Overall Research Goals
Marine microorganisms are essential to the maintenance of our biosphere, yet we have only a fragmentary understanding of the diversity and function of microbial life in the oceans. The Microbial Ecology & Physiology Lab studies the composition, diversity, and function of microbial communities, with the objective of understanding the relationship between microorganisms and their role in the ocean biogeochemical cycles. A better understanding of the interactions between the biosphere and geosphere is key to elucidating the role of microbes in the environment, and we contribute to this understanding with our research. The ocean contains a vast array of microbes whose metabolism and physiology remain largely unknown due to a lack of cultivated representatives. This is particularly true for the 'dark ocean', i.e., the parts of the ocean beyond the thin veneer where phototrophic processes dominate.
To this end, the Microbial Ecology & Physiology Lab is undertaking analyses of microbial communities that integrate cultivation-dependent and cultivation-independent techniques, and is pursuing approaches beyond the mere description of microbial diversity to help unravel the governing forces behind the patterns of microbial species distribution. Special interests include the microbial ecology of hydrothermal vents including the subseafloor biosphere, microorganisms involved in sulfur cycling, as well as the evolution and the environmental importance of autotrophic carbon fixation pathways other than the Calvin-Benson-Bassham cycle. These so-called alternative carbon fixation pathways are now recognized to be of much greater importance than previoulsy thought (see also Hügler & Sievert, 2011)
Focus on Autotrophic Microbes in Subseafloor at Deep-Sea Vents
For example, we are currently utilizing molecular biological tools with concomitant analysis of lipids and their stable isotopic compositions as well as microscopic identification of environmental samples and activity measurements to provide a comprehensive assessment of the importance of sulfur oxidation in the subsurface at deep-sea vents. We are attempting to assess the potential importance of carbon fixation pathways other than the Calvin-Benson-Bassham (CBB) cycle for the productivity of this ecosystem. Our present knowledge of organisms responsible for inorganic carbon fixation at hydrothermal vents is inadequate, despite the fact that these organisms form the basis of these ecosystems. Given the prevalence of Epsilonproteobacteria at hydrothermal systems, and the fact that cultivated representatives are autotrophic, it is likely that these organisms contribute significantly to primary organic matter production at hydrothermal vents. These and other autotrophic microbes at vents are using the reductive tricarboxylic acid (TCA) cycle for autotrophic carbon fixation, suggesting that this cycle might be more significant for carbon production at hydrothermal vents than previously thought. Thus, a picture begins to emerge questioning the paradigm of the CBB cycle being at the base of the food web of deep-sea hydrothermal vents.
New Insights into Shrimp Epibiosis
The deep-sea hydrothermal vent shrimp Rimicaris exoculata harbors a specialized epibiotic bacterial community in its enlarged gill chamber. Together with colleagues in Germany we have now further elucidated the functional roles of the epibionts by idendifying the pathways involved in carbon and energy metabolism. Highly specific epibiotic associations between bacteria and invertebrates such as these are a very common phenomenon at deep-sea hydrothermal vents, contributing to overall biomass production at these sites. See the article in PLoS One for more information. Also featured on 'WHOI Image of the Day'.