| Summary: | Algicidal bacteria combined with the ability of aerobic denitrification is considered to be a promising way to control harmful cyanobacterial bloom and remove nitrogen. However, the effect of these bacteria on the vertical distribution of colonial cyanobacteria and nutrients remained unknown. In this study, two algicidal and denitrifying bacteria were respectively co-cultured with the colonial <i>Microcystis aeruginosa</i> to construct the microcosm systems, and then the cyanobacteria number, the ratio of bacterial to cyanobacterial abundance, the content of dissolved nitrogen, phosphorus and organic carbon in different water layers were investigated. The results showed that the distribution difference of <i>Microcystis</i> among the vertical water layers was further enlarged due to the short-term influence of algicidal bacteria <i>Brevundimonas diminuta</i> and <i>Pseudomonas stutzeri</i>. The number of <i>Microcystis</i> in the lower layer was further reduced by the inhibitory effect of the algicidal bacteria. However, there was a dramatic increase in the number of <i>Microcystis</i> in the upper layer, even when the ratio of algicidal bacteria to cyanobacteria increased significantly. <i>B. diminuta</i> and <i>P. stutzeri</i> both greatly promoted the removal of dissolved total nitrogen in the upper and middle layers of cyanobacteria blooming water, but they also boosted the release of dissolved phosphorus in all layers. These results enable us to better understand the possible limitations of algicidal bacteria in their application to control cyanobacteria blooms.
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