Abstract
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.
Highlights
Pristine wetlands play a significant role in global carbon cycling and function as sinks for atmospheric CO2 [1] [2]
The organic matter (OM) content of the samples was measured by the loss on ignition (LOI) method, and the OM content and LOI are not exactly the same they strictly correlate with each other
In this study we found that an uncultured group represented by a cloned 16S rRNA gene sequence obtained from grass roots, clone TM1 [44], was the most abundant acidobacterial group in all subsurface peat samples as well as in the clay layer accounting for up to 59.8% of the total sequence number retrieved from 1.5 - 2.0 m depth
Summary
Pristine wetlands play a significant role in global carbon cycling and function as sinks for atmospheric CO2 [1] [2]. They harbour one third of the global soil carbon pool [3] [4] and are an important global source of methane [5], which is produced during anaerobic degradation of organic matter. Ombotrophic raised bogs represent unique habitats for microorganisms, being very acidic and receiving water and minerals only from precipitation. These conditions favour the dominance of Sphagnum mosses, which form acidic, nutrient-poor, decompositionresistant Sphagnum peat [7] [8]
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