Disruption Of Aggregates Research Articles

Tillage and Crop Rotation Effects on Mechanical Properties and Structural Stability of a Sandy Loam Soil in a Semi-arid Environment

Tillage has strong influence on soil architecture and thus modifies soil matrix-pore system. Short-term (7 years) changes in soil mechanical properties (macro-and micro-level) were evaluated in pigeon pea-wheat (P-W), cotton-wheat (C-W) and maize-wheat (M-W) cropping systems (CS). Tillage systems were: no tillage (NT) and conventional tillage (CT) with or without crop residue retention (+R/-R). Soil bulk density didn't change appreciably. Soil resistance to penetration at 10–20 cm layer reduced under NT system with residue retention (NT+R), owing to greater soil water content. Maintaining residue, irrespective of tillage, improved soil aggregation and bulk soil organic carbon content (total, particulate and KMnO4-oxidizable C), promoting a better root-zone hydro-physical regime in all CS. Effect of tillage on water-stability of aggregates was observed at 0–7.5 cm layer only, in air-dried, compared to field-moist samples. The tillage-CS interactions had impact on mean weight diameter (MWD) of air-dried aggregates at 0–7.5 cm layer. The MWD was higher in NT+R under P-W than any other tillage/residue-CS combination. Residue incorporation in CT also resulted in greater macro-aggregates (>0.25 mm), and thereby larger MWD. Disruption of aggregates through different energy inputs was the least under NT+R, indicating predominantly higher amount of water-stable aggregates, providing a better soil structure.

CubeSat Particle Aggregation Collision Experiment (Q-PACE): Design of a 3U CubeSat mission to investigate planetesimal formation

Observations of the collisional evolution of particle ensembles in a microgravity environment are necessary to characterize the processes that lead to the formation of planetesimals, km-size and larger bodies, within the protoplanetary disk. The two current theories of planetesimal formation, namely growth through binary sticking collisions and gravitational instability within the protoplanetary disk, have difficulties in explaining how particles grow beyond a centimeter in size. In this paper we describe the CubeSat Particle Aggregation and Collision Experiment (Q-PACE), a Low Earth Orbit 3U CubeSat mission that will provide a high-quality, long duration microgravity environment in which we will observe collisions between particles under conditions relevant to planetesimal formation. We have designed a series of experiments involving a broad range of particle size, density, surface properties, and collision velocities to observe collisional outcomes from bouncing to sticking as well as aggregate disruption in tens of thousands of collisions.

β2-Type Amyloidlike Fibrils of Poly-l-glutamic Acid Convert into Long, Highly Ordered Helices upon Dissolution in Dimethyl Sulfoxide

Replacing water with dimethyl sulfoxide (DMSO) completely reshapes the free-energy landscapes of solvated proteins. In DMSO, a powerful hydrogen-bond (HB) acceptor, formation of HBs between backbone NH groups and solvent is favored over HBs involving protein's carbonyl groups. This entails a profound structural disruption of globular proteins and proteinaceous aggregates (e.g., amyloid fibrils) upon transfer to DMSO. Here, we investigate an unusual DMSO-induced conformational transition of β2-amyloid fibrils from poly-l-glutamic acid (PLGA). The infrared spectra of β2-PLGA dissolved in DMSO lack the typical features associated with disordered conformation that are observed when amyloid fibrils from other proteins are dispersed in DMSO. Instead, the frequency and unusual narrowness of the amide I band imply the presence of highly ordered helical structures, which is supported by complementary methods, including vibrational circular dichroism and Raman optical activity. We argue that the conformation most consistent with the spectroscopic data is that of a PLGA chain essentially lacking nonhelical segments such as bends that would provide DMSO acceptors with direct access to the backbone. A structural study of DMSO-dissolved β2-PLGA by synchrotron small-angle X-ray scattering reveals the presence of long uninterrupted helices lending direct support to this hypothesis. Our study highlights the dramatic effects that solvation may have on conformational transitions of large polypeptide assemblies.

