The "bacteria-algae" system plays an important role in water ecosystems. The effects of bacteria in phycospheres on the growth of Microcystis aeruginosa under in-situ nutrient stimulation were studied to explore the bacteria-algae interaction during a cyanobacteria bloom. The results showed that LB medium could inhibit the growth of M. aeruginosa, and the algicidal rate was 86.49%. Sodium acetate, glucose, and sodium citrate could promote M. aeruginosa, and the growth rate was more than 50%. The addition of nutrients in M. aeruginosa could have changed the biocoenosis in the phycosphere and increased the species richness by 16S rRNA gene sequencing, and the number of bacteria in the phycosphere increased dramatically in the LB medium and peptone groups. The physiological and biochemical responses showed that algae suffered serious lipid peroxidation, and superoxide dismutase (SOD) and catalase (CAT) activities first increased significantly and subsequently decreased under the oxidative stress of LB medium or peptone. Scanning electron microscopy (SEM) indicated that the surface of algae cells appeared wrinkled, invaded, and atrophied under LB medium stimulation, whereas bacteria in the phycosphere significantly increased. Furthermore, six strains of algicidal bacteria were isolated from the LB medium and peptone groups, and the algicidal rate of Bacillus sp. A1 was 97.55%, which confirmed that the phycosphere of M. aeruginosa included algicidal bacteria. Therefore, appropriate external nutrient stimulation can produce algicidal bacteria in situ to prevent cyanobacterial blooms.
Keywords: Microcystis aeruginosa; algal-bacterial interaction; algicidal bacteria; antioxidant enzyme system; cyanobacterial bloom; phycosphere.