Inhibition of pine wood nematode Bursaphelenchus xylophilus by rhizobacterium Bacillus velezensis FZB42

Abstract:

[Objective] Pine wilt disease caused by the pine wood nematode Bursaphelenchus xylophilus is a destructive disease of pines and one of the most dangerous forestry diseases in China. Bacillus velezensis strains are widely used in agriculture as microbial agents for promoting plant growth and the major bacterial resources in China's microbial fertilizer industry. In this study we evaluated the inhibition of Bu. xylophilus by Ba. velezensis. [Methods] Ba. velezensis FZB42 was used as a representative strain in the study. The inhibition was determined using supernatants of FZB42 cultures under different conditions, the supernatants of different mutants, the extract of plantazolicin, and the direct FZB42 contact on the mortality/survival rate of Bu. xylophilus. An FZB42 mutant deficient in biofilm formation was constructed and its effect on the survival rate of Bu. xylophilus was also determined.[Results] Compared with Landy medium, the supernatant of FZB42 cultured in LB medium had a significant inhibitory effect on Bu. xylophilus. The supernatant collected at the 48^th hour after inoculation was more inhibitory than that collected at the 24^th hour. The inhibitory efficacy improved with the increase of supernatant concentration and treatment time. Using LB culture supernatant collected at the 48^th hour to treat nematodes for 48 h could result in a mortality rate of the nematodes as high as about 50%. The tests with the supernatants of different mutants and the culture extracts showed that plantazolicin, a bacteriocin reported to have a nematocidal activity against Caenorhabditis elegans, had no inhibitory effect on Bu. xylophilus. Direct contact experiments also showed that FZB42 significantly decreased the survival rate of Bu. xylophilus, although the bacterial biofilm formation could enhance Bu. xylophilus resistance to stress. [Conclusion] We demonstrated with laborious but strict assays that Ba. velezensis FZB42 had an inhibitory effect on the pine wood nematode Bu. xylophilus. The molecular basis and mechanism of the inhibitory effect need to be further explored, but it has proved to be not related with plantazolicin. As a group of biocontrol strains with good safety, profound basis research and high degree of development, the potential application value of Ba. velezensis in the control of the pine wood nematode deserves our attention.