Chemolithotrophic, sulfur‐oxidizing bacteria from a marine, shallow hydrothermal vent of Vulcano (Italy)

Samples of water and sediment from a marine, shallow hydrothermal vent in Vulcano (Eolian Islands, Italy) were collected during an annual cycle of observations in order to study the occurrence and distribution of aerobic, chemolithotrophic, sulfur‐oxidizing bacteria that can grow with thiosulfate as sole energy source. Twenty‐five pure cultures were isolated, all of which were gram‐negative, rod‐shaped bacteria. They were tested for morphological, cultural, biochemical characteristics and for antibiotic sensitivity. The results were arranged in a data matrix and analyzed by Sokal and Michener's similarity coefficient and clusterized according to variance. Three distinct clusters, represented, respectively, by Thiobacilius‐like bacteria isolated directly from the vent‐water, Pseudomonas‐like heterotrophs from sediment in the immediate vicinity of the vent, and Thiobacterium‐like forms from both water and sediment samples, were distinguished according to their ecophysiological properties. The presence of obligate and facultative sulfur‐oxidizing bacteria in the sulfide‐containing hydrothermal water suggests that the rod‐shaped bacteria isolated from the site contribute to the oxidative phase of the sulfur‐cycle in this habitat. No filamentous forms were encountered. The chemosynthetic activity of sulfur‐oxidizing bacteria adds to the primary productivity of the photosynthetic microorganisms living in the water column and at the sediment surface.