Year Of Incubation Research Articles

Effect of fly ash on carbon mineralization of biochar and organic manures added to mine spoil

Mine spoil is deprived of organic carbon. Reclamation and re-vegetation of mine spoil initiate photosynthetic carbon fixation and add soil organic matter. Fly ash (FA) generated from coal-fired power stations can be used for reclamation of mine spoil. Our research was aimed to assess the effect on FA on carbon mineralization of organic manures and biochar added to mine spoil. Incubation experiments were conducted to assess the carbon mineralization of farmyard manure (FYM), chicken litter (CL), plant litter (PL), and biochar (BC) added to mine spoil in the presence and absence of FA. After 1 year of incubation, the cumulative CO2 emission was lower for the FA-added mine spoil and it was higher for PL (4.42 vs. 5.09 g CO2–C/kg soil, with and without FA, respectively) and CL (3.75 vs. 4.07 g CO2–C/kg soil) followed by FYM (1.86 vs. 1.97) and BC (0.67 vs. 0.54 g CO2–C/kg soil). The labile C pool was significantly lower for FA-added mine spoil, whereas the stable carbon pool was higher in FA-added soils: FYM (1.4 vs. 0.6 g CO2–C/kg soil) and CL (2.20 vs. 3.17 g CO2–C/kg soil). Substrate-induced respiration, microbial biomass carbon (MBC), and dissolved organic carbon (DOC) were significantly higher under PL, CL, and FYM. FA increased MBC, but decreased DOC. Overall, FA decreased CO2 emission from mine spoil probably due to the interaction of organic matter with the surfaces on FA and the resultant physical protection against microbial decomposition.

The stabilizing mechanism of cadmium in contaminated soil using green synthesized iron oxide nanoparticles under long-term incubation.

Despite numerous studies having been conducted on the stabilization of heavy metal contaminated soil, our understanding of the mechanisms involved remains limited. Here green synthesized iron oxide nanoparticles (GION) were applied to stabilize cadmium (Cd) in a contaminated soil. GION not only stabilized soil Cd, but also improved soil properties within one year of incubation. After GION application both the exchangeable and carbonate bound Cd fractions decreased by 14.2-83.5% and 18.3-85.8% respectively, and most of the Cd was translocated to the residual Cd fraction. The application of GION also strongly altered soil bacterial communities. In GION treatments, the abundance of Gemmatimonadetes, Proteobacteria, and Saccharibacteria increased which led to a shift in the dominant bacterial genera from Bacillus to Candidatus koribacter. The variation in bacteria confirmed the restoration of the contaminated soil. The most abundant bacterial genus and species found in GION treatments were related to (i) plant derived biomass decomposition; (ii) ammoxidation and denitrification; and (iii) Fe oxidation. GION application may enhance the formation of larger soil aggregates with anaerobic centers and coprecipitation coupled Fe (II) oxidization, ammoxidation and nitrite reduction followed by Fe mineral ripening may be involved in Cd stabilization. The predominant stabilization mechanism was thus coprecipitation-ripening-stabilization.

Plant litter decomposition in a semiarid rangeland of Argentina: species and defoliation effects

Plant litter decomposition is critical for terrestrial ecosystem productivity. Poa ligularis Nees ex Steud and Nassella tenuis (Phil.) Barkworth are native, desirable perennial grasses in central Argentina’s rangelands. Amelichloa ambigua (Speg.) Arriaga & Barkworth is only consumed when a better forage is unavailable. Litter traps were used to collect aboveground litter during two years. In March 2012, six bags, each one containing either leaf blade (three bags, one per species) or root litter (three bags, one per species) of the three species were located below the canopy of each replicate plant of the studied species (hereafter referred to as ‘location’). Blade litter bags were located on the soil surface, and root litter bags buried at 10cm soil depth. This allowed evaluation of the effects of defoliation, the different species canopies and the microbial community activity around their roots on decomposition of above- and belowground litter. For each species, twenty plants were either defoliated twice (5cm stubble height) or remained undefoliated during the growing season. Litter bags were collected after 2, 7, 13 and 24 months incubation. The study was repeated in 2013, with additional bags were placed for N content determination on leaf blade and root litters. Aboveground litter production was highest in P. ligularis; however, no differences were observed among species when the effect of plant size was eliminated. Aboveground litter of desirable species had higher N content and decomposed faster than that of A. ambigua. The opposite was recorded for root litter. Defoliation had no effect on litter decomposition, but location effects were detected after one year of incubation. Desirable perennial grasses promoted organic matter loss from litter, a key factor in increasing soil fertility in this semiarid ecosystem.

