The previous work done on microbial diversity of hydrothermal vents will be continued on a limited number of questions, mostly in order to gain a better understanding of the hydrothermal ecosystem functionning.
Microbial mats are present on numerous hydrothermal vent fields. These microbial mats are dominated by large sulfur oxidizing filamentous Bacteria often affiliated (according to microscope observations) to Beggiatoa and Thioploca. At Lucky Strike vent field on the Mid-Atlantic Ridge, Azores triple junction, microbial mat surfaces were shown to be in constant increase according to the observations performed over 10 years during oceanographic cruises and might compete with invertebrates/symbiont associations. At Lucky strike microbial mats are covering the mussels ( Bathymodiolus azoricus) assemblages or are settled directly on hydrothermal deposits.
In order to understand their role in the hydrothermal ecosystem the phylogenetic and the metabolic diversity of microbial mats will be investigated in parallel with the characterisation of their environment (temperature, sulphide gradient, pH, oxygen concentration…). Identification of microbial species will be first performed by studying the diversity of 16S rRNA encoding genes and will be completed by the diversity study of functional genes and cultural approaches.
The hydrothermal shrimp Rimicaris exoculata
Our project is focused on the dominant megafaunal species found at the Mid-Atlantic Ridge and at the triple junction point of the Indian Ocean, which currently remains poorly studied : the caridean shrimp Rimicaris exoculata , belonging to the family Alvinocarididae. Rimicaris exoculata (Williams and Rona, 1986) is particularly abundant, forming dense, motile swarms around the active chimney walls (Segonzac, 1992, 1993; Gebruk et al., 1993) and seems to ingest mineral particules. First experiments have shown that the shrimp is neither a detritivor nor a predator. Rimicaris exoculata have an unusually enlarged gill chamber housing epibiotic bacteria, most abundant on shrimps mouthparts, bacteriophore structures and the inner surface of the branchiostegites (Casanova et al., 1993). More recently, a local bacterial population in the shrimp gut have been identified and could serve as a source of nutrition (Zbinden and Cambon-Bonavita, 2003). Rimicaris exoculata occurs at different Atlantic vent sites (such as Rainbow, TAG, Logatchev or Snake Pit), each with different fluid compositions, especially considering the sulphide, methane, hydrogen and iron concentrations. Regarding these variations, microbial metabolisms occurring within the shrimp environment could be very different. In the next year (2008-2011), the objectives of the project are to determine the impact of various geochemical factors on the epibiotic composition and the main pathways/metabolisms which lead to host/epibionts adaptations and exchanges, using molecular (phylogeny and functional) and cultural approaches..
For more information on deep-sea hydrothermal vents, consult the following links: (1) exploration of mid-oceanic ridges, (2) how does a hydrothermal vent system function?, (3) what is the composition of hydrothermal fluids?, (4) what is the associated fauna?