| Summary: | The pine wood nematode (PWN) <i>Bursaphelenchus xylophilus</i> is the pathogen that causes pine wilt disease (PWD), a devastating forest disease. PWN-associated bacteria may play a role in PWD. However, little is known about the endo-bacteria in PWN. We analyzed the diversity of endo-bacteria in nine isolates of PWNs from <i>Pinus massoniana</i> Lamb. in nine epidemic areas from three Chinese provinces by high-throughput sequencing of 16S rDNA and isolated and identified culturable endo-bacteria through construction of a 16S rDNA phylogenetic tree and Biolog microbial identification. We also examined the effects of endo-bacteria on PWN fecundity, antioxidant capacity, and virulence using sterile nematodes as a control. While the dominant endo-bacteria in PWNs from different regions exhibited no significant difference in the classification levels of class and genus, their proportions differed. <i>Pseudomonas</i> and <i>Stenotrophomonas</i> were highly abundant in all PWN isolates. A total of 15 endo-bacterial strains were successfully isolated and identified as six species: <i>Stenotrophomonas maltophilia</i>, <i>Pseudomonas fluorescens</i>, <i>Kocuria palustris</i>, <i>Microbacterium</i> <i>testaceum</i>, <i>Rhizobium radiobacter</i>, and <i>Leifsonia aquatica</i>. We also found that <i>P</i>. <i>fluorescens</i> significantly increased the egg production of PWN, and that both <i>P</i>. <i>fluorescens</i> and <i>S</i>. <i>maltophilia</i> enhanced the mobility of PWN under oxidative stress and reduced the content of reactive oxygen species by increasing antioxidant enzyme activity in PWN. These strains also accelerated the development of PWD, and <i>P. fluorescens</i> had a more beneficial effect on PWN than <i>S</i>. <i>maltophilia.</i> Diversity exists among the endo-bacteria in PWNs from different regions, and some endo-bacteria can promote PWN infestation by enhancing the fecundity and antioxidant capacity of the nematode. Our study contributes to clarifying the interaction between endo-bacteria and PWN.
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