The potential of metabolites released by Bacillus subtilis CH21 for the effective Control of the harmful cyanobacterium Raphidiopsis raciborskii

Microorganism-based biocontrol strategies for harmful cyanobacterial blooms have gained increasing attention due to their ecological compatibility and species-specific targeting. Despite this, research on algicidal bacteria effectiveness against the invasive cyanobacterium Raphidiopsis raciborskii remains limited. Research has been conducted on the Bacillus subtilis strain CH21, which was isolated from Chaohu Lake in China. exhibiting potent indirect anticyanobacterial activity against R. raciborskii . Within 48 h of exposure, the cell-free filtrate of strain CH21 achieved 96.2 % removal efficiency of R. raciborskii cells. Physiological and morphological analyses revealed severe disruption of the photosynthetic apparatus (Fv/Fm and Yield values reduced to zero within 16 h), oxidative stress (elevation in malondialdehyde content and reactive oxygen species, reduction in superoxide dismutase and catalase activity), and cellular damage, including pseudovacuole collapse, the degradation of polyphosphate granules and cytoplasmic leakage. Metabolomic profiling identified surfactin-class lipopeptides as putative bioactive agents, which demonstrated exceptional stability across a wide thermal (25–121 °C) and pH (3–13) range. These findings highlight B. subtilis CH21 as a promising candidate for targeted biocontrol of R. raciborskii blooms, supporting the development of environmentally mitigation technologies to be used in cases where it is difficult to control R. raciborskii by external nutrient loading reduction or if the response to such loading reductions are slow.