Allelopathic Activities Between Microcystis Aeruginosa And Anabaena Flos-aquae

In recent years,the eutrophication trend of lakes in China has become more serious,resulting in a large number of algal blooms.Each year in the spring and summer seasons,the different algal blooms occur in many lakes such as Taihu Lake,Dianchi Lake,Chaohu Lake,etc.and the reason may be due to the biological characteristics of algae and interactions between different algae.Besides the competition for light and nutrients between algae in the water body,they often affect each other's growth through the release of secondary metabolites,which is one of the reasons for the formation of algal predomination.Therefore,exploring the allelopathy between algae and analyzing possible allelochemicals are of great significance for elucidating the origin of the dominant species of lake algae and the formation mechanism of cyanobacteria blooms.In this paper,two common water-borne cyanobacteria—Microcystis aeruginosa and Anabaena flos-aquae in eutrophic shallow lakes were studied.Under laboratory conditions,three different methods,mixed culture,added filtrate culture,and addition of different components of the filtrate,were used to explore the possible allelopathy between the two cyanobacteria.The results showed that when BG-11 medium was used,and the density of M.aeruginosa and A.flos-aquae was higher than 105 cells/mL,the mixed culture ratio(density ratio)of the two algae was 1:1,1:2,and 2:1,respectively,M.aeruginosa had a certain promoting effect on the growth of A.flos-aquae.However,A.flos-aquae had a certain growth inhibition effect on the growth of M.aeruginosa.When adding filtrate solution,the addition of different volume fractions of A.flos-aquae could effectively inhibit the growth of M.aeruginosa,and the inhibitory effect was enhanced with the increase of the ratio of filtration solution.However,when added the filtrate of logarithmic growth phase of M.aeruginosa to the culture solution of A.flos-aquae,the addition of filtrate with 50%of the volume fraction showed a certain promotion effect compared to the control group,but the addition of filtrate with 100%of the volume fraction showed a certain inhibitory effect.The addition of filtrates with different volume fractions from decaying period of M.aeruginosa showed promoting effects on the growth of A.flos-aquae.Under the conditions of phosphorus deficiency,the inhibition effects on the growth of M.aeruginosa and A.flos-aquae were different in the mixed culture.The C18 solid-phase extraction cartridge was used to extract the secondary metabolites from the culture medium of logarithmic growth phase of A.flos-aquae.Then the enriched cartridges were eluted with dichloromethane followed by methanol,and the obtained extracts were used to conduct algal inhibition tests and qualitative analysis.The extract of dichloromethane had little effects on the growth of M.aeruginosa,while the extract of methanol had significant inhibitory effects on the growth of M.aeruginosa.When the concentration of the extract of methanol in the culture liquid of M.aeruginosa was 12 times that of the culture medium of A.flos-aquae,the algal inhibition rate reached 75.4%after 15 days of culture.At the same time,the extract of dichloromethane was obtained by liquid-liquid extraction for algal inhibition experiments.The results also showed that the extract had no effect on the growth of M.aeruginosa.The components of the extract of methanol were qualitatively analyzed by liquid chromatography-quadrupole time-of-flight mass spectrometry(HPLC-Q-TOF-MS).One of the potential allelochemicals was initially analyzed with the molecular weight 210.9499.The possible molecular formula was C4H5NO5S2.The growth inhibition of M.aeruginosa was tested by adding anatoxin-a,a toxin from A.flos-aquae,at a concentration of 0.1 mg/L and 1.0 mg/L,respectively.The results showed that anatoxin-a cannot be an allelochemical.