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Front. Microbiol. | doi: 10.3389/fmicb.2018.02823

High microbial diversity despite extremely low biomass in a deep karst aquifer.

 Olivia S. Hershey1,  Jens Kallmeyer2, Andrew Wallace3, Michael D. Barton4 and  Hazel Barton1*
  • 1University of Akron, United States
  • 2Helmholtz Center Potsdam German Geophysical Research Center (GFZ), Helmholtz Association of German Research Centers (HZ), Germany
  • 3Northern Kentucky University, United States
  • 4Joint Genome Institute (JGI), United States

Despite the importance of karst aquifers as a source of drinking water, little is known about the role of microorganisms in maintaining the quality of this water. One of the limitations in exploring the microbiology of these environments is access, which is usually limited to wells and surface springs. In this study, we compared the microbiology of the Madison karst aquifer sampled via the potentiometric lakes of Wind Cave with surface sampling wells and a spring. Our data indicated that only the Streeter Well (STR), which is drilled into the same hydrogeologic domain as the Wind Cave Lakes (WCL), allowed access to water with the same low biomass (1.56 - 9.25 x 103 cells mL-1). Filtration of ~300 L of water from both of these sites through a 0.2 μm filter allowed the collection of sufficient cells for DNA extraction, PCR amplification of 16S rRNA gene sequences, and identification through pyrosequencing. The results indicated that bacteria (with limited archaea and no detectable eukaryotic organisms) dominated both water samples; however, there were significant taxonomic differences in the bacterial populations of the samples. The STR sample was dominated by a single phylotype within the Gammaproteobacteria (Order Acidithiobacillales), which dramatically reduced the overall diversity and species richness of the population. In WCL, despite less organic carbon, the bacterial population was significantly more diverse, including significant contributions from the Gammaproteobacteria, Firmicutes, Chloroflexi, Actinobacteria, Plantomycetes, Fusobacter and Omnitrophica phyla. Comparisons with similar oligotrophic environments suggest that karst aquifers have a greater species richness than comparable surface environs. These data also demonstrate that Wind Cave provides a unique opportunity to sample a deep, subterranean aquifer directly, and that the microbiology of such aquifers may be more complex than previously anticipated.

Keywords: karst, cave, freshwater, aquifer, Ultra-oligotrophic, Bacteria

Received: 26 Jul 2018; Accepted: 02 Nov 2018.

Edited by:

D'Arcy R. Meyer-Dombard, University of Illinois at Chicago, United States

Reviewed by:

Veljo Kisand, University of Tartu, Estonia
Daniel Colman, Montana State University, United States  

Copyright: © 2018 Hershey, Kallmeyer, Wallace, Barton and Barton. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Hazel Barton, University of Akron, Akron, 44325, Ohio, United States, bartonh@uakron.edu