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By Matt Selensky
By Matt Selensky


Caves around the world harbor myriad microbiota that thrive in these dark, energy-starved subsurface environments. Located in central Kentucky, Mammoth Cave is the longest known cave system on Earth, encompassing over 580 km of mapped passages <ref name = SmithOlson2007>[https://scholarcommons.usf.edu/ijs/vol36/iss2/6/ Smith T, and Olson RA. (2007) A taxonomic survey of lamp flora (algae and cyanobacteria) in electrically lit passages within Mammoth Cave National Park, Kentucky. <i>International Journal of Speleology</i>, 36: 105-114.]</ref>. Although a cave-wide assessment of the its microbial ecology has never been performed, site-specific studies have elucidated intriguing characteristics of some Mammoth Cave microbes. Microbes found in the karstic sediments beneath two shallow water pools within Mammoth Cave were inferred to exhibit high diversity and total cell densities, reaching 1.4 × 10<sup>7</sup> cells per g wet sediment <ref name = RusterholtzMallory>[https://link.springer.com/article/10.1007/BF00170249 Rusterholtz KJ, and Mallory, LM. (1994) Density, activity, and diversity of bacteria indigenous to a karstic aquifer. <i>Microbial Ecology</i>, 28:79-99.]</ref>. Densities and activity of the chemolithoautotrophic Nitrobacter sp. were determined to be significantly higher in the caves relative to the surface. These nitrifying bacteria have been suggested to play a role in the formation of widespread saltpeter (KNO<sub>3</sub>) deposits found in the cave by oxidizing bat guano N or other surface-sourced N transported underground <ref name = FliermansSchmidt>[https://scholarcommons.usf.edu/ijs/vol9/iss1/1/ Fliermans CB, and Schmidt EL. (1977) Nitrobacter in Mammoth Cave. <i>International Journal of Speleology</i>, 9: 1-19.]</ref>. A seep rich in hydrocarbons and sulfide in Marianne’s Pass brings additional energy sources into the cave for microorganisms <ref name = Olson2013>[https://digitalcommons.wku.edu/cgi/viewcontent.cgi?article=1098&context=mc_reserch_symp Olson R. (2013). Potential effects of hydrogen sulfide and hydrocarbon seeps on Mammoth Cave ecosystems. <i>Mammoth Cave Research Symposia</i>, 28: 25-31.]</ref>. No published work appears to be available that describes sulfur-oxidizing bacteria in Mammoth Cave. However, a 16S rRNA gene clone survey of nearby Parker Cave demonstrates the widespread abundance of Thiothrix sp. living in the underground and euxinic Sulphur River <ref name = Angert1998>[https://pubs.geoscienceworld.org/msa/ammin/article-abstract/83/11-12_Part_2/1583/43432 Angert, ER, Northup, DE, Reysenbach, AL, Peek, AS, Goebel, BM, and Pace, NR. (1998) Molecular phylogenetic analysis of a bacterial community in Sulphur River, Parker Cave, Kentucky. <i>American Mineralogist</i>, 83: 1583-1592.]</ref>. Caves untouched by humans inherently lack light; however, artificial lamps placed in “show cave” sections of Mammoth sustain photosynthetic algal and cyanobacterial populations <. Such microorganisms are otherwise thought to be transient, washing into the cave either after heavy rains or via riverine input (Lavoie 2017). Fungi commonly colonize and decompose organic matter such as rat fecal pellets or dead crickets that occasionally litter the cave passages. The most notorious fungus that is found in Mammoth Cave is Pseudogymnoascus destructans, the causative agent of white nose syndrome in bats (Lavoie 2017). Other eukaryotes that are found in the cave include amoebas and other “protists” that tend to colonizing standing pools of water (Barr and Kuehne 1971). It is becoming clearer that the microbial communities of Mammoth and other caves are greatly involved in the N, S, and C cycles. We are only just beginning to gain a system-level understanding of shallow subsurface microbial ecology.
