety, its categories and
interaction with a host cell. Special attention is paid to the
endocytobiosis between some ciliates and highly infectious bacteria
Holospora or other alpha-proteobacteria, as well as to life cycles and
strategies of Eb of different ciliates. From ecological point of view we
can assume that association with Eb sometimes is useful for the host
cell, especially in unstable environment like littoral marine zone or
river’s estuary. However, quite low percentage of bacteria infection in
most ciliate’ populations, revealed so far, appears to indicate that
majority of Eb are either parasites or commensals, but not true
symbionts. Dynamic of some bacterial infections, first of all infectious
ones, in natural ciliate’ populations looks epidemic. In some years
and places the number of infected populations increases and then
infected cells become rare for a long time. There is a great need for a
more extensive field-based research in this key sub-discipline of
symbiosis.
Rare ciliate species (Ciliophora, Protista) revealed from
brackish water habitats with oxygen deficiency.
Sergei I. Fokin 1,2 , Letizia Modeo 1 , Ilaria Andreoli 1 , Filippo Ferrantini 1 ,
Franco Verni 1 and Giulio Petroni 1
1
Department of Biology, University of Pisa, 56126, Italy
2 Department of Invertebrate Zoology, St. Petersburg State
University, 199034, Russia
Sonderia pharyngea. Cell size 80-130 μm; all ventral ciliary rows
extending from posterior end; cytopharynx is almost tubular,
sometimes as long as a half of the body; there are few trichocysts.
Found in salinity 5-12‰.
Parablepharisma bacteriophora. Cell size 70-110 μm; has about 50
membranelles on the left side of the large vestibulum; undulated
membrane is very conspicuous – up to 30 μm long; 2 micronuclei;
contractile vacuole closed to posterior end; According to SSrRNA
sequence it clustered with Spirotrichea, very basal to the group.
Found in salinity 22‰. All body surfaces of both mentioned species
are covered with sulfur bacteria.
Copemetopus sp. (subsalsus?). Cell size 150-300 μm; has about 50
membranelles on the left side of large vestibulum (up to half of the
body) and additional 8-12 units of very long cirri (up to 80 μm)
decorate external apical-left part of the mouth area. Cilia tuff in
anterial part of dorsal side; macronucleus has dumbbell shape;
micronuclei are numerous (9-13). According to SSrRNA sequence it
is clustered with Spirotrichea, very basal to the group. Found in
salinity 5-8‰.
All mentioned rare species were isolated in Italy. Probably previous
single finds of the cilates connected with insufficient investigation of
the habitats.