Study On Prevention And Control Of Spirogyra In Sea Cucumber Culture Lagoon Based On Co-treatment Strategy With Mixed Bacteria And Microalgae

The huge biomass of Spirogyra in the sea cucumber lagoon seriously affects the yield of sea cucumber,which leads to a significant decline in economic benefits.It has become one of the key problems encountered by the sea cucumber breeding industry.At present,the commonly used physical and chemical algae removal methods not only fail to achieve the algae removal effect,but also produce drug resistance and cause secondary pollution of water bodies.The biological algae removal method prevents and controls the Spirogyra in the sea cucumber lagoon to have green safety and effective characteristics.This thesis aims to make use of the relationship between the bacterial phase and the microalgal phase in the water system,and to explore the mechanism of action by the combination of Bacillus and Chlorella sp.on the inhibition of Spirogyra,and provide a new type for the prevention and control of Spirogyra.At the same time,it provides a theoretical basis for the prevention and control technology of macroalgae in the sea cucumber breeding industry.The experimental results are as follows:(1)The two strains of Bacillus cereus W1 and Bacillus subtilis W2 used in this experiment were both preserved strains in our laboratory.In addition,two strains of W3 and W4 were screened from rotten Spirogyra,and the results of colony morphological,molecular biological and physiological and biochemical identification showed that W3 was Bacillus methylotrophicus and W4 was Bacillus laterosporus.By strains suitable growth temperature and temperature of water for aquaculture environment,chose four strains under the condition of 28? cultivate 36 h,the OD value tends to be stable.The four strains showed no antagonism through the test of antagonism,which could be mixed as the Bacillus complex agent for the experiment.(2)Water samples from the sea cucumber culture lagoon were collected as the experimental water bodies,and fresh Spirogyra was collected as the research object for the experiment.The results showed that the co-treatment of Bacillus and Chlorella sp.had the most significant effect on Spirogyra.Compared with the control group within 15 days of the experiment,Spirogyra changed from emerald green to yellowish brown,quality of Spirogyra reduced from 50.0 g to 10.3 g,chlorophyll a content decrease rate nearly 40 %,active substances MDA content increased by 67.23 %,compared with the control group were significant differences(P < 0.05),antioxidant enzymes SOD,POD and CAT activity were decreased.Therefore,the combination of Bacillus complex agent and Chlorella sp.caused stress on Spirogyra and directly acted on it.The growth of Spirogyra was inhibited by destroying its antioxidant enzyme system and causing the disintegration of Spirogyra cells to reduce the intracellular active substances,indicating that the combination of the Bacillus and Chlorella sp.could degrade Spirogyra.(3)The combination of Bacillus complex bacteria and Chlorella sp.has a regulatory effect on the water body of sea cucumber,which reduces the content of ammonia nitrogen,nitrite,sulfide concentration and chemical oxygen demand in the water.Under the combined action,effective control and improvement have been achieved.Through the functions of Bacillus and Chlorella sp.,the ecosystem of the water body gradually restores balance,opens a virtuous cycle of water environment,and improves water quality.The combination of the Bacillus and Chlorella sp.indirectly regulates the water quality to inhibit the Spirogyra,thereby achieving the effect of preventing and controlling the Spirogyra.In summary,through the Bacillus bacterial phase and the beneficial Chlorella sp.algae phase in microalgae,the effect of the combined bacteria and algae on the Spirogyra was studied.The mode and mechanism of action are clarified.The results show that the combination of bacteria and algae has a certain inhibitory effect on the macroalgae Spirogyra,and plays a role in regulating the water purification of the water body,and it provides a practical reference and theoretical basis for the prevention and control of macroalgae Spirogyra.