Microbial and Geochemical Variability in Sediments and Biofilms from Italian Gypsum Caves

In Europe, several gypsum karst regions occur among which the gypsum karsts located in Emilia-Romagna (UNESCO World Heritage Site since 2023) and Sicily are notable. The sediments, spring water microbial aggregates, and wall biofilms from three caves, Re Tiberio, Befana (Emilia-Romagna), and the Sicilian Santa Ninfa, have been studied from a microbiological and geochemical point of view. The samples of wall biofilms from gypsum caves were exclusively composed of Bacteria, while the sediments showed negligible abundances of Archaea. The two most abundant phyla in most sediments and biofilms were Actinomycetota and Pseudomonadota, whereas the microbial aggregates floating in the spring waters of Befana Cave showed a deviation from the typical abundance pattern as Campylobacterota replaced Actinomycetota, and the abundances of Bacteroidota and Desulfobacterota were high. The most abundant genus in the wall biofilms was Crossiella (Actinomycetota), but it was absent in the water aggregates collected in Befana Cave. The abundances of Crossiella in the cave sediments were very low. The dominant genera in Befana microbial aggregates showed different abundances and microbial composition when compared with the previously studied Frasassi and Fetida thermal sulfuric acid caves, located in Central and South Italy, respectively, suggesting that the community composition of the microbial aggregates is specific for each cave and related to the geochemistry of the sulfidic spring. Also, a different microbial community composition was found in Befana water aggregates with respect to the wall biofilms from Befana and Santa Ninfa caves. In the case of sediments, they significantly clustered together indicating that the microbial communities associated with sediments are similar, independently from the cave and possible other environmental parameters.