Influence of pH and redox on mobilization of inositol hexakisphosphate from oligotrophic lake sediment

It has been suggested that inositol hexakisphosphate (IP6) contributes to the release of phosphorus (P) from lake sediments, but a mechanistic understanding remains elusive. We investigated the potential mobilization and mineralization of myo- and scyllo-IP6 from the sediment of an oligotrophic Danish lake known to contain high concentrations of inositol phosphates. Solution 31P NMR spectroscopy was used to determine changes in myo- and scyllo-IP6 in laboratory microcosms incubated under either oxic or anoxic conditions. In addition, we incubated sediment slurries adjusted to pH between 4.9 and 6.6, with and without addition of myo-IP6, and induced redox changes by adding starch and sulfate. We observed no significant changes in myo- or scyllo-IP6 after 1 year of incubation under anaerobic conditions. A sequential extraction procedure revealed that one half of the added myo-IP6 was recovered in the humic acid fraction (acid-insoluble organic matter) and the other half in the fulvic acid fraction (acid-soluble organic matter). Reduction in redox potential by starch addition did not mobilize myo-IP6, but myo-IP6 bound to humic acids was released to the pore water when the pH was increased to ≥ 5.8. This pH-induced mobilization of IP6 occurred in parallel with increases in dissolved iron and organic matter, suggesting the release of IP6 bound to humic acids through metal bridges. We conclude that myo-IP6 mobilization from this oligotrophic lake sediment is driven by changes in pH rather than by changes in the redox potential.

Positive and negative effects of UV irradiance explain interaction of litter position and UV exposure on litter decomposition and nutrient dynamics in a semi-arid dune ecosystem

Solar radiation mediated photodegradation of leaf litter has been studied substantially as it plays important roles in the cycling of carbon (C) and nutrients in dryland ecosystems. However, the mechanism by which ultraviolet (UV) radiation and its interaction with litter quality and microbial degradation affect dryland litter decomposition is still uncertain. A field experiment was carried out in semiarid Mu Us inland dunes of Inner Mongolia, China to investigate the effects of UV radiation and litter position on leaf litter decomposition of eight contrasting species (three perennial grasses, three shrubs, two annual forbs) representing different litter qualities over a whole year of incubation. The results showed that UV radiation increased mass loss of suspended litters for two perennial grasses and two annual forbs, but had no significant effect on the other four species considered; across species the percentage increase in mass loss ranged from 4.5 to 27.3% with an average of 13.7%. C release from suspended litters in response to UV radiation showed similar patterns with mass loss. Nitrogen (N) release from litters on the soil surface was lower than in suspended position because the former was involved in N immobilization driven by microbial decomposition. There were no net effects of UV radiation on decomposition rates of surface litters possibly due to the positive effects of photochemical process offsetting negative effects on microbes. Multiple linear regressions showed that the C:N ratio of initial leaf litter and leaf dry matter content (LDMC) could predict the rate of litter decomposition, in which litter C:N ratio had stronger influence. The findings, based on multiple species, highlight the importance of photodegradation on litter nitrogen and/or carbon mineralization in drylands as mediated by different abiotic and biotic drivers.

