Influence of biofilms on the water repellency of urban soil samples

ArticleinHydrological Processes 21(17):2276 - 2284 · August 2007with 49 Reads
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Abstract
Water repellency is an important phenomenon in soil systems and is influenced by physical, chemical and biological factors. Studies on the influence of bacteria or surface-attached bacteria (biofilms) on soil water repellency are rare. In this study, we investigated the influence of hydrophilic and hydrophobic bacteria on soil wettability. Three different soil bacteria, Variovorax paradoxus, Bacillus sphaericus and an α-Proteobacterium, were investigated in different states (vegetative cells and spores in the case of Bacillus sphaericus). The bacteria, isolated from urban soils in the Berlin Tiergarten Park and from a sewage field (in Berlin-Buch), were grown in a bioreactor on sterilized soil samples and in batch cultures on four different synthetic materials with hydrophobic and hydrophilic surfaces, to form biofilms. Surface hydrophobicity of the overgrown material was determined by the water contact angle, and cell surface characteristics of bacteria were measured using the zeta potential and a hexadecane-two-phase-system. The α-Proteobacterium and Variovorax paradoxus were classified as hydrophobic, and Bacillus sphaericus was classified as hydrophilic. Contact angles of the overgrown synthetic materials showed a significant influence of the respective material, but differences between the bacteria were not significant. The differences between the materials may be due to effects of the material on biofilm growth or EPS properties. EPS form biofilm matrices and are mainly responsible for aggregate cohesion. The bacterial EPS of the hydrophobic α-Proteobacterium were more hydrophilic than the cell walls, while those of Bacillus sphaericus were less hydrophilic. In contrast to the artificial materials, differences in contact angle for the inoculated soil sample showed significant differences between the bacterial strains. The α-Proteobacterium was able to hydrophobize the soil sample, while Bacillus sphaericus showed significant hydrophilization. The results clearly demonstrate the effect of bacterial biofilms on soil wettability. Copyright

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    Background and Objectives: Soil Water Repellency (SWR) is one of the dynamic soil characteristics that either reduce water penetration in the soil or prevent it. In the northern forest areas of Iran, fire is one of the most important environmental concerns and is one of the main causes of the change in soil water repellency phenomenon. Therefore, this study aims to investigate prescribed fire effect on the soil of forest areas of Toshen's watershed, temporal variability and its interaction with physical and chemical properties of soil in Golestan Province. Materials and Methods: Soil of forest areas in the slope class of 15-30% and depth of 0-5 cm of soil surface was studied in 30 replications in laboratory. Physical and chemical properties of soil, including percent of clay, silt and sand, soil organic matter, pH, EC and aggregate stability (MWD) were investigated before and after fire. In order to study the effects of fire on soil water repellency in laboratory conditions, prescribed fire was applied. SWR was determined with Water Drop Penetration Time and Molarity of an Ethanol Droplet tests, before and after fire. Results: According to the WDPT test, before the fire, 100% of plots were wettable (class 1), but one day after the fire, 100% of the plots were showed slightly water repellent (class 2 and 3). The MED test showed that all plots were wettable (class 0) before the fire. One day after the fire, the intensity of SWR increased, so that 30, 50 and 20% of the plots were slightly water repellent (class 1), moderately water repellent (class 2) and less strongly water repellent (class 3), respectively. Investigating the process of temporal variability of both SWR indices showed that the SWR class after the fire is temporary and up to one month after that, the SWR classes is greatly reduced. The results showed that there are good correlations between two post-fire hydrophobic tests. (R2=0.85). There was a moderate correlation between two WDPT and MED SWR tests with pH, EC, MWD and soil organic matter, but as for soil texture components, there was poor correlation. Relatively poor SWR correlations with soil physical and chemical characteristics indicate that these changes are not likely to be the main cause of SWR changes. Some of these changes can be explained by the variability of aggregate stability after the fire. These changes in the mechanical stability of the soil structure can be caused by two main mechanisms: (1) Changes in the composition of the solid components in the soil that increase the cohesion forces between the particles in the aggregates. Consequently, the stability of the soil structure against the physically destructive forces increases. (2) Changes in the physicochemical properties of the soil solution (an increase in the EC) that prevent clay dispersion and microaggregate destruction (physicochemical mechanism). Conclusion: Finally, the results of this study showed that despite the high wettability in loess soils, fire can be an external factor that causes a weak and immediate increase in SWR. The slightly soil water repellent may be due to the following: (i) SWR often occur in coarse soils with high organic matter. (ii) The samples were taken from the soil surface layer (0-5 cm), while the fire can cause some organic matter to accumulate in the subsurface layers and cause SWR on lower horizons.
  • Article
    The organic matter cycle is one of the most fundamental processes in ecosystems affecting the soil and controlling its functions. The soil complex microbiome is made up of thousands of bacterial and hundreds of fungal strains that coexist on the many different available organic carbon sources. In natural plant communities, freshly fallen leaf-litter and dead roots are subject to decomposition by a complex food-web composed of both microbial saprotrophs and invertebrate detritivores. The litter chemical composition varies dramatically among species in relation to plant life forms (conifer, broadleaf, nitrogen-fixing, graminoid) and, within species, with plant organs (leaf, root, woody tissues). This paper reviews the usefulness of advanced chemical technologies to study the composition of both plant litter and organic amendments, supporting the description of their mechanism of action and attention to their potential applications. First, a critical review is presented on the limitations of C/N and lignin/N ratios, still widely used as basic indicators of litter chemistry. Second, the potential of the solid state 13C-CPMAS NMR is reported as a powerful tool to assess the chemical composition of both litter and organic amendments. Finally, six different study cases are reported to provide evidence of the usefulness of such metabolomic approach for the description of organic matter chemistry aimed to an effective prediction of its impact on soil ecosystem functions.
  • Article
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    Soil-water content (θ) and soil organic carbon (SOC) are key factors controlling the occurrence and magnitude of soil-water repellency (WR). Although expressions have recently been proposed to describe the nonlinear variation of WR with θ, the inclusion of easily measurable parameters in predictive WR(θ) models is still lacking. In this study, a simple empirical beta function was suggested to describe the effect of changing soil-water content on the change of WR given as apparent contact angle (α) measured by the molarity of ethanol droplet (MED) method. The beta function for predicting α(θ) is based on measurement of WR on air-dry soil and three additional model parameters: the water contents at which the maximum WR (highest α) occurs and where WR ceases (α = 90 degrees), and the maximum α value. The MED data for three data sets from literature comprising WR measurements across moisture conditions for 19 soils were used to test the model. The beta function successfully reproduced all the measured soil-water repellency characteristic, α(θ), curves. Significant correlations were found between model parameters and SOC content (1%-14%). The model was independently tested against data for further three soils and performed accurately for all three. Consequently, we suggest that the α(θ) model represents a useful strategy to predict the entire soil-water repellency characteristic curve, and thus potential risks for enhanced runoff and preferential (fingered) soil-water flow at given initial soil-water contents, from measurements of only air-dry soil-water repellency and SOC content. ABBREVIATIONS MED: molarity of ethanol droplet; SOC: soil organic carbon; SWRCC: soil-water repellency characteristic curve; WR: water repellency
  • Chapter
    A large number of studies over the past four decades have demonstrated the ubiquity of preferential flow in diverse soils. Because of its significant impacts on ecosystem services and environmental quality, preferential flow in soils has become a crucial issue in both the scientific community and policymaking. Despite increasing attention and research efforts on this topic, a theoretical bottleneck and a technological bottleneck continue to impede further advancement in understanding, modeling, and managing preferential flow. The theoretical bottleneck refers to the lack of a cohesive conceptual framework to integrate major space-time factors that govern the occurrence and dynamics of preferential flow in soils. The technological bottleneck refers to the inadequacy of observational techniques for detecting and quantifying complex preferential flow patterns, particularly in situ. To help breakthrough these two bottlenecks, we first summarize the dominant controls of preferential flow across a wide variety of soils and landscapes based on a synthesis of 190 case studies. A framework of six key categories of controls is developed to assess the susceptibility of various soils to preferential flow. Mechanisms of different controlling factors affecting preferential flow are then discussed using the proposed framework. To address the technological bottleneck, we summarize recent applications of soil moisture sensor networks and geophysical imaging methods to characterize preferential flow in field soils, especially repeatedly and noninvasively. Finally, a future outlook on predicting the magnitude of preferential flow and enhancing field observation of preferential flow is presented.
