Ulrich Gosewinkel

Conductimetric determination of soil urease activity

Abstract A fast and sensitive method to determine urease activity in soils is described. It involves extraction of NH4‐N with 1 N. KC1 : 0.01 N HC1 and measurement of NH4 concentration by electroconductivity using a steady state flow system across a membrane. Sampling was done directly from the extracts with an automatic sampler at 40 samples per hour. The detection limit for NH4‐N was below 0.05 ppm in the extract. Extracts could be stored at room temperature for 17 hours before measuring NH4. No post‐treatment hydrolysis of urea occured.

Degradation and enantiomeric fractionation of mecoprop in soil previously exposed to phenoxy acid herbicides - New insights for bioremediation.

Phenoxy acid-contaminated subsoils are common as a result of irregular disposal of residues and production wastes in the past. For enhancing in situ biodegradation at reducing conditions, biostimulation may be an effective option. Some phenoxy acids were marketed in racemic mixtures, and biodegradation rates may differ between enantiomers. Therefore, enantio-preferred degradation of mecoprop (MCPP) in soil was measured to get in-depth information on whether amendment with glucose (BOD equivalents as substrate for microbial growth) and nitrate (redox equivalents for oxidation) can stimulate bioremediation. The degradation processes were studied in soil sampled at different depths (3, 4.5 and 6m) at a Danish urban site with a history of phenoxy acid contamination. We observed preferential degradation of the R-enantiomer only under aerobic conditions in the soil samples from 3- and 6-m depth at environmentally relevant (nM) MCPP concentrations: enantiomer fraction (EF)<0.5. On the other hand, we observed preferential degradation of the S-enantiomer in all samples and treatments at elevated (μM) MCPP concentrations: EF>0.5. Three different microbial communities were discriminated by enantioselective degradation of MCPP: 1) aerobic microorganisms with little enantioselectivity, 2) aerobic microorganisms with R-selectivity and 3) anaerobic denitrifying organisms with S-selectivity. Glucose-amendment did not enhance MCPP degradation, while nitrate amendment enhanced the degradation of high concentrations of the herbicide.

DECOMPLEXATION OF PHOSPHATASE FROM EXTRACTED SOIL HUMIC SUBSTANCES WITH ELECTRON DONATING REAGENTS

A substance with phosphatase activity was isolated from a field soil. The isolation procedure involves two steps. First ammonium humates are formed by intermittent shaking of soil in 1.0 N ammonium acetate (pH 7.0) for 20 h. They are extracted by repeated rinsing with distilled water, after the ammonium acetate has been removed by filtration. The filtrate is dialyzed and freeze-dried. Then the phosphatase active part is isolated from the humic substances by decomplexation with 17.0 mM tetramethyl-p-phenylenediamine (TMePDA). The dialyzed filtrate accounted for 3.2% of the soils phosphatase activity. During freeze-drying 95.4% of the filtrates phosphatase activity was lost. A total of 1.77 g of freeze-dried filtrate was obtained per kilogram of soil; it had a phosphatase activity of 9.85 μmol p-nitrophenyl phosphate per gram per hour. Twenty-four percent of this enzyme activity was recovered in the step with TMePDA in a clear supernatant, while 97.3% of the solids was precipitated. The freeze-dried filtrate was found to be clay-free by x-ray analysis. The possibility of microorganisms being the immediate source of the phosphatase extracted is excluded by the initial filtration step, application of toluene, and sterility checks with nutrient agar plates and microscopic examination. The extracted phosphatase activity is heat-sensitive and follows Michaelis-Menten kinetics. It is suggested that the extracted phosphatase activity is enzymatic and resembles a fraction of the free phosphatase enzymes in soil. The bonding mechanism between enzyme and humic substances is discussed. Evidence is presented that free soil phosphatase is bonded to humic substances in the form of electron donor acceptor complexes, the humic substances being the acceptor.

High-Flow-Rate Impinger for the Study of Concentration, Viability, Metabolic Activity, and Ice-Nucleation Activity of Airborne Bacteria

The study of airborne bacteria relies on a sampling strategy that preserves their integrity and in situ physiological state, e.g. viability, cultivability, metabolic activity, and ice-nucleation activity. Because ambient air harbors low concentrations of bacteria, an effective bioaerosol sampler should have a high sampling efficiency and a high airflow. We characterize a high-flow-rate impinger with respect to particle collection and retention efficiencies in the range 0.5-3.0 μm, and we investigated its ability to preserve the physiological state of selected bacterial species and seawater bacterial community in comparison with four commercial bioaerosol samplers. The collection efficiency increased with particle size and the cutoff diameter was between 0.5 and 1 μm. During sampling periods of 120-300 min, the impinger retained the cultivability, metabolic activity, viability, and ice-nucleation activity of investigated bacteria. Field studies in semiurban, high-altitude, and polar environments included periods of low bacterial air concentrations, thus demonstrating the benefits of the impingers high flow rate. In conclusion, the impinger described here has many advantages compared with other bioaerosol samplers currently on the market: a potential for long sampling time, a high flow rate, a high sampling and retention efficiency, low costs, and applicability for diverse downstream microbiological and molecular analyses.

