Screening Of Algicidal Bacteria From Red Tide In Shenzhen Seastrand And Research On Algicidal Compounds From Arenibacter Sp.6A1

Harmful algal blooms?HABs?have caused large-scale red tides which damage marine ecosystems and also pose potential threats to human health.Prevention and control of red tide is a worldwide project.Biological approaches are considered to be one of the potential tools to regulate HABs.In this study,we collected red tide seawater samples from Dongshan wharf in Shenzhen,from which a total of 41 strains,including 34 bacterial and 7 actinomycete strains,were isolated by three different isolation methods.All isolates have been characterized by 16s rDNA gene sequence.25 isolates exhibited algicidal activities against red tide causing alga,Akashiwa sanguine.Among them,three strains exhibited the strongest activities at 1%volume concentration?inhibition rate?90%?.Arenibacter sp.6A1 was selected for further study.Scare-up fermentation was then carried out and six pure compounds were isolated from the culture supernatant and identified as thymine?1?,cyclo?L-Pro-L-Tyr??2?,uracil?3?,pyrrole-2-carboxylic acid?4?,4-hydroxybenzoic acid?5?,and anthranilic acid?6?.Algicidal activities of these compounds were tested against A.sanguinea,alone with two other red tide algae Alexandrium tamarense and Chattonella marina.4 exhibited algicidal effects on all the three algae,with the EC₅₀of 30.4?g·mL^-1,40.2?g·m L^-11 and 57.8?g·mL^-1,respectively.pH dependent experiment?PH 6.0-9.0?showed that lower pHenhanced algicidal effect of 4against A.sanguinea.5 exhibited the highest algicidal activities on A.tamarense with EC₅₀0 at 54.5?g·mL^-1.Methyl esterification of 5 and 6 enhenced their algicidal acitivities.Other compounds did not show apparent activities at the highest concentration of 100?g·m L^-1.Cells ofthreealgaesco-cultured with pyrrole-2-caboxylic acid(50?g·mL^-1)were observed under an optical microscope and a scanning electron microscope?SEM?.4 promoted A.sanguinea and C.marina cell disruption and induced cell leakage.Cells of A.tamarense sank to the bottom of the plate,SEM observations clearly revealed that cell cytomembranes were invaginated,fractured,and perforated.Unknown bacterial strains gathered around the holes of the algae cells.This study laid a good foundation for mechanism and application research of Arenibacter sp.6A1 against red tide algae,A.sanguinea.