Speaker: Mark Lever, Marine Science Institute, The University of Texas at Austin
Title: Population dynamics of methane-cycling microorganisms in subseafloor sediments
Host: Kehua You
Abstract: Marine sediments harbor Earth’s biggest reservoir of methane. The episodic release of this methane to the atmosphere has been linked to climatic shifts in Earth’s past. Most of this methane is produced by methane-producing archaea (methanogens) in subsurface sediment layers, where these archaea dominate the terminal step of organic matter mineralization. Despite the great importance of methanogens in the sedimentary and global carbon cycle, only few studies have succeeded in detecting and characterizing their in situ abundances and distributions. Recent publications from my laboratory have contributed to changing that and revealed the presence of a near-ubiquitous “rare biosphere” of methanogens from coastal sediments to deep sea trenches and even the Earth’s oceanic crust. In some locations, the same taxa dominate over a wide range of temperatures (2º to 65ºC), redox zones, and lithologies, while in others there is a clear taxonomic zonation that suggests periods of growth- and mortality-driven turnover of major methanogenic taxa along burial-related geochemical gradients. The observed patterns in methanogenic community zonation raise fundamental questions regarding the drivers of microbial community structure and growth in marine subsurface environments.