Anoxic environments in earth's history are the subject of intense research and debate. Low temperature sulfur redox gradients are a diagnostic feature of these paleoenvironments. Microbial sulfur-oxidizers populating redox gradients in modern environments are extremely diverse, originating in at least 7 major prokaryotic lineages. The lipid signatures of these microorganisms are poorly known, but are of great interest as potential molecular fossils (biomarkers). The proposed project targets missing information about lipid compositions and ecological characteristics of low-temperature sulfur-oxidizing lithoautotrophs. Data gathered in this work will have significance for studies of ancient anoxic environments representing major biological and geochemical benchmarks in earth's evolution such as the initial appearance of oxygen-producing phototrophs, the global oxidation of the surface earth, Neoproterozoic snowball earth events, the Permian/Triassic extinction, and other periods of global ocean anoxia. Study of samples from photic and aphotic modern sulfide gradients will establish an ecological and biogeochemical context for interpreting organic biosignatures in sulfidic environments throughout the geologic record. It will also contribute basic ecological understanding of how microorganisms are assembled in microbially-dominated ecosystems such as those present on the early earth. This project supports our long-term goal of forging stronger links between the chemistry of lipids in microorganisms abundant in the environment, the evolution of lipid synthesis pathways, and the geologic record of lipid molecular fossils. Mentoring of graduate and undergraduate students is at the core of the project, which will support two Ph.D. students and 6 summer undergraduate research students. This project will also involve 4 undergraduate mechanical and electrical engineering undergraduate students doing senior capstone projects via Penn State's Learning Factory. Research results will be communicated to the general public in the form of "Earthcaches", web-organized geographical challenge games that convey site-specific information about microbial diversity, evolution, deep time, biogeochemical cycling, and environmental quality.
