Fungi inhabiting the microbialites of the alkaline lake in Pantelleria island (Italy): biodiversity across a submerged-emerged transect

The Bagno dell'Acqua alkaline lake in Pantelleria island, Italy, is characterized by CO2 emissions, alkaline waters with a pH of around 9, and strongly oxidizing conditions. The lake is home to actively growing microbialites rich in calcium carbonates and silica precipitates. The lake's sediments are dominated by Mg-smectite clays associated with K-feldspars and Ca-carbonates, and the presence of volcanic glass and minor phases like pyroxene and hematite has been observed. These extreme conditions impact the fungal diversity in the sediments and microbialites, offering insights into the adaptation of fungi to high pH values. A transect from the lake's margins to the line of vegetation was used as a sampling scheme to evaluate the impact of alkaline water on the fungal communities in the first 5 cm of sediment depth. High-throughput sequencing of the fungal internal transcribed spacer 2 (ITS2) molecular marker region, performed with the Illumina NovaSeq PE250, was applied to compare the alpha and beta biodiversity of the microbialite samples. Fungi were also isolated using classic culturing and the lake sediment as the culture medium. The strains isolated from the submerged sediments are entirely different from those obtained from the microbialites that were exposed to the air at the time of sampling, suggesting the overlap of two distinct fungal communities, those that colonize the surfaced material (airborne species) and instead the species that seem to inhabit the submerged plant material. The latter appeared poorly pigmented compared to the species isolated from the vegetation line.