Bacterial dynamics in spring water of alpine karst aquifers indicates the presence of stable autochthonous microbial endokarst communities

Abstract

Spring water of two alpine karst aquifers differing in hydrogeology but of nearby catchments were investigated for their bacterial population dynamics. Dolomite karst aquifer spring 1 (DKAS 1) represents a dolomitic-limestone karst aquifer spring showing high average water residence time and relative constant flow. Limestone karst aquifer spring 2 (LKAS 2) constitutes a typical limestone karst aquifer spring with a dynamic hydrological regime and discharge. Dolomite karst aquifer spring 1 yielded constantly lower cell counts and biomasses (median of 15 x 10(6) cells l(-1) and 0.22 microg C l(-1)) as the LKAS 2 (median of 63 x 10(6) cells l(-1) and 1.1 microg C l(-1)) and distribution of morphotypes and mean cell volumes was also different between the considered systems, indicating the influence of hydrogeology on microbial spring water quality. Molecular bacterial V3 16S-rDNA profiles revealed remarkable constancy within each spring water throughout the investigation period. Time course analysis of a flood event in LKAS 2 further supported the trend of the temporal constancy of the microbial community. Except for one case, retrieval of partial and full length 16S rDNA gene sequences from the relative constant DKAS 1 revealed similarities to presently known sequences between 80% to 96%, supporting the discreteness of the microbial populations. The gathered results provide first evidence for the presence of autochthonous microbial endokarst communities (AMEC). Recovery of AMEC may be considered of relevance for the understanding of alpine karst aquifer biogeochemistry and ecology, which is of interest as many alpine and mountainous karst springs are important water resources throughout the world.

How Deep Can Surface Signals Be Traced in the Critical Zone? Merging Biodiversity with Biogeochemistry Research in a Central German Muschelkalk Landscape

“…The prokaryotic population densities are similar in the target aquifers of the two aquifer assemblages, ranging from 2.7 × 10 6 to 3.8 × 10 8 cells L −1 over time (Opitz et al, 2014), which is similar to microbial abundances observed in spring water of alpine karst aquifers (Farnleitner et al, 2005). Quantitative PCR targeting bacterial and archaeal 16S rRNA genes suggested that archaea form a fraction of 0.03-8.2% of the total microbial population across different transect locations.…”

“…Carbonate rocks cover over 20% of the Earth's ice-free continental area and karst aquifers represent important drinking water reservoirs, supplying up to 25% of the world's population with fresh water (Ford and Williams, 2015). Previous investigations of the microbial inventory of karst aquifers primarily focused on spring water or caves that allow easier access, pointing to the presence of autochthonous microbial endokarst communities but also to high temporal dynamics, indicated by the episodic occurrence of allochthonous soil bacteria within the spring water communities (Farnleitner et al, 2005;Pronk et al, 2008;Shabarova et al, 2013). However, less information is available for groundwater obtained from drilled boreholes within a karstic limestone setting (Gray and Engel, 2013).…”

“…Although we have only little general knowledge of the inhabitants of the subsurface, mostly from aquifers (e.g., Goldscheider et al, 2006;Amalfitano et al, 2014) or karst conduits and caves (Brigmon et al, 1994;Farnleitner et al, 2005;Pronk et al, 2008), they are increasingly subject to human impacts. These include direct impacts through activities like heat and energy exchange, structure-altering resource extraction, and use for waste disposal or gas storage.…”

Review: Microbial biocenoses in pristine aquifers and an assessment of investigative methods

“…This technique makes it possible to compare the microbial biocenoses from different samples, and to analyse their similarities using statistical methods. Non-parametric statistical analyses can be applied to combine these results with other sets of environmental data (Dewettinck et al 2001;Farnleitner et al 2005;Fromin et al 2002). Microscopic analyses and flow cytometry, combined with specific coloration techniques, can be used to characterise the morphological diversity of microbial communities, e.g.…”

“…In groundwater from different types of aquifers, planktonic cell numbers often range between 10 4 and 10 6 cells mL −1 , about two orders of magnitude lower than the number of benthic cells. The culturable counts are much lower, often less than 10 cells mL −1 (Farnleitner et al 2005;Haveman and Pedersen 2002;Marxsen 1988;Ultee et al 2004). These studies show that the number of attached (benthic) cells most often exceeds the number of suspended (planktonic) cells, and that most of the bacteria are non culturable and in a state of reduced activity.…”