Mineralogy and Microbiology of Cave Vermiculations from Frasassi, Italy PDF Download

Author: Shavonne Morin
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Languages : en
Pages : 0

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Book Description
Vermiculations are microbe-packed organic-rich sediment deposits that form in striking "worm-like" anastomosing patterns on cave walls. Vermiculations occur in a wide variety of morphologies and colors and share some characteristics with soil since they are made up of clay-sized mineral particles associated with both humified and labile organic matter. They are a common feature across caves of many different environments but are particularly extensive in the Frasassi cave system where they were first described (Bini et al., 1978). This study investigated the mineral composition of 30 unvermiculated and 5 unvermiculated samples from the Frassasi cave walls. The color of vermiculations was investigated with the Munsell color system. Fifteen samples were then analyzed for their bacterial, archaeal, and fungal community compositions. Lastly, multivariate analysis was conducted on each of the datasets to evaluate any trends. The 30 vermiculated and 5 unvermiculated samples had mineralogy dominated by the presence of quartz, calcite, gypsum, and muscovite. Two additional minerals, baryte and microcline, were identified in minor amounts. Principal components analysis (PCA) revealed that higher elevation samples have a tendency to contain more calcite. Munsell color analysis revealed that vermiculations are most commonly a light grayish brown color (10YR 6/4). PCA ordination showed that increasing gypsum content is correlated with an increasing Munsell color value, associated with lighter colors. Gypsum was only found in samples less than five meters above the water table, as gypsum occurring at higher elevations is likely to have been redissolved by dripping water. Prokaryotic microbial communities were dominated by putative lithoautotrophs. Sequences affiliated with six genera, all bacterial, were particularly dominant among the samples: Thioprofundum, Acidiferrobacter, Nitrospira, Thiobacillus, Gaiella, and Gemmata. Close relatives of known sulfur-oxidizing species dominated the communities, and close relatives of known ammonia-oxidizing, nitrite-oxidizing, nitrate-reducing, and methanotrophic bacteria and archaea were also present. Samples at increasing heights above the water table contain higher amounts of Thioprofundum. Bacterial and archaeal communities show that vermiculations may play an important role in the cave sulfur and nitrogen cycles. The fungal community of vermiculations was dominated by the genus Mortierella, a common soil saprotroph. Fungal community composition is highly variable across samples. Notable abundant genera include Cladosporium, Mrakia, Tarzetta, and Penicilium as they are known to prefer the moderate to cool climates of the Frasassi cave system (Thomas-Hall et al., 2010; Kirk et al., 2008; Samson et al., 2004). Fungal communities contain relatives of common soil fungi, suggesting either that the communities are influenced by the fungal community in the soil above, or that related fungi are adapted to the soil-like habitat in vermiculations. Understanding vermiculation mineralogy allows for a greater understanding of how microorganisms create macrostructures via the incorporation of local sediments. Vermiculations have the potential to be a visual biosignature for subsurface life on off-planet caves.