Study Of The Growth And Toxigenicity Characters Of Dinophysis Acuminata

Dinophysis spp. is a cosmopolitan genusandat least ten species have been confirmed to produce lipophilic shellfish toxins（eg. okadaic acid, its derivatives and pectenotoxins）. Toxins from these organisms accumulatein shellfish through filter feeding and in turn threaten public health. Although attentions have been paid to factors that might influence the toxin production of Dinophysis, no clear relationship has been demonstrated between DSP events and the concentration of the causative organism. Therefore, based on successful isolation of several strains of Dinophysis acuminata, we examined the effects of food chain and alternative nutrient status on the ecophysiological characters. The main content and results are as follows:1. The first documentthe successful isolation and culture of Dinophysis acuminata（DAYS01） from the offshore of Xiaoping Island, Yellow Sea, China.2. Effects of temperature and prey type on the physiological and toxigenic characteristics of this Chinese genus were investigated. The results showed that the growth rate and population of Dinophysis increased with the higher temperature.The growth rate and biomass at 10, 15 and 20 ℃ are 0.09, 0.21, 0.32 d^-1 and 120, 2483, 7150 cell m L^-1respectively. However, cellular DTX1 and PTX2 did not show any relationship with the temperature. Okadaic acid（OA）, dinophysistoxin 1（DTX1） and pectenotoxin 2（PTX2） were the major toxin components of DAYS01, with the highest toxin contents of 0.54, 0.05 and 18.49 pg cell^-1, respectively. Prey type had no significant influence on growth rate and cellular toxicity, but had effect on the biomass and total toxin content in D.acuminata cultures（DAYS01）, suggesting that the local ciliate type was possibly one of the reasons of toxin geographical variability of Dinophysis in the field.3. Additionally, picked D.acuminata and D.caudata were directly analyzed for DSP and PTXs. Interestingly, no OA or DTX1 but PTX2 were detected in the field D.acuminata cells, possibly due to the insufficient biomass. OA(1.88 pg cell^-1), DTX1(3.16 pg cell^-1) and PTX2(2.88 pg cell^-1) were the dominate components of field D. caudata cells.4. A strain of D.acuminata（DAEP01） was used to test the effect of M.rubrum and cryptophyte cells on growth and toxin production of Dinophysis. The results showed that Dinophysis had significant growth when simply fed with extraction from M.rubrum culture, with the growth rate of 0.12 d^-1. The highest growth rate(0.25 d^-1) and highest cell density(3902±234 cell m L^-1) of D.acuminata were detected when supplied with half ciliate debris and half intact ciliate cells, indicating that the uptake of organic substrate from M.rubrum cultures would possibly be enhanced by the present of living prey.However, no growth was found when supplied with either intact Teleaulax amphioxeia cells or its debris. Significantly more cellular and accumulated toxin content was detected in D.acuminata with half ciliate prey crushed than that without additional cell debris but exposed to the same concentration of living ciliate. Cellular DTX1 and/or OA were significantly greater in the cultures containing the cell debris and organic substrates of M.rubrum culture than that in the control, while dissolved OA and DTX1 were significantly higher in the cultures containing cryptophyte origin organic substrates,indicating that dissolved organic substances may play a role in enhancing the DSP toxin production. No clear pattern was observed in PTX2 production among treatments with living M.rubrum prey, but intracellular and extracellular PTX2 production exhibited an significant increase in the cultures simply containing M.rubrum cell extraction than that in the cryptophyte treatments and the control. All these results suggested that organic nutrients from the prey organisms could be utilized by Dinophysiscells as a nutrient source and influence the toxin production.In conclusion, the study reveals the relationship between Dinophysis or DSP toxins and temperature, prey type or its species in the local area. The DSP toxins increased with the addition of prey or prey debris, which could be a reason of variation in toxin contents of different strains of Dinophysis in the field.