Abstract
Geothermal environments are characterized by dynamic redox and temperature fluctuations inherited from the exposure of deeply-sourced, hot, reducing fluids to low-temperature, oxidizing ambient environments. To investigate whether microbial assemblages shifted in response to the changes of a redox state within acidic hot ponds, we collected three paired water and sediment samples from the Tatun Volcano Group, assessed metabolic roles of community members, and correlated their functional capabilities with geochemical factors along depth. Molecular analyses revealed that Sulfolobus spp., Acidianus spp. and Vulcanisaeta spp. capable of respiring elemental sulfur under oxic and/or low-oxygen conditions were the major archaeal members in planktonic communities. In contrast, obligate anaerobic Caldisphaera spp. dominated over others in bottomdwelling communities. Bacteria were only detected in one locality wherein the majority was affiliated with microaerophilic Hydrogenobaculum spp. Cluster analyses indicated that archaeal communities associated with sediments tended to cluster together and branch off those with water. In addition, the quantities of dissolved oxygen within the water column were substantially less than those in equilibrium with atmospheric oxygen, indicating a net oxygen consumption most likely catalyzed by microbial processes. These lines of evidence suggest that the segregation of planktonic from bottom-dwelling archaeal assemblages could be accounted for by the oxygen affinities inherited in individual archaeal members. Community assemblages in geothermal ecosystems would be often underrepresented without cautious sampling of both water and sediments.
Highlights
One distinctive feature in geothermal systems is that deeply-sourced, hot, reducing fluids discharged along fractures interact with cool, oxidized environments near the Earth’s surface, creating steep redox and temperature gradients
As most water bodies that could link to the interactions between subsurface and surface processes in the volcanically influenced area are restrained within individual hot ponds, little attention has been paid in investigating how the transition of a redox state driven by atmospheric oxygen controls the distribution of functionality and community assemblage in water columns and bottom sediments
Samples were collected from the Tatun Volcano Group (TVG) in northern Taiwan (Fig. 1) where the majority of rocks are andesite with a minor fraction of basalt (Chen and Wu 1971)
Summary
One distinctive feature in geothermal systems is that deeply-sourced, hot, reducing fluids discharged along fractures interact with cool, oxidized environments near the Earth’s surface, creating steep redox and temperature gradients. Thermophilic microbes exploit such chemical disequilibria to harvest metabolic energy in accordance with their intrinsic physiological capabilities (Meyer-Dombard et al 2005; Shock et al 2005; D’Imperio et al 2008). The factors that control the distribution, function and great effort has been dedicated to the isolation of novel thermophilic microorganisms and exploration of genetic diversity, the overall community function is not well constrained This is due to the fact that the inference of potential metabolism based on the sequence identity is often hindered by the great genetic distance from the known cultures (D’Imperio et al 2008; Perevalova et al 2008). As most water bodies that could link to the interactions between subsurface and surface processes in the volcanically influenced area are restrained within individual hot ponds, little attention has been paid in investigating how the transition of a redox state driven by atmospheric oxygen controls the distribution of functionality and community assemblage in water columns and bottom sediments
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