Dynamic variations in profile of intra- and extracellular paralytic shellfish toxins during the growth cycle of Alexandrium species and their accumulation in mussels

Abstract

The toxigenic Alexandrium species can secrete paralytic shellfish toxins (PSTs) into seawater during their growth, potentially threatening marine organisms and human health. The release of intracellular toxins during the growth cycle of Alexandrium spp. and the uptake of dissolved PSTs by shellfish are still not clear. Three strains of A. minutum GY-H46, A. minutum ATDH and A. pacificum ATHK were used to explore the dynamic variations in profile of intra- and extracellular toxins during their growth cycles. And a comparative study was carried out on the accumulation and tissue distribution of PSTs in mussels Mytilus unguiculatus exposed to the dissolved and particulate toxins during a 5-days period. Results showed that the toxin cell quotas increased rapidly during the early exponential growth period, then decreased gradually and plateaued at the stationary growth period for ATHK and ATDH, while gradually increased during the stationary growth period for GY-H46. The toxin cell quotas for GY-H46, ATDH and ATHK ranged from 8.3 to 21.5, 5.3 to 11.7 and 7.4 to 9.3 fmol cell−1, respectively, during the whole growth cycle. The contents of extracellular toxins increased gradually throughout the growth of GY-H46, ATDH and ATHK, and the molar mass percentage of extracellular toxins ranged from 53% to 72%, 20% to 46% and 36% to 68%, respectively. Mussels can actively uptake the dissolved PSTs from seawater medium, and mainly accumulate toxins in the digestive glands. The accumulation level of PSTs from the dissolved phase by mussels was about 1% of that from feeding on microalgal cells. The results of this study will contribute to a comprehensive understanding of the dynamic release of intracellular PSTs during microalgal growth and the accumulation of dissolved toxins by shellfish.