Stress Gene Expression in Crassostrea gigas (Thunberg, 1793) in response to experimental exposure to the toxic dinoflagellate Prorocentrum lima (Ehrenberg) Dodge, 1975

Harmful algal blooms (HABs) are natural phenomena with different effects on the aquatic environment that affect both human economy and health. Several genomic studies have been done to characterize the effects of contaminants on Crassostrea gigas. However, oysters' molecular response to HABs exposure needs to be studied more. In this study, we challenged C. gigas with Prorocentrum lima, a diarrhoetic toxin producer, under controlled experimental conditions considering dinoflagellate density and exposure time (acute and sub-chronic) as variables. The expression profile of six stress response genes was analysed by semiquantitative RT-PCR: Glutamine synthetase (GS), Glutathione S-transferase (GST), heat shock protein 70 (HSP70), and heat shock protein 90 (HSP90), CuZn superoxide dismutase (SOD) and melanogenic peroxidase (POX). The results revealed that these gene expressions depend on exposure time and cell concentration. In general, an increased expression was observed in all tested cell densities as immediate response to exposure (0-3 h); whereas lower expression levels than control were observed after 6 h. Treatment with 3,000 cells mL(-1) promoted higher expression than control on most genes after 336 h of exposure. This is the first report providing information at molecular level on C. gigas response to dinoflagellate blooms.