Interactions Between Bacillus Cereus L7, L8and Skeletonema Costatum

The aims of the research were focused on interactions between Algicidal Bacteria L7, L8and Skeletonema costatum and the role which algicidal bacteria play in the developmentperiod and decay period during cyanobacteria blooms. In this research, algicidal bacteriastrain L7, L8and Skeletonema costatum were selected as research objects. Changes of bothpopulations and the influence mechanism between all populations were studied in fourrespects.Suspension, treated sterile filtrate and mixed bacteria of L7and L8were co-cultured withSkeletonema costatum，in order to know algicidal effect, algicidal approach, stability of algalbioactive metabolites and optimum condition of mixed bacteria. Algicidal Bacteria L7and L8have strong algicidal effect on Skeletonema costatum by Indirect way, algal bioactive havegood heat-stability and bad acid-stability, the best ratio of L7and L8mixture were2:1.L7and L8with6initial population densities were co-cultured with Skeletonemacostatum and Skeletonema costatum with5initial population densities were co-cultured withL7and L8，which in order to know the role of initial population densities on influencemechanism of L7and L8on Skeletonema costatum. Higher initial population density of L7and L8prohibit Skeletonema costatum, lower initial population density ones stimulateSkeletonema costatum. Skeletonema costatum prohibit L7after some time later, Skeletonemacostatum of high density prohibit L8after some time later.In order to know the role of metabolites on interaction between algicidal bacterias andSkeletonema costatum, intracellular and extracellular metabolites of L7and L8wereco-cultured with Skeletonema costatum, intracellular and extracellular metabolites ofSkeletonema costatum were co-cultured with L7and L8medium. When population densitiesof L7were lower than7.82×109, intracellular metabolites of L7stimulate Skeletonemacostatum, when population densities of L7were7.82×1010, intracellular metabolites of L7prohibit Skeletonema costatum on the7th day respectively; metabolites of L8have similarresults. Extracellular metabolites of Skeletonema costatum inhibited the growth of L7and L8,intracellular metabolites of Skeletonema costatum had no obvious effect on L7but stimulatethe growth of L8. In order to know the effect of extracellular metabolites and intact algal solution ofSkeletonema costatum to algicidal effect, add extracellular metabolites and intact algalsolution of Skeletonema costatum into the culture of L7and L8. All extracellular metabolitesand intact algal solution of Skeletonema costatum stimulate algicidal effect.