N-186. Sediment Archaea Community Depth Profile from Lake Fryxell, McMurdo Dry Valleys, Antarctica

C. Tang, B. Lanoil;
Univ. of California, Riverside, CA.

Lake Fryxell (FRX), a perennially ice covered lake in the McMurdo Dry Valleys of Antarctica, has a dynamic methane cycle and has been shown to have Archaeal communities in the anoxic bottom waters and surface sediments. To better understand the diversity and contribution of Archaea to biogeochemical cycles in the sediments, we characterized the Archaeal 16S rRNA gene diversity in a depth profile of a sediment core collected in November 2006 from the deepest water depth of FRX. Archaea-specific 16S rRNA gene clone libraries were constructed; each depth had between 73 to 92 clones (552 clones total). Clones were grouped by DGGE, RFLP and sequencing into 22 OTUs (>97% similarity). All depths showed low diversity (5 to 11 total OTUs) with 1 to 3 dominant OTUs. Two methanogenic archaea (MA) OTUs (designated G3 and G6/7/8), dominate all depths, except the deepest one (12-14 cm depth) which is dominated by a Crenarchaeota lineage (designated G11). OTU G3 is most similar to Canditatus Methanosphaerula paulstris which is associated with the hydrogenotrophic Methanomicrobiales. OTU G6/7/8 is associated with the acetoclastic Methanosarcinales. The relative abundance of G3 and G6/7/8 in clone libraries has a reverse linear relationship (R²=0.79), possibly indicating different methanogenic substrate distribution in the sediments. Cluster analysis indicated that the 0-2 cm, 2-4 cm, 4-6 cm, and 8-10 cm depth samples were highly similar; this observation is further supported by principle components analysis (PCA) of community composition. Both approaches show the 6-8 cm and 12-14 cm depth samples are disparate communities. The dominance of MA in FRX sediment archaea community from 0-10 cm depth corroborate previous findings of high methanogenesis activity in FRX sediments; however the shift to Crenarchaeota in deeper sediments indicates a distinct change in microbial driven biogeochemical processes at this depth. Neither the methanogens’ distribution nor the whole Archaea community level similarity have depth-related trends, possibly suggesting interlayered geochemistry with different availability of methanogenesis substrates.