Analysis and optimization of process parameters for in vitro biomineralization of CaCO(3) by Klebsiella pneumoniae, isolated from a stalactite from the Sahastradhara cave

Stalactite is a speleothem which is usually made up of calcium carbonate crystals. In the present study the bacterial isolates, recovered from a stalactite from the Sahastradhara cave, were screened for their ability to precipitate calcium carbonate in order to understand whether mineralization in caves is a biogenic process or not. Five bacterial isolates were found to precipitate calcium carbonate via urease. The most potent bacterial isolate was identified as Klebsiella pneumoniae (accession number MG946801) based on 16S rDNA sequencing. The optimized conditions, for calcium carbonate precipitation, determined by response surface methodology using CCD were found to be: 1.5625% urea, 19.98% inoculum level, 6.98 pH and 38 h 24 min. The morphology and crystalline structure of the precipitated mineral were revealed by SEM. EDX analysis confirmed the presence of carbon, oxygen and calcium in a precipitated crystal. XRD analysis confirmed the crystalline structure of a mineral with rhombohedral shape and 166 Å crystal size. This bacterium can serve as a promising candidate for producing bioconcrete.