Microbial Characteristics of a Submerged Karst Cave System in Northern Florida

Abstract

Karst aquifer systems contain submerged caves that act as conduits for subterranean water flow and are subject to rapid surface recharge at points such as sink holes and submerging streams. We examined the microbial communities in six conduits of the Northern Florida Wakulla Springs cave system and in several hydrologically connected surface sinks. Culturable bacteria were assessed using both oligotrophic and copiotrophic media, and specific media for Enterococcus and Escherichia coli. Culture independent methods included using 16S rRNA PCR amplified DNA for T-RFLP analysis and development of clone libraries for sequencing. Pronounced seasonality was found in all microbiological parameters suggesting responsiveness to surface conditions from recharge of the groundwater despite near constant groundwater temperature. Other differences may reflect the character of the drainage areas feeding different conduits and flow rates and flow reversals that affected residence time in cave conduits. In a region of groundwater flow divide, elevated numbers of a plate counts, flocculent material, and a sulfide smell were reflected in T-RFLP pattern differences. Sequence data from five selected sampling locations revealed the presence of Enterobacter and Klebsiella sequences in surface waters, but not in conduits. One conduit contained a high percentage of sequences with close homology to the archaeal species Thermococcalles archaeon. Other cave-specific sequences were found that do not match previously characterized bacteria. Overall, the data suggest both temporal and spatial differences in the microbial communities within the extensive cave system conduits feeding the spring vent, reflecting both drainage area influences and undocumented subterranean microbial diversity.