  • Article
    The occurrence and consequences of soil water repellency (SWR) have been reported in many parts of the world, but little is known on the reasons and mechanisms of SWR in grasslands. Although considerable advances have been made in the past 10 years in understanding the impact of hydrophobic organic compounds on water repellency, there is still a considerable amount to be learnt. Of particular importance is the interaction between soil chemical characteristics and SWR in soil. The research gaps and seeks to understand how soil water repellency in grasslands of Inner Mongolia is influenced by soil chemical properties. The SWR of soil samples (n = 80) at the surface of the grassland (0–10 cm) collected in Xi Linhot was measured using the Water Drop Penetration Time Test (WDPT), and the relationship between soil chemical properties (e.g. soil organic matter, SOM) and SWR was studied in grassland soils. Results showed that SWR reached a peak value with an average of 80 s when the soil water content was 10.7%, the relationship between WDPT values and soil water contents showed a one-peak distribution. Soil water repellency increased exponentially with organic matter contents, total N, and available N and poorly correlated with carbonate, available P, available K and pH in grassland soils. Our results can provide the influencing factors of soil water repellency and promote soil amelioration.
  • Article
    In this paper, sediment particles are used as carriers, natural water is configured to nutrient water to cultivate biofilm. The environmental scanning electron microscope is used to capture the particle surface morphology variation after biofilm growth on sediment. Analysis on obtained gray images shows that the sediment surface morphology has changed greatly because of the biofilm growth. Sediment group becomes co-adhesive and forms reticular structure or floc structure. The surface derivative of biofilm sediment is more concentrated to zero than that of original biofilm, in which, the difference of gradient amplitude characteristics in X direction and Y direction are 4.11% and 2.19% respectively, and the difference of second-derivative amplitude characteristics is 28.84%. All these show that the surface micro morphology of sediment particles after biofilm growth becomes smoother.
  • Article
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    Soil water repellency (WR) occurs worldwide and affects hydrologic processes such as infiltration, preferential flow, and surface erosion. The degree of WR varies with soil organic C (SOC) and water contents. In this study, we measured WR (by ethanol molarity) as a function of moisture conditions for two soil profiles (17 layers, of which 13 exhibited WR), representing different vegetation and SOC between 0.6 and 14%. Generally, WR was found at SOC >= 2%. Based on measured data, a two-region water repellency (TRWR) model was developed. The model assumes two linear regions in a WR vs. pF (= log[-psi], where psi is the soil water matric potential in centimeters of H(2)O) plot, with linear increase in WR from the moisture content where WR first occurs during drying to the maximum WR at pF(WR-max), and a linear decrease from pFWR-max until ambient air-dried conditions. The van Genuchten soil water retention model was used to convert WR-theta (where theta is the volumetric water content) to WR-pF. The TRWR model fitting parameters, slopes, and intercepts, were all highly correlated with SOC (R(2) > 0.8). The TRWR model was tested against an independent data set for five soils with 2 to 12% SOC and predicted well the measured WR-theta and WR-pF relations. For high-SOC surface soils, the TRWR model seems promising to predict WR from fully wettable to ambient air-dried conditions, i.e., within the interval where WR-induced fingered water flow probably occurs. Finally, our data imply that clay saturation by SOC (quantified by the so-called Dexter index) is useful for predicting if soils are likely to exhibit WR.
  • Article
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    La exposición del suelo a temperaturas altas durante la ocurrencia de un incendio forestal, puede inducir el desarrollo de repelencia al agua y otros efectos que alteran la calidad del suelo, entre los que destacan: cambios en el contenido de carbono y de materia orgánica, pérdida de suelo, aparecimiento de flujos preferenciales y erosión. En este trabajo se determinó la severidad y persistencia de la repelencia al agua alcanzada por un suelo previamente quemado dentro de una zona de 13,4 has en el Parque Metropolitano en la Ciudad de Quito. La determinación de la persistencia de la repelencia al agua del suelo se realizó utilizando la metodología de tiempo de penetración de una gota de agua (WDPT) y la severidad de la repelencia se determinó utilizando el test de molaridad de etanol (MED). Los valores más altos de persistencia a la repelencia al agua, fueron determinados a los cuatro meses de haber ocurrido el incendio y permitieron clasificar al suelo afectado por fuego como “Fuertemente Repelente”. Se observó que la persistencia de la repelencia inducida por el fuego fue transitoria y disminuyó con relación al tiempo, determinándose un decremento de la repelencia en las muestras analizadas a los siete y nueve meses. No se encontró una relación definitiva entre el incremento de la repelencia al agua y el aumento de la materia orgánica, que presentó el promedio de concentración más alta a los cuatro meses de ocurrido el incendio (5,88 %).
  • Research
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    PHD Thesis on the influence of preferential flow in the texture contrast soils of Tasmania
  • Article
    Soil water repellency (SWR) has been reported to regularly occur in many soils under various climatic conditions. Despite the commonness of this soil property the mechanisms leading to the occurrence of SWR are largely unknown. The aim of this experiment was to test the hypothesis that the basidiomycete Agaricus bisporus promotes SWR, and that this fungal-induced SWR is dependent on soil moisture and temperature. We report that A. bisporus strongly induces SWR. We further show that the water content during the cultivation of A. bisporus on soil as well as drying temperature of the soil after the incubation experiment significantly affected SWR. Water drop penetration time (WDPT) of the soil ranged from 0.5 s in the samples cultivated at high soil water content (20%, w/w) and subsequently freeze dried, to more than 162 min in the soils that were kept at the low water content (13.8%, w/w) and were subsequently dried at 80 °C. These findings show that fungal activity potentially can promote dramatic SWR. The strong increase in SWR due to heating of the soil to 80 °C supports the view that SWR can be caused by a rearrangement of organic substances. For this reason, we discuss surface-active proteins produced by basidiomycetes as potential drivers of the SWR observed in our experiment.
  • Article
    Many regions of the world are predicted to experience water scarcity due to more frequent and more severe droughts and increased water demands. Water use efficiency by plants can be negatively affected by soil water repellency (SWR). It is timely to review existing techniques to remedy SWR. Ideally remediation addresses the origins of a problem. However, the fundamental mechanisms of how and why SWR develops are still poorly understood. In this review it was hypothesized that SWR occurs where the balance of input–decomposition of organic matter is impaired, due to either increased input or decreased decomposition rates of hydrophobic substances. Direct and indirect strategies to remedy SWR were distinguished. While direct remediation aims at abolishing the causes of SWR, indirect strategies seek to manage sites with SWR by treating its symptoms. The 12 reviewed strategies include applying surfactants, clay, slow-release fertilizers, lime, and fungicides, bioremediation of SWR through stimulating earthworms, choosing adapted vegetation, irrigation, cultivation, soil aeration and compaction. Some of the techniques have been applied successfully only in laboratory experiments. Our review highlights that it is not straightforward to cure SWR based on easily measurable and site-specific soil and vegetation properties, and that long-term, large-scale field experiments are required to improve the understanding of the evolution of SWR as cornerstone to develop cost-effective and efficient remediation strategies. We also identified current research gaps around the diagnosis and prevention of SWR.
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    Hydrophobicity is the phenomenon where the soil has reduced wettability, usually associated with coating of soil particles by hydrophobic organic substances. This study aimed to provide a description of the hydrophobicity occurrence, highlight recent discoveries about the origin of phenomenon and discuss the main hydro-physical properties and chemical processes linked to the development of hydrophobic behavior in soils. Hydrophobicity is associated with other factors such as soil moisture, presence of some fungi species, particle size, soil pH and occurrence of burnings. The causative substances may be provided by local vegetation, through deposition or decomposition. The dependence and combination of different factors that influence hydrophobicity in soils lead to a spatial and temporal variability of the phenomenon, with negative consequences in the processes of infiltration and water percolation, affecting the three-dimensional distribution and dynamics of soil moisture. Thus, the occurrence of a hydrophobic character requires special attention, especially regarding soil use and management.