Dominant effects of organic carbon chemistry on decomposition dynamics of crop residues in a Mollisol

Understanding the change in chemical composition of crop residues during their decomposition is crucial to elucidate the mechanisms underlying the effects of residue retention on soil carbon (C) sequestration and nutrient cycling. Here a field experiment was carried out to investigate the decomposition process of maize, soybean, and wheat residues in a cultivated Mollisol in northeast China over a year. Using a litterbag method, we monitored the dynamics of residue mass loss, concentration of C and nitrogen (N), and C/N ratio, and evaluated the decomposition rates of residues and C functional groups. Chemical compositions of the crop residues were determined by solid-state 13C nuclear magnetic resonance spectroscopy, and the cellulose crystallinity, lignin concentration, and syringyl to guaiacyl (S/G) ratio of lignin were estimated. After one year of incubation in field conditions, mass loss was 57% for soybean residues, significantly greater than 52% for maize and 45% for wheat. The decomposition rate of residues significantly decreased from 0.223 to 0.379 month−1 during the first month to 0.054–0.076 month−1 over the whole period. The proportion of decomposed C ranged at 57–63% among different residues, and had a positive relationship with the mass loss of O-alkyl C, di-O-alkyl C, and carbonyl C. The decomposition rates of these three C functional groups were greater in soybean than those in maize and wheat residues, which was also the case for lignin S/G ratio, possibly accounting for the higher decomposition extent of soybean residues. As decomposition progressed, the C chemistry of maize, soybean, and wheat residues exhibited an increasing divergence, which was mainly related to relative decreases in O-alkyl C and di-O-alkyl C contents, and relative increases in phenolic C and aromatic C contents in the residues. Net N release was observed for all residues after one-year decomposition, and was significantly related to the mass loss of alkyl C, O-alkyl C, and aromatic C. Overall, our study provides insight into chemical changes of crop residues over the degradation processes in the field, and highlights the significant effects of organic C chemistry on residue decomposition.

Enzyme-mediated formulation of stable elliptical silver nanoparticles tested against clinical pathogens and MDR bacteria and development of antimicrobial surgical thread

BackgroundSilver nanoparticles (AgNPs) are believed to be emerging tool against various infectious diseases including multi-drug resistant (MDR) bacteria. In the present study, in vitro synthesis of AgNPs was optimized using 1:50 ratio of macerozyme (25 μg/μl) and 1 mM AgNO3 incubated at 80 °C for 8 h. AgNPs were characterized by UV–Visible spectroscopy, dynamic light scattering (DLS), scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD).ResultsCharacterization studies suggest the synthesis of elliptical, stable and crystalline AgNPs with an average size of 38.26 ± 0.4 nm calculated using TEM. The XRD pattern revealed the face-centered-cubic (fcc) form of metallic silver. Good shape integrity and dispersion of AgNPs after 1 year of incubation confirmed their stability. AgNPs were exibited the antimicrobial property against ten pathogenic bacteria, three molds and one yeast. The AgNPs also revealed remarkable antimicrobial activity against three MDR strains i.e. Extended spectrum beta-lactamase positive Escherichia coli, Staphylococcus aureus (MRSA) and Teicoplanin resistant Streptococcus Pneumoniae. The AgNPs coated surgical threads (suture) were revealed the remarkble antibacterial activity against three MDR strains. This is the first report to synthesize antimicrobial elliptical AgNPs using enzymes.Conclusion The results suggest the possibilities to develop the nanoparticles coated antimicrobial medical fabric to combat against MDR infection.

Selenate redistribution during aging in different Chinese soils and the dominant influential factors

To date, few works have attempted to determine the effect of soil types on Selenium aging process and the possible influential factors. In this study, the differences in Se speciation distribution and availability in 15 Chinese typical agricultural soils were investigated using spiked selenate for the entire year. Results evidenced that after one year of incubation, Se transformed from soluble fraction to Fe/Mn oxides and organic matter bound fractions in neutral or alkaline soils (pH 7.09–8.51) and from exchangeable fraction to residual fraction in acidic soils (pH 4.89–6.82). The available Se content in all soils declined rapidly at the initial stage of aging, with most of the neutral or alkaline soils reaching equilibrium after 109 d, whereas the acidic soils reached equilibrium after only 33–56 d. The available Se content in soil decreased constantly during the entire aging process in S4 (Xinjiang Gray desert soil), S12 (Anhui Yellow brown earths), and S15 (Hunan Krasnozems). Elovich model was the best model (R2 > 0.80) in describing the Se aging process. Estimated time for exogenous Se reaching the distribution of available Se in corresponding native soils extended from 9.7 y to 50.2 y, indicating a much longer time was required for spiked soil to reach equilibrium. Soil pH was the most significant factor directly and negatively influencing the aging process (p < 0.05), while organic matter played a dual role on Se speciation. Results could provide reference for the selection of unified equilibrium time on Se-spiked experiment.

