Microbial diversity at a shallow-water hydrothermal vent in the Tyrrhenian Sea

Despite their wide distribution, shallow-water hydrothermal vents have not been explored as extensively as their deep-sea counterparts. In this study we investigated the bacterial diversity of a shallow-water vent in Tor Caldara, Tyrrhenian Sea, Italy. This site is characterized by gas emissions connected with the activity of the Alban Hills. Prior studies showed that the gas emissions are composed mainly of CO₂, H₂S and CH₄ and a temperature anomaly is absent. The presence of conspicuous microbial filaments was observed in the proximity of the gaseous discharge. We carried out a 16S rRNA diversity analysis on the cDNA extracted from the filament sample to identify the active bacterial population. We obtained 3354 reads, which clustered in 420 unique OTUs. Our results show that Gammaproteobacteria dominated the population (65.20%) followed by Bacilli (29.10%). Thiotrichales constituted about 89% of the Gammaproteobacteria, probably due to the high abundance of sulfide. Staphylococcaceae accounted for 93% of the Bacilli. These findings suggest that autotrophy and heterotrophy may co-exist in this environment, which is influenced by the availability of terrigenous organic carbon. In conjunction with the 16S rRNA-based assessment of diversity, we enriched and isolated bacteria using different culture conditions. The isolates obtained were related to Marinobacter hydrocarbonoclasticus, Exiguobacterium aestuarii, Vibrio neocaledonicus, Thiomicrospira frisia and Sedimenticola selenatireducens and confirm and expand the diversity assessed through 16S rRNA analysis. This integration of culture-based and molecular analyses is providing qualitative and quantitative insight into the bacterial diversity at the shallow-water vent in Tor Caldara.