Submarine caves, cavities and niches characterized by H2S-containing vents are to be considered as extreme ecosystems that are particularly interesting for their inhabiting microflora, as well as for the overall chemical, geological and biological parameters. The latter are usually represented by lower eukaryotic forms that are physically distributed following the in situ concentration and gradient of micronutrients, O2 and H2S, and also temperature and pH.

However the biota is primarily characterized by prokaryotes (both autotrophic and heterotrophic) adapted to anoxic condition and capable to form extensive biofilms on the rocky surfaces. The absence of solar irradiation, the chemo-physical traits and the fact that prokaryotes are the only living forms in specific areas of these cavities well justify the definition of such habitats as extreme.

Our research was mainly focused on the microbial ecology of still poorly characterized extreme environments such as hydrothermal and sulphidic submarine caves. These ecosystems are unique sites where the fundamentally biological role is played by prokaryotes due to the unsuitability of the environment for higher forms of life. Ecological and geological data are already available but very few insights as far as regard microbiology have so far been achieved in order to describe these fascinating habitats. The autoctonous thermophilic and thermotolerant microorganisms leaving in these caves may have interesting physiological traits and eventually may lead to potential application in biotechnological processes.

Microbial strains isolated from these habitats are taxonomically described by traditional and molecular techniques, including SDS-PAGE and DGGE; moreover hydrolytic enzymes as well as bioactive molecules including biosurfactants are screened and characterized.

Preliminary results were obtained by a multiphasic approach on water, sediment and biological samples collected from: 1) a Blue Hole located in the Indian Ocean, characterized by a large and H2S-enriched area, by a defined chemocline at about - 40m depth, and by a maximum depth of - 85m; 2) submarine caves with H2S-enriched freshwater springs, located along the Palinuro Cape in the South of Italy.

Samples were used to inoculate enrichment media in order to investigate the most representative morphologies. Further and extensive studies were carried out by SEM and TEM analyses to determine the structural features of bacteria. The physiological patterns of microbial populations along the water column and in the bottom sediments were described by the BIOLOG system. Moreover the molecular biodiversity of the ecosystem was investigated in order to describe the distribution of microorganisms and their putative physiological roles.