The variation of microbial communities in a depth profile of an acidic, nutrient-poor boreal bog in Southwestern Finland

Natural bacterial communities impact the motility of isotopes, such as radionuclides, in the environment. As a result of post glacial crustal rebound radionuclides may escape the deep geological repository for spent nuclear fuel on Olkiluoto Island, Finland, and reach surface environments. Lastensuo Bog, a 5300-year-old raised bog in southwestern Finland, functions as analogue ecotope for bogs formed in Olkiluoto due to the crustal rebound. A core comprising the depth profile (0-7 m depth) of the bog including surface Sphagnum moss, peat and bottom clay was obtained using a stainless steel corer. High throughput sequencing was used to characterize the bacterial communities throughout the bog's depth profile. A total of 12,680 bacterial Operational Taxonomic Units (OTUs) (97% sequence similarity) were detected comprising altogether 40 different bacterial phyla. Of these, 13 phyla were present at all depths, accounting for 97% - 99% of the whole bacterial community. The bacterial communities differed notably through the bog's depth profile, dividing it into five distinct strata: 1) the Sphagnum moss layer; 2) 0.5-3.7 m; 3) 3.7-4.0 m; 4) 5.5-6.0 m deep peat; 5) the former seabed clay at 6.5-7.0 m depth. Acidobacteria, α- and γ-Proteobacteria dominated the surface community, but in the peat Acidobacteria contributed with up to 85% of the bacterial community. The estimated bacterial population density ranged between 2 × 109 and 5 × 1010 16S rRNA gene copies g-1 dry-weight peat. This study revealed that Lastensuo Bog had a highly diverse bacterial community. Most of the taxonomic groups belonged to thus far poorly characterized and uncultured bacteria with unknown physiological role. However, new insights into the distribution of bacterial taxa and their putative roles in organic carbon break down within the bog ecosystem have been obtained and an important baseline for further studies has been established.