Ecological Succession of Sulfur-Oxidizing - and During Colonization of a Shallow-Water Gas Vent.

In this study, we integrated geochemical measurements, microbial diversity surveys and physiological characterization of laboratory strains to investigate substrate-attached filamentous microbial biofilms at Tor Caldara, a shallow-water gas vent in the Tyrrhenian Sea. At this site, the venting gases are mainly composed of CO and HS and the temperature at the emissions is the same as that of the surrounding water. To investigate the composition of the total and active fraction of the Tor Caldara biofilm communities, we collected established and newly formed filaments and we sequenced the 16S rRNA genes (DNA) and the 16S rRNA transcripts (cDNA). Chemoautotrophic sulfur-oxidizing members of the (predominantly ) dominate the active fraction of the established microbial filaments, while (predominantly spp.) are more prevalent in the young filaments. This indicates a succession of the two communities, possibly in response to age, sulfide and oxygen concentrations. Growth experiments with representative laboratory strains in sulfide gradient medium revealed that () grew closer to the sulfide source than sp. (). Overall, our findings show that sulfur-oxidizing are the dominant pioneer colonizers of the Tor Caldara biofilm communities and that become prevalent once the community is established. This succession pattern appears to be driven - among other factors - by the adaptation of - and to different sulfide concentrations.