Disruption of amyloid aggregates by artificial ferritins

Abstract Presence of protein amyloid aggregates is associated with many neurodegenerative disorders, such as Alzheimer’s disease etc. The effect of magnetoferritin and reconstructed ferritin on the structure of lysozyme amyloid aggregates was studied using small-angle X-ray scattering, atomic force microscopy and thioflavin T fluorescence measurements. It has been shown that both magnetoferritin and reconstructed ferritin molecules affect the size, structure and amount of the amyloid fibrils. We assume that the anti-amyloid effect of magnetoferritin and reconstructed ferritin is due to the presence of iron in solutions but is not associated with the magnetic character of the iron oxide phases, i.e. magnetite/maghemite for magnetoferritin and ferrihydrite for ferritin.

Replicability of aggregate disruption by sonication—an inter‐laboratory test using three different soils from Germany

AbstractSonication is widely used for disruption of suspended soil aggregates. Calorimetric calibration allows for determining sonication power and applied energy as a measure for aggregate disrupting forces. Yet other properties of sonication devices (e.g., oscillation frequency and amplitude, sonotrode diameter) as well as procedure details (soil‐to‐water ratio, size, shape, and volume of used containers) may influence the extent of aggregate disruption in addition to the applied energy. In this study, we tested potential bias in aggregate disruption when different devices or procedures are used in laboratory routines. In nine laboratories, three reference soil samples were sonicated at 30 J mL−1 and 400 J mL−1. Aggregate disruption was estimated based on particle size distribution before and after sonication. Size distribution was obtained by standardized submerged sieving for particle size classes 2000–200 and 200–63 µm, and by dynamic imaging for particles < 63 µm. Despite differences in sonication devices and protocols used by the participants, only 16 in 216 tests of samples of the size fractions 2000–200 and 200–63 µm were identified as outliers. For the size fraction < 63 µm, fewer outliers were detected (8 in 324 tests). Four out of nine laboratories produced more than two outliers. In these laboratories, sonication devices differed from the others regarding oscillation frequencies (24 or 30 kHz compared to 20 kHz), sonotrode diameters (10 and 14 mm compared to 13 mm), and sonication power (16 W compared to > 45 W). Thus, these sonication device properties need to be listed when reporting on sonication‐based soil aggregate disruption. The overall small differences in the degree of disruption of soil aggregates between different laboratories demonstrate that sonication with the energies tested (30 and 400 J mL−1) provides replicable results despite the variations regarding procedures and equipment.

Changes in mechanical properties of concrete due to ASR

Alkali-Silica Reaction (ASR) is one of the most severe damage reactions of concrete. There are at least two different mechanisms of ASR: The most common is the rapid disruption of siliceous aggregates at the surface of the grain, which occurs in flint and opal sandstone, for example: The others are called slow reacting aggregates, and refer, for example, to cracking of the grain of greywacke and quartz porphyry. Both reactions are due to the dissolving of SiO2 by alkalis. The present paper reports on tests on slow reacting aggregates.While most studies in the literature concentrate on the expansion behavior of the aggregates, in this article focus is centered on the mechanical properties, such as strength and creep. The aggregates used are greywacke, quartz porphyry, and crushed sediments from the Upper Rhine Valley.

Relating soil organic matter composition to soil water repellency for soil biopore surfaces different in history from two Bt horizons of a Haplic Luvisol

