Metagenomic analysis of bacterial communities on Dokdo Island

Dokdo, located east of the mainland of South Korea, is a volcanic island designated as a natural monument of South Korea due to its ecological value. Dokdo is divided into Dongdo and Seodo, islands with geological differences. The soil bacterial communities on Dokdo (Dongdo and Seodo) were analyzed using the pyrosequencing method. There were 1,693 and 1,408 operational taxonomic units (OTU) from Dongdo and Seodo, respectively. The statistical analyses (rarefaction curves as well as Chao1, Shannon, and Simpson indices) showed that bacterial diversity was slightly higher in Dongdo than Seodo. From results of a BLASTN search against the Ez- Taxon-e database, the validated reads (obtained after sequence preprocessing) were almost all classified at the phylum level. From the phylum level down to the species level, the number of classified reads considerably decreased due to the absence of information concerning unculturable or unidentified bacteria to date. Among the 36 phyla identified, three phyla (Proteobacteria, Actinobacteria and Acidobacteria) accounted for around 74.64%. The taxonomic composition was similar at the higher ranks (family and above) between Dongdo and Seodo, but a little different at the genus level. There were also various differences in the relative abundance of taxonomic ranks between Dongdo and Seodo. In particular, the proportion of the genus Acidobacterium (of the phylum Acidobacteria) was about six times higher in Seodo than Dongdo. In addition, the percentage of the genus Mycobacterium (of the phylum Actinobacteria) was nearly three times higher in Seodo than Dongdo, and the proportion of the genus Gaiella was about 3.7 times higher in Dongdo than Seodo. Overall, through the metagenomic analysis, the number of species identified in Dongdo and Seodo was 1,239 and 1,055, respectively. This information on the numerous culturable and unculturable bacteria is expected to help in the screening of new species in Dokdo.