Toxic Responses of Different Shellfish Species after Exposure to Prorocentrum lima, a DSP Toxins Producing Dinoflagellate

Prorocentrum lima is a global benthic dinoflagellate that produces diarrhetic shellfish poisoning (DSP) toxins, which can be ingested by filter-feeding bivalves, and eventually pose a great threat to human health through food chain. After being exposed to P. lima, different bivalves may accumulate various levels of DSP toxins and display different toxic responses. However, the underlying mechanism remains unclear. Here, we found that the content of okadaic acid-equivalents (OA-eq) varied in the digestive glands of the three bivalves including Crassostrea gigas, Mytilus coruscus and Tegillarca granosa after P. lima exposure. The degree of esterification of OA-eq in the three bivalves were opposite to the accumulation of OA-eq. The digestive gland tissues of the three bivalve species were damaged to different degrees. The transcriptional induction of Nrf2 targeted genes such as ABCB1 and GPx indicates the functionality of Nrf2 pathway against DSP toxins in bivalves. The oyster could protect against DSP toxins mainly through ABC transporters and esterification, while the mussel and clam reduce the damage induced by DSP toxins mainly by regulating the expression of antioxidant genes. Our findings may provide some explanations for the difference in toxic response to DSP toxins in different shellfish.