Measure Of Microbial Activity Research Articles

An integrated evaluation of bioenhanced in situ LNAPL dissolution

Performance evaluation of in situ bioremediation processes in the field is difficult due to uncertainty created by matrix and contaminant heterogeneity, inaccessibility to direct observation, expense of sampling, and limitations of some measurements. The goal of this research was to develop a strategy for evaluating in situ bioremediation of light nonaqueous-phase liquid (LNAPL) contamination and demonstrating the occurrence of bioenhanced LNAPL dissolution by: (1) integrating a suite of analyses into a rational evaluation strategy; and (2) demonstrating the strategy's application in intermediate-scale flow-cell (ISFC) experiments simulating an aquifer contaminated with a pool of LNAPL (naphthalene dissolved in dodecane). Two ISFCs were operated to evaluate how the monitored parameters changed between a “no bioremediation” scenario and an “intrinsic in situ bioremediation” scenario. Key was incorporating different measures of microbial activity and contaminant degradation relevant to bioremediation: contaminant loss; consumption of electron acceptors; and changes in total alkalinity, pH, dissolved total inorganic carbon, carbon-stable isotopes, microorganisms, and intermediate metabolites. These measurements were integrated via mass-flux modeling and mass-balance analyses to document that in situ biodegradation of naphthalene was strongly accelerated in the “intrinsic in situ bioremediation” scenario versus “no bioremediation.” Furthermore, the integrated strategy provided consistent evidence of bioenhancement of LNAPL dissolution through intrinsic bioremediation by a factor of approximately 2 due to the biodegradation of the naphthalene near the pool/water interface.

Standardisation of the C:N ratio in ileal digesta changes relationships among fermentation end-products during in vitro hindgut fermentation in pigs

Undigested proteins that become available for the microbiota in the hindgut can be used as building blocks for bacterial cells, or can enter various catabolic pathways. Degradation via protein fermentation pathways is least preferred, as several fermentation end-products released can be toxic for the host. Directing microbial protein metabolism towards protein synthesis or degradative pathways that result in less toxic end-products, for example through nutritional interventions, is an interesting strategy for improving health. We studied variation in protein fermentation patterns, resulting from variation in substrate composition. Ileal digesta, obtained from cannulated pigs fed different protein sources, were subjected to fermentation in vitro under different conditions; (1) ileal digesta were fermented as-is, (2) ileal digesta were fermented after standardisation to a constant high C:N ratio, by addition of high fermentable carbohydrates and (3) ileal digesta samples were incubated under limiting N concentrations. Gas production was monitored as an indirect measure of microbial activity, and fermentation end-products at different points in time were analysed by gas chromatography and high resolution mass spectrometry. Using principal component analysis, we identified patterns in protein fermentation end-products and related them to the composition of ileal digesta. Protein-associated fermentation end-product concentrations of e.g. isovaleric-, isobutyric-, phenylacetic acid and p-cresol were negatively affected by the available amount of high fermentable carbohydrates combined with a high C:N ratio. The aforementioned fermentation end-products positively correlated with NH3 concentrations and negatively with short-chain fatty acid (SCFA) concentrations. Standardisation to a constant high C:N ratio changed their relationship; isovaleric-, isobutyric-, phenylacetic acid and p-cresol lost their correlation with NH3 concentrations, became positively correlated with SCFA concentrations, and now showed a positive correlation with available amounts of high fermentable carbohydrates. Our observations demonstrate an important role of the C:N ratio in the relationship between fermentation end-products. At constant C:N, protein fermentation end-products correlate with end-products of carbohydrate fermentation and NH3, often considered as a proxy for protein fermentation, loses its predictive power.

