Abstract: The symbiotic bacteria associated with entomopathogenic nematodes are potential biological resources in the field of agriculture and medicine. In this study, symbiotic bacteria were isolated directly through infective juveniles or the blood chamber of Galleria mellonella larvae which were infected by Heterorhabditis beicherriana. The symbiotic bacterium was identified as Photorhabdus luminescens based on morphology, physiological and biochemical characteristics and sequence analysis of 16S rDNA; phylogenetic analysis demonstrated the strain was shown to be part of the species of P. luminescens, but it was clearly sperated with clear separation from currently recognized subspecies. It is proposed to be a new subspecies. G. mellonella larvae injected with the cell diluent were used to test pathogenicity of the symbiotic bacterium. The strain C1 exhibited strong pathogenicity to the G. mellonella larvae. Mortality reached 100% at 72 h when one wax moth was inoculated with the concentration of 600 cfu/mL moth. The LC₅₀ was 213.13 cfu/mL at 24 h and 46.87 cfu/mL at 48 h. Our study will lay the foundation for the study of the pathogenic mechanism of H. beicherriana, thus leading to explore a new bacterial strain with important value.

Key words: Heterorhabditis beicherriana, symbiotic bacteria, morphological and physiological characteristics, 16S rDNA, pathogenicity