Snottites
Introduction
Caves are human-accessible, underground natural spaces that extend beyond areas where sunlight can reach (Northup). These caverns are commonly formed within limestone or other calcareous rocks, but can emerge in basaltic rock, gypsum, granite, talus, quartzite, ice, and sandstone. They can be developed in one of three ways: classical limestone formation, lava tube formation, and sulfuric-acid driven speleogenesis. In classical limestone caves, water absorbs CO2 as it runs through the soil zone and forms a dilute solution of carbonic acid. Limestone is exposed to this water at the water table, where the calcium carbonate from the bedrock is dissolved, forming caverns. Lava tube formation, on the other hand, involves lava flow from an active volcano. The lava on the surface cools quickly, creating a solid encasement. Once the lava below drains and the eruption ceases, an empty cavern is left behind. Finally, in sulfuric-acid driven speleogenesis, hydrogen sulfide rises in crevices in the earth until it reaches an oxygenated zone. Sulfuric acid then dissolves the limestone.
Crystals, sulfur mineral deposits, and a variety of microbial biofilms can be found in these latter, sulfide-rich cave systems. These formations include moonmilk, microbial mats in cave streams, biovermiculations, stream sediments, wall crusts and films, and snottites. Snottites have captivated cave-goers and scientists alike since the earliest publication on cave microbes by Hoeg in 1946 (Northup). These biofilms cover the walls with a thick snot-like film, from which they derive their particularly appropriate name. A variety of cave systems, the Frasassi caves in Italy, the Cueva de Villa Luz in Tabasco, Mexico (Cave (Cueva de Villa Luz)), Grotta di Rio Garrago, and Cueva Luna Azufre, are sites of intense research for these microbial populations, but these are not the only caves with these formations. The snottites are exceptionally acidic, with pH 0-2. The composition of these snottites is still unknown, they have been found include to Sulfobacillus, Aciditiobacillus, Halothiobacillus, and Acidimicrobium species, protists, filamentous fungi, and a proposed bacterial lineage TM6.
Scientists traditionally originally believed that most sulfide-rich limestone caves were formed by carbonic acid dissolution of carbonate, but recent studies now support the theory that these bacterial species have a large impact on the formation of limestone bedrock caves in the presence of sulfide-rich waters. Sulfur acid-driven speleogenesis, driven by circulation of sulfidic waters through limestone, is the common mechanism proposed by many studies. Originally this process was thought to occur through nonbiological processes, but this belief has since been modified by the discovery of the impact of bacteria, specifically Thiobacillus species, in these environments. Theses sulfur-oxidizing bacteria are now recognized as essential components in the disintegration of limestone and in the creation and expansion of caves.
These microorganisms also serve a function in the ecosystems of caves. Caves are fairly mild and predictable environments, but contain very limited resources due to the lack of sunlight necessary to support primary production of organic materials. Caves have three zones: the “entrance”, “twilight”, and “deep cave” zones. In the entrance zone, the outside environment has a large impact on the conditions. At the increased depth of the twilight zone cave conditions begin to overpower outside conditions and light becomes extremely limited. At the deep cave level, no light can penetrate, the humidity is high, and the temperature reaches MAST (Mean Annual Surface Temperature) for the region. (Northup) At this cave depth, no phototrophic material can grow, so organic material must be produced by some other means. Microorganisms are prime candidates for this role.
br>Introduce the overall topic of your paper. What microorganisms are of interest? Habitat? Applications for medicine and/or environment?
Role in Cave Formation
Include some current research in each topic, with at least one figure showing data.
Species identified
Include some current research in each topic, with at least one figure showing data.
Environmental Characteristics
Include some current research in each topic, with at least one figure showing data.
Conclusion
Overall paper length should be 3,000 words, with at least 3 figures.
References
Galdenzi, S et al. “Sulfidic Ground-Water Chemistry in the Frasassi Caves, Italy”. Journal of Cave and Karst Studies. 2008. Volume 70(2). p. 94-107.
Hose, L. D., and J. A. Pisarowicz. “Cueva de Villa Luz, Tabasco, Mexico: Reconnaissance study of an active sulfur spring cave and ecosystem”. Journal of Cave and Karst Studies. 1999. Volume 61(1). p. 13-21.
Jones, D, E. Lyon, and J. Macalady. “Geomicrobiology of Biovermiculations from the Frasassi Cave System, Italy”. Journal of Cave and Karst Studies. 2008. Volume 70(2). p. 76-93.
Macalady, J et al. “Dominant Microbial Populations in Limestone-Corroding Stream Biofilms, Frasassi Cave System, Italy”. Applied and Environmental Microbiology. 2006. Volume 72(8). p. 5596-5609.
Macalady, J. L., D. S. Jones, and E. H. Lyon. “Extremely acidic, pendulous cave wall biofilms from the Frasassi cave system, Italy”. Environmental Microbiology. 2007. Volume 9(6). p. 1402-1414.
Mulec, Janez. “Microorganisms in hypogean: examples from Slovenian karst caves”. Acta Carologica. 2008. Volume 37(1). p. 153-160.
Northup, D. E., and K. H. Lavoie. “Geomicrobiology of caves: a review”. Geomicrobiology Journal. 2001. Volume 18. p. 199-222.
Vlasceanu, L, S. M. Sarbu, A. S. Engel, and B. K. Kinkle. “Acidic cave-wall biofilms located in the Frasassi Gorge, Italy”. Geomicrobiology Journal. 2000. Volume 17. p. 125-139.
Edited by Paige Roberts, student of Joan Slonczewski for BIOL 238 Microbiology, 2009, Kenyon College.
