Original paper

Interactions between Bacillus cereus strain L7 and Anabaena flos-aquae during cyanobacterial blooms

Zhang, Han-zhi; Pan, Wei-bin; Chen, Bao-hua; Zhan, Shu-wei

Abstract

Growth of cyanobacteria can easily cause cyanobacterial blooms. Cyanobacteria-algicidal bacteria interactions are a major regulatory factor of cyanobacteria growth during the entire cyanobacterial bloom pe- riod. Interactions between algicidal bacteria (Bacillus cereus strain L7) and cyanobacteria (Anabaena flos-aquae) during cyanobacterial blooms were investigated in different axenic microcosms. Changes in the Bacillus cereus strain L7 and Anabaena flos-aquae cell concentrations, malondialdehyde concentrations, and concentrations of NH4+-N and NO3--N in microcosms were evaluated. Lower concentrations of Bacillus cereus strain L7 stimu- lated growth of Anabaena flos-aquae, while higher concentrations inhibited cyanobacterial growth. Bacillus cereus strain L7 growth was inhibited by extracellular metabolites of Anabaena flos-aquae but promoted by intracellular metabolites of the cyanobacteria. Bacillus cereus strain L7 may promote transformation of nitrate nitrogen into ammonium nitrogen that could be directly and easily utilized by Anabaena flos-aquae. However, higher Bacillus cereus strain L7 concentration (1.75 × 108 CFUs/mL) increased malondialdehyde concentration, suggesting it could damage cyanobateria via peroxidation. Thus, we concluded that cyanobacteria and algicidal bacteria have both mutualistic and antagonistic effects on each other. We also propose a model to illustrate the interactions between both populations during the bloom. This study allows us to better understand the interactions between algicidal bacteria and cyanobacteria during a cyanobacterial bloom and the role of algicidal bacteria during the development and declining stages of the bloom. In addition, this study will support the direct utilization of algicidal bacteria to control a cyanobacterial bloom.

Keywords

algicidal bacteriabacillus cereus strain l7anabaena flos-aquaecyanobacterial bloomscyano-bacteria-bacteria interactions