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

Acidic bioflms present on cave walls in the sulfidic region of the Frasassi Gorge, Italy, were investigated to determine their microbial composition a nd their potential role in cave formation and ecosystem functioning. All bi ofilm 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-r ay analysis was used to determine that the crystals present on the cave wal ls, associated with the microbial biofilm, were composed of calcium and bar ium sulfate. Ribosomal RNA-based methods to determine the microbial composi tion of these biofilms revealed the presence of at least two strains of pot ential acidophilic, sulfur-oxidizing bacteria, belonging to the genera Thio bacillus and Sulfobacillus. An acid producing strain of Thiobacillus sp. al so was obtained in pure culture. Stable isotope ratio analysis of carbon an d nitrogen showed that the wall biofilms are isotopically light, suggesting that in situ chemoautotrophic activity plays an important role in this sub surface ecosystem.