Isolation And Identification Of Algicidal Compounds From Bacillus Sp. Strain B1and Algicidal Mechanisms To The Harmful Algae

Phaeocystis globosa (P. globosa) has become one of dominant algae in Pearl RiverEstuary and broken out frequently in recent years, which have made greatly negativeeffects on the marine ecosystem and the national economy. Considering thedisadvantages of physical and chemical methods, biological methods have been a newresearch hotspot in the field of red tides treatment, especially isolation andidentification of algicidal bacteria and algicidal compounds.Bacillus sp. strain B1was previously isolated from the bloom of P. globosa inZhuhai, China. In this thesis, the range and mode of action of stain B1, isolation andidentification of algicidal compounds and algicidal mechanisms were studied. Themain results as follows:1. Bacillus sp. strain B1was able to eliminate P. globosa, Skeletonema costatum,Prorocentrum donghaiense and Heterosigma akashiwo by excreting extracellularactive compounds. When the dosage of B1filtrate was4%(VB1filtrate/Valgalculture=1/25), the algicidal effect of the filtrate to the four algae was: P. globosa＞S.costatum＞P. donghaiense＞H. akashiwo. And the algicidal rates were92.3%、91.8%、89.4%�'�84.4%, respectively.2. The extracellular active compounds produced by strain B1were isolated andpurified by ODS-A column chromatography and HPLC. Four algicidal compoundswere eventually obtained and their algicidal activities to P. globosa were46.9%,50.3%,55.0%and55.7%respectively. The four compounds were further analyzed byQ-TOF-MS and PeakView Software determined the compounds corresponding topeaks2-5to be L-histidine, o-tyrosine, N-acetylhistamine and urocanic acid on thebasis of the accurate mass information, the isotopic pattern and MS/MS spectra.3. The bacteria-free filtrates from strain B1were isolated and purified by silica gelcolumn chromatography, Sephadex G-15column chromatography and HPLC. Twopurified substances were collected and their algicidal rates were59.5%and54.6%.The two compounds were determined to be prolyl-methionine and hypoxanthine by Q-TOF-MS and PeakViewTMSoftware.4. The algicidal activity experiment of algicidal compounds showed thatL-histidine was only toxic to P. globosa, while o-tyrosine, N-acetylhistamine,urocanic acid, prolyl-methionine and hypoxanthine could inhibit the growth of P.globosa, P. donghaiense, H. akashiwo and S. costatum. The results suggest that the sixalgicidal compounds produced by strain B1have algicidal effects on multiple algae.5. The tests demonstrated that the algicidal compounds secreted by strain B1could significantly inhibit SOD and CAT activities of P. globosa cells, whichcontributed to accumulated intracellular ROS. The high level of ROS increased theMDA content and the lipid peroxidation of P. globosa cells. Eventually, the cellularmembrane of P. globosa was broken down and intracellular compounds were released.The results suggested that the algicidal compounds from strain B1were able to kill P.globosa by disrupting the antioxidant systems of algal cells.