Identification of <italic>Bursaphelenchus xylophilus</italic>-killing bacterium HEBAU PA-7 and stability analysis of its fermentation filtrate

To identify the biocontrol bacteria strain HEBAU PA-7 against Bursaphelenchus xylophilus, its taxonomic status was determined by morphological observation and molecular biology techniques, and the nematicidal activity and stability of its fermentation filtrate were evaluated by direct contact method. The results indicated that the strain colonies were yellow‑green, circular, and vary in size, with rod‑shaped bacterial cells and polar flagella. HEBAU PA-7 was the most closely related to Pseudomonas aeruginosa, with a homology up to 99.93%. The fermentation filtrate of strain exhibited strong nematocidal activity against B. xylophilus, achieving a corrected mortality rate of 100% after 72 hours of treatment with a 10‑fold dilution. The nematocidal activity of the fermentation filtrate was unaffected by temperature, proteinase K or ultraviolet radiation, but was sensitive to strong acids and alkalis, with an optimal pH value range of six to eight. The fermentation filtrate of strain HEBAU PA-7 demonstrated strong nematocidal activity and environmental stability, providing a reference for the development and utilization of this strain.