Speaker: Sean Jungbluth
Department of Oceanography, University of Hawaii
Title: Microbial diversity in anoxic, subseafloor basaltic fluids
Abstract: The subsurface basement basalt environment is an exploratory frontier on Earth that is relevant to astrobiology topics related to extraplanetary subsurface microbial life, chemosynthetic ecosystems, and origins of life. Hydrothermal circulation of fluids through the porous and permeable ocean basement fuels a deep subsurface microbial community that remains poorly characterized due to the logistical and methodological constraints associated with sampling the sediment-covered seafloor. Ocean Drilling Program and Integrated Ocean Drilling Program holes penetrating 1.2-3.5 million-years old sediment-covered basaltic crust of the Juan de Fuca Ridge flank fitted with Circulation Obviation Retrofit Kit (CORK) borehole observatories have enabled sampling of chemically-reducing basement fluids over the course of multiple years (2008-2014). Consistent and reliable access to pristine fluids from the ocean crust is due to improvements to CORK observatories, through incorporation of microbiologically-friendly materials, and fluid sampling techniques and equipment. Snapshots of basement fluid microbial diversity and community structure have been obtained through small subunit ribosomal RNA gene cloning and tag sequencing from five boreholes that access a range of basement ages and temperatures at the sediment-basement interface. By analyzing ~1.7 million reads of the small subunit ribosomal RNA gene by next-generation Illumina sequencing from marine sediment, deep seawater, and 24 crustal fluid samples spanning multiple years and boreholes, a distinct subseafloor biosphere dominated by the domain Bacteria was uncovered. Fluids from a single borehole sampled annually over the course of three years each had distinct microbial community structure and were dominated by the Proteobacteria. This window of access to the marine basement biosphere reveals a microbial landscape more spatially and temporally heterogeneous than previously recognized. Analyses such as these provide a framework for future research investigating the astrobiological implications, evolutionary and functional diversity, population genetics, and activity of the poorly understood deep subseafloor basement habitat.
Tea, coffee, and cookies will be available at 2:45pm.
Please bring your own mug.
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