  • Article
    Interfacial interaction properties are related to the surface properties of sediment particles. Surface properties and interfacial interactions are modified with the change in water environments. Experiments of surface pore characteristics and copper adsorption were performed to analyze the interfacial interaction of cleaned sediments and the original state sediments with the change of water environments. Physical and chemical adsorption apparatus was adapted to measure surface morphology characteristics of sediment particles. The experimental results reveal that cleaned sediments have richer surface pore structures and more complex surface topography. In copper ions adsorption experiments, saturated adsorption capacities of cleaned and original sediments are 0.854 g/kg, 4.525 g/kg, and adsorption/desorption ratios are 1.511 and 5.652, respectively. Original sediments have stronger ability of interfacial interaction than cleaned sediments. Contaminations are adsorbed to particle surfaces, which results in the change of the surface morphology of particles. Biomenbrane and humus adhered to the particles' surface enhance the interaction ability. With the change in water environments, interfacial interaction of sediment transformed from physical adsorption to chemical adsorption.
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    A hidrofobicidade pode ser entendida como a repelência do solo à água, dificultando o seu molhamento. Esse fenômeno está associado ao recobrimento das partículas do solo por substâncias orgânicas hidrofóbicas, sendo que atualmente existem inúmeros relatos de repelência à água em áreas de florestas de Eucalyptus e Pinus. Assim, este trabalho teve por objetivo revisar e elencar os aspectos relacionados à origem dos compostos hidrofóbicos e os seus efeitos na dinâmica da água no ambiente florestal, além de implicações no crescimento e desenvolvimento das árvores em florestas de Eucalyptus e Pinus. Reconhece-se que a vegetação local e algumas bactérias e fungos, em função da sua composição química, podem liberar substâncias orgânicas hidrófobas. Outro fator condicionante é a ocorrência de incêndios e queimadas, que induzem alterações nos compostos orgânicos e promovem o secamento do solo. Além disso, a composição granulométrica e o pH do solo podem estar indiretamente associados à ocorrência de repelência à água no solo. A existência de hidrofobicidade exige uma atenção diferenciada, principalmente em relação ao uso e manejo do solo, pois afeta diretamente o movimento da água na superfície e no interior do perfil de solo. Alterações na sortividade, redução da taxa de infiltração, escoamento superficial elevado e ocorrência de fluxo preferencial são os principais efeitos hidrológicos desse fenômeno. Em função das menores taxas de infiltração há aumento do escoamento superficial e redução da quantidade de água disponível, potencializando o processo erosivo e, consequentemente, afetando o crescimento e o desenvolvimento das plantas.
  • Article
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    Hydrophobic or water repellent soils slowly absorb water because of the low wettability of the soil particles which are coated with hydrophobic organic substances. These pose significant effects on plant growth, water infiltration and retention, surface runoff and erosion. The objective of this study was to compare the performance of tension micro-infiltrometer (TMI) and the water drop penetration time (WDPT) methods in the determination of the hydrophobicity index of eighteen soils from southern Brazil. Soil samples were collected from the 0-5 cm soil layer to determine particle size distribution, organic matter content, hydrophobicity index of soil aggregates and droplet penetration time of disaggregated and sieved soil samples. For the TMI method the soil samples were subjected to minor changes due to the use of macroaggregates to preserve the distribution of solid constituents in the soil. Due to the homogeneity of the soil samples the WDPT method gave smaller coefficients of variation unlike the TMI method where the soil structure is preserved. However, both methods had low coefficients of variation, and are thus effective for determining the soil hydrophobicity.
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    Heat waves, defined as events associating high temperatures with severe drought, are expected to become increasingly recurrent. Research has focused heavily on the impacts of drought and temperature increase on soil functioning and microbial diversity, but little attention has been paid to soil microbial community responses to combined heat-drought stresses. Heat waves, which combine heat and drought stresses, may induce different microbial responses to those observed in studies focusing on heat or drought alone. Microbial recovery strategies to withstand heat-drought conditions, along with patterns of microbial functional redundancy and complex interactions with the soil physical-chemical-biological interface may have marked effects on soil ecosystem functioning, particularly in agroecosystems through the rhizosphere. To better under stand how heat waves affect soil ecosystem functioning, we advocate the development of mechanistic approaches integrating individual to community level and biophysicochemical studies on the indirect effects of combined heat-drought stresses in microbial communities, observed through soil environment parameters in experimental and field studies. The challenge will be to define trait-based functional indicators of the microbial community response to heat waves, particularly the potential interrelatedness between the traits responsible for tolerance to drought and heat.
  • Article
    Biomineralization is a process that leads to the formation of minerals via a biologically or biotechnologically mediated route. This process is a new and innovative research area in geotechnological engineering and structural engineering because it has wide-ranging implications for the strengthening of soil, sand, stone, and cementitious materials. In the present study, we demonstrated the ability of Lysinibacillus sphaericus WJ-8 to precipitate 15.3 mg/mL of calcite and to degrade 415 μmol/mL of urea over a 120-h period. The cell surface hydrophobicity and sand adhesion of spores were higher than those of vegetative cells (77.2% vs. 24.0% and 54.1% vs. 7.8%, respectively). In addition, the bioconsolidated soil block samples had significantly smaller pores than did the control soil block samples. Scanning electron microscopy and energy dispersive spectroscopy analysis revealed that calcite crystals were frequently formed in the bioconsolidated soil block samples, but did not occur in the control soil block samples. In addition, sharp peaks in the X-ray diffraction spectra indicated that calcite (CaCO3) crystals constituted the predominant mineral in the bioconsolidated samples, whereas quartz (SiO2) crystals constituted the predominant mineral in the control samples.
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    This work presents the analysis of the influence of compost and reclamation substrate addition and mineral fertilizers application on leaching of mineral nitrogen, microbial activities, soil hydrophobicity and plant biomass production. To demonstrate the effect of compost, reclamation substrate and mineral nitrogen (Nmin) addition on above parameters, the pot experiment was performed. As a model crop, Deschampsia caespitosa L. was used and cultivated for 63 days in climate chamber. The leaching of Nmin was measured by application of ion exchange discs, soil hydrophobicity was determined based on the values of saturated hydraulic conductivity (Ksat) and microbial activity was expressed as basal (BR) and substrate induced respiration (SIR). Four variants (V1-V4) with different doses of fertilizers were prepared: V1 -control without addition of fertilizers; V2 -this variant of experiment was prepared as mixture of compost and arable land in ratio 7:3; V3 -90 g/m 2 of mineral fertilizers NPK (in the ratio 1:1:1) were applied there and into V4, dose 30 g of compost were applied. The significant differences (P < 0.05) in the detection of Nmin, values of Ksat and SIR were found. The highest decrease of mineral nitrogen leaching was observed by the simultaneous applications of compost (V4) to arable soil, about 50% in comparison with the variant V4 (application of mineral fertilization) and about 10% in comparison with the control. Variants with addition of compost (V2 and V4) showed higher values than variants without, which were measured at three stages (before application of Nmin -12 days after establishment of the experiment; after application of Nmin -34 days; at end of the experiment -63 days). During the experiment, two types of respiration were measured: BR and SIR. The significant differences in SIR were found between variants with addition of compost and variants without. The SIR (cumulative production of CO2) was higher about 25% in variants V2 and V4 compared to variants V1 and V3. The highest values of Ksat were found in variants with addition of compost. Conversely, the lowest value of Ksat was detected in variant with addition of Nmin. Low values of Ksat indicate an increased level of hydrophobicity.
  • Chapter
    The last decade has seen a dramatic rise in scientific interest in the field of bacterial adhesion and related subjects. Much of this interest has been directed in search of “specific interactions” between bacterium and substratum, such as those that are inhibited by specific sugar moieties. A second avenue of research has been the study of the role of less specific, hydrophobic interactions. Since it appears that this second avenue of research is being increasingly followed, reviews dealing with bacterial hydrophobicity and adhesion should be of use. The aims of the present chapter are to (1) present some relevant aspects of hydrophobic interactions; (2) describe the methodology available for measurements related to bacterial cell-surface hydrophobicity and the parameters they may measure; (3) discuss investigations dealing with surface components that promote or reduce bacterial hydrophobicity; and (4) survey studies related to the role of hydrophobic interactions in mediating bacterial adhesion to interfaces, traversing areas of environmental and medical interest.
