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Isotope geochemistry of the Movile Cave aquifer system : a southern source of water and reduced sulfur /
Abstract
Thesis (M.S.)--University of Cincinnati, 1998. Includes bibliographical references (leaves 107-113). Includes abstract.
... The 0.3-3 mm thick microbial mats float on the water in air pockets of the submerged passages. The atmosphere in the air bells contains 7-10% O 2 , 2-3.5% CO 2 , 1-2% CH 4 , with trace H 2 S, and only a few millimeters of the cave water below the mats are oxygenated (Sarbu et al., 1996;Popa, 1997;Badescu, 1998). Although the microbial communities from Movile Cave have been of interest for more than a decade (e.g., Sarbu et al., 1996;Vlasceanu et al., 1997;Rohwerder et al., 2003) and various metabolic guilds have been investigated (Hutchens et al., 2004), there has not been a concerted effort to describe the overall microbial diversity of the mats using a 16S rRNA framework. ...
Although ecosystems thriving in the absence of photosynthetic processes are no longer considered unique phenomena, we haveyet to understand how these ecosystems are energetically sustained via chemosynthesis. Ecosystem energetics were measuredin microbial mats from active sulfidic caves (Movile Cave, Romania; Frasassi Caves, Italy; Lower Kane Cave, Wyoming, USA; andCesspool Cave, Virginia, USA) using radiotracer techniques. We also estimated bacterial diversity using 16S rRNA sequences torelate the productivity measurements to the composition of the microbial communities. All of the microbial communities investigatedwere dominated by chemolithoautotrophic productivity, with the highest rates from Movile Cave at 281 g C/m2/yr. Heterotrophicproductivities were at least one order of magnitude less than autotrophy from all of the caves. We generated 414 new 16S rRNAgene sequences that represented 173 operational taxonomic units (OTUs) with 99% sequence similarity. Although 13% of theseOTUs were found in more than one cave, the compositions of each community were significantly different from each other (P≤0.001).Autotrophic productivity was positively correlated with overall species richness and with the number of bacterial OTUs affiliated withthe Epsilonproteobacteria, a group known for sulfur cycling and chemolithoautotrophy. Higher rates of autotrophy were also stronglypositively correlated to available metabolic energy sources, and specifically to dissolved sulfide concentrations. The relationship ofautotrophic productivity and heterotrophic cycling rates to bacterial species richness can significantly impact the diversity of highertrophic levels in chemolithoautotrophically-based cave ecosystems, with the systems possessing the highest productivity supportingabundant and diverse macro-invertebrate communities.
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