Abstract：For screening of high efficiency and safe nematicidal resource, a Bacillus strain YBf-10 which exhibits extreme toxicity to root-knot nematode was isolated from marine sediment. The 16S rRAN gene of this strain was amplified by PCR, then sequenced and analysed with Blast in NCBI. The result indicated that it showed 99% identity with the 16S rDNA of Bacillus firmus strain Z1-7. It means the isolated Bacillus strain is B. firmus. The YBf-10 strain was cultured in LB medium until spores were mature, the supernatant was harvested by centrifuged. The supernatant was diluted by 10-folds, and bioassay to 2nd stage juveniles (J2) of Meloidogyne hapla was conducted. The results showed that YBf-10 exhibited extreme toxicity, and the adjusted mortality reached to 50% at 24 h, and even up to 100% at 72 h. The supernatant could obviously suppress hatching of eggs of M. hapla to 80% at 48 h. For ascertaining the synthetic phase of the nematicidal substance, samples were collected at interval of culturing times, the supernatant of the samples was prepared by centrifugalization, and assayed toxicity to J2 of M. hapla. The result indicated that, from onset of the stationary phase, it exhibited obvious toxicity. The toxicity enhanced persistently during all the stationary phase, this meant that the nematicidal substance was synthesized at stationary phase of YBf-10 strain. The nematicidal activity of supernatant treated at 80℃ for 30 min showed no obvious change. The protein in supernatant was prepared by ammonium sulfate precipitation with 30% relative saturation, and exhibited no toxicity to J2 of M. hapla. Whereas, the supernatant removed protein exhibited the same nematicidal activity with the raw supernatant. The result indicated that the nematicidal substance produced by YBf-10 was micromolecular compound, not protein. On the basis of above research, we conclude that the Bacillus strain which exhibits toxic to nematode is characterized as Bacillus firmus, and it synthesizes micromolecular nematicdidal compound at stationary stage. The compound exhibits extreme virulence to root knot nematode, and supplies nematicidal resource for exploring biological control nematicide with the YBf-10 strain