Composition and activity of soil microbial communities in native and non-native vegetation of southern California

The proliferation of non-native plant species in novel habitats has altered plant community diversity, ecosystem carbon (C) and nutrient cycling, and disturbance regimes worldwide. However, the impacts of non-native plants on soil microbial community composition and activity are still poorly known, especially in semi-arid woodlands. Here we utilized next generation sequencing (16S rRNA sequencing of the V3-V4 regions) and measurements of microbial activity (respiration, net N mineralization, and enzyme assays) to determine how soil microbial composition and activity varied between native and non-native vegetation patches in coastal sage scrub (CSS) woodlands. We sampled eight CSS sites and collected topsoil (0–10 cm) samples from six paired native and non-native vegetation patches at each site. Native patches had significantly (p < 0.05) higher vegetation cover, dissolved organic C (DOC), and dissolved inorganic nitrogen (DIN) concentrations than non-native patches. β-glucosidase activity was significantly higher (ca. 10 nM g−2 h−1) and peroxidase activity was significantly lower (ca. 60 nM g−2 h−1) in non-native vegetation, while rates of net N mineralization and nitrification, phosphatase and NAGase activities, and respiration were not significantly different in native and non-native vegetation but were positively correlated with total soil C and N (r > 0.60; p < 0.05). Bacterial alpha- and beta-diversity were not significantly different (p > 0.05) between native and non-native patches; however, bacteria/archaea in the phyla Gemmatimonadota, Planctomycetota, Armatimonadota, Fibrobacterota, Thermoplasmatota, and Entotheonellaeota were over-expressed in non-native patches. Within these phyla there were 20 orders that were differentially expressed in native or non-native vegetation, and more than half (60 %) had significantly higher relative abundance in native vegetation. Our results indicate that the expansion of non-native vegetation in semi-arid woodlands significantly alters soil C and N, which feeds back on microbial activity and community composition.

Redox potential as a soil health indicator – how does it compare to microbial activity and soil structure?

Background and aimsRedox potential is a promising soil health indicator, which integrates the combined effect of chemical oxidation–reduction reactions into a single measurement. However, this method has been tested only on a few soils. The aim of this study was to test redox potential as a soil health indicator, to see if it responds to management practices and to compare it with existing soil health metrics for microbial activity (“CO2burst”) and soil structure.MethodsWe collected 35 soil samples in agricultural fields from a carbon farming trial, where contrasting management practices have been applied to increase carbon stock. The soil samples were dried, rewetted and analyzed for redox and microbial respiration during rewetting. In addition, soil structure, texture and organic matter content was measured. The data was analyzed for correlations between the indicators and for the differences between management and control fields.ResultsRedox was well correlated with microbial activity, structure, and texture. A low redox state was connected to high microbial activity, indicating bioavailable organic matter availability. Soils with good structure had an oxidized redox status, possibly reflecting high gas-transport. The carbon farming practices resulted in lower oxidation, possibly due to build-up of plant residues.ConclusionsThe findings supported the use of redox as a soil health indicator, but highlighted further research needs for identifying the shared mechanisms linking structure, redox and microbial activity. As such, redox can be a low-cost additional measurement to map changes in soil health, but it cannot replace existing structure or microbial activity measurements.

A downstream process control tool based on the redox dye resazurin for rapid and accurate measurement of microbial metabolic activity.

Many sophisticated water treatment plants need a reliable, fast, and economical microbial load detection method. We refined a colorimetric assay using the redox dye resazurin to assess viable microorganisms. Here, we have used a mixed bacterial suspension of significant multi-drug-resistant coliform bacteria isolated from hospital wastewater and constructed a resazurin reduction calibration curve which could accurately predict the level of microbial contamination. The number of viable microorganisms was calculated from calibration curve in terms of log colony forming units (CFU) per milliliter. Ultrasonication disinfection of bacterial suspension for a duration of 50min measured by resazurin assay depicted a reduction of 16.94%, 26.48%, and 37.69% at 410 W, 580 W, and 700 W, respectively. A synergistic effect of the combined methods of ultrasonication and heat disinfection treatments on raw wastewater and secondary wastewater effluent was observed and was also evaluated using both resazurin assay and standard plate count method. For raw wastewater, about 1.8 log reduction was observed for ultrasonication alone and 4 log CFU/mL reduction for thermosonication. In the secondary wastewater effluent, a reduction of 2.9 and 3.2 log CFU/mL was recorded for ultrasonication and thermosonication respectively. Resazurin microbial viability test results were highly comparable with conventional colony plate count for all treatment procedures, suggesting its appropriateness for quick and reliable wastewater sample microbial viability monitoring.

