First evidence of a potential antibacterial activity involving a laccase-type enzyme of the phenoloxidase system in Pacific oyster Crassostrea gigas haemocytes

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.

Metabolic profiling of the tissue-specific responses in mussel Mytilus galloprovincialis towards Vibrio harveyi challenge

“…The organ of gill can be directly attacked by marine pathogens and has been also investigated in shellfish immunology [12,14,15]. In this work, the metabolic profiles were profiled in both digestive gland and gill tissues from mussel M. galloprovincialis challenged by V. harveyi.…”

Responses of Mytilus galloprovincialis to bacterial challenges by metabolomics and proteomics

“…Routinely, both hepatopancreas and hemocytes of marine bivalves are used in immunology [2]. However, gills are the first organ interacting with the bacteria in the surrounding water and have been also studied in shellfish immunology together with hepatopancreas and hemocytes [15,16]. Therefore, in this work, the mussel gill was used for proteomic and metabolomic analysis on the responses to bacterial challenges.…”

Common European harmful algal blooms affect the viability and innate immune responses of Mytilus edulis larvae

“…3). In contrast, most other (chemical) stressors tend to reduce the PO activity of marine organisms [5,34,43,44]. Interestingly, acute DA exposure has been shown to increase the number of haemocytes in adult bivalves [19,36] while OA does not [47].…”

“…Phenoloxidase enzymes, which have antibacterial functions, can be detected in all life stages of M. edulis [15,20,44]. PO enzymes are most commonly found in adult haemocytes [45] but embryonic cells, which possess some phagocytic capacity, possess a restricted level of PO activity as well [20,45].…”

“…Regardless, no studies have assessed the impact of these toxins on the recruitment of bivalves up to now. Moreover, not a single study has examined the possible link between phenoloxidase (PO) innate immune activity, which is known to respond to anthropogenic stressors [5,34,43,44], and HAB exposure. Here, the common model organism Mytilus edulis was used to investigate whether these types of toxic HABs can have an effect on the viability, development and PO activity of bivalve larvae.…”