Freshwater eutrophication and cyanobacterial blooms have become a persistent global environmental challenge. Blooms dominated by Microcystis aeruginosa consume dissolved oxygen, degrade water quality and release microcystins that endanger aquatic organisms and public health. Conventional physical‑chemical treatments frequently bring drawbacks including high operational cost and environmental side‑effects, creating urgent demand for sustainable biological countermeasures.
A research team from Shandong Agricultural University has isolated and characterized an algicidal bacterial strain L2 from local eutrophic pond water. Combining morphological observation, physiological‑biochemical tests, 16S rRNA and whole‑genome ANI analysis, the team identified strain L2 as Bacillus velezensis . The strain has been deposited at China General Microbiological Culture Collection Center (CGMCC No.38496), with its genome sequence available under GenBank accession PP693440.
Laboratory co‑culture experiments demonstrated strong algicidal performance. Under 10 % inoculation volume, strain L2 achieved over 89 % inhibition rate against Microcystis aeruginosa within 7 d. Further tests comparing intact bacterial culture, cell‑free filtrate and bacterial cell resuspension revealed that L2 works primarily through indirect algicidal mode: it secretes extracellular metabolites rather than relying on direct physical contact with algal cells. The cell‑free filtrate reached 90.51 % algal‑inhibiting efficiency after 7 d, while resuspended bacterial cells only produced weak inhibition.
Scanning electron microscopy showed severe shrinkage and roughening of algal cells exposed to L2 metabolites. The phycobiliprotein, a key photosynthetic pigment complex of cyanobacteria, decreased sharply. Three‑dimensional fluorescence spectra indicated extracellular organic matter shifted from protein‑like fractions toward humic‑like substances during algal lysis. Using GC‑MS, the group pinpointed major algicidal components as fatty amides and cyclic dipeptides.
The strain maintained strong algicidal performance across a relatively wide range of initial algal densities and bacterial growth phases in laboratory tests. Even under high algal‑density conditions simulating severe bloom events, the 7 d inhibition rate remained above 86 %, indicating robust environmental adaptability of L2. Although log‑phase bacteria responded fastest to suppress algae, cell‑free filtrate collected from stationary‑phase cultures yielded the highest algicidal efficiency, because more extracellular algicidal metabolites had accumulated at this growth stage.
This study expands fundamental knowledge regarding the algicidal capabilities of Bacillus velezensis and clarifies the algicidal potential of fatty amides and cyclic dipeptides metabolites. It provides a valuable bacterial resource for eco‑friendly biological control of cyanobacterial blooms.
Nevertheless, direct large‑dose application of bacterial broth incurs high costs for field scenarios. The authors highlight that further work including bacterial immobilization modification, engineered strain construction, and systematic aquatic ecological risk assessment will be required to translate this laboratory‑based finding into real‑world water‑body applications.
This work was supported by the National Natural Science Foundation of China (42507114, 42577097), and the Natural Science Foundation of Shandong Province (ZR2025QC383).
ACTA MICROBIOLOGICA SINICA
Isolation, identification, and algicidal characterization of Bacillus velezensis L2
4-Oct-2026