A Bacillus sp. strain with antagonistic activity against Fusarium graminearum kills Microcystis aeruginosa selectively

- A Bacillus sp. strain AF-1 being antagonistic against both Fusarium graminearum and Microcystis aeruginosa was obtained.
- AF-1 secreted stable algicides to kill M. aeruginosa at low cell density.
- DNA damage, photosynthesis interruption, and reactive oxygen species accumulation might be the main causes of the cyanobacterial cell death.

Cyanobacterial harmful algal blooms (CyanoHABs) cause severe environmental problems, economic losses and threaten human health seriously. In the present study, a Bacillus sp. strain, designated as AF-1, with strong antagonistic activity against plant pathogenic fungus Fusarium graminearum was isolated from purple soil. Bacillus sp. AF-1 selectively killed Microcystis aeruginosa at low cell density (1.6 × 103 cfu/mL), and showed the strongest bactericidal activity against M. aeruginosa NIES-843 (Ae = 93%, t = 6 d). The algicidal substances originated from strain AF-1 were stable in the temperature range of 35-100 °C, and pH range of 3-11. Cell-free filtrate of AF-1 culture caused excessive accumulation of intracellular reactive oxygen species (ROS), cell death and the efflux of intracellular components of M. aeruginosa NIES-843 cells. The expression of genes recA, psbA1, psbD1, rbcL and mcyB, involved in DNA repair, photosynthesis and microcystin synthesis of NIES 843, were significantly influenced by the cell-free filtrate of AF-1 culture. Bacillus sp. AF-1 has the potential to be developed as a bifunctional biocontrol agent to control CyanoHABs and F. graminearum caused plant disease.

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