Zero pollution: recycling sea by-products of shellfish farming - Search for bactericidal biomolecules in the shell of mollusks of economic interest

To calcify their shells, bivalves secrete macromolecules (mainly proteins) that regulate the setting up of the crystalline units and remain included in the mineral phase. High-throughput proteomics techniques backed by transcriptomes show the complexity of this calcifying matrix, which has many molecular functions, including potential bactericidal power suspected by the presence of highly basic peptides contained in the matrix. This doctoral research investigates the antibacterial properties of the organic matrices extracted from economically important bivalve shells, specifically targeting marine Vibrionaceae pathogens. First the organic matrices were extracted from the shells, which led to the identification of both soluble (ASM) and insoluble (AIM) fractions. Then an antibacterial screening was conducted using disk diffusion and microdilution assays. The Pacific cupped oyster (M. gigas) and giant scallop (P. maximus) demonstrated particularly strong activity against pathogens, especially V. harveyi ORM4 and A. salmonicida. Proteomic analysis identified known antimicrobial peptides and proteins (AMPPs) in the extracts, attempting to correlate them with observed bioactivity. This exploratory project, at the interface of environmental geosciences, aquaculture, health, and cultural heritage conservation, aims to valorize an abundant marine co-product: empty shells from shellfish consumption. By developing sophisticated applications for these typically low-value recycled materials, this research contributes to establishing a virtuous circular economy. While promising results were obtained, further experiments are required to elucidate the bacteriostatic or bactericidal mechanisms of bivalve shell extracts. This work opens new perspectives in marine bacteria experimentation and natural resource bioprospecting, potentially leading to innovative applications in aquaculture, food safety, and environmental conservation.