Vibrio aestuarianus zinc metalloprotease causes lethality in the Pacific oyster Crassostrea gigas and impairs the host cellular immune defenses

• Published in: Fish & shellfish immunology 2010-11, Vol.29 (5), p.753-758
• Main Authors: Labreuche, Yannick, Le Roux, Frédérique, Henry, Joël, Zatylny, Céline, Huvet, Arnaud, Lambert, Christophe, Soudant, Philippe, Mazel, Didier, Nicolas, Jean-Louis
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Analysis of Variance; Animals; Base Sequence; Crassostrea gigas; DNA Primers - genetics; Enterotoxins - toxicity; Environmental Sciences; Extracellular products; Extracellular Space - chemistry; Hemocytes; Immunity, Cellular - drug effects; Life Sciences; Marine; Metalloendopeptidases - toxicity; Metalloprotease; Microbiology and Parasitology; Molecular Sequence Data; Open Reading Frames - genetics; Ostreidae - drug effects; Ostreidae - genetics; Ostreidae - immunology; Oyster; Sequence Analysis, DNA; Vibrio; Vibrio - enzymology; Vibrio aestuarianus; Vibrio splendidus
• ISSN: 1050-4648; 1095-9947
• DOI: 10.1016/j.fsi.2010.07.007

Extracellular products (ECPs) of the pathogenic Vibrio aestuarianus 01/32 were previously reported to display lethality in Crassostrea gigas oysters and to cause morphological changes and immunosuppression in oyster hemocytes. To identify the source of this toxicity, biochemical and genetic approaches were developed. ECP protease activity and lethality were shown to be significantly reduced following incubation with metal chelators, suggesting the involvement of a zinc metalloprotease. An open reading frame of 1836 bp encoding a 611-aa metalloprotease (designated Vam) was identified. The deduced protein sequence showed high homology to other Vibrio metalloproteases reported to be involved in pathogenicity. To further confirm the role of this enzyme in ECP toxicity, a plasmid carrying the vam gene under the control of an araC-P BAD expression cassette was transferred to a Vibrio splendidus related strain, LMG20012 T, previously characterized as non-pathogenic to oysters. Expression of Vam conferred a toxic phenotype to LMG20012 T ECPs in vivo and cytotoxicity to oyster hemocytes in vitro. Collectively, these data suggest that the Vam metalloprotease is a major contributor to the toxicity induced by V. aestuarianus ECPs and is involved in the impairment of oyster hemocyte functions.