Effects of Dominant Associated Bacteria Agrobacterium radiobacter Bx.F4 and Delftia tsuruhatensis Bx.Q2 on the Physiological Traits of Bursaphelenchus xylophilus: Insights from RNA-Seq Analysis

To investigate the role of bacteria associated with pine wood nematodes (PWNs), <i>Bursaphelenchus xylophilus</i> (Steiner & Buhrer) Nickle, we isolated two dominant bacterial strains (<i>Agrobacterium radiobacter</i> Bx.F4 and <i>Delftia tsuruhatensis</i> Bx.Q2) from <i>B. xylophilus</i> with different pathogenicity (highly pathogenic F and weakly pathogenic Q) identified in previous studies. In this study, <i>Agrobacterium radiobacter</i> Bx.F4 and <i>Delftia tsuruhatensis</i> Bx.Q2 were inoculated, respectively, to aseptic PWNs to identify the effects of dominant nematode-associated bacteria on the motility, egg laying, population growth, lifespan, feeding ability, and pathogenicity of PWNs. The results showed that <i>Agrobacterium radiobacter</i> Bx.F4 could significantly enhance the motility, egg-laying, population growth, lifespan, feeding ability, and pathogenicity of PWNs, while <i>Delftia tsuruhatensis</i> Bx.Q2 exhibited the opposite effects. Furthermore, using RNA-sequencing analysis, we found that the longevity regulatory pathways, along with the JNK, Wnt, and FOXO signaling pathways related to these genes were clearly enriched. These results indicate that dominant bacterial strains associated with <i>B. xylophilus</i> may regulate various metabolic activities within the nematode, thereby exerting a significant influence on its physiological state and pathogenicity. This also provides a potential strategy for the biocontrol of pine wilt disease (PWD).