ABSTRACT

EAR-0525453/EAR-0525561/EAR-0525500
One of the most profound discoveries emanating from molecular phylogenetic studies is that the "universal tree of life" is exclusively populated in its deepest branches by thermophiles. Two opposing theories about why this might be are:
Life first arose in a hydrothermal environment, possibly in the deep subsurface.
Thermophiles preferentially survived the "late heavy bombardment" of the Hadean Earth.
Since no sedimentary record survives from this period, it is not possible to address these theories directly through geology. Instead, we must look to modern geomicrobial processes to better understand controls on, and modes of, thermophilic life. Armed with this understanding, geological records may eventually yield more information on the physiological capabilities and nature of early life.

This proposal addresses geomicrobial processes at interfaces between mildly reducing hydrothermal fluids and oxidizing surface sediments or waters. Specifically, we will use a combination of molecular, chemical, and isotopic methods to identify the geomicrobial associations, metabolic strategies, nutrient, and energy requirements and geochemical signatures of streamer and biofilm-forming communities (SBC) of thermophilic and chemolithotrophic Bacteria and Archaea.

We will address the following questions:
1) What is the physiochemical basis for the occurrence of biofilm-forming Aquificales?
2) What is their primary carbon source and mode of carbon assimilation?
3) What are the identities of the Crenarchaeota that appear to co-colonize these systems?
4) Is there a co-dependence of these microbes and, if so, what is its basis?
5) Can biosignatures be used to distinguish thermophilic and mesophilic communities?
6) Might these systems leave a molecular record that could be traced back in time?

Scientific Merit: Through this research, we will learn more about the physiological basis for life at high temperatures and the characteristic biosignatures of thermophilic microbes. In particular, we will seek to discern if there is a symbiosis or simply a physical co-habitation of thermophilic Aquificales and Crenarchaea in the SBCs of Yellowstone National Park. These organisms occupy a special niche at the interface of hot, sub-subsurface hydrothermal fluids and a "cold" and oxidizing atmosphere. In seeking to increase understanding of microbes and biogeochemical processes operating at this interface and the strategies used to derive energy and nutrients, our proposal is firmly aligned with the aims and objectives of the Biogeosciences Program. In combining cutting-edge geochemical and microbiological approaches, we will also be generally improving methods and research techniques for the study of geomicrobial processes.

Broader Impacts: This proposal focuses on teaching and training and will support the training of a new postdoctoral investigator and graduate student at MIT and will provide unparalleled research opportunities for undergraduates interested in the biogeosciences, including significant collaborative interactions in the field and laboratory at three institutions. Providing meaningful and positive research experiences in multidisciplinary science to college undergraduates is critical to fostering the next generation of researchers and educators. Because the focal point of our research is one of the US's most visited national parks, there will be enhanced opportunities for public dissemination of our results. We will work directly with the Park Service to develop educational materials, including scientifically sound treatment of the philosophical and practical aspects of fundamental research pertaining to "origins of life" and "limits of life" concepts.

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