Ultrastructural detection of intracellular bacterial symbionts in the wood-inhabiting nematode Bursaphelenchus mucronatus (Nematoda: Aphelenchoididae)

Abstract

Summary Ultrastructural observations of the wood-inhabiting fungal- and plant-feeding nematode, Bursaphelenchus mucronatus, revealed intracellular bacteria in the male and female gonads. In males, bacteria were present inside the testis epithelial cells, spermatocytes, spermatids and immature spermatozoa. Spermatheca of females contained amoeboid pseudopod-bearing mature spermatozoa with bacteria closely associated with the sperm nucleus. Tissues of the females studied were free from bacteria. The gram-negative bacteria in their localisation, size, ultrastructure, and especially characteristic internal bundle of parallel filaments, were identified preliminary as related to the genus Cardinium (Bacteroidetes), which includes obligate endosymbionts of diverse arthropods and is known to be associated with several species of plant-parasitic nematodes.