Spatial and temporal dynamics at an actively silicifying hydrothermal system

Abstract

Steep Cone Geyser is a unique geothermal feature in Yellowstone National Park (YNP), Wyoming, actively gushing silicon-rich fluids along outflow channels possessing living and actively silicifying microbial biomats. To assess the geomicrobial dynamics occurring temporally and spatially at Steep Cone, samples were collected at discrete locations along one of Steep Cone's outflow channels for both microbial community composition and aqueous geochemistry analysis during field campaigns in 2010, 2018, 2019, and 2020. Geochemical analysis characterized Steep Cone as an oligotrophic, surface boiling, silicious, alkaline-chloride thermal feature with consistent dissolved inorganic carbon and total sulfur concentrations down the outflow channel ranging from 4.59 ± 0.11 to 4.26 ± 0.07 mM and 189.7 ± 7.2 to 204.7 ± 3.55 μM, respectively. Furthermore, geochemistry remained relatively stable temporally with consistently detectable analytes displaying a relative standard deviation <32%. A thermal gradient decrease of ~55°C was observed from the sampled hydrothermal source to the end of the sampled outflow transect (90.34°C ± 3.38 to 35.06°C ± 7.24). The thermal gradient led to temperature-driven divergence and stratification of the microbial community along the outflow channel. The hyperthermophile Thermocrinis dominates the hydrothermal source biofilm community, and the thermophiles Meiothermus and Leptococcus dominate along the outflow before finally giving way to more diverse and even microbial communities at the end of the transect. Beyond the hydrothermal source, phototrophic taxa such as Leptococcus, Chloroflexus, and Chloracidobacterium act as primary producers for the system, supporting heterotrophic growth of taxa such as Raineya, Tepidimonas, and Meiothermus. Community dynamics illustrate large changes yearly driven by abundance shifts of the dominant taxa in the system. Results indicate Steep Cone possesses dynamic outflow microbial communities despite stable geochemistry. These findings improve our understanding of thermal geomicrobiological dynamics and inform how we can interpret the silicified rock record.

Keywords: Steep Cone Geyser; Yellowstone National Park; geochemistry; hydrothermal spring; microbial ecology; microbial mats; rock record; silicification.

Figure 1

(A) Overview of Yellowstone National Park, with Sentinel Meadow demarked by the red dot. Steep Cone Geyser is located within the Sentinel Meadow Hot Springs Group. Map was created in Mapbox (OpenStreetMap contributors, 2022). (B) Satellite image of the Sentinel Meadow Hot Springs Group with Steep Cone Geyser indicated by white arrow. (C) Image of Steep Cone Geyser from the South taken in August 2021. Black arrow indicates location of sampled outflow channel.

Figure 2

Sampled outflow path at Steep Cone Geyser for each sampling date.

Figure 3

Dot and box plot illustrating geochemical stability down the sampled transect across sampling dates of parameters of interest. Filled dot colors indicate sampling date while box colors indicate measured parameter. Dots are arranged from left to right, oldest to most recent samples for each distance, respectively. Dates are shown as year-month-day.

Figure 4

Dot and box plot of alpha diversity metrics down the sampled transect across the different sampling dates. Filled dot colors indicate sampling date. Dots are arranged from left to right, oldest to most recent samples for each distance, respectively. Top–Pielou’s evenness. Bottom–Estimated Richness using Breakaway. Error bars indicate the standard deviation calculated from biological replicates (n = 3). Dates are shown as year-month-day.

Figure 5

(A) Time-lag of Bray-Curtis distances of bacterial and archaeal communities from biofilm samples sampled at Steep Cone Geyser. Dots represent pairwise comparisons between a sample and the previous sampling date. (B) Distance-lag plot of Bray-Curtis distances of bacterial and archaeal communities from biofilm samples sampled at Steep Cone Geyser. Dots represent pairwise comparisons between two samples at different distances. Trend lines were determined using Geom_smooth in the R package stats: loess, with trends being fit using loess regression. Dates are shown as year-month-day.

Figure 6

Heat map of the top 15 taxa within the bacterial and archaeal communities from 16S rRNA gene sequencing. Taxa are named by phylum and genus or lowest classification. Values indicate the mean percent relative abundance. Data is faceted by sampling date and ordered down the sampling transect. Dates are shown as year-month-day.

Figure 7

16S rRNA gene mean percent relative abundances of genera (or lowest classification) determined to be statistically significant by SIMPER, DNA differential abundance analysis, and cDNA differential abundance analysis. Panels are faceted by distance (m) from the hydrothermal source. Circle sizes indicate mean percent relative abundance. Colors indicate general putative metabolisms associated with the most abundant ASVs in each genus according to NCBI BLAST searches and literature review. Dates are shown as year-month-day.