Acidic cave-wall biofilms located in the Frasassi Gorge, Italy, 2000, Vlasceanu L. , Sarbu S. M. , Engel A. S. , Kinkle B. K. ,

Acidic bioflms present on cave walls in the sulfidic region of the Frasassi Gorge, Italy, were investigated to determine their microbial composition and their potential role in cave formation and ecosystem functioning. All biofilm samples examined had pH values <1.0. Scanning electron microscopy of the biofilms revealed the presence of various filaments and rods associated in large clusters with mineral crystals. Qualitative energy-dispersive x-ray analysis was used to determine that the crystals present on the cave walls, associated with the microbial biofilm, were composed of calcium and barium sulfate. Ribosomal RNA-based methods to determine the microbial composition of these biofilms revealed the presence of at least two strains of potential acidophilic, sulfur-oxidizing bacteria, belonging to the genera Thiobacillus and Sulfobacillus. An acid producing strain of Thiobacillus sp. also was obtained in pure culture. Stable isotope ratio analysis of carbon and nitrogen showed that the wall biofilms are isotopically light, suggesting that in situ chemoautotrophic activity plays an important role in this subsurface ecosystem

Extremely acidic, pendulous cave wall biofilms from the Frasassi cave system, Italy, 2007, Jennifer L. Macalady, * Daniel S. Jones And Ezra H. Lyon

The sulfide-rich Frasassi cave system hosts an aphotic, subsurface microbial ecosystem including extremely acidic (pH 0?1), viscous biofilms (snottites) hanging from the cave walls. We investigated the diversity and population structure of snottites from three locations in the cave system using full cycle rRNA methods and culturing. The snottites were composed primarily of bacteria related to Acidithiobacillus species. Other populations present in the snottites included Thermoplasmata group archaea, bacteria related to Sulfobacillus, Acidimicrobium, and the proposed bacterial lineage TM6, protists, and filamentous fungi. Based on fluorescence in situ hybridization population counts, Acidithiobacillus are key members of the snottite communities, accompanied in some cases by smaller numbers of archaea related to Ferroplasma and other Thermoplasmata. Diversity estimates show that the Frasassi snottites are among the lowestdiversity natural microbial communities known, with one to six prokaryotic phylotypes observed depending on the sample. This study represents the first in-depth molecular survey of cave snottite microbial diversity and population structure, and contributes to understanding of rapid limestone dissolution and cave formation by microbially mediated sulfuric acid speleogenesis.