AUTHOR=Schmitt Paulina , Rosa Rafael D., Duperthuy Marylise , de Lorgeril Julien , Bachère Evelyne , Destoumieux-Garzon Delphine 

TITLE=The Antimicrobial Defense of the Pacific Oyster, Crassostrea gigas. How Diversity may Compensate for Scarcity in the Regulation of Resident/Pathogenic Microflora

JOURNAL=Frontiers in Microbiology

VOLUME=3

YEAR=2012

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2012.00160

DOI=10.3389/fmicb.2012.00160

ISSN=1664-302X

ABSTRACT=<p>Healthy oysters are inhabited by abundant microbial communities that vary with environmental conditions and coexist with immunocompetent cells in the circulatory system. In <italic>Crassostrea gigas</italic> oysters, the antimicrobial response, which is believed to control pathogens and commensals, relies on potent oxygen-dependent reactions and on antimicrobial peptides/proteins (AMPs) produced at low concentrations by epithelial cells and/or circulating hemocytes. In non-diseased oysters, hemocytes express basal levels of defensins (<italic>Cg</italic>-Defs) and proline-rich peptides (<italic>Cg</italic>-Prps). When the bacterial load dramatically increases in oyster tissues, both AMP families are driven to sites of infection by major hemocyte movements, together with bactericidal permeability/increasing proteins (<italic>Cg</italic>-BPIs) and given forms of big defensins (<italic>Cg-</italic>BigDef), whose expression in hemocytes is induced by infection. Co-localization of AMPs at sites of infection could be determinant in limiting invasion as synergies take place between peptide families, a phenomenon which is potentiated by the considerable diversity of AMP sequences. Besides, diversity occurs at the level of oyster AMP mechanisms of action, which range from membrane lysis for <italic>Cg</italic>-BPI to inhibition of metabolic pathways for <italic>Cg</italic>-Defs. The combination of such different mechanisms of action may account for the synergistic activities observed and compensate for the low peptide concentrations in <italic>C. gigas</italic> cells and tissues. To overcome the oyster antimicrobial response, oyster pathogens have developed subtle mechanisms of resistance and evasion. Thus, some <italic>Vibrio</italic> strains pathogenic for oysters are equipped with AMP-sensing systems that trigger resistance. More generally, the known oyster pathogenic vibrios have evolved strategies to evade intracellular killing through phagocytosis and the associated oxidative burst.</p>