Abstract
The aim of this study was first to identify lysozymes paralogs in the deep sea mussel Bathymodiolus azoricus then to measure their relative expression or activity in different tissue or conditions. B. azoricus is a bivalve that lives close to hydrothermal chimney in the Mid-Atlantic Ridge (MAR). They harbour in specialized gill cells two types of endosymbiont (gram—bacteria): sulphide oxidizing bacteria (SOX) and methanotrophic bacteria (MOX). This association is thought to be ruled by specific mechanism or actors of regulation to deal with the presence of symbiont but these mechanisms are still poorly understood. Here, we focused on the implication of lysozyme, a bactericidal enzyme, in this endosymbiosis. The relative expression of Ba-lysozymes paralogs and the global anti-microbial activity, were measured in natural population (Lucky Strike -1700m, Mid-Atlantic Ridge), and in in situ experimental conditions. B. azoricus individuals were moved away from the hydrothermal fluid to induce a loss of symbiont. Then after 6 days some mussels were brought back to the mussel bed to induce a re-acquisition of symbiotic bacteria. Results show the presence of 6 paralogs in B. azoricus. In absence of symbionts, 3 paralogs are up-regulated while others are not differentially expressed. Moreover the global activity of lysozyme is increasing with the loss of symbiont. All together these results suggest that lysozyme may play a crucial role in symbiont regulation.
Highlights
Bathymodiolus azoricus is a bivalve mollusc of the Mytilidae family that lives around hydrothermal vents on the Mid-Atlantic Ridge (MAR) [1]
Within the general frame of our researches on the biology of B. azoricus, the main goal of this study was to provide a comprehensive knowledge on the implication of lysozymes in the regulation of the symbiotic association between B. azoricus and SOX/MOX bacteria
Deep sea mussels Bathymodiolus azoricus were collected from one hydrothermal vent site (Lucky Strike, population of Montsegur, 37°17,286’ N, 32°16,530’ W; 1700 m depth) located on the Mid Atlantic Ridge during the BioBaz and MoMARSAT cruises (July/August 2013)
Summary
Bathymodiolus azoricus is a bivalve mollusc of the Mytilidae family that lives around hydrothermal vents on the Mid-Atlantic Ridge (MAR) [1] This mussel hosts two types of endosymbiotic γ-proteobacteria, one sulphide-oxidizing (SOX) and one methanotrophic (MOX), in specialized gill cells called bacteriocytes [2,3,4,5]. Involvement of Lysozymes in the Symbiotic Association between B. azoricus and Its Bacterial Symbionts ratio when the concentration of methane or sulphide changes [7,8,9,10] or a loss of symbionts in the absence of reduced compounds [11] The metabolism of these symbiotic bacteria is relatively well understood compared with that of the host [12,13,14,15]. Immunity is thought to be crucial in symbiotic associations to recognize, maintain or regulate symbionts populations [21,22,23]
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