Microbiology of the stalactites from Grotta dei Cervi, Porto Badisco, Italy

Abstract

The Grotta del Cervi, the most important record of neolithic art in Italy, was discovered in 1970. The complex, hollowed in oligocene limestone, is the fossil track of an ancient underground river and contains many paintings. The cave presents considerable biological colonization, mainly in the excavated sediments of the entrance, as well as in the narrow passages to the halls. Most apparent bacteria are actinomycetes with visible white mycelia. In addition, along the corridors, black and white spots can be observed in different, places and particularly on the stalactites. This communication is focused on the microbiological study of the stalactites, representing the biological colonization of calcite materials in a hypogean environment. Several taxa of actinomycetes like Agromyces, Rhodococcus, Streptomyces, Amycolatopsis, Arthrobacter ilicis, Micrococcus luteus, some grampositive bacteria (Staphylococcus aureus, Paenibacillus sp.) and the gramnegative Variovorax paradoxes were identified by using morphological and chemotaxonomic methods. The isolates were tested for their capacity to produce calcite crystals and cooperative growth patterns in culture media. A molecular method for fingerprinting the microbial communities present in the stalactites, temperature gradient gel electrophoresis (TGGE), was also used. Partial 168 rDNA sequences of the isolates were amplified via PCR and compared to amplicons from bacterial DNA retrieved directly from the stalactite surface. In this way isolates could be identified as the predominant species on the stalactites if matching to the main bands of the TGGE fingerprint.