CONTENT - International Society of Zoological Sciences

S20 ICZ2008 - Abstracts
results show firstly that tolerance to heat is not a pre-requisite for
life on a smoker wall and secondly that temperature resistance
does not appear to be a crucial factor for explaining differences in
distribution of shrimp species in a given vent sites. Moreover, the
thermal resistance of vent shrimp is comparable to those of other
non-vent tropical caridean species and thus does not place them
amongst the most thermophilic metazoans. In this study on deepsea
vent shrimp, we also investigate the influence of pressure on
temperature resistance properties since pressure-dependant
thermal characteristics have been reported for various biological
systems. First, we determined the upper thermal limit of M.
fortunata specimens originating from different sites and depths
(850 to 1700 m) and secondly we evaluated the upper thermal limit
of R. exoculata specimens originating from 2300 m, at different
pressures in pressurized aquaria. In the case of M. fortunata
originating from different depths, it appears that temperature
resistance properties are not influence by depth of occurrence.
However, for R. exoculata originating from 2300 m depth and
pressurized at different pressures, the temperature at which the
first signs of thermal discomfort occur seems to vary with pressure.
Further studies are required to better understand the role of
pressure in colonization processes.
Symbioses between deep-sea mussels (Mytilidae:
Bathymodiolinae) and chemosynthetic bacteria: diversity,
function and evolution
Sébastien Duperron
UPMC-Paris 6 & CNRS, UMR 7138 Systématique, Adaptation et
Evolution, 7 quai St Bernard, 75005 Paris, France
Mussels of the subfamily Bathymodiolinae thrive around chimneys
emitting hot fluids at deep sea hydrothermal vents, as well as at
cold seeps and on sunken organic debris such as sunken wood
and whale falls. Despite the absence of light-driven primary
production in these deep-sea ecosystems, mussels succeed
reaching high biomasses thanks to chemosynthetic, carbon-fixing
bacterial symbionts located in their gill tissue (1). Since the
discovery of mussel symbioses about three decades ago our
knowledge has increased, mainly regarding large vent and! seep
species, and new findings are published regularly. Recent studies
have pointed out new interesting facts such as the presence of
multiple symbionts in the gills of two cold seep mussels (2), the
distinct intra- or extracellular localization of bacteria in the gills of
mussel species from the same habitat (3), and the direct influence
of immediate environmental parameters on symbiont densities (4).
The study of smaller, less spectacular, species from cold seeps
and organic falls has also shed new light on the diversity and
evolution of mussel symbioses. In this talk, we’ll summarize
current knowledge about symbiosis in Bathymodiolinae, with an
emphasis on bacterial diversity and evolution. Future prospects will
be discussed.
Riftia pachyptila: a hydrothermal vent tubeworm as poster
child for thioautotrophic symbioses
Horst Felbeck
Scripps Institution of Oceanography, University of California San
Diego 0202, La Jolla, CA 92093, USA
Riftia pachyptila has no digestive tract as an adult and is
dependend on nutritional supply through intracellular
chemoautotrophic symbionts harbored in a special tissue, the
trophosome. The symbionts are acquired new in each generation
of the host. Their metabolic interactions with the host and the
origin of the free-living form have remained unclear for many years.
Recent information gained from proteomics and the sequencing of
the majority of the symbiont’s genome provides new clues about
its identity, metabolic capabilities and the presence of nonexpressed
genes. Apparently, only one species of symbiont, or
possibly several strains of one species, populates a specimen of R.
pachyptila. The name Endoriftia persephone has been proposed
for the symbiont. The symbiont may have two ways to fix CO2 as
autotrophic sources of carbon for itself and the host, the Calvin-
Benson cycle and the reductive tricarboxylic acid cycle. The
activity of the reductive tricarboxylic acid cycle could explain the
unusual carbon isotope ratio characteristic for the tubeworm. The
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relative significance of the two ways of carbon fixation may be
dependend on the environmental conditions. Non expressed
genes hint to possible capabilities of the symbiont as a heterotroph
while free-living between generations of the host.
