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 Epsilonproteobacteria and Gammaproteobacteria. At the carbonate-rich hot spring, that formed travertine structure, 9.7% of sequence reads affiliated with Thiofaba spp. In contrast, 38.74% of the total sequence reads at the sulfidic hot spring samples associated with the genus Sulfurimonas and Sulfurovum. In the archaeal community composition, Thermoplasmata 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.

洞穴是窥探深部地下极端生境的窗口，可为地下生命领域的未解之谜提供解答。此外，硫化物洞穴（sulfidic cave）是早期地球环境的重要类比模型，因其与早期地球环境存在诸多共通的环境特征，例如高硫浓度、高温及缺氧环境。位于土耳其代尼兹利的卡克立克洞穴（Kaklik Cave）拥有钙华（travertine）沉积地貌、富碳酸盐与富硫地热泉，作为硫化物洞穴拥有独特的生态系统。本研究首次利用高通量16S rRNA基因扩增子测序技术，对土耳其卡克立克洞穴内的微生物群落开展了分子生态学调查。每个样本平均可获得859~2416个操作分类单元（operational taxonomic units, OTU），涵盖25个细菌门与3个古菌门。细菌群落多样性结构总体上以ε-变形菌门（Epsilonproteobacteria）与γ-变形菌门（Gammaproteobacteria）占主导。在形成钙华构造的富碳酸盐热泉中，9.7%的测序读段（sequence reads）隶属于Thiofaba属（Thiofaba spp.）。与之相反，在硫化物热泉样本中，38.74%的总测序读段与硫单胞菌属（Sulfurimonas）及硫弯菌属（Sulfurovum）相关联。在古菌群落组成中，热原体纲（Thermoplasmata）是所有采样区域中丰度最高的类群。454焦磷酸测序读段（454-pyrotag）的分析结果揭示了氨氧化、亚硝酸盐氧化、硫氧化、硫还原、二氧化碳固定及固氮等潜在代谢通路。