Isolation Of Algicidal Bacterium And Microbial Agent Preparation For Karenia Mikimotoi

Karenia mikimotoi is a kind of fish-toxin harmful algae.It bloom s occurring frequentl y in the coastal areas of China in recent years.It causes serious harm to the coastal aquaculture and ecos ystem,and ultimatel y affecting human health.It is urgent to establish a safe and efficient prevention and control s ystem for this kind of algae.Recent study results showed that the microbial control of harmful algae bloom is one of the safe,efficient,ecological friendl y,and thus most promising methods.In this study,the algicidal bacteria of K.mikimotoi were isolated,and the optimized culture meth ods were carried out.Finall y,the red tide control materials were prepared to achieve higher control effect on K.mikimotoi.The main results are as follows:Two algicidal bacterias were isolated from the surface water of Tongxin Bay,Lianjiang,Fujian Province after a red tide event.The two bacteria were namely FDHY-MQ5 and FDHY-MZ2,respectivel y.For shaking flask culture,The 24 h algicidal rates of the two strains were94.3%～98.2%and 92.6%～97.9%with the volum ratio of bacteria to algae1%,respectivel y.Their 16S r DNA showed that both of the two strains belonged to Pseudoalteromonas,and they were gram-negative,motile,and had no spores or metachromatic particles.The fermentation process of two algicidal bacteria s were optimized based on 2216E.The optimal culture conditions of FDHY-MQ5 were as follows:0.5%peptone,1.5%starch,p H 7.5,fermentation time 48 h,temperature 20℃,liquid volume 30%,rotation speed 200 r/min,inoculation volume 3%.After optimization,OD₆₀₀ and dry weight per unit volume were2.25 and 2.05 times higher than those before optimization,and the yield increased significantly（p<0.05）.The optimal culture conditions of FDHY-MZ2 strain were as follows:0.5%peptone,1.5%starch,p H 7.5,fermentation time 48 h,temperature 20℃,liquid volume 20%,rotating speed 150 r/min,inoculation volume 5%.After optimization,OD ₆₀₀ and dry weight per unit volume were 1.70 and 1.90 times higher than those before optimization with increased significantl y（p<0.05）.Through the optimization of culture that processes in 5 L fermentor,the optimal fermentation process of FDHY-MQ5 was obtained as follows:temperature 20℃,initial medium p H 7.5,liquid volume 70%,inoculum volume 3%,ventilation volume 0.34 vvm,rotation speed 300 r/min,feeding with the whole medium after fermentation time of 30 h.After optimization,the OD₆₀₀ and dry weight per unit volume of bacteria liquid increased by4.49 times and 3.87 times respectivel y,and the algicidal rate increased b y13 times.The optimal fermentation conditions of FDHY-MZ2 were as follows:temperature 20℃,initial medium p H 7.5,liquid volume 70%,inoculum volume 5%,ventilation 0.34 vvm,rotation speed 300 r/min,and feeding with the whole medium after fermentation time of 36 h.After optimization,the OD ₆₀₀ and dry weight per unit volume of bacteria liquid were increased by 3.99 and 2.89 times,respectivel y,and the algicidal rate was increased by 19 times.The algicidal materials of algicidal bacteria were develop ed.The preparation process of FDHY-MQ5 bacterial powder was as follows:inlet air temperature 110℃,injection flow rate 400 m L/h.The process conditions of FDHY-MZ2 were as follows:inlet air temperature 140℃,injection flow rate 250 m L/h.The two bacteri a were immobilized by gel beads,the best processing technology is:2%alginate（SA）,SA:bacteria=1:2,4%Ca Cl₂,nozzle size 1000μm,cross-linking time 60 min,intensit y coefficient is100%.The size of gel beads is 2.54±0.08 mm,and the algae l ysing rate is98%,which can be reused times.