Bacterial and archaeal community structure of two adjacent calcite speleothems in Kartchner Caverns, Arizona, USA

Information concerning the bacterial and archaeal communities present on calcite speleothems in carbonate caves is of interest because the activity of these microbes has been implicated as a potential biogenic component in the formation of secondary mineral deposits. In addition, these speleothems may harbor unique, previously unidentified microbes. The current study presents a comparative analysis of the superficial bacterial and archaeal community structure of multiple stalactites from two different cave formations located in close proximity to each other in a nonhuman-impacted area of Kartchner Caverns, Arizona, USA. PCR-denaturing gradient gel electrophoresis analysis (PCR-DGGE) revealed that microbial communities sampled from stalactites of a single speleothem are more similar to each other than to the communities sampled from stalactites of an adjacent speleothem, suggesting that both bacterial and archaeal communities are speleothem-specific. SR-XRD analysis confirmed that both speleothems sampled were primarily calcite, but subtle differences were detected in the elemental composition profiles obtained from ICP-MS analysis indicating that substrate geochemistry was also speleothem-specific. PhyloChip analysis of composite samples from both speleothems revealed a broad diversity of phyla represented in the bacterial communities, while bacterial and archaeal bands sequenced from the DGGE profiles confirmed the presence of unique phylotypes not closely related (< 96% similarity) to any sequences deposited in the GenBank database.