抄録
Bacterial endosymbionts significantly affect the ecology, evolution, and development of the host by
manipulating host physiology to enhance host fitness. Wolbachia and Cardinium species are among the
most widespread endosymbionts, infecting a range of hosts including animal-, insect-, and plant-parasitic
nematodes, arachnids, and insects. Previous research has shown that some plant- and animal-parasitic
nematodes harbor Wolbachia and/or Cardinium. While these studies have suggested a range of Wolbachia
and Cardinium species in plant-parasitic nematodes, large-scale screening in nematodes is rare. We
report a novel interaction between Cardinium and fungal-feeding nematodes. Polymerase chain reaction
(PCR) screening using primers specific for Wolbachia and Cardinium was conducted in 182 strains of 27
nematode species. While Wolbachia was not detected, Cardinium-specific PCR amplicons were obtained
from three strains of Aphelenchus avenae. Phylogenetic analysis indicated that these Cardinium strains
were distinct from previously described strains. However, fluorescence in situ hybridization analysis
did not detect Cardinium in the gonads. Genome analysis showed low abundance of Cardinium in the
nematode. Moreover, Southern blot analysis showed the Cardinium sequence is not derived from A. avenae
genome, suggesting an extremely low abundance of Cardinium exists in A. avenae cells. Desiccation
tolerance assays showed no significant difference in survival between Cardinium-positive and -negative
strains, although Cardinium-positive strains tended to have higher survival rates.
