COG3 Seminar: Elizabeth Trembath-Reichert (WHOI)

Elizabeth Trembath-Reichert, WHOI
Friday, September 15, 10:00am to 11:00am

"Microbial activity approaching geologic timescales: Methyl-compound use and slow growth characterize life in 2 km-deep subseafloor coal and shale beds"

The past decade of scientific ocean drilling has revealed seemingly ubiquitous, slow growing microbial life within a range of deep biosphere habitats. IODP Expedition 337 expanded these studies by successfully coring Miocene-aged coal beds 2 km below the seafloor hypothesized to be “hot spots” for microbial life. To characterize the activity of coal-associated microorganisms from this site, a series of stable isotope probing (SIP) experiments were conducted using intact pieces of coal and overlying shale incubated at in situ temperatures (45ºC). The 30-month SIP incubations were amended with 2H2O as a passive tracer for growth and different combinations of 13C- or 15N-labeled methanol, methylamine, and ammonium added at low (μM) concentrations to investigate methylotrophy in the subseafloor biosphere. Although the cell densities were low (50 to 2000 cells/cm3), bulk geochemical measurements and single cell targeted nanometer-scale secondary ion mass spectrometry (NanoSIMS) demonstrated active metabolism of methylated substrates by the thermally-adapted microbial assemblage, with differing substrate utilization profiles between coal and shale incubations. The conversion of labeled methylamine and methanol was predominantly through heterotrophic processes, with only minor stimulation of methanogenesis. These findings were consistent with in situ and incubation 16S rRNA gene surveys. Microbial growth estimates in the incubations ranged from several months to over 100 years, representing some of the slowest direct measurements of environmental microbial biosynthesis rates. Collectively, these data highlight a small, but viable, deep coal bed biosphere characterized by extremely slow growing heterotrophs that can utilize a diverse range of carbon and nitrogen substrates.

About the Speaker

Research Interests: Microbial metabolism in energy-limiting conditions. | Complexities of carbon and nitrogen burial and utilization in subsurface systems. | Microbial network/community dynamics in sedimentary environments.

About this Seminar

The Chemical Oceanography, Geology, Geochemistry, and Geobiology Seminar [COG3] is a student-run seminar series. Topics include chemical oceanography, geology, geochemistry, and geobiology. The seminars take place on Fridays from 10-11am in Building E25, Room 119, unless otherwise noted (term-time only).