Microbial-mineral interactions are ubiquitous and crucial aspects of geochemical cycling at the Earth's surface. Significant progress has been made towards identifying how specific groups of microorganisms interact with minerals, especially Fe oxides. However, there has been little work on how microbes make and break elemental sulfur (S(0)), though geologists have postulated microbial involvement in producing economic S(0) deposits. Chemical and biological controls on this process are not well understood, and will require a better understanding of factors affecting S(0) production and consumption within microbial biofilms.
Sulfur-cycling in the deep subsurface Frasassi cave system has been the target of several previous investigations due to its unique biogeochemistry and relative accessibility to human exploration. The cave ecosystem is sustained by microbial chemosynthesis taking place near the surface of its perenially sulfidic and microoxic aquifer. Conspicuous white biofilms in the cave waters contain 20 to 80% elemental sulfur by mass. Thus its geochemical and microbiological features make Frasassi a promising system for investigating microbial interactions with S(0), an important solid-phase intermediate in the sulfur cycle. Enigmatic Epsilonproteobacteria from the globally distributed and largely uncultivated Sulfurovumales clade are major players in Frassasi biofilms. They are especially abundant in waters with high sulfide and low oxygen supply, conditions which should lead to S(0) accumulation due to limited availability of electron acceptors. Using Frasassi biofilms and enrichment cultures as a model system, investigators are combining metatranscriptomics, correlative electron microscopy, and geochemistry with field and laboratory experiments to develop new understanding of S(0)-accumulating biofilm communities. This research will improve understanding of (i) the microbial role in producing geologic S(0) deposits; (ii) mechanisms for microbial interactions with solid phase S(0); and (iii) the metabolic capabilities of currently uncultured Epsilonproteobacteria. The research supports the long-term goal of integrating genetic and geochemical understanding of modern and ancient S biogeochemistry.
Project funds provide for the mentoring of two graduate students and a postdoctoral scholar. The proposed project provides outstanding opportunities for outreach to the general public due to interest in caves and extreme microbes. Images and microbial cultures from the project will be utilized in two highly successful annual events: PSU Exploration Day and PSU Geosciences Dept. "Shake, Rattle, Rocks". These events reach more than 2000 K-12 students and parents last year and 150 third grade students. Project microslide cultures will be incorporated into a hands-on grade 6-12 teacher workshop and the College of Earth, Ocean and Environment's annual Coast Day on the Lewes campus, a 34-year tradition that now attracts thousands of community members. Results will also be shared as part of the DE Sea Grant At Sea newsletter, and Sea Talk radio segments on NPR.
