| Chattonella marina is known to be one of the most toxic red tide organisms. The blooms formed by C. marina have caused great damages to cultured fish and shellfish in South Chinese coasts, which are becoming a potential threat to Chinese coastal environments and mariculture. C. marina is shown to produce many toxic secondary metabolin such as haemolytic toxins, reactive oxygen species (ROS) etc., of whichs, haemolytic toxins may be responsible for the dead of the fish. However, the effect of environmental factors, especial, biological factor on the secondary metabolin production in C. marina are ignored and poorly understood. To explore the production mechanism of the haemolytic toxins in C. marina, in this paper, the effects of environmental factors, such as temperature, nutrient, and biological factors on the growth rate and production of haemolytic toxins in C. marina are studied by orthogonal experiments under laboratory conditions.According to the results, salinity, temperature and light intensity had not significant effects on the growth of C. marina during the salinity of 22-45, temperature of 20-30℃and light intensity of 2000-4500 lx. The effect of salinity on the haemolytic toxin production of C. marina was more prominent than those of temperature or light intensity. Of all the culture conditions under a salinity of 22, 33, 45, temperature of 20, 25, 30℃and light intensity of 2000, 3000, 4500 lx, the maximal growth rate was under 45, 30℃and 2000 lx, while the maximal toxin production was under 22, 20℃, 4500 lx. Low salinities were favourable to the haemolytic toxin production, but not to the algal growth. When the growth of algae was limited, haemolytic toxin production increased, which indicated that the effect of salinity on the haemolytic toxin production of C. marina was related with algal physiological state.Iron and nitrogen had significant effects on the growth of C. marina, while nitrogen and phosphonium had significant effects on the haemolytic toxin production of C. marina. Of all the culture conditions in iron concentration of 0, 0.492, 4.92 and 24.6mg·L-1 nitrogen concentration of 0, 7.5, 75 and 375mg·L-1 and phosphonium concentration of 0,0.5,5 and 25mg·L-1 the growth rate was maximal when the optimal concentration of three nutrients were as followed: iron concentration of 0.492 mg·L-1, nitrogen concentration of 375 mg·L-1 phosphonium concentration of 5 mg·L-1, while the maximal toxin production was in iron concentration of 0 mg·L-1, nitrogen concentration of 375mg·L-1, phosphonium concentration of 0.5 mg·L-1.When C. marina was cocultured with P. donghaiense or A. tamarense in a glass bottle containing a cage with a sealed nylon-mesh bottom, where C. marina cell did not contact with the other two algae except for the culture solution, the growth and haemolytic toxin production of C. marina all increased. However, the growth of P. donghaiense and A. tamarense were inhibited significantly. These results suggested that the haemolytic toxins in C. marina might be allelopathic chemicals, which had an important role in the inter-algae competition. Meanwhile, the similar phenomenon was also discovered on the coculture of C. marina and Moina mongolica. The haemolytic toxin production of C. marina significantly increased when coculture with M. mongolica, indicating the potential roles of haemolytic toxins in the anti-grazing.
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