May 26 2016
Dr. Stephanie Carr, Bigelow Laboratory for Ocean Sciences
Methanosaeta, are you my methanogen?
The Adélie Basin, located ~100km off shore of Antarctica’s Wilkes Land Margin, is an anoxic, eutrophic sedimentary environment. During IODP Expedition 318, a 103 m sediment core was collected for microbiological and geochemical studies. Stable carbon isotope analysis of dissolved CO2 indicates an enrichment of δ13C values with depth. This enrichment is indicative of the autotrophic selection of dissolved 12CO2 over 13CO2, which corresponds to increasing methane concentrations suggesting methanogenesis (a maximum of 12.8 mM at 18 meters below sea floor). Surprisingly, previous pyrosequencing of SSU rRNA gene amplicons identified relatively low amounts of known archaea (<7%) and very few sequences from known methanogens (<0.2%). An additional PCR screen for the gene mcrA also failed to recognize the presence of potential methanogens. This unsatisfying dearth of genomic evidence for methanogens precludes a deeper understanding of CH4 cycling in this environment. To better identify the missing methanogenic community of this basin, an integrated approach of metagenomics, single cell genomics, and stable carbon isotope analysis of intact polar lipid techniques was applied to these sediments. Lipid analyses identified isotopically light hydroxyarchaeol and glycerol dialkyl glycerol tetraether (GDGT) phospholipids, both suspected to be of methanogenic origin. Metagenomic analyses identified coding regions for both acetoclastic and autotrophic methanogenesis pathways. The majority of these coding regions were classified to the genus Methanosaeta, a well-known acetoclastic methanogen. This presentation takes a thorough look at the genus Methanosaeta, especially their methanogenic potential and their role in these and other marine subsurface environments.
Dr. Stephanie Carr earned her B.S. in Biochemistry from Hartwick College and a Ph.D. in Geochemistry from Colorado School of Mines. Her Ph.D. work, performed with advisor Dr. Kevin Mandernack, focused on carbon cycling in Antarctic marine sediments. She continued at the Colorado School of Mines under the advisement of Dr. John Spear and Dr. Beth Orcutt and was awarded a C-DEBI Postdoctoral Fellowship in 2013 to study the Candidate Phylum Atribacteria using single cell genomic techniques. In 2015 Dr. Carr was awarded a NSF-OCE Postdoctoral fellowship to study potential advantages of motility in subsurface crustal environments. She currently works at the Bigelow Laboratory for Ocean Sciences with Dr. Beth Orcutt.