Comparison of bacterial and archaeal communities from different habitats of the hypogenic Molnár János Cave of the Buda Thermal Karst System (Hungary)

Abstract

The Molnár János Cave is part of the northern discharge area of the Buda Thermal Karst System, and is the largest active thermal water cave in the capital of Hungary. To compare the prokaryotic communities, reddish-brown cave wall biofilm, black biogeochemical layers, and thermal water samples from the phreatic mixing zone of the cave were subjected to three investigative approaches, scanning electron microscopy, cultivation, and molecular cloning. According to the SEM images, multilayer network structures were observed in the biofilm formed by iron-accumulating filamentous bacteria and mineral crystals. Cultivated strains belonging to Aeromonadaceae and Enterobacteriaceae were characteristic from both water and subaqueous biofilm samples. The most abundant molecular clones were representatives of the phylum Chloroflexi in the reddish-brown biofilm, the class Gammaproteobacteria in the black biogeochemical layer, and Thiobacillus (Betaproteobacteria) in the thermal water samples. The reddish-brown biofilm and black biogeochemical layer's bacterial communities proved to be somewhat more diverse than that of the thermal water. The archaeal 16S rRNA gene clone libraries were dominated by thermophilic ammonia-oxidizer Nitrosopumilus and Nitrososphaera phylotypes in all three habitats. Considering the metabolic characteristics of known species related to the detected clones, it can be assumed that these communities may participate in the local sulfur and nitrogen cycles and may contribute to microbial mediated sulfuric acid speleogenesis.

Biofilm forming bacteria and archaea in thermal karst springs of Gellért Hill discharge area (Hungary)

“…The water physical and chemical profile of the studied Gellért Hill discharge zone is considerably differed from the Rose Hill area of BTKS. It can be traced back mainly to the dissimilarity in the water temperature, sulfate concentration, salinity and electric conductivity values .…”

“…Members of the phylum Chloroflexi are frequently retrieved from thermal waters and cave environments , and dominated the bacterial community of Molnár János cave , as well. In this hypogenic cave the host rock is the Upper Eocen Buda Marl Formation similarly to that found in the Rác Spa Nagy spring (RN) of Gellért Hill discharge area.…”

“…Biofilms developing in the discharge areas of BTKS are presumed to contribute to hypogenic karstification processes, as well . Preliminary microbiological examinations on the biofilms and thermal waters from different parts of the BTKS revealed the existence of extremophilic prokaryotic composition adapted to the special environmental conditions . Biofilm bacterial communities at all studied sites proved to be somewhat more diverse than that of the surrounding thermal waters .…”

“…Biofilm bacterial communities at all studied sites proved to be somewhat more diverse than that of the surrounding thermal waters . The reddish‐brown biofilms were dominated by facultative anaerobic, hydrogen or sulfur/thiosulfate‐oxidizing (chemolithoautotrophic) and thermophilic Sulfurihydrogenibium (Aquificae) in the well of Széchenyi Thermal Bath while multilayer filamentous structure forming representatives of the phylum Chloroflexi inhabited the Molnár János hypogene cave . However, regarding the biofilm community composition in the Gellért Hill of BTKS, our knowledge is still rather incomplete.…”

“…Preliminary microbiological examinations on the biofilms and thermal waters from different parts of the BTKS revealed the existence of extremophilic prokaryotic composition adapted to the special environmental conditions . Biofilm bacterial communities at all studied sites proved to be somewhat more diverse than that of the surrounding thermal waters . The reddish‐brown biofilms were dominated by facultative anaerobic, hydrogen or sulfur/thiosulfate‐oxidizing (chemolithoautotrophic) and thermophilic Sulfurihydrogenibium (Aquificae) in the well of Széchenyi Thermal Bath while multilayer filamentous structure forming representatives of the phylum Chloroflexi inhabited the Molnár János hypogene cave .…”