Baohe pill decoction treats diarrhea induced by high-fat and high-protein diet by regulating lactase-producing bacteria in intestinal mucosa.

This study aimed to investigate the effects of Baohe pill decoction (BPD) on microbial, lactase activity, and lactase-producing bacteria in the intestinal mucosa of mice with diarrhea induced by high-fat and high-protein diet (HFHPD). Thirty male Kunming (KM) mice were randomly divided into normal (NM), model (MD), and BPD groups. Diarrhea models were manufactured using HFHPD combined with a gavage of vegetable oil. At the end of modeling, the BPD group was given BPD (6.63 g·kg-1d-1) intervention twice daily for 3 d. The NM and MD groups were given equal amounts of sterile water. Subsequently, the intestinal mucosa of the mice was collected, one portion was used for microbial and lactase activity measurement, and the other portion was used for its lactase-producing bacterial characteristics by high-throughput sequencing technology. Our results showed that microbial and lactase activity of intestinal mucosa decreased significantly following diarrhea in mice (Pmicrobial < 0.05, Plactase < 0.001). After BPD intervention, microbial and lactase activity increased significantly (P < 0.01). The number of operational taxonomic units (OTUs), richness, and diversity index of lactase-producing bacteria increased in the BPD group compared to the MD group (P > 0.05), and the community structure were significant differences (P < 0.01). Compared to other groups, Saccharopolyspora, Rhizobium, Cedecea, and Escherichia were enriched in the BPD group. Notably, the relative abundance of the dominant lactase-producing genus Bifidobacterium decreased after BPD intervention. The mechanism of BPD in relieving diarrhea induced by HFHPD is closely related to the promotion of lactase activity in the intestinal mucosa, which may be achieved by regulating the structure of lactase-producing bacteria.

Non-charismatic waterbodies and ecosystem disservices: Mine pit lakes are underrepresented in the literature.

Pit lakes are one of the greatest legacies of open-cut mining. Despite the potential hazards of these lakes, they represent newly formed ecosystems with great scientific and ecological potential. Although thousands of pit lakes occur on every inhabited continent, with more being created, the microbial ecology of pit lakes is relatively under-researched. We evaluated the current state of microbial research in pit lakes by performing a Web of Science search and creating a literature database. Study lakes were categorized according to location and water quality (pH and conductivity) which is a key community and environmental concern. Research technology employed in the study was also categorized. We compared research effort in lakes, rivers, and streams which are the more "charismatic" inland aquatic ecosystems. Pit lake publications on microbes from 1987 to 2022 (n = 128) were underrepresented in the literature relative to rivers and streams (n = 321) and natural lakes (n = 948). Of the 128 pit lake publications, 28 were within the field of geochemistry using indirect measures of microbial activity. Most pit lake microbial research was conducted in a few acidic lakes in Germany due to social pressure for remediation and government initiative. Relatively few studies have capitalized on emerging technology. Pit lake microbial research likely lags other more charismatic ecosystems given that they are viewed as performing "ecosystem disservices," but this is socially complex and requires further research. Improving understanding of microbial dynamics in pit lakes will allow scientists to deliver safer pit lakes to communities.

