Crude extracts of the surface coat (SC) proteins of the pine wood nematode (PWN), Bursaphelenchus xylophilus, and purified flagellin from Pseudomonas fluorescens (GcM5-lA) isolate were bioassayed using symbiontic GcM5-lA and axenic PWNs, respectively. The results showed that the flagellin significantly increased the reproduction of axenic PWN and the SC protein extracts of the PWN promoted GcM5-lA multiplication. The finding is a new step to further elucidate the symbiotic mechanism between the PWN and its associated bacteria and the SC protein function in pine wilt disease. [ABSTRACT FROM AUTHOR]