Interactions Between Algicidal Bacteria Strain L7and Anabaena Flos-aquae

The aims of the research were focused on interactions between algicidal bacteria andcyanobacteria and the role which algicidal bacteria play in the development period and decayperiod during cyanobacteria blooms. In this research, algicidal bacteria strain L7andAnabaena flos-aquae were selected as research objects. Changes of both populations andthe influence mechanism between both populations were studied in three respects.(1) Polutation densities of algicidal bacteria strain L7and Anabaena flos-aquaeAlgicidal bacteria strain L7with6initial population densities were co-cultured with1.80×107cells/L Anabaena flos-aquae. Anabaena flos-aquae with5initial population densitieswere co-cultured with1.80×105cfu/mL algicidal bacteria strain L7. Both populations werealone cultured in BG11added the intracellular or extracellular metabolites of the opponent,respectively. Polutation densities were observed in each microcosm.Population densities of Anabaena flos-aquae were decreased to0cell/L on11th and7thday, respectively, when initial population densities of algicidal bacteria strain L7were2.74×106and2.74×107cfu/mL. From11th day to the end, average population densities ofAnabaena flos-aquae had no significant different between the other treatments (P>0.05).They were all higher than109cells/L.In the whole experiment, population densities of Anabaena flos-aquae with5initialpopulation densities had significant increased (P <0.01), higher than109cells/L, when theinitial population density of algicidal bacteria strain L7was1.80×105cfu/mL.Intracellular metabolites of both populations stimulated the growth of the opponent,while extracellular metabolites inhibited the growth of the opponent.Therefore, the interactive mode of both populations are as follows: when blooms withdominant species of Anabaena flos-aquae occur, the bloom cannot collapse, if the initialpopulation density of algicidal bacteria strain L7is not high enough to lyse cyanobacterialcells. However, algicidal bacteria release a plenty of intracellular metabolites into theenvironment after death because of short generation time to stimulate the growth of Anabaenaflos-aquae. Lastly, the maximum population density of the cyanobacteria during the bloom isnot determined by the initial population density of algicidal bacteria strain L7. Meanwhile,Anabaena flos-aquae inhibits the growth of algicidal bacteria strain L7by secretingextracellular metabolites. If the initial population density of algicidal bacteria strain L7reaches a threshold level to secrete enough algicidal components, the bloom will rapidly decline. The growth of the bacteria will be promoted, since a plenty of intracellularmetabolites of the cyanobacteria are released into the water body after cyanobacterial death.(2) Influences of algicidal bacteria strain L7on the nitrogen metabolism of Anabaenaflos-aquaeAlgicidal bacteria strain L7with2initial population densities were co-cultured withAnabaena flos-aquae. The results showed that1.75×107cfu/mL algicidal bateria strain L7stimulated the growth of Anabaena flos-aquae, increased the heterocyst frequency, decreasedNO3--N concentration in the medium, enhanced activities of nitrate reductase (NR), glutamatesynthetase (GOGAT),and the content of protein, inhibited the activity of glutamine synthelase(GS), and decreased the content of malondialdehyde (MDA), while1.75×108cfu/mLalgicidal bateria strain L7inhibited the growth of Anabaena flos-aquae, decreased theheterocyst frequency and the NO3--N concentration in the medium, enhanced activities of NR,GS, and GOGAT, increased the content of MDA, and declined the content of protein.Therefore, the mechanism of algicidal bacteria strain L7on the nitrogen metabolism ofAnabaena flos-aquae is as follows:1.75×107cfu/mL algicidal bacteria strain L7enhancedthe NO3--N assimulation rate and the nitrogen fixation of Anabaena flos-aquae, therebypromoting the protein synthesis and the nitrogen metabolism of Anabaena flos-aquae, while1.75×108cfu/mL algicidal bacteria strain L7caused the liquid peroxidation of Anabaenaflos-aquae cells and inhibited the protein synthesis and the nitrogen metabolism.(3) Metabolomics research for interactions between algicidal bacteria strain L7andAnabaena flos-aquaeAlgicidal bacteria strain L7and Anabaena flos-aquae were co-cultured or alone culturedin4types of mediums. According variety changes of intracellular or extracellular metabolitesof both populations, the mechanism of interactions between algicidal bacteria strain L7andAnabaena flos-aquae on metabolism is as follows: both algicidal bacteria strain L7andAnabaena flos-aquae may have influences on the opponent glycometabolism by eachintracellular metabolite, and then stimulate the growth of the opponent, while algicidalbacteria strain L7could secrete gibberellins to stinulate the growth rate of Anabaenaflos-aquae. However, the extracellular metabolites of algicidal bacteria strain L7probablyresult in the peroxidation of cyanobaterial cells by the changes of glycerophospholipidmetabolism in the Anabaena flos-aquae, and then inhibit the growth of Anabaena flos-aquae.Anabaena flos-aquae could inhibit the growth of algicidal bacteria strain L7cells by secretingmacrolides. However, the mechanisms of interactions between algicidal bacteria strain L7and Anabaena flos-aquae still need further confirmation.