Biodegradation of marine oil spills in the Arctic with a Greenland perspective

New economic developments in the Arctic, such as shipping and oil exploitation, bring along unprecedented risks of marine oil spills. Microorganisms have played a central role in degrading and reducing the impact of the spilled oil during past oil disasters. However, in the Arctic, and in particular in its pristine areas, the self-cleaning capacity and biodegradation potential of the natural microbial communities have yet to be uncovered. This review compiles and investigates the current knowledge with respect to environmental parameters and biochemical constraints that control oil biodegradation in the Arctic. Hereby, seawaters off Greenland are considered as a case study. Key factors for biodegradation include the bioavailability of hydrocarbons, the presence of hydrocarbon-degrading bacteria and the availability of nutrients. We show how these key factors may be influenced by the physical oceanographic conditions in seawaters off Greenland and other environmental parameters including low temperature, sea ice, sunlight regime, suspended sediment plumes and phytoplankton blooms that characterize the Arctic. Based on the acquired insights, a first qualitative assessment of the biodegradation potential in seawaters off Greenland is presented. In addition to the most apparent Arctic characteristics, such as low temperature and sea ice, the impact of typical Arctic features such as the oligotrophic environment, poor microbial adaptation to hydrocarbon degradation, mixing of stratified water masses, and massive phytoplankton blooms and suspended sediment plumes merit to be topics of future investigation.

Aeolian dispersal of bacteria in southwest Greenland: Their sources, abundance, diversity and physiological states

Abstract The Arctic is undergoing dramatic climatic changes that cause profound transformations in its terrestrial ecosystems and consequently in the microbial communities that inhabit them. The assembly of these communities is affected by aeolian deposition. However, the abundance, diversity, sources and activity of airborne microorganisms in the Arctic are poorly understood. We studied bacteria in the atmosphere over southwest Greenland and found that the diversity of bacterial communities correlated positively with air temperature and negatively with relative humidity. The communities consisted of 1.3×103 ± 1.0×103 cells m−3, which were aerosolized from local terrestrial environments or transported from marine, glaciated and terrestrial surfaces over long distances. On average, airborne bacterial cells displayed a high activity potential, reflected in the high 16S rRNA copy number (590 ± 300 rRNA cell−1), that correlated positively with water vapor pressure. We observed that bacterial clades differed in their activity potential. For instance, a high activity potential was seen for Rubrobacteridae and Clostridiales, while a low activity potential was observed for Proteobacteria. Of those bacterial families that harbor ice‐nucleation active species, which are known to facilitate freezing and may thus be involved in cloud and rain formation, cells with a high activity potential were rare in air, but were enriched in rain. Figure. No Caption available.

Application of Cytosense flow cytometer for the analysis of airborne bacteria collected by a high volume impingement sampler

Characterization of airborne bacterial cells requires efficient collection, concentration, and analysis techniques, particularly to overcome the challenge of their dilute nature in outdoor environments. This study aims to establish a rapid and reliable approach for quantification of bacteria in air samples. To do this, a high volume impingement sampler was applied to collect airborne bacteria from a wastewater treatment plant (WWTP). The bacterial cell density was estimated by a Cytosense flow cytometer (Cytobouy) and compared to quantitative PCR (qPCR) data based on 16S rRNA genes. The average bacterial cell density measured by Cytosense ranged from 1.1 to 2.5 × 104 cells m-3 of air and that estimated by qPCR ranged from 0.08 to 3.8 × 104 cells m-3 of air. Regression analysis showed no systematic difference in bacterial cell densities between two methods applied when the cells were analyzed in vivo, and statistical tests confirmed that Cytosense counts of unfixed samples provided realistic values. Bacterial cell densities and the amount of DNA extracted from the sample were significantly correlated with relative humidity on a sampling day. The results showed that the present method was reliable to estimate bacteria densities from the outdoor environment, and the analysis given by Cytosense was faster and more sensitive than qPCR method. In addition, the Cytosense gave valuable information about cell characteristics at different sampling conditions.