Cell interactions induced by bacterial infection processes
within the lateral zone of gill filaments of the lucinid Codakia
orbiculata.
Sylvie Gustave, Nathalie Elisabeth and Olivier Gros
UMR-CNRS 7138, Systématique-Adaptation-Evolution, Equipe
«Symbiose», Université des Antilles et de la Guyane, UFR des
Sciences Exactes et Naturelles, Département de Biologie. B.P.
592. 97159 Pointe-à-Pitre Cedex, Guadeloupe, France.
Codakia orbiculata (Montagu, 1802) is a shallow-water lucinid
which inhabits low sulfide sediments in seagrasses of Thalassia
testudinum, and harbors sulfuroxidizing endosymbiotic bacteria
within bacteriocytes of its gill filaments. Here, we attempted to
evidence the mechanisms that might underlie the adaptative
plasticity of the cells in the lateral zone of gill filaments. Two sets of
starved individuals (3-month and 5-month starvation periods) were
put back in their natural environment then collected at daily interval
before treatment with thymidine analogue bromodeoxyuridine
(BrdU) which is a cell division marker, or with cytosine analogue
cytosine arabinoside (Ara-C) which is an antimitotic agent.
Technical approaches were made by CARD-FISH,
immunoshistochemistry, and histology in order to monitor the
bacterial infection processes in correlation with the variation of cell
organization within gill filaments, and to detect the new synthetized
cells. In starved individuals, non symbiotic granule cells become
the majority cells while bacteriocytes disappeared, whereas during
bacterial colonization, these cells had been partially replaced by
bacteriocytes which became predominant. One explanation of
such cell variability might be cell proliferations regulated by the
number of endosymbionts within the bacteriocytes.
3D FISH for the quantification of methane- and sulphoxidising
endosymbionts in bacteriocytes of the hydrothermal vent
mussel Bathymodiolus azoricus
Sébastien Halary 1 , Virginie Riou 3,4 , Françoise Gaill 1 , Thomas
Boudier 2 and Sébastien Duperron 1
1 UMR 7138 Systématique Adaptation Evolution, équipe
Adaptation aux Milieux Extrêmes, Université Pierre et Marie Curie,
7 quai St Bernard, 75005 Paris, France; 2 UMR 7101 Neurobiologie
des Signaux Intercellulaires, Université Pierre et Marie Curie, 9
Quai St Bernard, 75005 Paris, Franc; 3 IMAR Centre of the
University of Azores, Department of Oceanography and Fisheries,
Rua Cais de Santa Cruz, 9900 Horta, Portugal; 4 Department of
Analytical and Environmental Chemistry, Vrije Universiteit Brussels,
Pleinlaan 2, 1040 Brussel, Belgium
Dual endosymbioses involving methane- and sulphur-oxidising
bacteria occur in the gills of several species of mussels from deepsea
hydrothermal vents and cold seeps. Variations of total and
relative abundances of symbionts depending on local
environmental parameters are not yet understood, due to a lack of
reliable quantification of bacteria in the host tissue. Here we report
the first attempt to quantify volumes occupied by each type of
symbiont in bacteriocyte sections from a vent mussel,
Bathymodiolus azoricus, using fluorescence in situ hybridization
(FISH) coupled to 3D microscopy and image analysis carried out
by a dedicated software which we developped. Bacteriocytes from
mussels recovered at different vent sites displayed significantly
different abundances of bacteria. Specimens kept in aquaria at
atmospheric pressure and exposed to an artificial pulse of sulphur
displayed an increase in absolute and relative abundance of
sulphur-oxidisers within their bacteriocytes. Distributions of all
measured parameters fitted normal distributions, indicating that
bacteriocytes from a specimen tend to display similar behaviours.
This study shows that symbiont volume quantification is tractable
using 3D FISH and confirms the impact of local environmental
parameters on symbiont abundances.