Geomicrobiological description of two contemporary hydrothermal pools in Uzon Caldera, Kamchatka, Russia, as models for sulfur biogeochemistry
Burgess, Elizabeth Adrienne
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The combination of geological activity and geographic isolation make Uzon Caldera, Kamchatka, Russia, an ideal location for geomicrobiological research. Two hydrothermal pools, Arkashin Shurf (Arkashin) and Zavarzin Spring (Zavarzin), were selected for geochemical and microbiological characterization over multiple years and scales. Arkashin has high arsenic concentrations relative to Zavarzin, which has abundant elemental sulfur. Grab samples were analyzed from a geomicrobiological perspective, to describe community structure in each pool based on sequence, lipid and stable isotope data. Based on sequence analysis and lipid distribution, Arkashin was inhabited by Hydrogenobaculum-related primary producers. Other community members included Desulfurella-, “Sphingobacteria“- and Variovorax-related microorganisms. Zavarzin was dominated by Chloroflexus, and heterotrophic microorganisms, including some Crenarchaeota. The community in Zavarzin was more diverse than in Arkashin. Additionally, nearly 20% of the sequences from Arkashin and over 50% of the sequences from Zavarzin represented uncultured and unclassified microorganisms. Core sample analyses indicated that in each pool the microbiology and geochemistry changed with depth over visible changes in color and texture. Surface sub-samples were similar to the grab samples. Autotrophic surface communities were replaced with microorganisms dependent on heterotrophic inputs or reduced hydrothermal carbon as depth increased. In Arkashin, variation in color of strata was associated with varying concentrations of As and S. The highest As and S concentrations were associated with the lowest concentrations of phospholipid fatty acids (PLFA). In Zavarzin, the highest sulfur and PLFA concentrations were associated with fine-textured surface samples. The patterns observed indicate the biomass and composition of microbial communities can shift considerably in association with macroscopically visible changes in geochemical conditions. The described geomicrobiological data represent sulfur biogeochemistry under distinct geochemical conditions. As- and S-concentrations are linked significantly in Arkashin. The microorganisms in Arkashin play a role in As-S cycling, in part through sulfate-reduction. In Zavarzin, elemental sulfur is abundant and sulfide from sulfate-reduction is a minor component of total sulfur concentrations. Cataloging the diversity and distribution of microorganisms in contemporary thermal environments and elucidating some of the variations that occur with depth at the edges of hydrothermal pools add to knowledge about the intersection of geochemistry and microbiology.