Study on the algicidal activity of culturable bacteria isolated from seawater in Weizhou Island
Objective To screen highly effective algicidal bacterial strains from the seawater in Weizhou Island,Guangxi Zhuang Autonomous Region,China.Three marine dinoflagellates were selected as the research object to study the algicidal efficiency and mechanism of those strains for the prevention and control of red tide.Methods The bacterial fermentation broth and dinoflagellate were co-cultured to determine the algicidal effect of the strains,determine the response rules of malondialdehyde(MDA)and antioxidant related enzyme systems in algae cells,analyze the composition of extracellular soluble organic matter(EDOM)in dinoflagellate,and predict the ability of the target strain to synthesize algicidal substances through KEGG and CAZy databases.Results Total 15 strains that showed algicidal activity against at least one species of dinoflagellate were screened out from 24 strains of bacteria.The total positive rate was 62.5％.Among them,strain M026 showed significant algicidal activity against three dinoflagellates.After inoculating 10％of M026 fermentation sterile filtrate and co-culturing for 3 days,the cell death rate of the three dinoflagellates reached 95.0％.The physiological and biochemical responses indicated that algae suffered serious lipid peroxidation,three related enzymes(SOD,CAT and APX)activities increased first and decreased subsequently under the oxidative stress of M026 sterile filtrate.Three-dimensional fluorescence spectroscopy results showed that the algae lysates were fulvic acid-like and protein-like substances.According to the analysis of draft genome,strain M026 contains potential secondary metabolite biosynthetic gene with algicidal activity,as well as a variety of plant cell wall degrading enzymes.Conclusion Due to the high algicidal efficiency and mechanism of strain M026,it can be used as a candidate strain to develop microbial algicidal agents.
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