Microbiological characterization of a sulfide‐rich groundwater ecosystem

Movile Cave, recently discovered in southern Romania, contains sulfide‐rich thermal waters in submerged passages, as well as isolated air pockets. The water surfaces within the air pockets are covered by substantial microbial biofilms, while the air bells contain an abundant and diverse community of terrestrial and aquatic animal species. Based on the results of dehydrogenase activity, fecal streptococci counts, and stable carbon isotope ratios, we propose that the cave community is biologically isolated and receives little, if any, organic carbon inputs from the surface environment. Several sulfide‐oxidizing chemoautotrophic bacteria were isolated from the cave waters. One putative Thiosphaera sp. strain, LV‐43, was further characterized. The presence and high level activity of RuBisCO was clearly demonstrated in this strain.