Calcium carbonate precipitation by cave bacteria isolated from Kashmir Cave, Khyber Pakhtunkhwa, Pakistan

The participation of numerous physicochemical and biological functions maintains the evolution and expansion of the remarkable nature. Due to its vast applicability in several engineering disciplines, naturally occurring bio-mineralization or microbially induced calcium carbonate (MICP) precipitation is attracting more interest. Cave bacteria contribute to the precipitation of calcium carbonate (CaCO₃ ). In the present study, soil sediments were collected from Kashmir cave, KPK, Pakistan, and plated on B4 specific nutrients limited medium for bacterial isolation and the viable bacterial count was calculated. Three bacterial strains named GSN-11, TFSN-14, and TFSN-15 were capable of precipitating CaCO₃ . These bacterial isolates were identified through 16S rRNA gene sequencing and strain GSN-11 was identified as Bacillus toyonensis, TFSN-14 as Paracoccus limosus and TFSN-15 as Brevundimonas diminuta. Enhanced CaCO₃ precipitation potential of these bacteria strains was observed at 25°C and pH 5. The precipitated CaCO₃ was confirmed by scanning electron microscopy, X-ray powder diffraction, and Fourier transform infra-red spectroscopy. The findings showed that the precipitates were dominated by calcite, aragonite, and nanosize vaterite. Current research suggests that precipitation of CaCO₃ by proteolytic cave bacteria is widespread in Kashmir cave and these bacterial communities can actively contribute to the formation of CaCO₃ by enhancing the pH of the microenvironment. RESEARCH HIGHLIGHTS: Kashmir cave inhabit potentially active bacteria in terms of biogeochemical processes. Cave bacteria significantly precipitated CaCO₃ . Calcite, aragonite, and nanosize vaterite were dominant in precipitates.