Research On The Toxicity Of A Newly Described Dinoflagellate Heterocapsa Bohainensis And Toxin Extraction

The frequent occurrence of harmful algal blooms endangers the coastal ecological environment.The algae Heterocapsa bohaiensis sp.nov is a newly described species of dinoflagellate associated with the toxic effect on Penaeus japonicus and larvae of Eriocheir sinensis in a coastal pond of Liaodong Bay China.A large outbreak in a short time affects the development of the aquaculture industry and even causes certain economic losses.The rotifer Brachionus plicatilis is used as live feed for aquaculture organisms including prawns and crabs larvae.To evaluate the potential toxicity of H.bohaiensis,the effects on Brachionus plicatilis and haemolytic activity were investigated in this study.Then,the concentrations of calcium were measured in B.plicatilis and erythrocytes.To isolate and extract algae toxins,this study also investigated the properties and the preliminary separation of algal toxins B.plicatilis were used as test subjects.The effects of placement time,illumination conditions,temperature and other conditions on the properties of toxins were studied.The toxic substance was then crudely extracted and the preliminary toxin structure was speculated.The results showed that H.bohaiensis had significant toxic effect on B.plicatilis,and the effect was dependent on the cell concentration and exposure time.H.bohaiensis were ingested by B.plicatilis.Significant rotifer growth suppression was observed in the ruptured cells of H.bohaiensis with ultrasonic and the cell suspension,but not in the cell-free filtrate,which indicated toxicity of H.bohaiensis to B.plicatilis was caused by living cells or released from broken cells.Relatively similar rotifer mortalities were induced both in the light and in the dark.The results of haemolytic activity were consistent with the toxicity.Haemolysis to erythrocytes was also caused in a cell density-dependent and time-dependent manner,and the ruptured cells of H.bohaiensis with ultrasonic exhibited haemolytic activity.Therefore,haemolytic toxins were considered to be involved in the toxic mechanism of H.bohaiensis against rotifers.Obviously increased fluorescence intensity was found in the stomach,which indicated the alteration of calcium homeostasis and membrane permeability after ingesting H.bohaiensis.The results indicated that prolonged placement time weakened of the toxicity of the ruptured cell suspension.Temperature had an impact on algae toxin,and the toxin remained stable below 25℃.Light conditions were not concerned with the toxicity of H.bohaiensis,which was consistent with exposure experiments of H.bohaiensis living cells.The acetonitrile extraction of H.bohaiensis showed significant toxicity effect and the wavelength of characteristic absorption was 300 ～ 310 nm,435 ～ 445 nm,590 ～ 600 nm and 660 ～ 665 nm.All of the results implicated haemolytic activity as a causative factor linked to the toxicity of H.bohaiensis against B.plicatilis.The results contributed to research the production and control of H.bohaiensis toxins.It was speculated that the toxin substance was a porphyrin derivative.After solvent extraction and separation,it is speculated that the toxin component of the Heterocapsa bohaiensis may be protein,alkaloid or organic acid.