Ultrastructural analysis of calcite crystal patterns formed by biofilm bacteria associated with cave speleothems

The ultrastructural morphology of calcium carbonate (CaCO3) crystals precipitated by eight culturable speleothemic biofilm bacteria associated with not-so-far explored caves of Meghalaya were studied using electron microscopy. The isolated bacteria under in vitro conditions precipitated CaCO3 in the media when supplemented with proper calcium source which was not the case in dead cells suggesting that calcification required metabolic activity in the speleothemic environment. Scanning electron microscopy revealed the presence of various polymorphs of calcite distinctly different from inorganic CaCO3 crystals. The polymorphic crystals ranged from filaments and rods associated in large clusters with mineral crystals to spiky needle. The results endorse the hypothesis that the isolated bacterial species contribute to active biogenic influence in the process of cave formations in the hypogean environment.