Analysis of 2000-yr eruption-affected soil microbial ecosystem of Miyake-jima Island

点击翻译按钮获取中文摘要

Miyake-jima Island is situated on western rim of the Pacific Ocean, about 180 km south of Tokyo. Mt. Oyama in the island erupted from July to September 2000, ejecting large amounts of volcanic ash and finally forming a large collapsed crater. Since the formation of the new crater, a large quantity of volcanic gas containing high concentrations of SO_2 and H_2S has been emitted. This study was aimed to characterize such volcano-affected soil ecosystems by culture-based and molecular genetic methods. We focused on the lithotrophic and heterotrophic bacterial communities in the 2000 volcanic ash deposits from an essentially unvegetated site near the crater. The pH of samples ranged from 3.0 to 3.6 and the contents of carbon and nitrogen were 0.03% and 0.01%, respectively. Total microscopic counts of bacteria were between 10^7 and 10^9/g and plate counts of heterotrophic bacteria were 10^6/g. Phylogenetic analysis of isolates and 16S rDNA clone library analysis revealed that the predominant bacteria were Thiomonas (41% of isolates and 5% of clones), Leptospirillum (39% of clones) and Acidithiobacillus (15% of clones). Further, the intact volcanic ash samples had activites of CO_2 and N_2 fixation and the clone library analyses targeting RubisCo and nitrogenase reductase genes revealed the predominance of the genes of Leptospirillum and Acidithiobacillus. The volcanic ash sample was subjected to stable isotope probing by using ^<15>N_2 to demonstrate the occurrence of N_2 fixation by these bacteria. Our results suggested that chemolithoautotrophic bacteria such as Fe oxidizers could be the pioneer organisms in the microbial ecosystem of the fresh volcanic ash deposit and contribute to the accumulation of carbon and nitrogen in the fresh volcanic deposits.