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    An Introduction to the Environmental Physics of Soil, Water and Watersheds presents an easy approach to understanding physical processes associated with the land surface and subsurface water and energy balance, with a brief treatment of transport.The book begins with a treatment of soil, its formation and composition, and properties associated with soil strength and characterization with moisture. Next is a description of the properties of liquids wherein concepts such as pressure, energy, buoyancy, and waves are addressed. This is followed by the treatment of evapotranspiration and infiltration. The book then discusses overland flow, erosion and deposition, and transport by rivers. The behavior of flow in the subsurface, namely, saturated and unsaturated flow and contaminant transport, completes the book.
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    Microbial exopolysaccharides are mainly relatively simple polymers composed of repeating units of 2–6 sugars to which acetate and pyruvate are often attached. Their synthesis from sugar nucleotides involves assembly on C55 isoprenoid alcohol phosphate and extrusion from the cell.
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    We developed an effective system to eliminate bacteria from modified tap water using a positively-charged carbon felt electrode. Particles with stronger negative charges are adsorbed more readily to a positively-charged carbon felt electrode. The zeta potential of bacteria suspended in modified tap water was measured by a microscopic electrophoresis method based on the electrophoretic mobility of bacteria particles. Bacteria electro-adsorption to the electrode was examined by bioassay. The mean zeta potential of the bacteria, Escherichia coli was −12mV, Staphylococcus aureus was −13mV, Bacillus subtilius spore was −20mV, and Saccharomyces cerevisiae was −7mV. E. coli, S. aureus, and B. subtilius spore were reduced with electrolytic current on their zeta potential conditions. But S. cerevisiae was almost eliminated at zero mA in modified tap water in spite of the smallest magnitude of its zeta potential. These results were considered using DLVO theory. S. cerevisiae had the property of a soft particle the same as blood erythrocyte. Therefore it may be that S. cerevisiae was adsorbed on the carbon electrode not only by electrostatic trapping, but also by specific adsorption between cells and carbon fibers. B. subtilius spore had the property of colloidal particles which can be treated with the DLVO theory. E. coli and S. aureus were at an intermediate level between S. cerevisiae and B. subtilius. It may be that the positively-charged carbon felt electrode effectively adsorbed various bacteria in water.
  • Article
    Previous studies have attributed hydrophobilicity in sandy soils to alkaline extractable macromolecular complexes, as well as lipid fractions, but have not included wettable soils for comparison. Our study was conducted to compare the alkaline-extractable and lipid fractions of a nonwettable soil to a wettable soil from creeping bentgrass (Agrostis stolonifera L. var. stolonifera) sand greens. Samples were collected from two sites and several extraction sequences performed on each. Humates were extracted in 1.25 mol L-1 NaOH. Alkaline-extractable fractions were separated by precipitation with 6 mol L-1 HCl. Acid precipitated and nonprecipitated fractions were purified, lyophilized, and analyzed by Fourier transform infrared spectroscopy. In addition, the acid nonprecipitated fractions, which included fulvic acids, were analyzed by solid-phase 13C nuclear magnetic resonance spectroscopy Lipid fractions were extracted with a soxhlet apparatus using either hexane or methanol as solvent. Lipid fractions were analyzed by gas chromatography-mass spectroscopy. No qualitative differences were observed with Site 1 extracts, and it appeared that hydrophobicity may have been at least partly due to physical or structural differences. Qualitative differences were observed with Site 2 extracts when initially extracted with methanol.
  • Article
    Water repellence was detected in an Oxic Paleustalf medium-textured surface soil (27% clay), under direct drilling but not under conventional cultivation and was apparently seasonal in nature. Water repellence was reproduced in the laboratory, and was associated with fungal hyphae growing on the organic-matter-rich surface layer. Water repellence significantly slowed infiltration when water was applied at 40-mm suction using a sorptivity tube. The seasonally developed water repellence found in the direct-drilled soil was probably the result of enhanced fungal growth due to the absence of soil disturbance and presence of a permanent layer of organic matter. -from Author
  • Article
    Water repellency can significantly reduce crop and pasture establishment and production in sandy soils. Management practices that increase the rate of water infiltration into dry soils following the first rains at the end of the dry season were investigated. In the laboratory, addition of water to water repellent soil and maintenance of warm moist conditions produced a gradual decline in water repellency. This was supported by results in the field which showed that under daily irrigation there was a gradual decline in water repellency over time. However, under dryland conditions, other mechanisms to increase water infiltration had to be found. In the laboratory, after the addition of lime and kaolinite clay, there was an initial rapid decline in repellency, indicative of a physical mechanism, followed by a more gradual decline suggesting a biological response. In the field, under dryland conditions, the addition of lime and kaolinite clay resulted in a reduction in water repellency, and in the case of lime, this effect increased with the size of application. Estimates of the numbers of wax-degrading bacteria in the treated soils, using a most-probable-number assay, showed at least a 10-fold increase in lime-treated sands, but not in the clay-treated sands. The results suggest that lime may provide a viable alternative for increasing the wettability of soils by physical mechanisms and by promoting microbial activity by bacteria responsible for wax degradation, resulting in more consistent plant germination and establishment, and increased crop yields.
  • Article
    The water repellency of a sandy lucerne pasture soil is critically dependent on aqueous extraction and subsequent drying procedures. Freeze-drying converts a very severely water-repellent soil into a readily wettable soil, but subsequent rewetting and oven-drying regenerates water repellency. These changes are ascribed to changes in the molecular conformation of the organic matter. Prolonged shaking detaches organic matter coatings from sand particles and so reduces repellency. Allowing for these effects, it is shown that a sequence of alcohol-benzene extraction, acid leaching, and NaOH extraction removes the major part of the water-repellent substances present.
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    Full-text available
    The vast majority of microorganisms live and grow in aggregated forms such as biofilms and flocs (“planktonic biofilms”). This mode of existence is lumped in the somewhat inexact but generally accepted expression “biofilm”. The common feature of all these phenomena is that the microorganisms are embedded in a matrix of extracellular polymeric substances (EPS). The production of EPS is a general property of microorganisms in natural environments and has been shown to occur both in prokaryotic (Bacteria, Archaea) and in eukaryotic (algae, fungi) microorganisms. Biofilms containing mixed populations of these organisms are ubiquitously distributed in natural soil and aquatic environments, on tissues of plants, animals and man as well as in technical systems such as filters and other porous materials, reservoirs, plumbing systems, pipelines, ship hulls, heat exchangers, separation membranes, etc. (Costerton et al. 1987; 1995; Flemming and Schaule 1996). Biofilms develop adherent to a solid surface (substratum) at solid-water interfaces, but can also be found at water-oil, water-air and solid-air interfaces. Biofilms are accumulations of microorganisms (prokaryotic and eukaryotic unicellular organisms), EPS, multivalent cations, biogenic and inorganic particles as well as colloidal and dissolved compounds. EPS are mainly responsible for the structural and functional integrity of biofilms and are considered as the key components that determine the physicochemical and biological properties of biofilms.
