Yellowstone Biofilm Geochemistry Analysis

Biomass from eight sites in YNP (Table S1A) were collected and processed as previously described (11 (link)). Briefly, samples were collected in 2017 using sterilized forceps or pliers and stored on dry ice in transit. DNA (250 mg) was extracted using the Qiagen Powersoil kit following the manufacturer’s protocol. Sulfide, Fe²⁺, and dissolved silica were measured onsite using a DR1900 portable spectrophotometer (Hach Company, Loveland, CO). Water samples were filtered through 0.2-μm polyethersulfone syringe filters (VWR International, Radnor, PA, USA) and analyzed for dissolved inorganic carbon (DIC) concentration, δ¹³C and δ¹⁵N as described previously (25 (link)). Field blanks composed of filtered 18.2 MΩ/cm deionized water, transported to the field in 1-L Nalgene bottles, were processed on site using the equipment and techniques previously described (11 (link)). To determine site dissimilarity, we generated a principal-component analysis using sample water geochemistry, geographic location, and biofilm isotopic data (Table S1A) (11 (link)). We converted all raw data to Z-scores (z = x – mean(x)/sd(x)), and principal components of transformed data were generated using the rda function in vegan (69 ) and plotted using ggplot2.