Hydrogen dynamics in soil organic matter as determined by &amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C and &amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt;H labeling experiments

Abstract. Understanding hydrogen dynamics in soil organic matter is important to predict the fate of 3H in terrestrial environments. One way to determine hydrogen fate and to point out processes is to examine the isotopic signature of the element in soil. However, the non-exchangeable hydrogen isotopic signal in soil is complex and depends on the fate of organic compounds and microbial biosyntheses that incorporate water-derived hydrogen. To decipher this complex system and to understand the close link between hydrogen and carbon cycles, we followed labeled hydrogen and labeled carbon throughout near-natural soil incubations. We performed incubation experiments with three labeling conditions: 1 – 13C2H double-labeled molecules in the presence of 1H2O; 2 – 13C-labeled molecules in the presence of 2H2O; 3 – no molecule addition in the presence of 2H2O. The preservation of substrate-derived hydrogen after 1 year of incubation (ca. 5 % in most cases) was lower than the preservation of substrate-derived carbon (30 % in average). We highlighted that 70 % of the C–H bonds are broken during the degradation of the molecule, which permits the exchange with water hydrogen. Added molecules are used more for trophic resources. The isotopic composition of the non-exchangeable hydrogen was mainly driven by the incorporation of water hydrogen during microbial biosynthesis. It is linearly correlated with the amount of carbon that is degraded in the soil. The quantitative incorporation of water hydrogen in bulk material and lipids demonstrates that non-exchangeable hydrogen exists in both organic and mineral-bound forms. The proportion of the latter depends on soil type and minerals. This experiment quantified the processes affecting the isotopic composition of non-exchangeable hydrogen, and the results can be used to predict the fate of tritium in the ecosystem or the water deuterium signature in organic matter.

In situ and laboratory non-additive litter mixture effect on C dynamics of Sphagnum rubellum and Molinia caerulea litters

The accumulation of carbon in peatlands originates from the slow rate of Sphagnum litter decomposition. Vegetation shifts can alter the Sphagnum decomposition rate through a litter mixture effect. This is rarely studied in peatlands. In a site colonised by vascular plants, we examined the effect of mixing litters of Sphagnum species with those of Molinia caerulea and Betula spp. on litter carbon (C) dynamics. We tested that water content and pH may explain the potential non-additive litter mixing effect. Litter bags with Sphagnum cuspidatum or Sphagnum rubellum and M. caerulea or Betula spp. were placed in situ, in a Sphagnum decomposing environment and retrieved after 1 year of incubation. In the laboratory, the specific interaction between S. rubellum and M. caerulea was investigated. Solid, soluble and gaseous forms of C were studied in addition to the fluorescence of the dissolved organic matter (FDOM). Laboratory and field experiments showed that there is a non-additive effect of mixing S. rubellum and M. caerulea litter on C dynamics. The analyses of FDOM suggested a relatively higher living biomass in the laboratory-measured mixture than in the expected one. The in situ S. rubellum moist environment could stimulate the decomposition of M. caerulea that experiences much drier conditions in its native environment. In the laboratory experiment, M. caerulea were kept moist, and no significant difference in water content between the measured and expected mixture was found. Also, pH decreased in the measured mixture, ruling out any direct effect on microbial activity. The non-additive mixture effect observed in the laboratory may be triggered by an increase of the microbial biomass. This increase was not explained by direct moisture or a pH effect. The suggested hypothesis that a lower pH could affect the availability of labile organic substrate through increased organic matter (OM) hydrolysis and thus stimulate microbial growth has to be further studied.

