The distribution of microbial taxa in the subsurface water of the Kalahari Shield, South Africa

Microbial communities within deep subsurface environments were analyzed by 16S rRNA gene cloning. Clone libraries from 27 borehole fluid, 7 mining-contaminated, and 5 rock samples were compared. Borehole fluids derived from deep fractures were populated by microbial communities with low diversity with an average of 11 and 5 bacterial and archaeal OTUs respectively. Low taxa richness was likely driven by limited biogeochemical reactions available for growth and not extreme parameters such as pH and temperature. Novel taxa of Firmicutes were discovered, commonly found in warm, slightly alkaline, anoxic fracture fluids. Highly divergent lineages of Archaea, unique to South African deep subsurface fracture fluids, are also described. Clone library clustering analyses based on LIBSHUFF phylogenetic relatedness revealed distinct groups of samples corresponding with sample source and geochemistry.