Nematodes are the most abundant animal species on the Earth and soil nematodes including C. elegans play an important role in the soil food web. Recent studies indicate that soil nematodes can be used as a suitable indicator for assessing soil environment, because it has been shown that the population balance among soil nematodes are affected by their surrounding environment. Since the current morphology-based methods for soil nematode identification require high level of skills and experience, we aimed to establish an improved method for soil nematode identification by the sequence barcode-based approach.
Here, we have developed the improved procedures for the DNA barcode analysis with 18S ribosomal RNA (18S rRNA) gene in nuclear DNA and the cytochrome c oxidase subunit I (
cox-1) gene in mitochondrial DNA. Using the procedure, we have isolated nematodes from the soils of the flower bed in the campus and the field cultivated with soy bean and successfully clarified taxonomic structures of the soil nematode community based on the sequence analysis of 18S rRNA gene. This analysis showed abundant distributions of nematode species in the genera Xiphniema and Mylonchulus in the flower bed soil, and the genera Cephalobus, Acrobeloides and Distolabrellus in the field soil, respectively. Furthermore, we have comparatively analyzed the nematode population in the field cultivated with soy bean by the barcode analyses with the 18S rRNA gene and
cox-1 gene, suggesting that the barcode analysis with the
cox-1 gene could clarify more detailed taxonomic structure than that with the 18S rRNA gene. In conclusion, the barcode-based analysis of soil nematodes may be useful for further assessment of soil environment.