Diversity of methanogens in Lake Kivu sediments

Meromictic Lake Kivu contains enormous, and contemporarily increasing quantities of dissolved methane of primarily biological origin. So far, knowledge about the archaeal communities in its sediment, including methanogens, is very limited. In this study, we provide the first culture-independent insight into the archaeal communities in Lake Kivu sediments. T-RFLP analysis suggests considerable heterogeneity in archaeal community composition varying with sampling location and sediment properties. Sediments expected to be influenced by groundwater inflows and those from the deepest parts of the main basin harbor distinct archaeal communities. This diversity reflects local geochemical conditions influenced by groundwater inflows and also the influence of the strong vertical physicochemical gradients in Lake Kivu’s water column itself. Our study indicates that archaeal communities are highly variable within the lake, and this variability should be taken into account when assessing biogeochemical functioning of lake sediments. Overall, the Lake Kivu sediment archaeal clone library revealed a remarkable phylogenetic diversity harboring globally distributed archaeal clades, clades not previously known as freshwater sediment archaea, and sequences only distantly related to any previously known archaeal sequences. Surprisingly, only two out of 167 sequenced clones showed an affiliation with known methanogens of the order Methanosarcinales. Furthermore, we found no clones related to the widely distributed freshwater-sediment hydrogenoclastic methanogens of the order Methanomicrobiales, or any other known methanogens. These findings potentially indicate an involvement of yet undetermined environmental archaea in methanogenesis.

Publications and presentations

• Local sediment conditions and depth structure unique archaeal communities in the anoxic sediments of meromictic Lake Kivu. Bhattarai S., Ross K.A., Schmid M., Bürgmann H., (submitted to Microbial Ecology).
• Archaeal communities in Lake Kivu. Bhattarai S., Ross, K.A., Schmid, M., Wüest A., Vazquez F., Bürgmann H. Poster: Symposium “Methane in Lakes and Wetlands”, University of Bern, Switzerland, September 12, 2011
• The unique geomorphology, geochemistry and archaeal composition of the subaquatic springs that sustain Lake Kivu’s stratification. Ross K.A., Pasche N., Bhattarai S., Vazquez F., Bürgmann H., De Batist M., Anselmetti F.S., Schmid M., Wüest A. Poster: 5th International Limnologeological Congress, Konstanz, Germany, August 31 - September 3, 2011