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Project 14

Molecular dialog and gill plasticity during bacterial colonization in lucinid bivalves

PhD position. Supervisors: Sébastien Duperron (UniParis) and Prof Andreas Schramm (UniAarhus) (with input from Oliver Gros, UniAntilles). Host: UniParis. Secondment internship: UniAarhus

Rationale

Tropical shallow water lucinids are known to harbor sulfur-oxidizing gill-endosymbionts as described in several marine invertebrates inhabiting sulfidic environments from vents to shallow-water environments. Due to the fact that it is possible to induce spawning, culture aposymbiotic juveniles and infect them with either gill-endosymbiont purified fractions or free-living bacteria from an environmental stock, they represent an unique model to study the molecular mechanisms existing between host and bacteria during the establishment of symbiosis.

Objectives

i) By using interspecific infections, we aim to demonstrate that the bacterial association with one lucinid species is not irreversible. ii) The first molecular events underlying the initiation of such symbiotic relationships between the host and its bacteria will be analyzed. iii) The expression of putative targeted proteins will be knocked down to identify their specific role in the symbiosis processes.

Key methods

Cross-infection experiments with two tropical lucinids (Codakia orbiculata and C. orbicularis), in situ imaging techniques (CARD-FISH, electron microscopy). Aposymbiotic individuals (primitively aposymbiotic juveniles or adults cured from their symbionts) will be confronted with purified bacterial fractions and the expression of genes examined using substractive mRNA analyses, immunohistochemistry, western blot analysis and proteomic analyses (in collaboration with Prof Schweder, UniGreifswald). The specific and functional role of the targeted genes within the trophic relationship will be assessed using the siRNA method. Knock-down gene transcription will be achieved using real time quantitative PCR analysis, CARD-FISH, western blot and immunohistochemistry. The ability to culture aposymbiotic individuals will allow the analysis of the different steps of the infection process in the aposymbiotic juveniles and adults cultivated in aquaria. The inverse process (i.e. loss of the endosymbionts) will be checked on adults collected in their natural habitat and placed in 0.22 µm filtered and sterile seawater.