Predicting the denitrification capacity of sandy aquifers from in situ measurements using push–pull &amp;lt;sup&amp;gt;15&amp;lt;/sup&amp;gt;N tracer tests

Abstract. Knowledge about the spatial variability of in situ denitrification rates (Dr(in situ)) and their relation to the denitrification capacity in nitrate-contaminated aquifers is crucial to predict the development of groundwater quality. Therefore, 28 push–pull 15N tracer tests for the measurement of in situ denitrification rates were conducted in two sandy Pleistocene aquifers in northern Germany. The 15N analysis of denitrification-derived 15N-labelled N2 and N2O dissolved in water samples collected during the push–pull 15N tracer tests was performed using isotope ratio mass spectrometry (IRMS) in the lab and additionally for some tracer tests online in the field with a quadrupole membrane inlet mass spectrometer (MIMS) in order to test the feasibility of on-site real-time 15N analysis. Aquifer material from the same locations and depths as the push–pull injection points was incubated, and the initial and cumulative denitrification after 1 year of incubation (Dcum(365)) as well as the stock of reduced compounds (SRC) was compared with in situ measurements of denitrification. This was done to derive transfer functions suitable to predict Dcum(365) and SRC from Dr(in situ). Dr(in situ) ranged from 0 to 51.5 μg N kg−1 d−1. Denitrification rates derived from on-site isotope analysis using MIMS satisfactorily coincided with laboratory analysis by conventional IRMS, thus proving the feasibility of in situ analysis. Dr(in situ) was significantly higher in the sulfidic zone of both aquifers compared to the zone of non-sulfidic aquifer material. Overall, regressions between the Dcum(365) and SRC of the tested aquifer material with Dr(in situ) exhibited only a modest linear correlation for the full data set. However, the predictability of Dcum(365) and SRC from Dr(in situ) data clearly increased for aquifer samples from the zone of NO3−-bearing groundwater. In the NO3−-free aquifer zone, a lag phase of denitrification after NO3− injections was observed, which confounded the relationship between reactive compounds and in situ denitrification activity. This finding was attributed to adaptation processes in the microbial community after NO3− injections. It was also demonstrated that the microbial community in the NO3−-free zone just below the NO3−-bearing zone can be adapted to denitrification by NO3− injections into wells for an extended period. In situ denitrification rates were 30 to 65 times higher after pre-conditioning with NO3−. Results from this study suggest that such pre-conditioning is crucial for the measurement of Dr(in situ) in deeper aquifer material from the NO3−-free groundwater zone and thus for the prediction of Dcum(365) and SRC from Dr(in situ).

Usage of X-ray absorption spectroscopy and extractive fractionation in studies of the Cu (II) and Zn (II) ions in soils

XANES spectroscopy is an effective method for the study of bonds between metals and soil components. The study of structural organization in different soil samples and soil phases saturated with Cu 2+ and Zn 2+ ions by using XANES allowed determining the mechanism of their interaction with soil phases and all the chemical bindings taken place in the course of this process. Changes in the structure of the metal ion, in particular breakdown of the symmetry of electron orbits of atoms, take place due to interaction with soil components. Application of this method demonstrated that the state of copper and zinc introduced in chernozem as oxides did not change after one year of incubation. Copper is absorbed after being introduced as soluble salts, and copper ions are incorporated in the octahedral and tetrahedral sites of minerals and bonded with humic materials at the expense of covalent bond and the formation of coordination humate copper complexes. Zinc included into octahedric structures of layered minerals and hydro(oxides) can be inner-and outer-sphere adsorbed. It is shown that the action of the metal bound to soil components becomes weakened in case of increasing the Cu and Zn load (from 2000 to 10000 mg/kg) especially applied in the form of soluble salts. Extractive fractionation of metal compounds in chernozem samples, artificially contaminated with copper and zinc salts serves as evidence of absorbing the applied Cu 2+ ions by the soil organic matter and Zn 2+ ions – by silicates, carbonates, and Fe-Mn oxides.

