Study On The Effect Of Linoleic Acid On The Growth Of The Red Tide Microalga Karenia Mikimotoi And Its Extracellular Oxidation

The development of aquaculture in the coastal areas and the discharged of sewage and industrial wastewater have caused excessive nutrient release in the water body,which increased the eutrophication degree in marine water and further lead to more frequent outbreaks of red tide.In recent years,the red tide outbreak with a tendency of scale expansion,longer effective time,increasing risks,and global spread.Red tides are complex ecological anomalies,which have caused great harm to the economic development along the coastal areas,ecological environment,and human health.Therefore,it has already become an extremely urgent requirement to find a safe and effective treatment to prevent and control red tide.In contrast to physical and chemical methods,biological methods are mainly applied through the allelopathic effects and the interaction between living organisms which include competition and predation to inhibit the growth of red tide microalgae and no secondary pollution to the environment,which has a good prospect.In this study,Karenia mikimotoi,which is dominant in red tide species,was selected as the tested algae,and linoleic acid?LA?,which is commonly secreted by macroalgae,such as Sargassum thunbergii and Corallina pilulifera,was chosen as the tested drug,to reveal the influence of LA on Karenia mikimotoi,and the extracellular oxidative process of LA,to improve the mechanism of prevent and control red tide by macroalgae.The results of research are as follows:1.Effects of LA on the growth and metabolism of K.mikimotoi?1?LA exerts a biphasic effect of“low-promotion,high-suppression”on K.mikimotoi growth,contrasted with control group,low LA concentration?<500?g/L?could accelerate thegrowth of K.mikimotoi,whereas high LA concentration?>500?g/L?could inhibit the growth ofK.mikimotoi.?2?Reactive oxygen species?ROS?results implied that,under the action of LA,ROS content in K.mikimotoi was significantly increased at relatively higher LA concentrations?1200?g/L and 2000?g/L?at 6 h and 12 h.However,ROS content in K.mikimotoi was no significant difference between all the groups at 24 h.Results showed that the high concentration of LA could induce oxidative stress of K.mikimotoi in a short time.?3?The content of soluble protein in K.mikimotoi was significantly increased at relativelyhigher LA concentrations?1200?g/L and 2000?g/L?at 12 h and 24 h under the action of LA,respectively.The content of photosynthetic pigment content?chlorophyll a and carotenoid?in K.mikimotoi was significantly increased in all LA groups at 48 h under the action of LA.Results showed that LA have a certain affects on the metabolism of K.mikimotoi.?4?Detecting the leakage rate of lactate dehydrogenase?LDH?could reflect the damage of K.mikimotoi plasma membrane.The leakage rate of LDH increased firstly and then decreased under the influence of LA,and reached its maximum at 48 h,this result indicated that LA could destroy cell plasma membrane integrity of K.mikimotoi.2.Effects of LA on the physicochemical properties of K.mikimotoi culture mediumOxidation reduction potential?ORP?represents the redox status of the water body,and p H level reflects the degree of acidity and alkalinity of the water body.Under the action of LA,ORP level was significantly decreased and pH level was no significant difference of K.mikimotoi culture medium at 6 h and 12 h;ORP level was no significant difference and pH level was significantly decreased of K.mikimotoi culture medium at 72 h and 96 h.The ORP and pH showed a negative correlation.It could be attributed to the extracellular oxidation of LA and small molecules produced by the extracellular oxidation of LA.3.Studies on the extracellular oxidation of LA?1?In this experiment,put LA in the same culture conditions of K.mikimotoi?light,temperature,ventilation,etc.?,it can simulate the extracellular oxidation environment with the same culture conditions and no contacting with the growth system of K.mikimotoi,to explore the process of LA extracellular oxidation.By GC-MS assay,it turned out that the relative content of LA was 96%after 6 h,24 h and 96 h,indicating that the process of LA oxidation is slow and the relative content of oxidation products is low in the culture conditions of K.mikimotoi.?2?This research used the Fe²⁺/Vc system to simulate the extracellular oxidation environment of the growth system of K.mikimotoi,to explore the oxidation effect of free radicals on LA.According to the change law of the content of the conjugate dienes?CD?and thiobarbituric acid reactive substances?TBARS?between the early period and the late period to assume the process of LA oxidation.With time of culture,the content of the CD increased at first and then decreased,the content of the TBARS gradually decreased,indicating that the free radicals of the growth system of K.mikimotoi may promote the extracellular oxidation of LA.