  • Article
    Fungi are thought to affect soil slaking resistance and bypass flow by inducing low levels of water repellency on soil pore surfaces. This was investigated in a laboratory study on arable field soil by selectively inhibiting fungi and/or bacteria with biocides and adding ground barley shoot substrate (2 mg g−1 soil) to half of the samples. The fungicide Captan and the bactericide Bronopol were used alone and in combination at a concentration of 1 mg g−1, resulting in different levels of microbial respiration and active fungal biomass (ergosterol) after 8 days of incubation. Repellency was measured on the surface and on an internal fracture of the soil cores. Wet–dry cycles were applied to some samples to investigate the persistence of water repellency. Substrate addition caused the greatest increase to water repellency after incubation, suggesting that microbial activity affects repellency. The drying surface of the soil had greater repellency than the internal fracture surface. No clear trends could be found between the level of fungal biomass and repellency; this was most evident in soils treated with bactericide and substrate. Despite having the highest fungal biomass (P0.05). Wetting and drying cycles caused significant changes to repellency and structure. Ethanol sorptivity indicates pore structure and its value changed least in the soil that had the greatest fungal biomass (i.e. bactericide treated with substrate), indicating that fungal populations protected soil structures from slaking stresses. Given the poor relationship found between fungal biomass and water repellency, these results suggest that other microbial or physico-chemical processes were involved. Our findings do not support previous research that reported a close link between water repellency and fungal biomass. However, given the strong evidence of fungal-produced hydrophobins and the close links between soil structural stability, repellency and fungal biomass found in field studies, the effectiveness of the biocides used in this study or the influence of different fungal species could have influenced the results and thus requires greater investigation.
  • Article
    1H NMR relaxometry is applied for the investigation of pore size distributions in geological substrates. The transfer to humous soil samples requires the knowledge of the interplay between soil organic matter, microorganisms and proton relaxation. The goal of this contribution is to give first insights in microbial effects in the 1H NMR relaxation time distribution in the course of hydration of humous soil samples. We observed the development of the transverse relaxation time distribution of the water protons after addition of water to air dried soil samples. Selected samples were treated with cellobiose to enhance microbial activity. Besides the relaxation time distribution, the respiratory activity and the total cell counts were determined as function of hydration time. Microbial respiratory activities were 2–15 times higher in the treated samples and total cell counts increased in all samples from 1×109 to 5×109 cells g−1 during hydration. The results of 1H NMR relaxometry showed tri-, bi- and mono-modal relaxation time distributions and shifts of peak relaxation times towards lower relaxation times of all investigated soil samples during hydration. Furthermore, we found lower relaxation times and merging of peaks in soil samples with higher microbial activity. Dissolution and hydration of cellobiose had no detectable effect on the relaxation time distributions during hydration. We attribute the observed shifts in relaxation time distributions to changes in pore size distribution and changes in spin relaxation mechanisms due to dissolution of organic and inorganic substances (e.g. Fe3+, Mn2+), swelling of soil organic matter (SOM), production and release of extracellular polymeric substances (EPS) and bacterial association within biofilms.
  • Article
    A streptomycin-resistant variant of Xanthomonas campestris was grown in defined nutrient- deficient media in both batch and continuous culture. The production, composition and viscosity of the extracellular polysaccharide (xanthan) synthesized by this strain were influenced by the fermentation time and nutrient exhaustion in batch culture and by the dilution rate in continuous culture. The specific rate of exopolysaccharide synthesis was maximal during exponential growth in all of the nutrient-deficient media studied although some xanthan was formed during stationary phase. The concentration of exopolysaccharide decreased at later stages of stationary phase in some cultures. Both the extent of acylation and the consistency index of xanthan isolates were low or minimal during exponential growth, maximal in polysaccharide isolated as the growth rate fell and usually lower after this time. Between dilution rates of 0.03 and 0.06 h-' in chemostat culture, the cell and exopolysaccharide dry weights were independent of dilution rate, the specific rate of xanthan synthesis decreasing at lower growth rates. Although the variation in the acyl content and consistency index was less than that observed in batch culture, exopolysaccharide isolated at higher dilution rates tended to have a higher acetyl content, lower pyruvyl content and lower consistency index.
  • Article
    Water repellency in soils is caused by waxy coatings on particles and can seriously limit agricultural production. Bioremediation of these soils, using wax-degrading bacteria isolated from soils and other sources rich in microorganisms, was investigated. Wool wax, a complex mixture of fatty acids and alcohols, was used to select bacteria capable of metabolising hydrophobic compounds. Of the 37 stable isolates, two-thirds were actinomycetes. These organisms are known for their ability to metabolise a wide range of organic compounds. Degradation of waxes associated with soil particles is facilitated by the production of biosurfactants that emulsify hydrophobic compounds. Measurement of biosurfactant production indicated that those isolates that grew best on hydrocarbon were also the most prolific biosurfactant producers. Inoculation of water-repellent soils, under controlled conditions, with the most efficient wax-degrading bacterial isolates resulted in significant improvements in soil wettability.
  • Article
    Rapid methods for measuring the severity of water repellence were assessed in 101 sandy soils from South Australia. The molarity of aqueous ethanol droplets that were absorbed by the soil in 10 s, the time of water droplet entry and the infiltration rate of water from a small ring infiltrometer were compared with the soil-water contact angle and with each other. Relationships between the tests were fitted by linear, quadratic and cubic regressions and were highly significant (100r2 = 70-92). The relationships were used to provide ratings of repellence normally found in the field. Factors which affect the measurement of repellence in the field were examined. Abrasion of sand particles during light sieving had only small effects on repellence, but more vigorous abrasion through rotational movement of the sand reduced repellence markedly. Repellence decreased with increasing temperature. Simple corrections for temperature were calculated and presented in figures as isorating charts. The moisture content of the soil had large and variable effects on the repellence tests. At moisture contents between oven and air dry (pF 5.6) there was little effect on the ethanol droplet or infiltration rate tests. Measurements by the ethanol droplet test were not reliable at moisture contents greater than air dry. At soil water contents between air dry and wilting point (pF 4.2), the infiltration rate of water was either unchanged or decreased in different soils. It then increased rapidly and reached a constant value near field capacity (pF 2.5). The infiltration rate also decreased when the time of moistening of the soil before the tests were made was extended from 20 to 168 h. It is recommended that repellence tests be made on oven- or air-dry soils. The aqueous ethanol and water droplet, and infiltration rate of water tests are all suitable for rapid assessment of repellence in the field.
  • Article
    Current views that aggregation of soils results from by-products of microbial growth and that filamentous microorganisms contribute very little to physical binding are reviewed. The microscopical examination of soils and aggregates showed fungal mycelium to be persistent in well-aggregated soils, but relatively deficient in soils lacking structure. Cases are cited where physical properties of soils depend upon the presence of filamentous microorganisms: (1) Surface crusts on sands in open plant communities where algae dominate the coenoses with filamentous fungi; (2) the aggregation of deeper horizons of sands by adhesive fungal mycelium; (3) the sand capping to clay subsoils in solonetzic soils bound by abundant fungal mycelium and microbial gums; (4) the water repellence of sandy soils associated with the growth of microorganisms, particularly basidiomycete fungi; (5) the progressive improvement of crumb structure in fine-textured soils associated with increased development of persistent mycelium after several years under pasture.
  • Article
    Microbial extracellular polysaccharides (EPS) contribute to the stability of soil aggregates. Nitrogen supply affects microbial growth and metabolism. The effects of fertilizer and cover crop N supply on EPS production and soil aggregation were examined in an irrigated annual cropping system. EPS can be important factors affecting soil structure in cultivated soils and that EPS production can be managed by N supply. The HF carbohydrate content may be a useful indication of the effects of soil nutrient and organic matter management on microbial EPS production. -from Authors
  • Article
    Full-text available
    We present a multi-wavelength comparison of the Antennae galaxies (NGC 4038/39). We compare Chandra X-ray data (Fabbianno et al. 2001), VLA radio maps (Neff et al., 2000). We also discuss these interacting galaxies.
  • Article
    Water-repellency in non-wetting sands is due to hydrophobic waxes present on the surface of sand grains and contained in particulate organic matter present in these sands. This study investigates the physicochemical characteristics of these natural waxes and compares them to waxes extracted from potential original source materials. Non-polar and polar hydrophobic wax extracts were obtained from whole non-wetting sand, and its individual constituents, and associated organic matter. These included the sand fraction, the intrinsic particulate organic matter, tree litter, eucalyptus leaves, bark, lucerne and lupin plants, and fungi and actinomycetes isolated from these sands. Waxes were characterized for their hydrophobic properties and composition of their chemical constituents. The hydrophobicities of the waxes were assessed by measuring the water-repellency induced after treating acid washed sand with wax extracts. Non-polar and polar wax extracts of the tree litter displayed hydrophobic properties that were similar to the corresponding waxes isolated from non-wetting sand and intrinsic particulate organic matter. Unlike these plant-derived waxes, the microbial wax extracts possessed different hydrophobic properties. Characterization of the components of the extracted waxes by GC-MS analysis showed a strong similarity in the composition of waxes isolated from non-wetting sand, tree litter and other plant material. The major components found were unbranched and branched C16 to C36 fatty acids and their esters, alkanes, phytanols, phytanes, and sterols. Some of these components were not detected in the microbial waxes. Unextracted samples, as well as wax extracts of non-wetting sand, intrinsic particulate organic matter, tree litter and fresh plant material were further analysed by solution and solid state NMR spectroscopy which indicated the relative content of the different chemical species present.
