A Window to the Subsurface: Microbial Diversity in Hot Springs of a Sulfidic Cave (Kaklik, Turkey)

Caves are windows to the extreme habitats of deep subsurface, and provide answers of unknowns about the underground life. Furthermore, sulfidic caves are important analogues for the early Earth environments, since some environmental conditions are common, such as high sulfur concentration, high temperature and oxygen-poor conditions. Kaklik Cave (Denizli, Turkey) with its travertine formation, carbonate- and sulfur-rich thermal springs, exhibits a unique ecosystem as a sulfidic cave. This study represents the first molecular survey of the microbial community in the Kaklik Cave, Turkey using high-throughput 16S rRNA gene amplicon sequencing analysis. An average of 859–2,416 operational taxonomic units per sample were observed including 25 bacterial phyla and 3 archaeal phyla. The bacterial diversity profiles were generally dominated by <i>Epsilonproteobacteria</i> and <i>Gammaproteobacteria</i>. At the carbonate-rich hot spring, that formed travertine structure, 9.7% of sequence reads affiliated with <i>Thiofaba</i> spp. In contrast, 38.74% of the total sequence reads at the sulfidic hot spring samples associated with the genus <i>Sulfurimonas</i> and <i>Sulfurovum</i>. In the archaeal community composition, <i>Thermoplasmata</i> was the most abundant group in all sampling areas. The 454-pyrotag results provide leads about ammonia-, nitrite- and sulfur-oxidation as well as sulfur-reduction, carbon dioxide fixation, and nitrogen fixation.