Urease Activity and Deposition of Calcium Carbonate Layers on a 16th Century Mughal Monument

In the present study, bacterial populations capable of re-precipitating calcium carbonate were isolated from the exterior oozed-out calcite deposition of Salabat Khan Tomb, a 16th-century Mughal monument in western India. The deposits were analysed for identification of the materials that led to microbial induced calcite precipitation (MICP) on the surface of the monument. Quantification of MICP by XRD and visualization by SEM showed direct involvement of these isolates in the precipitation of calcium carbonate. FTIR spectra showed clear peaks for calcite along with a peak of methane probably due to dead bacterial cells. Preliminary examination, isolation and partial sequencing of 16S rRNA gene showed that the major microbial population participating in calcite precipitation is heterotrophic and includes mainly Bacillus sp., Arthobacter sp., Agromyces indicus and Aquamicrobium sp. In future, the process may be applied for the conservation of many limestone/ marble monuments using MICP in India and elsewhere.