nai

Project Progress

Our primary research objective is to better understand the origins and adaptive radiation of an ancient and biogeochemically significant assemblage of microorganisms, the sulfate-reducing prokaryotes (SRP). In overview, we have:

• Refined understanding of the contribution of lateral gene transfer to the adaptive radiation of sulfate reducing bacteria
• Identified energy sources sustaining SRP in geothermal habitats
• Explored the diversity and distribution of SRP in habitats possibly similar to those that existed on early earth (microbial mats and hot springs).

Lateral Gene Transfer. In collaboration with Dr. Michael Wagner’s laboratory (University of Vienna) we identified a lineage of bacteria that was the likely source of genes in the pathway for sulfate respiration inherited by a distantly related clade via lateral gene transfer (Zverlov, Klein et al. 2005).

Energy Sources. Studies of two geothermal sites in Yellowstone National Park (Obsidian Pool and Black Sediment Pool) confirmed that H₂ was an important energy source for sulfate respiration. Enrichment on a H₂-based medium resulted in the isolation of organisms related to Ammonifex degensii, most likely representing a new genus of autotrophic sulfate-reducing bacteria. Endogenous rates of sulfate reduction were measured at additional geothermal sites in the Shoshone Geyser Basin, identifying three new springs of appreciable activity. DNA recovered from one site revealed a novel, and likely early diverging, lineage of sulfate reducing bacteria (Köenneke, de la Torre et al. 2004).

Microbial Mat Community. Photosynthesis drives highly predictable diel fluctuations of chemical structure in microbial mat communities, most notably as manifested by periodic extremes of oxygen and sulfide at the near surface. A fine-structure mapping of a geothermal mat in Yellowstone National Park and a hypersaline microbial mat in Guerrero Negro (Baja Sur, Mexico) associated diel variation in regional community structure with changing chemistry (Dillon, Fishbain et al. In preparation; Dillon, Miller et al. Prepared for submission). These studies revealed two major forms of adaptive response, populations that periodically migrate and those that are relatively sessile (Dillon, Miller et al. Prepared for submission).

Clone libraries of dsrAB and 16S rRNA gene sequences now being analyzed for both the Yellowstone and GN Microbial Mat systems have revealed additional novel sulfate reducers (Dillon, Miller et al. In preparation).