Analysis of the microbial communities in soils of different ages following volcanic eruptions

Volcanism is a primary process of land formation. It provides a model for understanding soil-forming processes and the role of pioneer bacteria and/or archaea as early colonizers in those new environments. The objective of this study was to identify the microbial communities involved in soil formation. DNA was extracted from soil samples from the Llaima volcano in Chile at sites destroyed by lava in different centuries (1640, 1751, and 1957). Bacterial and archaeal 16S rRNA genes were analyzed using quantitative polymerase chain reaction (qPCR) and Illumina MiSeq sequencing. Results showed that microbial diversity increased with soil age, particularly between the 1751 and 1640 soils. For archaeal communities, Thaumarchaeota was detected in similar abundances in all soils, but Euryarchaeota was rare in the older soils. The analysis of bacterial 16S rRNA genes showed high abundances of Chloroflexi (37%), Planctomycetes (18%), and Verrucomicrobia (10%) in the youngest soil. Proteobacteria and Acidobacteria were highly abundant in the older soils (16% in 1640 and 15% in 1751 for Acidobacteria; 38% in 1640 and 27% in 1751 for Proteobacteria). The microbial profiles in the youngest soils were unusual, with a high abundance of bacteria belonging to the order Ktedonobacterales (Chloroflexi) in the 1957 soil (37%) compared with the 1751 (18%) and 1640 (7%) soils. In this study, we show that there is a gradual establishment of the microbial community in volcanic soils following an eruption and that specific microbial groups can colonize during the early stages of recovery.