  • Article
    The understanding of soil water repellency in its complexity requires knowledge of the mechanisms leading to changes in surface characteristics. Wetting kinetics may serve as means to investigate the origin of soil water repellency, but have been scarcely investigated yet. We observe the wetting kinetics of soil samples from two locations via the time-dependent shape of sessile drop (TISED) at three temperatures. We show that drop penetration may be exceeded by evaporation for high water drop penetration time (WDPT). The time-dependent change of drop shape and apparent contact angle is explained by surface hydrophilisation including the change from Cassie-Baxter into Wenzel's state. We identify principal differences in the nature of water repellency between the two investigated locations: Only the samples from the former sewage field, Buch, lose most initial differences in wettability upon air drying and storage. Wetting of these samples requires an activation energy of 65–94 kJ mol−1, indicating chemical reactions as rate-limiting step. In contrast, wetting of the samples from the inner city park, Tiergarten, requires an activation energy of 42 kJ mol−1 for the repellent and 8–20 kJ mol−1 for the wettable samples, which suggests physico-chemical and physical processes as rate-limiting steps. Our study shows for the first time that the process of soil wetting can be monitored by TISED assessment, and that assessment of the temperature dependence of the wetting kinetics allows distinguishing between different natures of wetting and soil water repellency. It therefore represents a novel approach to investigate wetting processes. Combination of such approaches with spectroscopic investigations will help to deepen our understanding on possible causes of water repellency. They further help to understand the great variety of suggested causes of repellency and indicate locational material-specific effects rather than one general cause for water repellency. Copyright
  • Article
    A review of the basic structure of microbial biofilm reveals that at least three conceptual models exist: (i) heterogeneous mosaic biofilm, (ii) penetrated water-channel biofilm and (iii) dense confluent biofilm. When consideration is given to the effects of growth resource, it may be that all three variants are correct but form at widely different substrate concentrations. Experimental research with bacterial colonies and models of the latter using cellular automata have confirmed this view. Use of cellular automata to model biofilm growth give results which strongly suggest that biofilm structure is largely determined by substrate concentration.
  • Article
    Soil water repellency is commonly assessed using the Water Droplet Penetration Time (WDPT) and Molarity of Ethanol (MED) or Critical Surface Tension (CST) tests. The former is a kinetic measurement indicating the persistence of water repellency; the latter, a thermodynamic measurement, gives the initial severity of water repellency. This study aims to provide a theoretical framework to understand (i) what determines differences in persistence and initial severity of soil water repellency and (ii) correlations between such data. A linear free energy relationship between Solution Droplet Penetration Time (SDPT) and the difference between the surface tension of the droplet solution, γsol, and the Critical Surface Tension of the soil, γcx, has been derived. Here: γsol is the surface tension of water (for WDPT) or the solution being used (SDPT); N is the number of adsorbed molecules per unit area; k the Boltzmann constant; T the temperature; A is 1/SDPT when γcx = γsol; and f is an experimentally determined parameter. WDPT, SDPT (ethanol/water and propan-1-ol/water), and CST measurements for a group of sandy soils support this analysis. The value of f obtained (4·2 ( ± 0·4)), suggests that the surface free energy contribution to the free energy of activation of wetting is given by the difference between the cohesive energy of the molecular film adsorbed on the soil grains and that of the wetting solution. In this interpretation: γcx is determined by the cohesive energy of the organic film adsorbed on the soil; WDPT is determined by the difference in cohesive energies between this adsorbed film and the droplet solution; and soil-to-soil variations in both WDPT and γcx are due to organic films of different cohesive energies present on the soil particles. For aqueous solutions of simple linear alcohols and ketones, SDPT depends on γsol but is independent of the compound used to control γsol. Copyright
  • Article
    Some soils develop severe water repellency several years or decades following oil contamination. We previously reported on the characteristics of three such soils. Here we report on the characteristics of putative water-repellent substances in them. We examined the effectiveness of various polar, nonpolar and amphiphilic solvents for removal of water-repellent substances in three nonwettable soils. Only the amphiphilic solvent mixture isopropanol/14.8 M ammonia (7:3, vol/vol) (IPA/NH4OH) completely eliminated soil water repellency in all three soils. We thus define putative water-repellent substances as those substances whose removal from soil by IPA/NH4OH removes water repellency. High-resolution CPMAS 13C-NMR spectroscopy and thermal desorption followed by conventional gas chromatography/mass spectroscopy with electron impact ionization (GC/EI/MS) and GC/MS with chemical ionization (GC/CI/MS) were used to characterize extracted putative water-repellent substances. We conclude that: (i) the identified representatives of these substances consist mostly of homologous series of long-chain and polycyclic aliphatic organic compounds; namely, n-fatty acids, n-alkanes, and cycloalkanes, and that (ii) they are of petroleum origin rather than plant or microbial origin.
  • Article
    Soil microbes produce exudates which upon drying become water-repellent, thus altering hydraulic properties. The influence of microbial activity caused by adding plant nutrients on the hydraulic characteristics of soil aggregates is reported. Soil aggregates were collected from a field that had been fertilized with different amounts of nitrogen. Aggregates were also incubated with different nutrient treatments in the laboratory. Their sorptivity, hydraulic conductivity and water repellency were measured with a new device. Adding nitrogen was found to decrease sorptivity and hydraulic conductivity because of increased water repellency in the field. In the laboratory studies, the addition of nutrients caused severe water repellency in the soil aggregates. Respiration studies identified a large increase in biological activity following nutrient amendment which produces water-repellent materials.
  • Article
    The potential influence of pH on water repellency in soils has already been mentioned in some studies, but no clear correlation between these parameters has been found to date. In addition, although correlations of water content and water repellency have been found in numerous studies, the influence of drying and subsequent storage conditions on water repellency are still unclear. In this study, a series of samples showing water repellent and wettable conditions respectively at field moist states from two urban locations were compared regarding two main aspects: (i) the influence of artificial pH-changes on their wetting behaviour and (ii) sample wettability changes during drying for different drying temperatures. The assumption made in a study by Hurraß and Schaumann (2006) on the same sample site, that differences in wettability of closely neighboured samples from one sample location can be interrelated with differences in pH, was confirmed. However, in contrast to the assumption that rising pH will improve the wettability and decreasing pH will intensify water repellency, we found a maximum in water repellency at a pH above the initial pH. The results from drying samples at different temperatures confirmed the dependence of water repellency development on the drying temperature. Additionally, we could confirm the conclusion from previous studies that the water content alone cannot explain the water content–WDPT (water drop penetration time) relationship. The results from drying and pH changes show that some location specific factors, like the number of pH active functional groups, may be relevant for sample wettability. As additional mechanism, which may be partly antagonistic to the influence of the water content, we assume temperature-dependent conformational changes in SOM (Soil Organic Matter). It seems that aspects of these conformational changes may additionally be governed by pH in one of our two locations. Copyright © 2007 John Wiley & Sons, Ltd.
  • Article
    A microcosm system is described which permits assessment of the progressive growth of filamentous fungi through soil. We report on its application to measure the effects of Coriolus versicolor and Phanerochaete chrysosporium upon the sorptivity and water repellence of a mineral soil, measured using a miniature infiltration device. Both fungal species caused moderate sub-critical repellence. Since the pore structure was unaffected, the repellence was probably due to hydrophobic substances of fungal origin. This is the first report of changes in soil repellence caused by the growth of potential xenobiotic bioremediating fungi. The potential consequences are discussed.