Caves around the world harbor myriad microbiota that thrive in these dark, energy-starved subsurface environments. Located in central Kentucky, Mammoth Cave is the longest known cave system on Earth, encompassing over 580 km of mapped passages<ref name = SmithOlson2007>[https://scholarcommons.usf.edu/ijs/vol36/iss2/6/ Smith T, and Olson RA. (2007) A taxonomic survey of lamp flora (algae and cyanobacteria) in electrically lit passages within Mammoth Cave National Park, Kentucky. <i>International Journal of Speleology</i>, 36: 105-114.]</ref>. Although a cave-wide assessment of the its microbial ecology has never been performed, site-specific studies have elucidated intriguing characteristics of some Mammoth Cave microbes. Microbes found in the karstic sediments beneath two shallow water pools within Mammoth Cave were inferred to exhibit high diversity and total cell densities, reaching 1.4 × 10<sup>7</sup> cells per g wet sediment<ref name = RusterholtzMallory>[https://link.springer.com/article/10.1007/BF00170249 Rusterholtz KJ, and Mallory, LM. (1994) Density, activity, and diversity of bacteria indigenous to a karstic aquifer. <i>Microbial Ecology</i>, 28:79-99.]</ref>. Densities and activity of the chemolithoautotrophic Nitrobacter sp. were determined to be significantly higher in the caves relative to the surface. These nitrifying bacteria have been suggested to play a role in the formation of widespread saltpeter (KNO<sub>3</sub>) deposits found in the cave by oxidizing bat guano N or other surface-sourced N transported underground<ref name = FliermansSchmidt>[https://scholarcommons.usf.edu/ijs/vol9/iss1/1/ Fliermans CB, and Schmidt EL. (1977) Nitrobacter in Mammoth Cave. <i>International Journal of Speleology</i>, 9: 1-19.]</ref>. A seep rich in hydrocarbons and sulfide in Marianne’s Pass brings additional energy sources into the cave for microorganisms<ref name = Olson2013>[https://digitalcommons.wku.edu/cgi/viewcontent.cgi?article=1098&context=mc_reserch_symp Olson R. (2013). Potential effects of hydrogen sulfide and hydrocarbon seeps on Mammoth Cave ecosystems. <i>Mammoth Cave Research Symposia</i>, 28: 25-31.]</ref>. No published work appears to be available that describes sulfur-oxidizing bacteria in Mammoth Cave. However, a 16S rRNA gene clone survey of nearby Parker Cave demonstrates the widespread abundance of Thiothrix sp. living in the underground and euxinic Sulphur River<ref name = Angert1998>[https://pubs.geoscienceworld.org/msa/ammin/article-abstract/83/11-12_Part_2/1583/43432 Angert, ER, Northup, DE, Reysenbach, AL, Peek, AS, Goebel, BM, and Pace, NR. (1998) Molecular phylogenetic analysis of a bacterial community in Sulphur River, Parker Cave, Kentucky. <i>American Mineralogist</i>, 83: 1583-1592.]</ref>. Caves untouched by humans inherently lack light; however, artificial lamps placed in “show cave” sections of Mammoth sustain photosynthetic algal and cyanobacterial populations<ref name = SmithOlson2007/>. Such microorganisms are otherwise thought to be transient, washing into the cave either after heavy rains or via riverine input<ref name = Lavoie2017>[https://link.springer.com/chapter/10.1007/978-3-319-53718-4_16 Lavoie, KH (2017) Mammoth Cave Microbiology. In: <i>Mammoth Cave: A Human and Natural History.</i> edited by HH Hobbs, RA Olson, EG Winkler, and DC Culvers, Springer International Publishing, Cham, pp 235-250.]</ref>. Fungi commonly colonize and decompose organic matter such as rat fecal pellets or dead crickets that occasionally litter the cave passages. The most notorious fungus that is found in Mammoth Cave is Pseudogymnoascus destructans, the causative agent of white nose syndrome in bats <ref name = Lavoie2017/>. Other eukaryotes that are found in the cave include amoebas and other “protists” that tend to colonizing standing pools of water <ref name = Lavoie2017/>. It is becoming clearer that the microbial communities of Mammoth and other caves are greatly involved in the N, S, and C cycles. We are only just beginning to gain a system-level understanding of shallow subsurface microbial ecology.


