EXTREMELY ACIDOPHILIC MICROORGANISMS ACROSS PH AND TEMPERATURE GRADIENTS IN VALLES CALDERA NATIONAL PRESERVE

The Valles Caldera is an active geothermal system located near Jemez Springs in Northern New Mexico. Within the Caldera and across the Jemez Mountains, volcanic gasses containing H2S and CO2 interact with the surface waters, creating volcanically-influenced, chemical energy-rich pools and streams. In this study, we describe geochemical controls on acidophilic, sulfur-cycling microbial communities from two regions along the western margin of the Caldera: the highly acidic and sulfidic Sulfur Springs area, and artificial and natural acidic lakes and streams in Alamo Canyon. Volcanically influenced waters in these areas have pH values ranging from 1.16 to 5.72, sulfide concentrations ranging from 1.1 µM to 966.4 µM, and temperature measuring 9.1℃ to 54.9℃. We used culture independent analysis to explore if and how the strong gradients in pH, temperature and sulfide influence the extremophilic microbial communities’ abundance, diversity and composition. Here we report results from 16S rRNA gene “amplicon” sequencing, fluorescence in situ hybridization (FISH), and cell counts. Preliminary non-metric dimensional scaling analysis of rRNA gene libraries showed that temperature and pH are both significantly correlated with community composition, indicating that these environmental parameters could be driving microbial diversity across the region overall. Cell counting showed total microbial abundance as high as 3.15 𝗑 109 cells/gram sediment, but there was not a clear pattern in cell abundance versus any measured environmental parameter. These results indicate that pH, temperature, and sulfide concentration are controlling microbial diversity and composition, independent of microbial abundance. FISH confirmed rRNA gene library results, showing that Acidithiobacillus to be one of the most abundant genera across the most acidic samples. Amplicon libraries showed that other chemolithotrophic sulfur oxidizing acidophilic bacteria, such as Sulfuriferula, Thiomonas and Acidiphilium, dominate less acidic, low temperature samples. We will also continue systematic sampling efforts and measurement of geochemical parameters conducted over summer 2023 in order to evaluate microbial resilience as geochemical conditions change across this dynamic landscape.