Limited carbon cycling due to high-pressure effects on the deep-sea microbiome

Deep-sea microbial communities are exposed to high-pressure conditions, which has a variable impact on prokaryotes depending on whether they are piezophilic (that is, pressure-loving), piezotolerant or piezosensitive. While it has been suggested that elevated pressures lead to higher community-level metabolic rates, the response of these deep-sea microbial communities to the high-pressure conditions of the deep sea is poorly understood. Based on microbial activity measurements in the major oceanic basins using an in situ microbial incubator, we show that the bulk heterotrophic activity of prokaryotic communities becomes increasingly inhibited at higher hydrostatic pressure. At 4,000 m depth, the bulk heterotrophic prokaryotic activity under in situ hydrostatic pressure was about one-third of that measured in the same community at atmospheric pressure conditions. In the bathypelagic zone—between 1,000 and 4,000 m depth—~85% of the prokaryotic community was piezotolerant and ~5% of the prokaryotic community was piezophilic. Despite piezosensitive-like prokaryotes comprising only ~10% (mainly members of Bacteroidetes, Alteromonas) of the deep-sea prokaryotic community, the more than 100-fold metabolic activity increase of these piezosensitive prokaryotes upon depressurization leads to high apparent bulk metabolic activity. Overall, the heterotrophic prokaryotic activity in the deep sea is likely to be substantially lower than hitherto assumed, with major impacts on the oceanic carbon cycling.

Decoupled cycling of carbon, nitrogen, and phosphorus in a grassland soil along a hillslope mediated by clay and soil moisture

Grasslands extend across a variety of topographies including non-flat hilly areas with varied soil texture and moisture that can mediate soil biogeochemical cycling of carbon (C), nitrogen (N) and phosphorus (P). In this study we examined soil organic C, total N and P pools (both inorganic and organic), as well as gross N mineralisation (GNM, as a measure of microbial activity and N dynamics) and microbial C, N and P in winter and spring along a grassland hillslope. Our results showed that variation in soil clay and associated soil moisture were the most important mediators affecting C and N dynamics along the grassland elevational gradient. Total organic C pools were highest where the clay content was highest, likely because of the sorption capacity of clay stabilising organic matter against microbial decomposition. Likewise, the variation in soil organic N pools along the hillslope was mostly controlled by clay and soil moisture effects on microbial stabilisation of organic N. Furthermore, microbial C, N and GNM increased with increased soil moisture, suggesting that microbial activity was limited by soil moisture. In contrast, soil P pools were not related to clay and soil moisture, while soil organic P was decoupled from soil organic C and N pools along the hillslope. Possibly, differences in microbial stabilisation and mineralisation pathways (oxidation for C and N, hydrolysis for P), microbial homeostatic regulation of C, N and P, and P fixation resulted in a decoupling of P from C and N cycling in this grassland. We conclude that variation in clay and associated soil moisture along grassland hillslopes can have important but non-unidirectional effects on soil C, N and P cycling.

Soil Quality Enhancement with Orchard Age in Pecan Orchards of the Southeastern U.S. Coastal Plain

Pecan (Carya illinoinensis) orchards in Georgia and throughout the southeastern United States are commonly established from land that had previously been used for row cropping systems. Soil quality is characteristically low in the loamy-sand, low pH soils of the southeastern Coastal Plain. Changes in land use are known to exhibit different effects on soil quality; however, no studies specifically address soil enhancement from converting row crop land to pecan orchards in this region. Sampling was conducted in eight counties throughout the coastal plain of South Georgia in 2020 and 2021. The objectives of this study were to analyze and compare soil quality indicators of pecan orchards of varying ages and adjacent row crop fields. Soil quality indicators analyzed include soil organic matter (SOM), active carbon or permanganate oxidizable carbon (POXC), aggregate stability, cation exchange capacity (CEC), bulk density, porosity, Solvita CO2-Burst, SLAN (Solvita labile-amino nitrogen), pH, and total N. Results from this study demonstrate that pecan orchards under commercial management had higher soil quality compared with row crop fields based on the indicators measured. Active carbon and Solvita CO2-Burst measurements suggest that pecan orchards exhibited significantly higher rates of microbial activity and soil respiration. Indicators of soil microbial activity such as active carbon and Solvita CO2-Burst were strongly correlated with SOM, which explained much of the variation observed in these measurements of soil microbial activity. Selected soil quality indicators also provide evidence that the soil quality of commercial pecan orchards in this region improves with orchard age.

