Screening Of A Highly Effective Algicidal Bacteria And Studying Its Algicidal Mechanism

In this study,a batch of algicidal bacterial strains were isolated and identified from seawater during an Akashiwo sanguinea bloom in Dongshan,Shenzhen.The algicidal characteristics of the most potend strain 6A1 were further investigated,which including microscopic structure changes,photosynthetic parameters and activities of antioxidant enzyme system.Our results indicated that this algicidal bacterium could be a potential bio-agent applied in controlling harmful algal blooms?HABs?in the future.The main findings are listed below:?1?A total of 9 algae algicidal strains were isolated and named as 7,9,11,12,YK,4A1,6A1,2C1 and C1R,respectively.Through 16S rDNA PCR sequencing analysis,7 was identified as Paracoccus sp.,9 was identified as Alteromonas sp.,11was identified as Pseudoalteromonas sp.,12 was identified as Bacillus sp.,4A1 was identified as Pseudoalteromonas sp.,YK and 6A1were both identified to be species of Arenibacter,2C1 was identified as Muricauda sp.,and C1R was identified to be Mesorhizobium sp.;?2?Results showed that the most potent strain 6A1 could indirectly algicidal cells through heat-resistant extracellular algicidal substances.The lysing effect was selective,as among the eighteen algal strains tested,only the growth of A.sanguinea,Chattonella marina,Alexandrium tamatense,Prorocentrum minimum and Heterosigma akashiwowere significantly inhibited with the addition of 6A1supernatant;?3?The algicidal characteristics of 6A1 on three algal species,A.sanguinea,C.Marina and A.tamatense were further investigated.Results showed that the addition of 6A1 supernatant could lyse all the algal cells within 2 h,although the lowest required volumes were different.For the most sensitive A.sanguinea,a relative volume of 1%?bacterial supernatant to algal culture?could cause 100%cell death within 2 h,while for C.Marina and A.tamatense,the lowest effective volume was5%and 10%,respectively.Along with the changes in the structure of algal cells,various physiological and biochemical parameters in the algal cells were also been observed.Addition of 6A1 supernatant caused significant changes of the activities of antioxidant enzyme system?SOD,CAT and MDA?in algal cells,and the with species-specific characters among the three tested species;?4?The extra cellular active substances secreted by 6A1seemed to be heat resistant,non nucleic acid and non polysaccharide.We isolated and identified six compounds from 6A1 supernatant through chromatography and nuclear magnetic resonance spectroscopy.Among them,three compounds showed certain inhibitory effects on the tested algal species.Subsequent structural identification showed that theywerepyrrole-2-carboxylicacid,Phydroxybenzoicacidandmethyl4-hydroxybenzoate.The strongest algae lysing compound among the three is pyrrole-2-carboxylic acid which could cause 50%growth inhibition of algal cells within 2 h with the concentration of 100 g mL^-1.None of the isolated compounds caused 100%cell death on any of the algal species.This study has confirmed the strong algae lysing efficiency of the strain 6A1,but its active substances have not been completely determined.