Aquifer recharge viewed through the lens of microbial community ecology: Initial disturbance response, and impacts of species sorting versus mass effects on microbial community assembly in groundwater during riverbank filtration.

Riverbank filtration has gained increasing importance for balancing rising groundwater demands and securing drinking water supplies. While microbial communities are the pillar of vital ecosystem functions in groundwater, the impact of riverbank filtration on these communities has been understudied so far. Here, we followed changes in microbial community composition based on 16S rRNA gene amplicon sequence variants (ASVs) in an initially pristine shallow porous aquifer in response to surface water intrusion during the early stages of induced riverbank filtration over a course of seven weeks. We further analyzed sediment cores for imprints of river-derived ASVs after seven weeks of riverbank filtration. The onset of the surface water intrusion caused loss of taxa and significant changes in community composition, revealing low disturbance resistance of the initial aquifer microbial communities. SourceTracker analysis revealed that proportions of river-derived ASVs in the groundwater were generally <25%, but locally could reach up to 62% during a period of intense precipitation. However, variation partitioning showed that the impact of dispersal of river-derived ASVs on changes in aquifer microbial community composition was overall outweighed by species sorting due to changes in environmental conditions caused by the infiltrating river water. Proportions of river-derived ASVs on aquifer sediments were <0.5%, showing that taxa transported from the river into the aquifer over the course of the study mainly resided as planktonic microorganisms in the groundwater. Our study demonstrates that groundwater microbial communities react sensitively to changes in environmental conditions caused by surface water intrusion, whereas mass effects resulting from the influx of river-derived taxa play a comparatively minor role.

Sorption and biodegradation parameters of selected pharmaceuticals in laboratory column experiments.

Pharmaceutically active compounds have increasingly been detected in groundwater worldwide. Despite constituting a risk for human health and ecosystems, their fate in the environment has still not been exhaustively investigated. This study characterizes the transport behavior of five selected pharmaceutically active compounds (antipyrine, atenolol, caffeine, carbamazepine and sulfamethoxazole) in two sediments (coarse quartz sand and sandy loam) using column experiments with long-term injection of spiked groundwater. Transport parameters were estimated using an analytical reactive transport model. When five selected compounds were injected simultaneously, transport behavior of antipyrine, carbamazepine and the antibiotic sulfamethoxazole were similar to the conservative tracer in both sediments and under varying redox conditions. Atenolol and caffeine were retarded significantly stronger in the sandy loam sediment than in the coarse quartz sand. Biodegradation of caffeine was observed in both sediments after an adaption period and depended on dissolved oxygen. The identification of biodegradation processes was supported by monitoring of intracellular adenosine triphosphate (ATPitc) as a measure for microbial activity. ATPitc was present in varying concentrations in all sediments and was highest when biodegradation of pharmaceuticals, especially caffeine, was observed. When only caffeine and sulfamethoxazole were injected simultaneously, sulfamethoxazole was degraded while caffeine degradation was reduced. The latter seemed to be influenced by low concentrations in dissolved oxygen rather than the presence of the antibiotic sulfamethoxazole. Results of these experiments emphasize the impact on pharmaceutical sorption and (bio)degradation of sediment type and redox conditions, as well as available time for microbial adaption and the combination of pharmaceuticals that are released together into groundwater.

Sensitization to Hymenoptera venom in pollen allergic patients: Frequency and involvement of cross-reacting carbohydrate determinants (CCD).

Sensitization to Hymenoptera venom in patients without a history of systemic allergic reactions to Hymenoptera stings is frequently found and can be due to the presence of specific IgE to cross-reactive carbohydrate determinants (CCD). This study investigates 105 pollen allergic subjects for the presence of specific IgE to honeybee or wasp venom, pollen, the MUXF3 carbohydrate epitope from bromelain and recombinant Hymenoptera venom components. In addition, in a subgroup of patients (n = 10) a basophil activation test (BAT) using bee and wasp venom was performed. Specific IgE to Hymenoptera venom was detected in 45.7% of the pollen allergic subjects and in 26.7% of the non-atopic controls, both without a history of systemic allergic reactions to Hymenoptera stings. The high sensitization rate in atopic patients could partially be explained by cross-sensitization between pollen and Hymenoptera venom due to specific IgE to CCDs. In our study population, only 20% showed a sensitization to CCDs. Primary sensitization due to sting exposure, high total IgE values or unspecific binding and detection of low affinity antibodies in the test procedure could be reasons. Thus, determination of specific IgE to Hymenoptera venom in patients without a history of systemic allergic reactions as screening test is not recommended.

Selection imposed by local environmental conditions drives differences in microbial community composition across geographically distinct groundwater aquifers.

