Shell repair in the clam Ruditapes philippinarum, affected by the Brown Ring Disease (BRD): a biochemical and serologica
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Shell repair in the clam Ruditapes philippinarum, affected by the Brown Ring Disease (BRD): a biochemical and serological study Nolwenn Trinkler1, Frédéric Marin2, Nathalie Guichard2, Maylis Labonne1, Jean –François Bardeau3 and Christine Paillard1 1
IUEM, UMR CNRS 6539, Technopole Brest Iroise, 29280 Plouzané, France. Laboratoire de Biogéosciences, UMR 5561, Université de Bourgogne, 6 bd Gabriel, 21000 Dijon, France. 3 LPEC, UMR CNRS 6087, Université du Maine, 72085 Le Mans Cedex 9. 2
ABSTRACT For more than two decades, the edible clam Ruditapes philippinarum has been affected by the Brown Ring Disease (BRD), a bacterial infection characterized by the formation of a brown organic deposit in the internal side of the valves. Although this infection is often lethal, in some cases specimens can overcome it by remineralizing the shell over the organic deposit. The goal of the present study is to compare biochemically and immunologically the shell matrices of repaired and healthy zones. Our data suggest that the repair zones exhibit certain variability, which would be the direct consequence of a modification of the secretory regime of calcifying tissues responsible of the repair process.
INTRODUCTION In 1987, mass mortalities affected the cultured manila clam Ruditapes philippinarum, in particular in Landeda (North Finistère, Brittany), the first production site in France (with a production of 500 tons of Manila clams at that time) [1, 2]. In 1989, Paillard and Maes showed that mortalities were correlated with the presence of a brown deposit on the inner surface of the valves. This disease, named Brown Ring Disease (BRD) was found to be caused by a bacterium Vibrio tapetis [1]. Vibrio tapetis colonizes the periostracum and inhibits the normal process of shell biomineralization. The response of the clam to the bacterium attack consists in the production and accumulation of a brown organic matrix on the inner and peripheral surface of the shell, in contact with the mantle tissues. When the hemolymph and the soft tissues are colonized, the clam rapidly dies. However, in some cases, clams overcome the infection by secreting a mineralized white layer, which covers and fully isolates the brown organic deposit [3, 4]. This study focuses on the shell repair process. Previous physical investigations on repaired specimens with scanning electron microscopy, Raman spectrometry and Wave-length Dispersive Spectrometry microprobe have shown the quantitative importance of the organic matrix before and during the recovery process: first, the brown deposit is almost totally organic. Then, in the mineralized repaired zone, the level of organic matrix remains high [5]. The aim of this study is to characterize and compare the organic matrix extracted from healthy and repaired zones in the shell of the Manila clam, in order to understand the repair process. To this end, three batches of repaired specimens were selected. The different shell matrices were extracted, quantified, and qualitatively compared on 1D electrophoresis.
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