Life in restrictive environments and its interaction with biogeochemical cycling and mineralization are of paramount importance for understanding modern and ancient biogeochemical cycles, as well as similar interactions in bioengineered systems. Anaerobic, acidic, sulfidic, thermal springs (AASTS) represent potentially important settings for the earliest organisms on Earth, and the phototrophs inhabiting them (e.g., green sulfur bacteria) are excellent candidates for Earth's earliest photosynthesizers. If environments similar to AASTS were more widespread on the early Earth, the paleo-significance of thermophilic green sulfur bacteria for the global biogeochemical cycling of carbon and sulfur could be immense, and its implications to other element/metallic cycling and mineralization could also be very significant. Understanding phototrophic communities in AASTS could also have practical implications for waste treatment and energy production. The long-term goal of this incubation project is to model the linkage between (i) coupled biogeochemical cycling of sulfur, carbon and other nutrients and (ii) the metabolic activities of phototrophic communities in AASTS. The working hypothesis is that the existence and biodiversity of phototrophic communities are emergent properties of the coupled geochemical cycles in these environments. The cycling of carbon and sulfur in AASTS, along with other environmental parameters (e.g., pO2, pH, T), stabilizes the community composition, which in turn affects the distribution of carbon and sulfur compounds available to microbial communities downstream. This incubation project is specifically designed to establish the basic microbiological and biogeochemical characteristics of AASTS, and lay the foundation for quantitative modeling of the interactions between the two. Modeling of emergent properties of AASTS, specifically the non-linear interactions and feedback between the microbial community and the abiotic environment, requires absolute estimates of microbial diversity and quantification of fluxes of crucial life-sustaining components (e.g., sulfur and carbon). To accomplish this goal classical microbiological and 16S rRNA-based molecular techniques are being utilized to characterize the microbial composition of two recently discovered AASTS inhabited by thermophilic green sulfur bacteria in the Philippines. In parallel, field studies of sulfur, carbon and overall geochemical cycling in the same AASTS are being carried out, focusing on characterizing sulfur and carbon speciation, and using stable S, C and H isotope compositions of isolated species and select biomarkers to study the cycling of these components in these unique microbial habitats. Examining the isotope composition of inorganic sulfur and carbon species in the associated thermal waters will allow the assessment of the magnitude and sequence of S utilization and C fixation in these microbial communities. Finally, preliminary modeling of coupled S and C cycling in relation to the microbial distribution and structure in AASTS will be performed. The initial model will examine species fluxes, transport and transformation in the water column of AASTS, specifically focusing on the interaction between geochemical fluxes and microbial occurrence, composition and distribution. This project plans to foster interdisciplinary scientific research and education for undergraduates, graduate students, international collaborators and the public. Highlights include development of a web-based multi-level Virtual School on Biocomplexity in AASTS and workshops for the Philippine and US collaborators on the same topic. Given the global recognition of the need to preserve and understand unique microbial systems for fundamental and biotechnical reasons, plans are incorporated for strong international partnerships in research and education.