Accelerated foliar litter humification in forest gaps: Dual feedbacks of carbon sequestration during winter and the growing season in an alpine forest

Can forest gaps lead to constrained litter decomposability by redistributing heat and moisture conditions, thereby increasing carbon sequestration from plant to soil via litter humification in alpine forests? We studied mass losses, humic substances, humic acid, fulvic acids, as well humification degrees and humification ratios in six foliar litters with a field litterbag experiment from the gap center, canopy gap and expanded gap to the closed canopy in winter and the growing season in an alpine forest of the east Tibetan Plateau. Humification degrees of 18%–45% for birch, 15%–40% for fir, 8%–30% for willow, 14%–26% for cypress, 9%–25% for larch and 7%–19% for azalea foliar litter were observed in forest gaps and the closed canopy over one year of incubation. Small amounts of humic substances accumulated in winter, whereas considerable humic acid accumulated, but fulvic acid mineralized during the growing season. Compared with the closed canopy, foliar litter humification in forest gaps was lower in winter but greater in the growing season, implying a dual role of forest gaps in carbon sequestration between winter and the growing season. Carbon sequestration could be accelerated in forest gaps. Reduced snow cover under a scenario of winter warming would stimulate soil carbon storage in these alpine forests.

Composted organic wastes from the pharmaceutical and agro‐food industries induce soil bioactivity and nodulation in alfalfa

Environmentally friendly agriculture needs to reduce the use of synthetic fertilizers and to reclaim nutrients from organic wastes. In this study the effect of five doses (0, 12, 24, 48 and 96 t ha(-1) ) of two two-phase olive mill waste (TPOMW)-based composts on the bioactivity and chemical characteristics of an agricultural soil and their potential to fertilize alfalfa (Medicago sativa) and stimulate nodulation were assessed during a two-year incubation experiment. The two composts were prepared either with the olive mill waste alone (compost A), which served as control, or mixed with a liquid fatty-proteinaceous hydrolyzate waste (FPH) from the pharmaceutical industry (compost AH). Compost AH resulted in greater N immobilization than compost A because the former supplied the soil with easily degradable C and N, which increased microbial biomass and activity. Both compost mineralizations during the first year of incubation supplied the soil with more nutrients (mainly N), more so with A than with AH. Nevertheless, plant growth was similar in soils amended with either A or AH. Both composts induced nodulation similarly and the highest dose (96 t ha(-1) ) increased the formation of nodules by a factor of 11 compared with the four lower doses. TPOMW serves as an effective ground material for co-composting with liquid wastes such as FPH. TPOMW supplies key nutrients and stimulates nodulation in alfalfa.

Non-culturability and Nisin Production of Lactococcus lactis

We studied formation of non-culturable forms of three bacteriocin (nisin) producing strains of Lactococcus lactis sub sp. lactis: MSU, 729 and F-116 under carbohydrate starvation stress. Two different types of inoculum were applied: A) unwashed cells with culture liquid, B) cells washed twice with normal 0,9%saline. Resulting total numbers of cells were 0.6 1.0×108 cells/ml for both types of inoculum. Population obtained using type A inoculum demonstrated active growth phase within first 1-5 days of incubation (up to 2.4×109 cells/ml) while those obtained using type B inoculum did not grow within that period. Type B population of strain MSU showed phenotypic dissociation that resulted in appearance of micro colonies. After that, we observed active growth phase (up to 5.2×109 cells/ml). Type B cultures of strains 729 and F-116 did not grow during the whole experiment. It was shown that type A population shifted into non-culturability faster than type B. This is due to differences in metabolic strategies and stress sensitivity of these types of population. After 1 year of incubation (383 days) culturability decreased by 3 orders of magnitude for type B (5 orders for type B population of strain MSU) and by 6 orders of magnitude for type A population. We also observed considerable reduction of cell size for type A population of strains 729 and F-116. Studies of bacteriocin activity showed that in type B population cells were up to 78 times more productive compared to those of type A cultures. This phenomenon can be explained by differences in survival strategies of population that use antibacterial potential of bacteriocins for their benefit.

