In 1977, at about 2,100 meters deep, hydrothermal vents were discovered on the eastern Galapagos ridge. Following this predicted finding, numerous hydrothermal vent chimneys and diffuse venting have been discovered over the whole East Pacific Rise from 21° North to 38° South of latitude. On these submarine chimneys, temperature can rise to about 400°C, oxygen is scarce and the concentrations of sulfide, heavy metals, reduce compounds and radionucleides are considerably higher than those currently observed in coastal polluted environments.
"Black smoker at a mid-ocean ridge hydrothermal vent."
Image ID: nur04506, National Undersearch Research Program (NURP) Collection Location: Atlantic Ocean Photographer: P. Rona Credit: OAR/National Undersea Research Program (NURP); NOAA.
However, as incredible as it may seem, living organisms as shellfishes and annelids, for example, were found exploiting symbiotic or free-living chemoautotrophic bacteria in these places.
In order to face these extreme conditions, these organisms have developed specific adaptations during the course of evolution as opposed to intertidal / coastal species for which exposure to toxicants is fairly new (less than a few hundreds years ago.
As an example, polychaetes inhabiting hydrothermal vents have developed large gills and produce hemoglobine in order to capture oxygen with a great efficiency and also to be able to detoxify hydrogen sulphide.
The hydrothermal species presently studied for adaptative strategies to environmental stressors are mainly alvinellid polychaetes: Alvinella pompejana (which lives at the hottest place of the hydrothermal environment) and Paralvinella grasslei (which lives in cooler places of this environment), together with Bathymodiolus thermophilus (mussel) and Riftia pachyptila (tubeworm).
From left to right: The alvinellid polychaete, Alvinella pompejana credit picture: IFREMER. A hydrothermal mussel, Bathymodiolus thermophilus, credit picture: IFREMER. Giant tubeworms Riftia pachyptila photographed at 2 630 meters deep during an oceanographic cruise in 2002, credit photograph: www.planete-energies.com.
Scientists are mainly interested in understanding how hydrothermal species have adapted to high temperatures, reduced compounds and heavy metals. In fact, although these species have developed common strategies to survive hostile conditions, they also present subtle differences according to the habitat they are exposed to. Differences within hydrothermal species or between hydrothermal species and less resistant species like coastal species may be detected on genes by tracking adaptative mutations or assessing their level of expression at populations or species scales. Genomic studies are helping a lot in the understanding of inner mechanisms taking place in response to stresses. Genes and gene networks involved in such mechanisms are being identified following the sequencing of cDNA libraries of 4 targeted hydrothermal vent species:
Alvinella pompejana, Paralvinella grasslei, Bathymodiolus azoricus and Lepetodrilus elevatus
Reproduction is generally much affected by environmental factors. Effect of environmental factors will be looked at on the expression of the genes implied in reproduction but also on developmental genes.
Comparative genomics enables scientists to compare genes across organisms adapted to extreme conditions versus more sensitive phylogenetic relatives associated to the coastal / intertidal environments. Functional genomics is another important approach used in these studies as it enables to understand the function of genes and how their expression can change the response to stress. Genes displaying a differential level of expression according to habitat are thus being described. cDNA microarrays and ESTs libraries have been developed in order to study genes under different conditions of stresses (see transcriptomics). Proteomic studies are also carried out in order to identify novel proteins involved in the response to stresses. Datasets will be further investigated using bioinformatic tools and multivariate analyses.
Francesco Paolo Patti from the Bentic Ecology Laboratory in the Stazione Zoologica Anton Dohrn, Napoli (partner #22) is coordinating a work package called ‘Adaptive variation’ in which projects dedicated to vent organisms are listed. These projects are actually coordinated by Didier Jollivet from the Station Biologique de Roscoff (SBR, partner #2) and are part of the Alvinella transcriptome project coordinated by Olivier Poch from the Institut de Génétique et de Biologie moléculaire et cellulaire (IGBMC) of the University of Strasbourg and Franck Zal also from the SBR and done at the Genoscope in Evry (France).
Because these organisms are particularly adapted to extreme conditions (described previously), they may produce novel proteins or selective-devised new functions from well known molecules. In fact, because the vent microflora and some of the vent eukaryots are subject to extreme temperatures, they have developed more thermostable enzymes together with a rapid turnover of these proteins and probably more efficient chaperoneins under these conditions. One of these enzymes, the Taq polymerase, is used in the process of copying DNA before cellular division which is a fundamental mechanism in life. Because of its resistance to high temperatures, it presents an interest for biotechnologies: this enzyme can be used in molecular biology experiments and more specifically, in the Polymerase Chain Reaction which is commonly used by molecular biologists. Other proteins involved in the cellular machinery (translation and traduction, see genetics) are also of great interest for biotechnologies but also in pharmaceutics and cosmetics (e.g. anti-aging creams).
Generally, annelids have strong regenerating capacities. It would therefore be interesting to investigate this question concerning alvinellid polychaetes. In fact, identifying the genes involved in such a process could be interesting for medical research (regeneration of tissues, of the spinal cord, etc.).
To know more about hydrothermal vents: http://www.ocean.udel.edu/deepsea/level-2/geology/vents.html
Contributed by Stephanie Ries
