Evaluation of the bacterial diversity and current travertine strength of Kaklik cave in Honaz, Deni̇zli̇, Türki̇ye

In this study, the current travertine strength and bacterial diversity of Kaklık Cave was analyzed in Honaz, Türkiye. In this context, on-site strength tests were carried out using a needle penetrometer testing device and the samples were taken from each needle penetration test point for microorganism analyses. Overall, a total of 22 phyla were detected, and the Kaklık Cave displayed the highest abundance of Proteobacteria (78.60%), Actinobacteria (71.60%), Cyanobacteria (72.40%) and Bacteriodetes (11.10%). The relative abundance of archaeal was dominated by Euryarchaeota (24.70%), while the archaeal community exhibited a low abundance of Thaumarchaeota (1.40%). According to the mechanical parameters of current travertine deposition, the travertine deposits on slope surfaces of terraces (ATA2), the side wall of the cave (ATA6) and the terraced pool (ATA1) had high strength values. Also, the calcite composition of these travertines was verified by FESEM analysis. A total of 22, 31 and 33 families were characterized in ATA2, ATA1, and ATA6, respectively. Current travertine deposition on the ceiling environment (ATA3, ATA4 and ATA5) has the lowest strength and, the anhydrite (CaSO₄) and bassanite (CaSO₄.1/2H₂O) were detected in these travertines. The relative abundance of the Proteobacteria phylum in the high-strength and calcite-containing samples was 67.20%, 78.60% and 49.90% respectively. The microbial effect on the strength of these samples was clearly visible. Because the Proteobacteria phylum was absent from other samples containing calcium sulfate. This result can be interpreted the contribution of this phylum members to travertine strength and calcite mineralization, but further research needs to be done.