Phylogenetically Distinct Bacteria Involve Extensive Dechlorination of Aroclor 1260 in Sediment-Free Cultures

Microbial reductive dechlorination of the persistent polychlorinated biphenyls (PCBs) is attracting much attention in cleanup of the contaminated environment. Nevertheless, most PCB dechlorinating cultures require presence of sediment or sediment substitutes to maintain their dechlorination activities which hinders subsequent bacterial enrichment and isolation processes. The information on enriching sediment-free PCB dechlorinating cultures is still limited. In this study, 18 microcosms established with soils and sediments were screened for their dechlorination activities on a PCB mixture – Aroclor 1260. After one year of incubation, 10 out of 18 microcosms showed significant PCB dechlorination with distinct dechlorination patterns (e.g., Process H, N and T classified based on profiles of PCB congeners loss and new congeners formation). Through serial transfers in defined medium, six sediment-free PCB dechlorinating cultures (i.e., CW-4, CG-1, CG-3, CG-4, CG-5 and SG-1) were obtained without amending any sediment or sediment-substitutes. PCB dechlorination Process H was the most frequently observed dechlorination pattern, which was found in four sediment-free cultures (CW-4, CG-3, CG-4 and SG-1). Sediment-free culture CG-5 showed the most extensive PCB dechlorination among the six cultures, which was mediated by Process N, resulting in the accumulation of penta- (e.g., 236-24-CB) and tetra-chlorobiphenyls (tetra-CBs) (e.g., 24-24-CB, 24-25-CB, 24-26-CB and 25-26-CB) via dechlorinating 30.44% hepta-CBs and 59.12% hexa-CBs after three months of incubation. For culture CG-1, dechlorinators mainly attacked double flanked meta-chlorines and partially ortho-chlorines, which might represent a novel dechlorination pattern. Phylogenetic analysis showed distinct affiliation of PCB dechlorinators in the microcosms, including Dehalogenimonas and Dehalococcoides species. This study broadens our knowledge in microbial reductive dechlorination of PCBs, and provides essential information for culturing and stimulating PCB dechlorinators for in situ bioremediation applications.

Predicting the denitrification capacity of sandy aquifers from shorter-term incubation experiments and sediment properties

Abstract. Knowledge about the spatial variability of denitrification rates and the lifetime of denitrification in nitrate-contaminated aquifers is crucial to predict the development of groundwater quality. Therefore, regression models were derived to estimate the measured cumulative denitrification of aquifer sediments after one year of incubation from initial denitrification rates and several sediment parameters, namely total sulphur, total organic carbon, extractable sulphate, extractable dissolved organic carbon, hot water soluble organic carbon and potassium permanganate labile organic carbon. For this purpose, we incubated aquifer material from two sandy Pleistocene aquifers in Northern Germany under anaerobic conditions in the laboratory using the 15N tracer technique. The measured amount of denitrification ranged from 0.19 to 56.2 mg N kg−1 yr−1. The laboratory incubations exhibited high differences between non-sulphidic and sulphidic aquifer material in both aquifers with respect to all investigated sediment parameters. Denitrification rates and the estimated lifetime of denitrification were higher in the sulphidic samples. For these samples, the cumulative denitrification measured during one year of incubation (Dcum(365)) exhibited distinct linear regressions with the stock of reduced compounds in the investigated aquifer samples. Dcum(365) was predictable from sediment variables within a range of uncertainty of 0.5 to 2 (calculated Dcum(365)/measured Dcum(365)) for aquifer material with a Dcum(365) &gt; 20 mg N kg−1 yr−1. Predictions were poor for samples with lower Dcum(365), such as samples from the NO3− bearing groundwater zone, which includes the non-sulphidic samples, from the upper part of both aquifers where denitrification is not sufficient to protect groundwater from anthropogenic NO3− input. Calculation of Dcum(365) from initial denitrification rates was only successful for samples from the NO3−-bearing zone, whereas a lag-phase of denitrification in samples from deeper zones of NO3− free groundwater caused imprecise predictions. In our study, Dcum(365) of two sandy Pleistocene aquifers was predictable using a combination of short-term incubations and analysis of sediment parameters. Moreover, the protective lifetime of denitrification sufficient to remove NO3− from groundwater in the investigated aquifers is limited, which demonstrates the need to minimise anthropogenic NO3− input.

