Long Lives and Deep Roots: Ecophysiology of cold seep vestimentiferans.
C. R. Fisher*, D. C. Bergquist*, J. K. Freytag*, J. P. Andras*, D. Julian†, and M. Van Horn*,
*The Department of Biology, The Pennsylvania State University, University
Park PA 16802. USA
†Department of Zoology, University of Florida, Gainsville FL
Vestimentiferan tubeworms were first discovered associated with hydrothermal vents, and the species found on most mid-ocean ridges are adapted to the energy-rich but ephemeral vent environment. The tubeworms found around cold seeps in the Gulf of Mexico are similar to their vent relatives in that they have no mouth, gut or anus and also rely on their chemoautotrophic bacterial symbionts for nutrition. However, we have found that the most abundant cold seep vestimentiferan species, Lamellibrachia cf luymesi, has a very different physiological ecology and life history than its vent relatives. Individuals of Lamellibrachia cf luymesi live in excess of 170 - 250 years and the co-occurring Escarpid-like species lives at least as long. Sulfide is generally undetectable (<0.1µm) around the plumes (gill-like gas exchange organs) of the seep tubeworms while it is consistently present in substantial quantities in the interstitial waters around the buried posterior ends of the tubeworms. Their posterior ends are permeable to sulfide and we have recently demonstrated that at least one species, Lamellibrachia cf luymesi can take up sulfide across the roots at rates sufficient to fuel net inorganic carbon uptake by the worm. This adaptation provides the tubeworms access to a much more stable and longer lasting source of sulfide and provides the explanation for the growth and abundance of tubeworms in areas where sulfide is not detectable in the water above the sediments. It also has significant implications for the evolution of their life history traits and for the structure of the associated faunal assemblages.
Adaptations of deep-sea Molluscs to hydrothermal vent and cold seeps constraints
A. Fiala-Médioni
Université P.M. Curie (Paris 6), Observatoire Océanologique, 66650 Banyuls-sur-Mer
Symbioses account for the major portion of the biomass at most deep hydrothermal
vent and cold seep sites. Among symbiotic organisms colonizing such environnements
associations Molluscs-Bacteria appear as the more widely distributed.
In some Atlantic or in West Pacific back arcs basins , Mytilids are the
dominant organisms. When in some cold seep sites , Vesicomyids account
up to 100% of this biomass .
Occupying the cold pole of these sites, they are dependant on a variable
mixture of hot fluids rich in chemical energy and cold sea water providing
oxygen.
The specific structural and physiological adaptations of these symbiotic
organisms are related to the two main constraints in such environments
: use chemical energy and resist to toxicity of sulfides and heavy metals
.
The energy used in chemosynthetic processes is driven throught the oxydation
of chemical compounds, mainly : sulfide, methane or both . All Vesicomyids
house in their hypertrophied gills sulfur-oxidizing symbionts, when Mytilids
appeared more flexible and can be associated either with sulfur-oxidizing
or methanotrophic or both symbionts.
Symbiotrophy appear as the general rule among the different molluscs as
demonstrated by fatty acids analyses ; yet, some mixothrophy could occur
in some shallover sites or in gastropods. An active lysosomic resorption
of the bacteria is observed in all species; this heterophagic process
might represent the main way for transfer of organic molecules from the
symbiont to the host as well as a mechanism of regulation of the bacterial
population
The chemical environment of vents is comparable to highly polluted habitats:
the combination of high sulfide and high levels of heavy metals gives
to the vent environments a highly toxic character for most animals.
Specific adaptations appear in vent symbiotic molluscs in order to detoxify
sulfide as well as to bioaccumulate and detoxify high concentrations of
heavy metals through different mechanisms.
How do vestimentiferan tubeworms survive in vent and seep environments?
Horst Felbeck and C. Arndt#
Scripps Institution of Oceanography, 0202, La Jolla, CA 92093
(hfelbeck@ucsd.edu)
#presently: EMA University, Institute for Microbiology, Jahnstr. 15 D-17487
Greifswald, Germany
The hydrothermal vent and seep environments are extremely hostile to
commonly known life. High concentrations of sulfide, temporary lack of
oxygen, and low availability of food are common characteristics. Yet,
dense communities of animals harboring specific adaptations have formed
in these areas.
My talk will concentrate on the different metabolic adaptations found
in vestimentiferans to allow them to obtain nutrition through an uptake
of inorganic materials and to survive periods of anoxia by reversing the
metabolic pathway of sulfide oxidation to the reduction of elemental sulfur.
In addition, I will present and discuss novel ways to determine the metabolic
abilities of unculturable symbionts by using molecular techniques such
as expressing of symbiont genes in culturable microorganisms and sequencing
of the symbionts' genome. The genome of the Riftia pachyptila symbiont
has been sequenced to date to 70% and numerous genes have been tentatively
identified.
Oxygen, carbon dioxide and sulfide transport in the symbiotic tubeworm Riftia pachyptila
F.H. Lallier
CNRS-Univ Paris 6, Station Biologique de Roscoff
The giant tubeworm Riftia pachyptila is actually a very effective symbiosis between an annelid-like host and hemoautotrophic bacteria. These are remotely located from the environment, inside specialized cells of an internal organe of the host, the trophosome. The symbionts are very specialized sulfide-oxydising bacteria which use eclusively H2S, CO2 and O2 for their carbon fixation metabolism. The establishment of this symbiosis has thus required a number of specific adaptations on the host part in order to fuel its bacteria with the necessary metabolites. This paper will present recent advances on the mechanisms allowing the extraction, transport and delivery of sulfide and carbon dioxide, from the deep-sea hydrothermal vent environment to the vicinity of the bacteria. It will focus on the functional morphology of the gill, the structure and function of hemoglobins, capable of binding oxygen and ! sulfide at the same time, and on the characterization and localization of carbonic anhydrase and proton pumps, deeply involved in CO2 transport.
M.C. De Cian, A.C. Andersen, J.Y. Toullec* and F.H. Lallier
Ecophysiologie, Station Biologique de Roscoff, UPMC-CNRS-INSU, BP74,
29682 Roscoff cedex, France, and
* CNRS-EP2028 - Ecole Normale Superieure, 75230 Paris Cedex 05, France
The giant tubeworm Riftia pachyptila is a strict symbiosis with
sulfur oxidizing bacteria, found around the East-Pacific Rise hydrothermal
vents. The bacteria are located intracellularly in vacuoles of bacteriocytes
which form a specialized organ, the trophosome. To fuel their metabolism
the bacteria need molecular CO2 as a carbon source,
and O2 and H2S as energy source.
Carbon dioxide acquisition takes place at the plume level by diffusion
and is transported mainly as bicarbonate in the blood towards the trophosome.
We have developed a model of CO2 transport involving
anion exchangers (AE) and carbonic anhydrases (CA).
In this study we present a new cellular approach, using isolated cell
suspensions from plume and trophosome tissues. Worms collected on the
bottom (2600m- EPR) by submersible were repressurized at least 4 h using
thermostated pressure vessels. Viable cell suspensions have been obtained
from plume and trophosome tissues and we found that trophosome preparations
were indeed composed mainly of bacteriocytes, as indicated by in situ
hybridization with fluorescent probes specific for g proteobacteria. By
analyzing the extracellular and intracellular acid-base balance under
normo- or hypercapnic conditions with a variety of inhibitors we were
able to test the validity of the proposed model. In addition to this physiological
approach, we have started to sequence the two forms of CA. Plume CA has
been fully sequenced and a mRNA probe has been designed in order to localize
CA expression in Riftia tissues.