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Project Progress

1. Deep Subsurface Project: In collaboration with the URI “Subsurface Biosphere” NAI group, the phylogenetic analysis of deep marine subsurface sediments from organic-poor, low activity sites is finished (ODP sites 1225 and1231 in the Equatorial Pacific and Peru Basin). We are continuing with analyses of Peru margin sediments (ODP Sites 1227, 1228, 1229 and 1230), which have a higher organic carbon content and higher microbial activities. All phylogenetic analyses from these sites are based on rRNA. rRNA content is approximately proportional to metabolic activity; thus, we are characterizing the microbial populations that are alive and active, and exclude DNA by dead or inactive cells.

Results so far show very little geochemical evidence of the predominant marine anaerobic remineralization pathways, sulfate reduction and methanogenesis (Lever and Teske 2005, Teske, Lauer and Sørensen 2005). The active archaeal communities in the Peru Margin sites fall into several archaeal lineages that have been repeatedly detected in deep subsurface marine sediments and other subsurface habitats (MCG, Misc. Crenarchaeotal Group; MBG-B, Marine Benthic Group B; SAGMEG-1, South African Goldmine Euryarchaeotal Group 1). Thus, the distinct archaeal subsurface communities that we and others have detected previously based on rDNA sequencing surveys are not only present, they are also active.

Mark Lever has sampled deep sediments and subsurface basalt from IODP Leg 301, a transect of the eastern flanks of the Juna de Fuca Ridge (July/August 2004). These samples will be used for sequencing of functional genes.

2. Guaymas Project: We have finished and published the first combined phylogenetic analysis of dissimilatory and assimilatory sulfite reductases, including novel dissimilatory sequences from Guaymas (Dhillon et al. 2005). As a working model, primitive, monomeric sulfate reductases diverged early into mutually exclusive, deeply rooted branches of dimeric, assimilatory and dissimilatory reductases. This ancient divergence may preceed the archaeal — bacterial divergence, pending more archaeal data.

The initial survey of a key gene of methanogenesis, mcrA (the gene for the alpha subunit of coenzyme M methyl reductase) in Guaymas has been completed and is in press (Dhillon et al. 2005). Methanogen populations in Guaymas are phylogenetically and physiologically very diverse (Methanosarcinales, Methanomicrobiales, Methanococcales ). The sequences include novel lineages within the Methanosarcinales that are distinct from all other cultured and cloned Methanosarcinales, and from ANME-2 groups. Methanogens and sulfate-reducing bacteria competing for the same carbon substrates coexist in the same sediment horizons, an unusual occurrence in marine sediments. This dataset complements the earlier study of sulfate-reducing key genes in Guaymas (Dhillon et al. 2003).

Mark Lever is working on a mcrA sequencing of another Guaymas sediment sample set (with a very steep temperature gradient) that has not been analyzed yet. The initial screening showed deeply branching mcrA phylotypes parallel to the extremely thermophilic Methanopyrus lineage. Thus, these samples are most promising for the detection of novel mcrA phylotypes that fall outside all published Methanogen lineages (Unpublished).

Other: The second publication of Virginia Edgcombs NRC Postdoc in the Teske lab (2000-2002) has been published, on ecophysiology of hydrothermal vent archaea and their survival adaptations to extreme conditions (Lloyd, K.G., Edgcomb, V.P., Molyneaux , S.J., Wirsen, C.O., Atkins, M.S. & Teske, A. (2005) Applied and Environmental Microbiology 71: 6383-6387).