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[Objective] To isolate and screen the algicidal strains from samples of a eutrophic water body and study their algicidal characteristics and mode against Microcystis aeruginosa, thus providing a theoretical basis for the biological control of cyanobacterial bloom. [Methods] Strain identification was performed through morphological observation, physiological and biochemical tests, 16S rRNA gene sequence analysis, whole-genome sequencing, and average nucleotide identity (ANI) analysis. The algicidal effects under different inoculation amounts, bacterial growth phases, and initial algal densities were investigated. The algicidal mode was clarified by comparing the algicidal efficiency of cell-free filtrate and cell resuspension of the strain. The morphology of algal cells was explored by means of scanning electron microscopy (SEM). In addition, changes in physiological characteristics of algal cells were investigated through three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy. GC-MS was employed to identify the major algicidal substances after n-hexane extraction. [Results] A highly efficient algicidal strain L2 was obtained and identified as Bacillus velezensis (CGMCC No. 38496, GenBank accession No. PP693440). At an inoculation amount of 10%, the strain achieved the algal inhibition rate of 89.35% against M. aeruginosa after seven days. The algal inhibition rates of the cell-free filtrate and fermentation broth of L2 were 90.51% and 91.75% after seven days, respectively. While the algal inhibition rate of the cell suspension was only 15.10%. This phenomenon indicated that L2 indirectly inactivated M. aeruginosa by secreting extracellular active substances. The major algicidal substances secreted by strain L2 were identified as fatty amides and cyclic dipeptides. Algal cells exhibited shrinkage and surface roughening, with significantly decreased phycobiliprotein content during the algicidal process. In addition, the composition of extracellular organic matter shifted from protein-like substances to humic-like substances. [Conclusion] B. velezensis L2 exhibits high algicidal activity against M. aeruginosa. Algal cells are inactivated primarily through the indirect mode of extracellular substance secretion, which cause damage to the morphology of algae cells and inhibit the activity of the photosynthetic system. The strain L2 exhibits good potential for the biological control of cyanobacterial bloom.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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