nai

Project Progress

Deep Subsurface Project

Active archaeal communities. We are beginning to publish the results of our rRNA survey of selected deep subsurface sediments, focusing on active archaeal communities in the subsurface (Biddle et al. 2006, Sørensen and Teske 2006). All previous subsurface community analyses were based on DNA, which included the risk of detecting and analyzing remnant and fossil DNA from inactive or dead cells. At present, our published and unpublished work indicates the existence of phylogenetically distinct, active archaeal subsurface communities that are widespread in continental margins and other marine subsurface sediments.

{{ 1 }}

These archaeal lineages (Misc. Crenarchaeotal Group and Marine Benthic Group B) are presently uncultured. In collaboration with the URI and PSU Astrobiology teams, the primary carbon sources of these active subsurface archaeal communities were identified as buried organic carbon of photosynthetic origin; methane and CO₂ were excluded (Biddle et al. 2006). The phylogenetic diversity and environmental range of several of these conspicuous, active subsurface archaea was reviewed and discussed in Teske 2006 (ODP review chapter).

Functional genes. Work on functional gene detection in the subsurface continues. An initial dataset on mcrA genes, a key gene of methanogenesis, indicated the existence of acetoclastic methanogens belonging to a Methanosaeta sister lineage in the extremely methane-supersaturated sediment column of ODP Site 1230 (Inagaki et al. 2006; Lever et al. 2006, Astrobiology). At present, additional mcrA and dsrAB datasets from deep and coastal sediments are being processed.

{{ 2 }}

Organic-poor marine subsurface sediments. Alone among all ODP microbiology teams, we have worked on marine subsurface sediments in the central oceanic basins that are depleted in organic carbon, such as ODP Site 1225 in the equatorial Pacific. These sediments are difficult to study, due to energy and carbon depletion, low microbial activities and populations; however, they represent the largest oceanic habitat that dominates the Earth’s oceans on an areal basis. Preliminary results on archaeal and bacterial community composition at Site 1225 are published (Inagaki et al. 2006, Teske 2006); a detailed study is in preparation. Briefly, some subsurface archaeal lineages that are prominent in organic-rich continental margins reappear in these environments (Marine Benthic Group B), but they do not dominate the archaeal community which now includes a different set of lineages reflecting a very different habitat (Marine Benthic group A sister lineages, MG-I).

Guaymas Project

Anaerobic Methane-oxidizing Archaea. After publishing the results of the Guaymas Basin mcrA key gene survey discussed in the 2005 report (Dhillon et al. 2005. Appl. Environ. Microbiol), we are continuing habitat and microbial community studies of anaerobic methane-oxidizing archaea based on mcrA genes, due to the importance of these archaea for the early carbon cycle of the Earth and their unique ability to complete the anaerobic carbon cycle in an oxidative direction from methane to CO₂. These archaea are candidate organisms for driving carbon cycling in the deep marine subsurface biosphere. My graduate student Karen Lloyd has finished a detailed community structure and geochemical analysis of a methane seep in the Gulf of Mexico (analogous to Guaymas Basin, minus the hot temperatures), which has yielded an archaeal methane oxidizer community of ANME-1 archaea only (Lloyd et al. 2006, submitted). Such a highly biased community composition is very unusual and points to selective geochemical factors controlling community structure of anaerobic methane-oxidizing archaea, including salinity, oxygen exposure, and methane fluxes. Similar ANME-1 communities were found in coastal NC sediments (Lloyd et al. 2006, Astrobiology Abstract), indicating that ANME-1 archaea might be the dominant catalysts of methane oxidation in a wide range of typical marine sediments. We obtained additional continental slope and seep samples from the Gulf of Mexico on a cruise in October 2005 to test this hypothesis.

Other

We have at last completed and published 16S rDNA clone library studies that originated as side projects during CAN 1 on marine archaeal and bacterial communities across a hydrothermal vent chimney wall (Kormas et al. 2006) and across a hypersaline gypsum crust (Sørensen et al. 2006). These extremophilic microbiota were distinct from subsurface and methane seep communities, but their clone library profiles clearly reflect the specific geochemical and temperature gradients within these microenvironments. These studies show that clone library composition is indicative of biogeochemical controls in extreme environments, indicating that selective pressures in the subsurface habitat determine the subsurface results.

The second publication of Virginia Edgcomb, NRC Postdoc in the Teske lab 2000-2002, on ecophysiology of hydrothermal vent archaea and their survival adaptations to extreme conditions has been published (Lloyd et al. 2005).