Several studies have analyzed biogeographic distribution patterns of microbial communities across broad spatial scales. However, it is often unclear to what extent differences in community composition across different regions are caused by dispersal limitation or selection, and if selection is caused by local environmental conditions alone or additional broad-scale region-specific factors. This is especially true for groundwater environments, which have been understudied in this context relative to other non-subsurface habitats. Here, we analyzed microbial community composition based on exact 16S rRNA amplicon sequence variants (ASVs) from four geographically separated aquifers located in different regions along a latitudinal transect of ∼700 km across Germany. Using a combination of variation partitioning and ecological null models revealed that differences in microbial community composition were mainly the product of selection imposed by local environmental conditions and to a smaller but still significant extent dispersal limitation and drift across regions. Only ∼23% of the total variation in microbial community composition remained unexplained, possibly due to underestimated effects of dispersal limitation among local communities within regions and temporal drift. No evidence was found for selection due to region-specific factors independent of local environmental conditions.

The D-A-(C) index: A practical approach towards the microbiological-ecological monitoring of groundwater ecosystems.

Groundwater is not only a vital resource, but also one of the largest terrestrial aquatic ecosystems on Earth. However, to date, ecological criteria are often not considered in routine groundwater monitoring, mainly because of the lack of suitable ecological assessment tools. Prokaryotic microorganisms are ubiquitous in groundwater ecosystems even under the harshest conditions, making them ideal bioindicators for ecological monitoring. We have developed a simple, inexpensive approach that enables ecological groundwater monitoring based on three microbiological parameters that can be easily integrated into existing routine monitoring practices: prokaryotic cell density (D) measured by flow cytometry; activity (A) measured as prokaryotic intracellular ATP concentrations using a simple cell-lysis-luminescence assay; and, as an optional parameter, the bioavailable carbon (C) measured as the concentration of assimilable organic carbon in a simple batch growth assay. We analyzed data for three case studies of different disturbances representing some of the main threats to groundwater ecosystems, i.e. organic contamination with hydrocarbons, surface water intrusion, and agricultural land use. For all three disturbances, disturbed samples could be reliably distinguished from undisturbed samples based on a single index value obtained from multivariate outlier analyses of the microbial variables. We could show that this multivariate approach allowed for a significantly more sensitive and reliable detection of disturbed samples compared to separate univariate outlier analyses of the measured variables. Furthermore, a comparison of non-contaminated aquifers from nine different regions across Germany revealed distinct multivariate signatures along the three microbial variables, which should be considered when applying our approach in practice. In essence, our approach offers a practical tool for the detection of disturbances of groundwater ecosystems based on microbial parameters which can be seamlessly extended in the future by additional parameters for higher sensitivity as well as flexibility.

Microbial contributions to coupled arsenic and sulfur cycling in the acid-sulfide hot spring Champagne Pool, New Zealand.

Acid-sulfide hot springs are analogs of early Earth geothermal systems where microbial metal(loid) resistance likely first evolved. Arsenic is a metalloid enriched in the acid-sulfide hot spring Champagne Pool (Waiotapu, New Zealand). Arsenic speciation in Champagne Pool follows reaction paths not yet fully understood with respect to biotic contributions and coupling to biogeochemical sulfur cycling. Here we present quantitative arsenic speciation from Champagne Pool, finding arsenite dominant in the pool, rim and outflow channel (55-75% total arsenic), and dithio- and trithioarsenates ubiquitously present as 18-25% total arsenic. In the outflow channel, dimethylmonothioarsenate comprised ≤9% total arsenic, while on the outflow terrace thioarsenates were present at 55% total arsenic. We also quantified sulfide, thiosulfate, sulfate and elemental sulfur, finding sulfide and sulfate as major species in the pool and outflow terrace, respectively. Elemental sulfur concentration reached a maximum at the terrace. Phylogenetic analysis of 16S rRNA genes from metagenomic sequencing revealed the dominance of Sulfurihydrogenibium at all sites and an increased archaeal population at the rim and outflow channel. Several phylotypes were found closely related to known sulfur- and sulfide-oxidizers, as well as sulfur- and sulfate-reducers. Bioinformatic analysis revealed genes underpinning sulfur redox transformations, consistent with sulfur speciation data, and illustrating a microbial role in sulfur-dependent transformation of arsenite to thioarsenate. Metagenomic analysis also revealed genes encoding for arsenate reductase at all sites, reflecting the ubiquity of thioarsenate and a need for microbial arsenate resistance despite anoxic conditions. Absence of the arsenite oxidase gene, aio, at all sites suggests prioritization of arsenite detoxification over coupling to energy conservation. Finally, detection of methyl arsenic in the outflow channel, in conjunction with increased sequences from Aquificaceae, supports a role for methyltransferase in thermophilic arsenic resistance. Our study highlights microbial contributions to coupled arsenic and sulfur cycling at Champagne Pool, with implications for understanding the evolution of microbial arsenic resistance in sulfidic geothermal systems.