Comprehensive Analysis of Bacterial Diversity in the Salt Walls of Khewra Salt Mine Using 16S rRNA Gene Sequencing

The Khewra Salt Mine, also known as the source of Himalayan Pink Salt, is the second-largest salt mine in the world and a significant site for salt export. The mine's salt exhibits both amorphous and crystalline textures, with colors ranging from white to deep red, contributing to its distinctive pink hue. While previous research has extensively explored the mine's soil, plants, and brine samples, little attention has been given to the salt walls, which are a major tourist attraction. This study aimed to investigate the bacterial diversity within the salt walls from four distinct locations, including an under-construction area sampled for the first time. From these four collection points, seven samples were gathered, yielding 19 isolates cultured on 2% NaCl nutrient agar. Bacterial isolates from the under-construction area (US1-1, US1-2, US2-1, and US2-2) and the museum walls (MS1-1 and MS1-2) underwent further biochemical, antibiotic sensitivity, and salt requirement testing, followed by 16S rRNA sequencing. Biochemical assays identified these isolates as gram positive, catalase and oxidase positive rods. All isolates were sensitive to chloramphenicol (30μg/ml). Salt tolerance tests classified them as slightly halophilic, thriving at 2-4% NaCl concentrations. Molecular characterization revealed two strains from the under-construction area, US1-1 and US2-2, as uncultured Bacillus species and Bacillus thuringiensis, respectively, both with 94% sequence similarity. These sequences have been submitted to NCBI under accession numbers OQ295687 and OQ692139. The phylogenetic results show monophyletic associations between these two strains which could be due to their shared salt location and common ancestors. The sequences of US1-2, US2-1, and MS1-1 were 100% identical to Bacillus licheniformis, while MS1-2 matched Staphylococcus saprophyticus with 100% similarity. These sequences have been submitted to NCBI as OQ978592, OQ978561, OQ978562, and OQ978593, respectively. The results of this study point towards significant diversity of bacteria, slightly halophilic, cocci or bacillus shaped. These halophilic bacterial strains, possessing salt-tolerant genes, present the need for further identification of bacterial colonies in the mine and their evolutionary patterns, which could also help uncover the role these microbes play in the ecosystem of the salt mine. Additionally, they show promise for industrial enzyme production.