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

Abstract

The Buda Thermal Karst System (BTKS) is an extensive active hypogenic cave system located beneath the residential area of the Hungarian capital. At the river Danube, several thermal springs discharge forming spring caves. To reveal and compare the morphological structure and prokaryotic diversity of reddish-brown biofilms developed on the carbonate rock surfaces of the springs, scanning electron microscopy (SEM), and molecular cloning were applied. Microbial networks formed by filamentous bacteria and other cells with mineral crystals embedded in extracellular polymeric substances were observed in the SEM images. Biofilms were dominated by prokaryotes belonging to phyla Proteobacteria, Chloroflexi and Nitrospirae (Bacteria) and Thaumarchaeota (Archaea) but their abundance showed differences according to the type of the host rock, geographic distance, and different water exchange. In addition, representatives of phyla Acidobacteria, Actinobacteria, Caldithrix, Cyanobacteria, Firmicutes Gemmatimonadetes, and several candidate divisions of Bacteria as well as Crenarchaeota and Euryarchaeota were detected in sample-dependent higher abundance. The results indicate that thermophilic, anaerobic sulfur-, sulfate-, nitrate-, and iron(III)-reducing chemoorganotrophic as well as sulfur-, ammonia-, and nitrite-oxidizing chemolithotrophic prokaryotes can interact in the studied biofilms adapted to the unique and extreme circumstances (e.g., aphotic and nearly anoxic conditions, oligotrophy, and radionuclide accumulation) in the thermal karst springs.

In situ modelling of biofilm formation in a hydrothermal spring cave

“…Concentrations of NH 4 + -N, NO 3 – N, and NO 2 – N were 0.2 mg L −1 , < 1 mg L −1 , and 0.2 mg L −1 , respectively. These results were also related to the values previously reported by Borsodi et al 6 and Enyedi et al 17 .…”

“…3 ). It could be presumed based on the previous studies, because members of this phylum were frequently detected as constituents of bacterial communities in different cave samples 6 , 22 – 26 . The water sample of the RT spring cave was dominated almost exclusively by an unclassified Hydrogenophilaceae (OTU3) that showed the highest sequence similarity with chemo-lithotrophic sulfur-oxidizing bacteria (Fig.…”

“…A possible reason for the low ammonia content in the BTKS is the oxidation of ammonia, in which members of both the Archaea and Bacteria may be involved. The ammonia-oxidizing archaea (AOA) organisms belonging to the phylum Thaumarchaeota appeared in high proportion in the archaeal clone libraries created from biofilms originated from the caves and spring caves of the BTKS 6 , 7 . For the members of the Archaea, an increasing temporal trend was observed in the biofilms from the fifteenth weeks, although the primer-pair which was used for amplification is rather Bacteria-specific 33 .…”

“…In addition, specific electrical conductivity, temperature and water level was measured continuously by a DATAQUA datalogger and was compared with the actual level of the Danube river. All other parameters were measured in the laboratory as previously described 6 , 7 .…”

INVESTIGATION OF A FLOWSTONE-LIKE HISTORICAL INDOOR-TRAVERTINE (RUDAS SPA, BUDAPEST, HUNGARY) USING THE14C “BOMB-PEAK”

“…Since microbiological analyses of other springs of the Gellért Hill by Borsodi et al (2012Borsodi et al ( , 2018, Anda et al (2014), Makk et al (2016) and Enyedi et al (2019) proved the presence of various bacterial communities, the role of preserved microbial biofilms in concentrating a range of trace elements in the Rudas travertine should also be taken into consideration. The elevated natural radioactivity also is apparently connected to biofilms, since biogeochemical precipitates readily adsorb 226 Ra and produce 222 Rn, which although short lived might be a problem when air quality is considered (Erőss et al 2012;Kovács-Bodor et al 2019).…”