Acidic cave-wall biofilms located in the Frasassi Gorge, Italy, 2000,
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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

Iron oxide-rich filaments: Possible fossil bacteria in Lechuguilla Cave, New Mexico, 2001,
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Provencio P. P. , Polyak V. J. ,

Reddish filaments in two fragments of unusual iron oxide bearing stalactites, 'the Rusticles' from Lechuguilla Cave, New Mexico, are found only within the central canals of the Rusticles. The curved, helical, and/or vibrioidal filaments vary from 1 to 6 mum in outer diameter and 10 to >50 mum in length. SEM and TEM show the filaments have 0.5-mum diameter central tubes, with goethite crystals radiating outwardly along their lengths. The diameter of the central tubes is consistent with the diameter of many iron-oxidizing filamentous bacteria. Although most iron oxide depositing bacteria do not deposit well-crystallized radiating goethite, we propose thick hydrous iron oxide was slowly crystallized from amorphous material to goethite, in place, over a relatively long period of time. From the gross morphology and the particular setting, we suggest this represents an occurrence of fossilized, acidophilic iron-oxidizing bacteria