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Bacterial diversity and community structure in polygonal tundra soils from Samoylov Island, Lena Delta, Siberia

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06_195_Liebner.qxp RESEARCH ARTICLE Summary. During the Arctic summer, bacteria are active above the permafrost in an environment with sharp temperature and oxygen gradients. The present study addressed the diversity and abundance of bacteria in soil layers near the surface and above the permafrost of the rim and center of a low-centered polygon in the Lena Delta, Siberia. 16S rRNA gene clone libraries revealed the presence of all major soil bacterial groups and of the candidate divisions OD1, OP5, and OP11, and indi- cated a small-scale heterogeneity of these polygonal tundra soils. The diversity at the top of the elevated polygon rim was sig- nificantly different from that of the bottom and from both water-saturated sites of the polygon’s center. The overall species- level diversity was very high (Shannon index of 5.3) but varied within the sites and decreased towards the permafrost table, coinciding with decreasing dissolved organic carbon (DOC) and phosphate concentrations. According to the number of oper- ational taxonomical units (OTUs) and cells visualized by fluorescence in-situ hybridization, Bacteroidetes and Actinobacteria were the dominant members of the bacterial community in all sites. Bacteroidetes contributed almost 50% to all Bacteria cells while sequences affiliated with Bacteroidetes/Chlorobi represented on average 23% of all OTUs. Our results provide evidence of the extremely diverse bacterial communities present in permafrost soils and of the influence of nutrient concentrations, oxygen, and DOC on diversity. [Int Microbiol 2008; 11(3):195-202] Key words: bacterial diversity · clone libraries · nutrient gradients · active layer · tundra · Siberian Arctic Introduction Members of the domain Bacteria represent the major group of organisms in soils, with a large number of cells (typically 109 bacteria/g soil) and level of diversity [8,48]. According to DNA reassociation kinetics and 16S rRNA gene sequence sim- ilarities, the number of bacterial species (per 100 g of

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