Microbially induced calcite precipitation in culture experiments: Possible origin for stalactites in Sahastradhara caves, Dehradun, India

摘要

Laboratory experiments involving calcium carbonate precipitation by bacteria isolated from stalactites sampled from three caves in Sahastradhara, Dehradun, India were conducted to determine whether geomicrobiolo-gical processes might be involved in stalactite forma-tion. Dominant bacteria inhabiting the Sahastradhara caves, confirmed by PCR amplification of 16S rRNA genes (16S rDNA), were Bacillus thuringiensis and Ba-cillus pumilis. Culture experiments confirmed their role in mineral precipitation.The ability of these bacteria to form CaCO3 crystals at different incubation tempe-ratures (5, 15, 25, 32° °C) indicated that 25° °C was optimum for calcite precipitation. The microbial community de-tected by DAPI staining showed a significant numberof cells (9-10 5 cells, g sed –1 ). Application of fluorescence in situ hybridization techniques, based on the presence of rRNA, shows a large number of active microbial cells (around 55% of the total cell number). The microbial community is dominatedby Eubacteria, mainly sul-phate-reducing bacteria (representing 10% of the to-tal microbial community), but Archaea were also present. Thin section petrography reveals that the sta-lactites consist of microcrystalline calcite, which occurs in chains probably attributed to bacterial precipita-tion. Thus, microbial activity and optimum temperature appear to be key factors promoting calcite precipita-tion and ultimately stalactite formation.