  • Article
    Variations of soil moisture conditions affect sorption properties of soil organic matter and the pore size distribution of the soils and thus are expected to have an impact on the availability of pollutants and nutrients in soils. At least two principal processes that occur when a soil-water contact is established, are involved. Wetting, which is the very first step, is governed by the interactions of water with the surface of soil organic matter (SOM). The wettability of the pore walls determines the pore accessibility for water. Only in wettable soils, water will occupy the smallest pores first. In the course of wetting, the wettability of the pore walls increases, leading to water redistribution. Swelling of SOM is accompanied by an increase of volume due to the water uptake of the solid SOM phase and will change the SOM polarity. Swelling will thus affect sorption processes in the bulk SOM phase and is expected to change the pore sizes. In this contribution, we investigated swelling and wetting kinetics of soil samples by H-NMR-Relaxometry. We found different effects of wetting and swelling on the development of relaxation time distribution and thus of the pore size distribution. Both swelling and wetting can be slow processes, lasting for up to some weeks. During this time, we found changes in the pore size distribution. For swelling phenomena, we observed a continuous change of the effective pore size, and for wetting phenomena, we found a change in water distribution in a probably rigid pore system. Thus, during swelling and wetting, neither pore size distribution nor sorbent properties of SOM nor hydraulic properties remain constant. Due to the slow kinetics, both processes play an important role in sorption, transport and accessibility for water in hydrophobic areas within a time scale of weeks after e.g. a rainfall event. This will affect the environmental availability and the transport of pollutants and nutrients in the field.
  • Article
    The culture supernatants of 126 bacterial strains isolated during screening for hydrophobic cell surfaces, were tested for the production of emulsifying agents. Forty-eight strains were found to produce effective emulsion-stabilizing substances during growth on glucose. The most effective emulsifying agents were isolated and could be divided into two chemical groups. The first group was separated from the isolated extracts by the use of thin-layer chromatography and detected as ninhydrin-negative, 4,4'-tetramethyldiamino-diphenylmethane-positive spots. The amino acid composition indicated surfactin and iturin, produced by one Bacillus species, and viscosin, produced by a Pseudomonas species. The second group was identified as polymeric substances. The chemical characterization of five polymers showed polysaccharides that were able to stabilize emulsions. From these the neutral and charged monosaccharides were determined qualitatively. The constituents of the five isolated polysaccharides were: strain 5, glucose, strain 17, rhamnose, glucose, glucuronic acid; strain 33, rhamnose, galactose, glucose. glucuronic acid; strain 113, fucose, galactose, glucose, galacturonic acid, glucosamine; strain 259, one unknown compound, rhamnose, galactose, glucuronic acid.
  • Article
    The occurrence of water repellent spots can inhibit a homogeneous wetting progress in soil. Although the wettability is an important factor for sorption and transport processes, the knowledge about the reasons for water repellent behavior and its effects on other soil properties is still insufficient. In this study, water repellent and wettable soil samples from two urban locations were compared. It was examined, to which extent differences in the actual water repellency of closely neighboring spots are associated to variable factors like the water content or to stable properties of soil organic matter (SOM). In order to analyze the interrelations between the moisture status and the wettability behavior, soil samples were either subjected to drying–remoistening cycles or pre-conditioned under various conditions. For the characterization of stable SOM properties, the soil samples were investigated by ESEM (Environmental Scanning Electron Microscope) and FT-IR spectroscopy. Beside the investigation of solid soil samples, selected properties of aqueous soil extracts were measured. The results of this study indicate that the water content is not the only factor responsible for the differences in actual water repellency. For different locations, the wettability behavior probably is based on different mechanisms. For one of the examined sites, differences in actual repellency of closely neighboring samples were interrelated with differences in pH and the ionic strength of the soil solutions. For both locations, amphiphilic substances probably are an important factor of influence for the wettability behavior. Additionally, the results suggest that the time which proceeds after a change of the moisture status in soil is an important factor for water repellency.
  • Article
    Full-text available
    Water repellency (hydrophobicity) of soils is a property with major repercussions for plant growth, surface and subsurface hydrology, and for soil erosion. Important advances have been made since the late 1980s in identifying the range of environments affected by water repellency, its characteristics and its hydro-geomorphological impacts. This review summarises earlier work, but focusses particularly on these recent advances and identifies remaining research gaps.The associations of water repellency with (a) soils other than coarse-textured ones, (b) an expanding list of plant species, and (c) a widening range of climates other than seasonally dry types have been recurrent themes emphasised in recent literature. Nevertheless, knowledge about the extent of water repellency amongst world soils is still comparatively sparse. Its origin by the accumulation of long-chained organic compounds on or between soil particles is now widely accepted, but understanding of their exact chemical composition and means of attachment to particle surfaces remains incomplete. The transient nature of water repellency has been found to be mainly associated with fluctuations in soil moisture, but the precise processes and required conditions for the changes from hydrophobic to hydrophilic and vice versa are so far only poorly understood.Significant advances relating to the hydro-geomorphological impacts of hydrophobic layers have been made since the late 1980s in identifying and separating the various effects of such layers on surface and subsurface water flow. It has become evident that these effects in turn are influenced by variables such as the frequency and effectiveness of flow pathways through hydrophobic layers as well as their position and transitory behaviour. Recent literature has continued to highlight the role of water repellency in promoting soil erosion and it is now recognised that it can promote rainsplash detachment and soil loss not only by water, but also by wind. Major research gaps, however, remain in (a) isolating the erosional impact of water repellency from other factors, and (b) identifying the exact role of, and the interactions between the different variables controlling development and effectiveness of flow pathways through hydrophobic soil. Improved understanding of the effects of soil water repellency will enable its overall role in surface and subsurface hydrological and erosional processes to become more clearly defined.
  • Article
    Bacteria that attach to surfaces (e.g., soil and living and decaying plant tissue) aggregate in a hydrated exopolymeric matrix of their own synthesis to form biofilms. Formation of these sessile communities fundamentally alters the microbial physical and chemical environment and microbial metabolic activities. Although there is much ecological, physiological, and genetic information relating to the activity of microbial biofilms, little is known about the chemical mechanisms by which the surrounding polymeric layer (called EPS) contributes to overall microbial enzyme processes. In particular, we hypothesize that the EPS layer, composed primarily of an extensive network of heterogeneous polysaccharides, forms an important interfacial boundary between the microorganisms (and their enzyme complexes) and the bulk solution. We draw inferences supporting our hypothesis from soil environmental, microbiological, and biochemical literature that emphasizes the physicochemical role of the cell wall and the EPS layer in regulating metabolite accumulation and transport prior to enzyme catalysis. We define the biofilm-cell wall assembly surface and conclude that the trends in biofilm enzymatic activity are fundamentally influenced by the chemical nature and functionality of the biofilm surface.
  • Article
    Reversible and irreversible surface charge modification of Bacillus subtilis (a gram-positive aerobe), Pseudomonas fluorescens (a gram-negative species) and polymeric microspheres was attempted using common chemicals. This study was undertaken to see if such chemicals could be used to alter significantly the transport of various bacterial species through porous media. Significant surface charge alterations were observed in the irreversible treatments as shown by zeta potential measurements. The changes were shown to be partly reversible as evidenced by much larger shifts in zeta potential in the presence of the chemicals. Sodium pyrophosphate was found to alter the surface charge most significantly. All three species showed similar trends.Experiments on the transport of these species through sandpacks showed that their transport was significantly enhanced by the presence of the chemicals. The excellent correlation between high surface charge and transportability clearly suggests that electrostatic interactions between bacteria and sand grains are a dominant factor in their retention. Other bacterial retention mechanisms such as polymer adhesion seem to be relatively unimportant, at least for the species studied here. The various mechanisms responsible for the improved transportability and the surface charge modification are discussed. The applications of the study to filtration and microbial-enhanced oil recovery are pointed out.
  • Article
    In the Netherlands, water repellent soils are widespread and they often show irregular moisture patterns, which lead to accelerated transport of water and solutes to the groundwater and surface water. Under grasscover, spatial variability in soil moisture content is high due to fingered flow, in arable land vegetation and microtopography play a dominant role. Examples are given of uneven soil moisture patterns in water repellent sand, loam, clay and peat soils with grasscover, and in cropped water repellent sandy soils. In addition, the influence of fungi on inducing soil moisture patterns is illustrated as well.
