| Dinoflagellate is one of the common harmful microalgae in aquaculture.The algal bloom of dinoflagellate will not only consume dissolved oxygen,but some species will produce toxins,which will seriously endanger the health of aquatic organisms.The timely elimination of harmful dinoflagellates in water is of great significance to ensure the health of aquatic organisms and the stability of water ecosystems.At present,the method of eliminating harmful dinoflagellates is mainly physical,chemical and biological method.Especially,algae-lysing bacteria have gradually become a hotspot in this field.To date,the research on algae-lysing bacteria mainly focuses on the screening and identification of strains.However,the research and development of fungicides is rare.An algae-lysing bacteria atrain A4 was obtained in the early stage of the study group.The strain had the specificity of algae-lysing,which could dissolve Scrippsiella trochoidea and it dose not have harmful effects for Chlorella pyrenoidosa,Cyclotella striata,Scenedesmus quadricauda,and other common beneficial microalgae.In this study,the strain A4 was used as the object to optimize the culture parameters in the response surface method.The fermentation process was studied for obtaining the technological parameters based on the 2L and 50 L fermentation system.Finally,the effects of different kinds of fermentation products on Scrippsiella trochoidea,Prorocentrum micans and Peridinium umbonatum were studied.This provides a basic reference for the production and application of strain A4.The results are as follows:1?Using the response surface method,the optimized culture parameters of strain A4 was obtained.The results showed that carbon source,nitrogen source and temperature were the most key factors.The optimum culture parameters were as follows: corn syrup 20.06 g·L-1,soybean protein 13.29 g·L-1,Na Cl 1 g·L-1,KH2PO4 0.20 g·L-1,Mg SO4 0.20 g·L-1,MnSO4 0.03 g·L-1 CaCl2 0.10 g·L-1,pH 7.00,temperature 30.26?,rotate speed 150 r·min-1,liquid volume 60%,inoculation quantity 1%.At the condition of this parameters,the predicted concentration was 1.24×109 CFU·mL-1 and the measured concentration was 1.19×109 CFU·mL-1.There was no significant difference between the predicted value and the measured value.It implies that the optimized model was significant for the guidance of fermentation.2?In order to study the "Amplification effects",the optimized parameters were applied to the 2 L and 50 L fermentation tank system,respectively.The results showed that the dissolved oxygen played an important role on the growth of strain A4.At the 2 L fermentation system,the rotate speed should be 600 r·min-1,and the air ventilation should be 4 L·min-1.At the 50 L fermentation system,the rotate speed should be 500 r·min-1,the air ventilation should be 30 L·min-1,and the pressure should be 0.03-0.05 MPa.At this condition,the concentrations of strain A4 were 6.23×109 CFU·mL-1 in 2 L fermentation system and 4.47×109 CFU·mL-1 in 50 L after 24 h cultivation,respectively.3?The fermentation products were prepared by centrifugation,fluidized bed drying and pulverization,and the fermentation products were obtained in 50 L fermentation system.Several types of fermentation products,such as fermentation broth,supernatant,powder and other fermentation products were obtained.Then,these different types of producte were added to the culture of Scrippsiella trochoidea,Prorocentrum micans and Peridinium umbonatum for the research of the lytic effect.The results showed that different types of products had good inhibitory effect on three kinds of dinoflagellates.Among them,the inhibitory effects of the bacterial powder activation group and the fermentation broth group were the best.Their inhibitory effect were both 100% on Scrippsiella trochoidea,were 99.39% and 99.88% on Prorocentrum micans,and 92.36% and 58.44% on Peridinium umbonatum.In consideration of the actual production,storage and transportation,powder product was the first choice.It is necessary to activate the powder product before use. |
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