| dc.description.abstract | Phenoloxidases (POs) are a group of copper proteins including tyrosinase, catecholase and laccase. In
several insects and crustaceans, antibacterial substances are produced through the PO cascade, participating in the direct killing of invading microorganisms. However, although POs are widely recognised as
an integral part of the invertebrate immune defence system, experimental evidence is lacking that these
properties are conserved in molluscs, and more particularly in the Pacific oyster Crassostrea gigas. In the
present study, Vibrio splendidus LGP32 and Vibrio aestuarianus 02/041 growths were affected, after being
treated with C. gigas haemocyte lysate supernatant (HLS), and either a common substrate of POs,
L-3,4-dihydroxyphenylalanine (L-DOPA), to detect catecholase-type PO activity, or a specific substrate of
laccase, p-phenylenediamine (PPD), to detect laccase-type PO activity. Interestingly, a higher bacterial
growth inhibition was observed in the presence of PPD than in the presence of L-DOPA. These effects
were suppressed when the specific PO inhibitor, phenylthiourea (PTU), was added to the medium.
Results of the present study suggest, for the first time in a mollusc species, that antibacterial activities of
HLS from C. gigas potentially involve POs, and more particularly laccase catalysed reactions. | |
