Free living ciliated protists from the chemoautotrophic cave ecosystem of Frasassi (Italy)

This study provides the first report on a community of free-living ciliated protists from the chemoautotrophic cave ecosystem of Frasassi, Italy. This subterranean groundwater ecosystem represents a hotspot of biodiversity that still needs to be fully explored with particular reference to microbial eukaryotes such as protist ciliates. A total of 33 taxa of ciliates were identified along with one species each of flagellate, heliozoans and naked amoebae, from four main sampling sites, namely, Grotta Solfurea (GSO), Lago Verde (LVE), Ramo Solfureo (RSO), and Pozzo dei Cristalli (PDC). The last consists of small microhabitats/ponds presenting different chemical–physical and biological parameters, such as sulfur and nutrient contents and the presence of bacterial biofilms. Furthermore, an analysis of the cryptic ciliate species biosphere as a ‘seedbank’ of diversity against cave ecosystem disturbance was also performed. This study also highlights some peculiar adaptations of cave-dwelling ciliates not described in their noncave-dwelling conspecifics, such as the extreme photosensitivity of Urocentrum turbo, the cannibalism of Coleps hirtus, the variable number of thorns in Aspidisca species as a defensive response to predation, and the frequent reorganization of ciliary structures in Euplotes aediculatus. The 18S rDNA sequences were generated for five species and were compared with those of the noncave-dwelling conspecifics. Finally, our results shed light on the still largely unknown ciliate diversity in the chemosynthesis-based sulfidic groundwater ecosystem of Frasassi.