Unique pioneer microbial communities exposed to volcanic sulfur dioxide

Newly exposed volcanic substrates contain negligible amounts of organic materials. Heterotrophic organisms in newly formed ecosystems require bioavailable carbon and nitrogen that are provided from CO₂ and N₂ fixation by pioneer microbes. However, the knowledge of initial ecosystem developmental mechanisms, especially the association between microbial succession and environmental change, is still limited. This study reports the unique process of microbial succession in fresh basaltic ash, which was affected by long-term exposure to volcanic sulfur dioxide (SO₂). Here we compared the microbial ecosystems among deposits affected by SO₂ exposure at different levels. The results of metagenomic analysis suggested the importance of autotrophic iron-oxidizing bacteria, particularly those involved in CO₂ and N₂ fixation, in the heavily SO₂ affected site. Changes in the chemical properties of the deposits after the decline of the SO₂ impact led to an apparent decrease in the iron-oxidizer abundance and a possible shift in the microbial community structure. Furthermore, the community structure of the deposits that had experienced lower SO₂ gas levels showed higher similarity with that of the control forest soil. Our results implied that the effect of SO₂ exposure exerted a selective pressure on the pioneer community structure by changing the surrounding environment of the microbes.