Spatio-temporal patterns of microbial communities in a hydrologically dynamic pristine aquifer

Seasonal patterns of groundwater and sediment microbial communities were explored in a hydrologically dynamic alpine oligotrophic porous aquifer, characterized by pronounced groundwater table fluctuations. Rising of the groundwater level in consequence of snow melting water recharge was accompanied by a dramatic drop of bacterial Shannon diversity in groundwater from H' = 3.22 ± 0.28 in autumn and winter to H' = 1.31 ± 0.35 in spring and summer, evaluated based on T-RFLP community fingerprinting. Elevated numbers of bacteria in groundwater in autumn followed nutrient inputs via recharge from summer rains and correlated well with highest concentrations of assimilable organic carbon. Sterile sediments incubated to groundwater in monitoring wells were readily colonized reaching maximum cell densities within 2 months, followed by a consecutive but delayed increase and leveling-off of bacterial diversity. After 1 year of incubation, the initially sterile sediments exhibited a similar number of bacteria and Shannon diversity when compared to vital sediment from a nearby river incubated in parallel. The river bed sediment microbial communities hardly changed in composition, diversity, and cell numbers during 1 year of exposure to groundwater. Summing up, the seasonal hydrological dynamics were found to induce considerable dynamics of microbial communities suspended in groundwater, while sediment communities seem unaffected and stable in terms of biomass and diversity.

Fouling and Degradation of Polycarbonate in Seawater: Field and Lab Studies

Biofouling and ensuing microbial mediated degradation of Bisphenol A polycarbonate was studied by immersing the samples in sea water of Bay of Bengal (Chennai, India) for 3 months and also under controlled laboratory conditions with marine mixed microbial consortia for 12 months. A 9% weight loss in the sample was observed after 1 year of incubation under in vitro laboratory conditions. A 5% reduction in number average molecular weight and an additional oligomer with a molecular weight of 930 was observed in the same sample. Contact angle decreased by 11% indicating an increase in the surface hydrophilicity. The specific heat decreased by 44% and glass transition temperature decreased by 3 °C with respect to the control indicating chain scission. Formation of new hydroxyl groups and cleavage of carbonate bonds in polycarbonate suggested biodegradation. About 9 μg mL−1 of Bisphenol A, a monomer of polycarbonate, as well as its oxidized products were detected in the supernatant. The nature of degradation in field and in vitro was different. It was predominantly oxidation in the former and hydrolysis in the later environment. A strain exhibiting hydrolase activity was isolated at the end of the 12 months from the in vitro mixed consortia and was identified, based on biochemical and 16S rDNA tests, as Pseudomonas sp. BP2 (GenBank accession no. EU920674).

In vitro receptivity of carbonate rocks to endolithic lichen-forming aposymbionts

Sterile cultured isolates of lichen-forming aposymbionts have not yet been used to investigate lichen–rock interactions under controlled conditions. In this study mycobionts and photobiont of the endolithic lichens Bagliettoa baldensis and Bagliettoa marmorea were isolated and inoculated with coupons of one limestone and four marbles commonly employed in the Cultural Heritage framework. After one year of incubation, microscopic observations of polished cross-sections were performed to verify if the typical colonization patterns observed in the field may be reproduced in vitro and to evaluate the receptivity of the five lithotypes to endolithic lichens. The mycobionts of the two species developed both on the surface of and within all the lithotypes, showing different penetration pathways which depend on mineralogical and structural features and highlight different receptivity. By contrast, algae inoculated with the coupons did not penetrate them. Observations suggest that the hyphal penetration along intrinsic discontinuities of rocks is a relatively fast phenomenon when these organisms are generally considered as slow-growing. Samples from limestone outcrops and abandoned marble quarries, colonized by the same species or other representatives of Verrucariaceae, showed penetration pathways intriguingly similar to those reproduced in vitro and highlighted that lichen-driven erosion processes only increase the availability of hyphal passageways after a long-term colonization. These results show that in vitro incubation of sterile cultured lichen-forming ascomycetes with rock coupons is a practicable experimental system to investigate the lichen–rock interactions under controlled conditions and, together with analysis in situ, may support decisions on conservative treatments of historical and cultural significant stone substrata.