Denitrification‐Driven Transcription and Enzyme Production at the River‐Groundwater Interface: Insights From Reactive‐Transport Modeling

AbstractMolecular‐biological data and omics tools have increasingly been used to characterize microorganisms responsible for the turnover of reactive compounds in the environment, such as reactive‐nitrogen species in groundwater. While transcripts of functional genes and enzymes are used as measures of microbial activity, it is not yet clear how they are quantitatively related to actual turnover rates under variable environmental conditions. As an example application, we consider the interface between rivers and groundwater which has been identified as a key driver for the turnover of reactive‐nitrogen compounds, that cause eutrophication of rivers and endanger drinking water production from groundwater. In the absence of measured data, we developed a reactive‐transport model for denitrification that simultaneously predicts the distributions of functional‐gene transcripts, enzymes, and reaction rates. Applying the model, we evaluate the response of transcripts and enzymes at the river‐groundwater interface to stable and dynamic hydrogeochemical regimes. While functional‐gene transcripts respond to short‐term (diurnal) fluctuations of substrate availability and oxygen concentrations, enzyme concentrations are stable over such time scales. The presence of functional‐gene transcripts and enzymes globally coincides with the zones of active denitrification. However, transcript and enzyme concentrations do not directly translate into denitrification rates in a quantitative way because of nonlinear effects and hysteresis caused by variable substrate availability and oxygen inhibition. Based on our simulations, we suggest that molecular‐biological data should be combined with aqueous geochemical data, which can typically be obtained at higher spatial and temporal resolution, to parameterize and calibrate reactive‐transport models.

Microbial activity evaluation and aerobic transformation of deep water offshore synthetic drilling fluids in soil: A case study of ternary mixture of synthetic ethyl esters of plants oil (Seep mixture) synthetic drilling fluid in agbami (Niger delta) deep water field

Approval for offshore discharge of cuttings drilled with synthetic-based drilling Fluids (SBFs) by environmental regulatory and protection agencies usually require detailed laboratory biodegradation analysis of the base fluid chemicals among others. This concept of using biodegradation test as an environmental fluid-compliance criterion is that a fluid that degrades readily in the laboratory will not persist for an extensive period of time in the offshore environment.Hence, this research focuses on microbial activity measurement and aerobic biodegradation of a newly developed synthetic ester fluid named “ternary mixture of synthetic ethyl esters of plants oil (SEEPmixture)” and its’ comparison with already existing synthetic deep water fluids (SHBF and SEBF) in Agbami deep water field. The chemical composition and components of each drilling fluid sample was analyzed by a GC system combined with a high resolution accurate mass (HRAM) spectrometer while a Fourier transform infra-red (FTIR) spectroscopy was used for functional group identification.The microbial activity of each soil sample that was contaminated with different base oils (drilling fluids) and that of the uncontaminated soil sample (control) was determined by trapping the carbon IV Oxide (CO2) evolved from each soil sample with a strong alkali solution of barium hydroxide (Ba(OH)2) as the microbial biomass actively decompose soil organic matter. The degradation of the drilling fluid chemicals was monitored under aerobic conditions.The soil contaminated with SEBF fluid chemical experienced a low microbial activity due to its low respiration (low amount of evolved carbon IV oxide per mg of soil) but a more pronounced adverse effect on microbial activity was experienced by soil contaminated with SHBF chemical. While microbial activities were not impaired with the SEEP mixture fluid chemical presence in the soil. Meanwhile, in regards to soil aerobic transformation, the SEEP mixture fluid took the shortest time of 13.6 days for it to decompose to half of its original concentration (5mg/kgsoil) from an initial concentration of 10 mg/kg soil. This implies that the fluid sample is readily and inherently biodegradable in soil. Whereas, the SHBF fluid sample required about 34.50 days for it to decompose to half of its original concentration. This indicates its non-readily biodegradable nature in soil. The half-life of the SEBF was 25 days and thus not readily biodegradable.

