OPTIMIZING CALCIUM CARBONATE PRECIPITATION BY MICROORGANISMS ISOLATED FROM CAVE POOLS

Although the deposition of calcium carbonate in cave pools was originally thought to be an abiotic process, we hypothesized that calcite deposits on Snowy River in Fort Stanton Cave and in pools from the Western Branch of Lechuguilla Cave are partially formed by microbial activity. To test this hypothesis, we cultured microorganisms from both cave environments and demonstrated that isolated microorganisms precipitated calcium carbonate, as evidenced by data from scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). In order to optimize calcite precipitation by organisms that thrive in low temperature cave environments, this study also explored the efficacy of five types of media in a low temperature calcite precipitation experiment. Calcite precipitating bacteria were isolated from ½ R2A cultures of small water samples and swabs of the submerged calcite from the two caves. Isolates were initially sub-cultured onto B4 media (Boquet et al. 1973) and incubated for two months at 25°C. Colonies were photographed with a Zeiss Discovery V.12 Stereoscope with AxioCam HRc camera and bacteria that appeared to be precipitating calcite were analyzed with scanning electron microscopy. SEM and EDS analysis after two weeks of incubation revealed the presence of calcite crystals on cultures from both Fort Stanton and Lechuguilla Caves. Isolated bacteria from these locations that exhibited good calcite precipitation were plated on five types of media and incubated at 6°C and 15°C for one month to determine the optimum media for low temperature calcite precipitation experiments. This study, in addition to optimizing media for calcite precipitating bacteria isolated from cave environments, highlights the potential role of bacteria in the formation of calcium carbonate deposits in Lechuguilla and Fort Stanton Caves, offering further evidence to support the claim that bacteria may be playing an active role in the formation of carbonate speleothems.