Abstract
Biogeochemical cycling of sulfur is relatively understudied in terrestrial environments compared to marine environments. However, the comparative ease of access, observation, and sampling of terrestrial settings can expand our understanding of organisms and processes important in the modern sulfur cycle. Furthermore, these sites may allow for the discovery of useful process analogs for ancient sulfur-metabolizing microbial communities at times in Earth’s past when atmospheric O2 concentrations were lower and sulfide was more prevalent in Earth surface environments. We identified a new site at Santa Paula Creek (SPC) in Ventura County, CA—a remarkable freshwater, gravel-bedded mountain stream charged with a range of oxidized and reduced sulfur species and heavy hydrocarbons from the emergence of subsurface fluids within the underlying sulfur- and organic-rich Miocene-age Monterey Formation. SPC hosts a suite of morphologically distinct microbial biofacies that form in association with the naturally occurring hydrocarbon seeps and sulfur springs. We characterized the geology, stream geochemistry, and microbial facies and diversity of the Santa Paula Creek ecosystem. Using geochemical analyses and 16S rRNA gene sequencing, we found that SPC supports a dynamic sulfur cycle that is largely driven by sulfide-oxidizing microbial taxa, with contributions from smaller populations of sulfate-reducing and sulfur-disproportionating taxa. This preliminary characterization of SPC revealed an intriguing site in which to study geological and geochemical controls on microbial community composition and to expand our understanding of sulfur cycling in terrestrial environments.
Abstract
Chemotrophic microorganisms gain energy for cellular functions by catalyzing oxidation‐reduction (redox) reactions that are out of equilibrium. Calculations of the Gibbs energy (∆Gr) can identify whether a reaction is thermodynamically favorable and quantify the accompanying energy yield at the temperature, pressure, and chemical composition in the system of interest. Based on carefully calculated values of ∆Gr, we predict a novel microbial metabolism—sulfur comproportionation (3H2S + SO42‐ + 2H+ ⇌ 4S0 + 4H2O). We show that at elevated concentrations of sulfide and sulfate in acidic environments over a broad temperature range, this putative metabolism can be exergonic (∆Gr<0), yielding ~30‐50 kJ/mol. We suggest that this may be sufficient energy to support a chemolithotrophic metabolism currently missing from the literature. Other versions of this metabolism, comproportionation to thiosulfate (H2S + SO42‐ ⇌ S2O32‐ + H2O) and to sulfite (H2S + 3SO42‐ ⇌ 4SO32‐ + 2H+), are only moderately exergonic or endergonic even at ideal geochemical conditions. Natural and impacted environments, including sulfidic karst systems, shallow‐sea hydrothermal vents, sites of acid mine drainage, and acid‐sulfate crater lakes, may be ideal hunting grounds for finding microbial sulfur comproportionators.
Abstract
Prokaryotic life has dominated most of the evolutionary history of our planet, evolving to occupy virtually all available environmental niches. Extremophiles, especially those thriving under multiple extremes, represent a key area of research for multiple disciplines, spanning from the study of adaptations to harsh conditions, to the biogeochemical cycling of elements. Extremophile research also has implications for origin of life studies and the search for life on other planetary and celestial bodies. In this article, we will review the current state of knowledge for the biospace in which life operates on Earth and will discuss it in a planetary context, highlighting knowledge gaps and areas of opportunity.
Abstract
With the generous support from the C-DEBI research exchange grant, I had the opportunity to participate in the International Geobiology Course, which was directed by Drs. Alex Session, Victoria Orphan, and Woody Fischer from the California Institute of Technology (in conjuction with the Agouron Institute, Simons Foundation and USC Wrigley Institute). In this course, I traveled with 15 other geobiology graduate students to Mono Lake, Naples Beach, and Santa Paula Creek where we learned how to collect biological and geochemical samples for analysis at Caltech. At Caltech, I learned cutting-edge laboratory techniques including SEM, stable isotope analysis, SIMS, and NanoSIMS. Finally, on Catalina Island, I worked with three other students on a project that investigated the sulfur cycle at Santa Paula Creek, which we will be presenting at the AGU annual meeting. Participating in this course provided not only comprehensive training in geobiology, but also a unique opportunity to network with established scientists and peers that I hope to collaborate with in the future. Since returning from this course, I have a stronger understanding of current interdisciplinary topics and questions in geobiology and the ways in which these ideas are addressed. I look forward to continuing to pursue research in geobiology and collaborating with the scientists I have connected with on this course.