Electrochemical measurement of microbial activity

Electrochemical measurement of microbial activity

Linking soil microbial community structure to potential carbon mineralization: A continental scale assessment of reduced tillage

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity.

Influence of land use on the microbiological properties of urban soils

Advancing towards sustainable cities needs a better understanding of all components of urban ecosystems, including soils, but the biological component of urban soils remains poorly studied compared to natural and agricultural soils. With the objective of advancing knowledge in this aspect, we studied the microbiological properties in 61 soils of the city of Santiago de Compostela (NW Spain), under several land uses (urban grassland, urban forest, urban garden, and periurban arable land). We determined thirteen extracellular enzymatic activities as a proxy of microbial community functioning, along with measures of microbial activity (basal respiration), microbial abundance (DNA extraction and real-time PCR), and the composition of microbial communities (Illumina MiSeq sequencing on 16S rRNA and ITS marker regions). Results showed a high variability in all of the microbiological variables among soils, reflecting the typical spatial heterogeneity of urban soils. Respiration and enzymatic activities were highly correlated to soil organic matter contents but not affected by land use within the city, with the exception of alkaline phosphomonoesterase activity, which was higher in urban garden soils and correlated positively to pH and availability of phosphorus and nitrogen. Unlike fungal abundance, we recorded a higher bacterial abundance in the urban grasslands than in the other land uses. While the composition of bacterial communities was structured in a more homogeneous, land use-dependent manner (33% variance, pAdonis = 0.001), the respective fungal communities were more heterogeneous and less influenced by group-dependent characteristics (18%, pAdonis = 0.001). Soil pH had a larger influence on the bacterial community composition (28% variance) compared to the fungal composition (8.5% variance). Overall, these findings provide evidence that the typically high soil heterogeneity of urban ecosystems is the main driving force for the urban soil microbiome, with soil organic matter determining largely microbial activity.

Photoheterotrophy by aerobic anoxygenic bacteria modulates carbon fluxes in a freshwater lake

Lakes are a significant component of the global carbon cycle. Respiration exceeds net primary production in most freshwater lakes, making them a source of CO2 to the atmosphere. Driven by heterotrophic microorganisms, respiration is assumed to be unaffected by light, thus it is measured in the dark. However, photoheterotrophs, such as aerobic anoxygenic photoheterotrophic (AAP) bacteria that produce ATP via photochemical reactions, substantially reduce respiration in the light. They are an abundant and active component of bacterioplankton, but their photoheterotrophic contribution to microbial community metabolism remains unquantified. We showed that the community respiration rate in a freshwater lake was reduced by 15.2% (95% confidence interval (CI): 6.6–23.8%) in infrared light that is usable by AAP bacteria but not by primary producers. Moreover, significantly higher assimilation rates of glucose (18.1%; 7.8–28.4%), pyruvate (9.5%; 4.2–14.8%), and leucine (5.9%; 0.1–11.6%) were measured in infrared light. At the ecosystem scale, the amount of CO2 from respiration unbalanced by net primary production was by 3.69 × 109 g CO2 lower over these two sampling seasons when measured in the infrared light. Our results demonstrate that dark measurements of microbial activity significantly bias the carbon fluxes, providing a new paradigm for their quantification in aquatic environments.

Short-Term Effect of Nitrogen Fertilization on Carbon Mineralization during Corn Residue Decomposition in Soil

The effect of N fertilization on residue decomposition has been studied extensively; however, contrasting results reflect differences in residue quality, the form of N applied, and the type of soil studied. A 60 d laboratory incubation experiment was conducted to ascertain the effect of synthetic N addition on the decomposition of two corn (Zea mays L.) stover mixtures differing in C:N ratio by continuous monitoring of CO2 emissions and periodic measurement of microbial biomass and enzyme activities involved in C and N cycling. Cumulative CO2 production was greater for the high than low N residue treatment, and was significantly increased by the addition of exogenous N. The latter effect was prominent during the first month of incubation, whereas N-treated soils produced less CO2 in the second month, as would be expected due to more rapid substrate depletion from microbial C utilization previously enhanced by greater N availability. The stimulatory effect of exogenous N was verified with respect to active biomass, microbial biomass C and N, and cellulase and protease activities, all of which were significantly correlated with cumulative CO2 production. Intensive N fertilization in modern corn production increases the input of residues but is not conducive to soil C sequestration.