  • Article
    Dry water repellent soils are known to inhibit water infiltration, ultimately forcing water to flow via preferential paths through the vadose zone. To study water flow and transport in a water repellent sandy soil, a bromide tracer experiment had been carried out, which started in the fall after winter wheat had been sown. Despite the uniform tracer application, soil core sampling indicated that bromide concentrations varied largely from place to place. Wetter sites in the experimental field received more bromide, due to lateral transport through a thin top layer. Wetting fronts infiltrated deeper here, leading to perturbed wetting fronts in the experimental field. In contrast to what was expected, the wetting front perturbations did not grow to fingers. Numerical results indicate that this was attributed to the relatively high soil water contents during the experiment, which caused the soil to be wettable instead of water repellent. The water-entry capillary pressure of the secondary wetting branch exceeds the air-entry capillary pressure of the primary drainage branch in this case. In the opposite situation, with the water-entry capillary pressure of the secondary wetting branch beneath the air-entry capillary pressure of the primary drainage branch, perturbations would have grown to fingers. Such a situation occurs during infiltration in initially dry, water repellent soil. The results presented illustrate the effect of antecedent moisture conditions on the formation of stable and unstable wetting fronts, and its relation to the moment of tracer application.
  • Article
    Full-text available
    Many soil micorganisms are able to produce extracellular polysaccharides (EPS). Electron microscopic observations of soils demonstrated that EPS are produced in soils and are closely associated with the surrounding clay particles. In the present study, experimental clay-polysaccharide associations were taken as models for the soil/biota interface, and their microstructure and physical properties were investigated.In the methodology, special attention was given to control the water potential and to preserve, as far as possible, the organizations of the original hydrated conditions.EPS increased the water retention of clay minerals or sands on desiccation and on rehydration, and reduced desiccation and rehydration rates. This was explained by the strong water-holding properties of EPS.Cryo-scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used, and showed that the polysaccharides occurred as a network of strands in the interparticle porosity of clay minerals. Polysaccharides changed the clay microstructure into an organo-mineral network with extensive interparticle bridging.The present results show that the clay-polysaccharide associations exhibit specific physical properties and microstructures that should affect biological functions and survival, for example through storage of water and buffering against water potential fluctuations. Clay-polysaccharide sheaths also take part in the binding of aggregates by soil biota.
  • Article
    Water-repellency in non-wetting sands is due to hydrophobic waxes present on the surface of sand grains and contained in particulate organic matter present in these sands. This study investigates the physico-chemical characteristics of these natural waxes and compares them to waxes extracted from potential original source materials.Non-polar and polar hydrophobic wax extracts were obtained from whole non-wetting sand, and its individual constituents, and associated organic matter. These included the sand fraction, the intrinsic particulate organic matter, tree litter, eucalyptus leaves, bark, lucerne and lupin plants, and fungi and actinomycetes isolated from these sands. Waxes were characterised for their hydrophobic properties and composition of their chemical constituents. The hydrophobicities of the waxes were assessed by measuring the water-repellency induced after treating acid washed sand with wax extracts.Non-polar and polar wax extracts of the tree litter displayed hydrophobic properties that were similar to the corresponding waxes isolated from non-wetting sand and intrinsic particulate organic matter. Unlike these plant-derived waxes, the microbial wax extracts possessed different hydrophobic properties.Characterisation of the components of the extracted waxes by gas chromatography-mass spectroscopy (GC-MS) analysis revealed a strong similarity in the composition of waxes isolated from non-wetting sand, tree litter and other plant material. The major components found were unbranched and branched C16 to C36 fatty acids and their esters, alkanes, phytanols, phytanes, and sterols. Some of these components were not detected in the microbial waxes.Unextracted samples, as well as wax extracts of non-wetting sand, intrinsic particulate organic matter, tree litter and fresh plant material were further analysed by solution and solid state Nuclear Magnetic Resonance spectroscopy which revealed the relative content of the different chemical species present.
  • Article
    In this study, the adhesion of bacteria differing in surface hydrophobicity was investigated. Cell wall hydrophobicity was measured as the contact angle of water on a bacterial layer collected on a microfilter. The contact angles ranged from 15 to 70 degrees. This method was compared with procedures based upon adhesion to hexadecane and with the partition of cells in a polyethylene glycol-dextran two-phase system. The results obtained with these three methods agreed reasonably well. The adhesion of 16 bacterial strains was measured on sulfated polystyrene as the solid phase. These experiments showed that hydrophobic cells adhered to a greater extent than hydrophilic cells. The extent of adhesion correlated well with the measured contact angles (linear regression coefficient, 0.8).
  • Adhesion of Candida albicans to the acrylic fitting surface of dentures can lead to the development of denture induced stomatitis and is suggested to be preceeded by the adhesion of indegeneous oral bacteria. Bacterial adhesion can be considered as a result of attractive van der Waals and repulsive electrostatic forces. In this paper we investigate the role of electrostatic interactions in the adhesion of oral streptococci to polymethylmethacrylate (PMMA), the most commonly employed denture-base material. Zeta potentials of the bacterial strains as well as of PMMA fillings were reduced by increasing the ionic strength in the buffer suspension, causing an elevated number of adhering S. mitis, S. sanguis and S. mutans. As streptococcal adhesion is suggested to be a prerequisite for the subsequent adhesion of Candida albicans, the use of more negatively charged denture-base materials can be recommended in order to prevent streptococcal adhesion and therewith adhesion of candidae, and the occurrence of denture-induced stomatitis.
  • Article
    Full-text available
    The zeta potential of cells of an attenuated vaccine Mycobacterium bovis, BCG, Tice substrain, was measured over a pH range of 1.5-11.0 at low electrolyte concentration. There was a marked electro-positive charge at low pH, the zero charge point, pH 4.4, being similar for viable and heat killed vaccine. At pH 6.5 the addition of sodium dodecyl sulphate or sodium tauroglycolate made little difference to the zeta potential. However, progressive addition of cetylpyridinium chloride reduced and finally reversed the charge to a maximum of +60 mV at a concentration of 1.5 x 10(-2) mol dm-3 surfactant. Higher concentrations reduced the charge although it remained positive. The nature of the adsorbing species on the cell surface is discussed since the Tice substrain has both cationic and anionic surface charges whereas the Glaxo strain is reported to only possess electro-negative phosphate surface groups. Some hydrophobic interaction involving lipid within the surface may also be involved.
  • Article
    Slime layers are being studied in our laboratories in an attempt to understand their functions in the control of pollution in natural streams. A method for fixing, staining, and embedding microorganisms in the intact slime has been developed. In this method, epoxy resin discs are placed in a holder and are introduced into a simulated stream. After various periods of time the discs are punched out of the holder into the fixative. The disc with the attached slime is fixed, stained (4% osmium tetroxide plus ruthenium red), dehydrated, and embedded in epoxy resin so that thin sections can be cut through the vertical plane of the slime mass. Such thin sections permit detailed examination of the attached layer, the surface-slime interface, the spatial relationships between cells in the vertical slime structure, and the strands of extracellular material between and around cells. No special attachment structures were noted as the cells appeared to be attached to the surface by extracellular material alone. This material was observed in strands and netlike forms between cells which are positioned 1 to 4 mum apart in the slime.
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    Although exopolysaccharides (EPSs) are a large component of bacterial biofilms, their contribution to biofilm structure and function has been examined for only a few organisms. In each of these cases EPS has been shown to be required for cellular attachment to abiotic surfaces. Here, we undertook a genetic approach to examine the potential role of colanic acid, an EPS of Escherichia coliK-12, in biofilm formation. Strains either proficient or deficient in colanic acid production were grown and allowed to adhere to abiotic surfaces and were then examined both macroscopically and microscopically. Surprisingly, we found that colanic acid production is not required for surface attachment. Rather, colanic acid is critical for the formation of the complex three-dimensional structure and depth of E. coli biofilms.