S43: Metagenomic analyses of active-layer and permafrost microbial communities during short-term thawing

Arctic tundra and wetlands may become an important source of greenhouse gases as increasing surface temperatures thaws the underlying permafrost and progressively deepen the active layer. To address this question we are currently performing long-term thawing experiments at 4^oC on eighteen, geochemically well-characterized, 1 meter long, intact cores of active-layer (0-70 cm depth) and permafrost which were collected from a 7 meter diameter ice-wedge polygon located near the McGill Arctic Research Station on Axel Heiberg Island, Canada. The temperatures at 5 cm, 35 cm, 65 cm, and below the permafrost table in the core are being recorded continuously. Pore water and gas samples from these depths in each core are collected every two weeks and analyzed for pH, anions, cations, H₂, CH₄, CO, O₂, N₂, CO₂ and δ¹³C of CO₂. Total community genomic DNA was isolated using FastDNA SPIN kit. Shotgun metagenome libraries were generated using 454 technology, and they yielded 298,760,868 bp equal to 0.11x coverage. Initial characterization of the metagenomic sequences with MG-RAST elucidated differences between the permafrost and active-layer, and indicated that the top 5 cm and permafrost (85 cm depth) samples have a microbial community structure that is significantly different from that of the samples at 35 cm and 65 cm, which are more similar to each other. If one week of thawing suffices to induce changes in the microbial community structure, then we anticipate that the variations in metagenome may correlate to the geochemical data and simulate normal onset of microbial activity during summer time.