Application of the D-A-(C) index as a\xa0simple tool for microbial-ecological characterization and assessment of groundwater ecosystems\u2014a\xa0case study of the Mur River Valley, Austria

The assessment and monitoring of the ecological quality and status of groundwater is a timely issue. At present, various assessment tools have been developed that now await application and validation. One of these, the D‑A‑C index, evaluates the microbiological-ecological quality of groundwater based on of prokaryotic cell counts, microbial activity measurements, and the qualitative characterization of dissolved organic carbon (DOM). The purpose of this paper is to illustrate the different ways of application of the D‑A-(C) index making use of a recently collected data set (n = 61) from the river Mur valley, Austria. First, we present an extension of the D‑A-(C) index by including measurements of dissolved organic matter quality (DOM) derived from fluorescence spectroscopy as additional variables to supplement the analysis of microbial cell density and activity levels. Second, we illustrate how the definition of a reference status for a ‘good’ microbiological-ecological state can improve the analysis and allow for a more sensitive and accurate detection of impacts on groundwater ecosystems. Based on our results, we advocate that the analysis be performed by making use of expert knowledge for the definition of reference sites to which target sites are to be compared.

Quantifying Microbial Activity In Situ: the Link between Cells and Cycles.

Metagenomic sequencing of environmental samples has dramatically expanded our knowledge of microbial taxonomic and metabolic diversity and suggests metabolic interdependence is widespread. However, translating these insights into knowledge of ecosystem function and, therefore, implications for local and global chemistry, remains a challenge. In this commentary, I argue that making direct measurements of microbial activity in situ is an essential step to confirm gene-based hypotheses of microbial physiology and bridge advances in microbial ecology with a predicative understanding of global chemistry and climate. Making these measurements across a range of spatial scales and experimentally manipulated conditions contributes to a process-based understanding and, therefore, more robust predictions of how activity will respond to changing environmental conditions. I discuss recent advancements in quantifying microbial activity in situ and highlight several lines of research in marine microbiology that leverage complementary genomic and isotopic methods to connect microbes and global chemistry.

A survey of greenhouse gases production in central European lignites

Due to changes in the energy market, it is projected that lignite excavation will be reduced in the near future. Cessation of exploitation is associated with restitution of natural water conditions and flooding of the resources left in the mines. Flooded lignite mines are a potential source of greenhouse gases (GHG) (CH4, CO2 and N2O), which should be monitored due to growing environmental concerns. Here, we aim to recognize GHG release from the lignites collected from the main deposits of Poland, Slovenia and Serbia. GHG production was studied along with a range of physical and chemical parameters that are crucial for microbial growth and activity.The microcosm experiments showed that the main gas emitted from the lignites was carbon dioxide. Daily CO2 production was highly variable. The highest values were recorded for detroxylitic lignite collected from the Konin deposit (402.05 nmol CO2 g-1 day-1) while the lowest were for the Kolubara xylitic lignite (19.64 nmol CO2 g-1 day-1). Methane production was much lower and ranged from nearly zero to 66.75 nmol g dry mass-1 d-1. Nitrous oxide production was not detected. It was found that CO2 production, being a general measure of microbial activity, was positively affected by NO3- concentration and redox potential. With respect to methane formation, the lower atmospheric oxygen exposure of the sample from the Velenje underground mine compared to the samples from the opencast mines has been identified as a possible cause of the high methane production. The overall global warming potential (GWP) of the gases released by xylitic lignite was lowest among the samples. Preferential extraction of the detritic lignites is suggested as a means to reduce GHG emissions from the abandoned lignite mines.