Comparison of hemolymph proteins from resistant and susceptible oysters, Crassostrea virginica, exposed to the parasite Haplosporidium nelsoni (MSX)

Abstract

Serum protein constituents in laboratory-reared stocks of oysters, Crassostrea virginica, susceptible to mortality caused by the parasite Haplosporidium nelsoni (MSX) were compared with constituents in resistant oysters exposed to the same level of infection activity. Virtually all of the susceptible oysters became infected and 71% died by the end of the 9-month study, while only half of the resistant group had patent H. nelsoni infections and only 7% died. Total serum protein concentrations fell sharply and in approximate proportion to disease intensity in oysters with systemic H. nelsoni infections. Oysters with heavy parasitism had about one-third the protein levels of uninfected individuals. When infections were confined to the gill, however, as was the case with mortality-resistant oysters, there was no depression of protein levels. In all oysters examined, SDS electrophoresis showed three rapidly migrating proteins, with molecular weights between 25,000 and 75,000, that comprised nearly all the total protein. Up to 12 larger proteins, with molecular weights up to 500,000, were also present, but with considerable individual variability in number and concentration. There was no obvious correlation of electrophoresis patterns with H. nelsoni disease or with genetic background. Results of the study suggest that depletion of certain metabolic substrates such as circulating protein and/or interruption of biosynthetic pathways by the parasite may be a primary cause of death in infected oysters.