==Geology of Mammoth Cave==
==Geology of Mammoth Cave==

Revision as of 22:29, 2 June 2020

Overview

By Matt Selensky

Caves around the world harbor myriad microbiota that thrive in these dark, energy-starved subsurface environments. Located in central Kentucky, Mammoth Cave is the longest known cave system on Earth, encompassing over 580 km of mapped passages[1]. Although a cave-wide assessment of the its microbial ecology has never been performed, site-specific studies have elucidated intriguing characteristics of some Mammoth Cave microbes. Microbes found in the karstic sediments beneath two shallow water pools within Mammoth Cave were inferred to exhibit high diversity and total cell densities, reaching 1.4 × 107 cells per g wet sediment[2]. Densities and activity of the chemolithoautotrophic Nitrobacter sp. were determined to be significantly higher in the caves relative to the surface. These nitrifying bacteria have been suggested to play a role in the formation of widespread saltpeter (KNO3) deposits found in the cave by oxidizing bat guano N or other surface-sourced N transported underground[3]. A seep rich in hydrocarbons and sulfide in Marianne’s Pass brings additional energy sources into the cave for microorganisms[4]. No published work appears to be available that describes sulfur-oxidizing bacteria in Mammoth Cave. However, a 16S rRNA gene clone survey of nearby Parker Cave demonstrates the widespread abundance of Thiothrix sp. living in the underground and euxinic Sulphur River[5]. Caves untouched by humans inherently lack light; however, artificial lamps placed in “show cave” sections of Mammoth sustain photosynthetic algal and cyanobacterial populations[1]. Such microorganisms are otherwise thought to be transient, washing into the cave either after heavy rains or via riverine input[6]. Fungi commonly colonize and decompose organic matter such as rat fecal pellets or dead crickets that occasionally litter the cave passages. The most notorious fungus that is found in Mammoth Cave is Pseudogymnoascus destructans, the causative agent of white nose syndrome in bats [6]. Other eukaryotes that are found in the cave include amoebas and other “protists” that tend to colonizing standing pools of water [6]. It is becoming clearer that the microbial communities of Mammoth and other caves are greatly involved in the N, S, and C cycles. We are only just beginning to gain a system-level understanding of shallow subsurface microbial ecology.

Geology of Mammoth Cave

A cross section of the Mammoth Cave region, demonstrating the karst nature of the area. From Palmer (2017)[7].

Microbial Ecology of Mammoth Cave

Expansion topic 1-3

Key Microbial Players

Conclusion

References

  1. ↑ 1.0 1.1 Smith T, and Olson RA. (2007) A taxonomic survey of lamp flora (algae and cyanobacteria) in electrically lit passages within Mammoth Cave National Park, Kentucky. International Journal of Speleology, 36: 105-114.
  2. ↑ Rusterholtz KJ, and Mallory, LM. (1994) Density, activity, and diversity of bacteria indigenous to a karstic aquifer. Microbial Ecology, 28:79-99.
  3. ↑ Fliermans CB, and Schmidt EL. (1977) Nitrobacter in Mammoth Cave. International Journal of Speleology, 9: 1-19.
  4. ↑ Olson R. (2013). Potential effects of hydrogen sulfide and hydrocarbon seeps on Mammoth Cave ecosystems. Mammoth Cave Research Symposia, 28: 25-31.
  5. ↑ Angert, ER, Northup, DE, Reysenbach, AL, Peek, AS, Goebel, BM, and Pace, NR. (1998) Molecular phylogenetic analysis of a bacterial community in Sulphur River, Parker Cave, Kentucky. American Mineralogist, 83: 1583-1592.
  6. ↑ 6.0 6.1 6.2 Lavoie, KH (2017) Mammoth Cave Microbiology. In: Mammoth Cave: A Human and Natural History. edited by HH Hobbs, RA Olson, EG Winkler, and DC Culvers, Springer International Publishing, Cham, pp 235-250.
  7. ↑ Palmer, A. Mammoth Cave Geology. In: Mammoth Cave: A Human and Natural History. edited by HH Hobbs, RA Olson, EG Winkler, and DC Culvers, Springer International Publishing, Cham, pp 235-250.

Authored for Earth 373 Microbial Ecology, taught by Magdalena Osburn, 2020, NU Earth Page.

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