Geomicrobiological study of the Grotta dei Cervi, Porto Badisco, Italy

Speleothems (active stalactites, wall concretions), rock walls, ceiling, and soils from the galleries of Grotta dei Cervi, Porto Badisco, Italy, were sampled to investigate the culturable heterotrophic microbial communities present in this cave. Sampling was carried out in a transect of about 230 m from the entrance to the central gallery where numerous Gram-positive bacteria were isolated from all studied sites. Members of the genera Agromyces, Arthrobacter, Rhodococcus, and particularly Streptomyces, of the order Actinomycetales, are spread throughout the whole cave. The ability of actinomycetes, and particularly of Nocardiopsis; to colonize salt-stressed environments is favored by the presence of ectoine, a compatible solute for osmotic adaptation. Selected actinomycete isolates were tested for the formation of crystals. Strains from all tested genera, except isolates of Gordonia and Nocardia; produced vaterite and/or calcite. Production of Mg-calcite was restricted to strains of Brachybacterium; Rhodococcus; and Streptomyces; whereas struvite was only precipitated by an unidentified isolate. These findings indicate that actinomycetes may play a role in the formation of mineral deposits in caves.