AbstractThe deposition of organic matter (OM), which is known for its high potential water repellency, on biopore walls can enhance preferential flow through these pores. In this study, OM composition determined with diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was related to soil water repellency (SWR) determined with sessile drop method, Wilhelmy plate method, and sorptivity tests. We hypothesized that the chemical composition (in terms of potential wettability index; a) is related to the physical properties (i.e., contact angle) of biopore walls, (b) depends on the history of the biopore, and (c) differs from the bulk soil matrix. Thus, the main objective was to identify the relation between OM composition determined with DRIFT spectroscopy and SWR in structured soils. The experiments were carried out on biopores and their surrounding soil matrices, excavated from 2 depths of a haplic Luvisol, with 3 different biopore histories (i.e., root channels, earthworm burrows, and root channels that were short‐term colonized by an earthworm). All measurements at intact biopore surfaces indicated a larger SWR at the surface of biopore walls as compared with the surrounding matrices and showed a higher proportion of hydrophobic functional groups. The OM composition determined with DRIFT spectroscopy correlated (R2 > .7) with contact angles (sessile drop method) that is in line with results of both water sorptivity and Wilhelmy plate method for soils with reduced wettability. The surfaces of short‐term colonized earthworm burrows had the most varying hydrophobic to hydrophilic components (A/B)‐ratio of all investigated biopore surfaces depending on soil depth. For biopore surfaces at this depth, contact angles >90° were frequently observed. The results also indicate that earthworms can lower SWR by aggregate disruption.

Changes in snow cover alter nitrogen cycling and gaseous emissions in agricultural soils

Climate change-related increases in winter temperatures and precipitation, as predicted for eastern Canada, may alter snow cover, with consequences for soil temperature and moisture, nitrogen cycling, and greenhouse gas fluxes. To assess the effects of snow depth in a humid temperate agricultural ecosystem, we conducted a two-year field study with (1) snow removal, (2) passive snow accumulation (via snow fence), and (3) ambient snow treatments. We measured in situ N2O and CO2 fluxes and belowground soil gas concentration, and conducted denitrification and potential nitrification laboratory assays, from November through May. Snow manipulation significantly affected winter N2O dynamics. In the first winter, spring thaw N2O fluxes in snow removal plots were 31 and 48 times greater than from ambient snow and snow accumulation plots respectively. Mid-winter soil N2O concentration was also highest in snow removal plots. These effects may have been due to increased substrate availability due to greater soil frost, along with moderate gas diffusivities facilitating N2O production, in snow removal plots. In the second winter, spring thaw N2O fluxes and soil N2O concentration were greatest for ambient snow plots. Peak fluxes in ambient snow plots were 19 and 24 times greater than in snow accumulation and snow removal plots, respectively. Greater soil moisture in ambient snow plots overwinter could have facilitated denitrification both through decreased O2 availability and increased disruption of soil aggregates during freeze-thaw cycles. Overall, results suggest that effects of changing snow cover on N cycling and N2O fluxes were not solely a direct effect of snow depth; rather, effects were mediated by both soil water content and temperature. Furthermore, the fact that treatments with greatest mid-winter belowground N2O accumulation also had greatest spring thaw N2O fluxes in both years suggests the hypothesis that high spring thaw fluxes were due not only to spring soil conditions, but also to an effect of soil conditions in frozen soils that had facilitated N2O production throughout winter.

Dynamic and structural evidence of mesoscopic aggregation in phosphonium ionic liquids.

Mesoscopic aggregation in aprotic ionic liquids due to the microphase separation of polar and non-polar components is expected to correlate strongly with the physicochemical properties of ionic liquids and therefore their potential applications. The most commonly cited experimental evidence of such aggregation is the observation of a low-q pre-peak in the x-ray and neutron scattering profiles, attributed to the polarity alternation of polar and apolar phases. In this work, a homologous series of phosphonium ionic liquids with the bis(trifluoromethylsulfonyl)imide anion and systematically varying alkyl chain lengths on the phosphonium cation are investigated by small and wide-angle x-ray scattering, dynamic-mechanical spectroscopy, and broadband dielectric spectroscopy. A comparison of the real space correlation distance corresponding to the pre-peak and the presence or absence of the slow sub-α dielectric relaxation previously associated with the motion of mesoscale aggregates reveals a disruption of mesoscale aggregates with increasing symmetry of the quaternary phosphonium cation. These findings contribute to the broader understanding of the interplay of molecular structures, mesoscale aggregation, and physicochemical properties in aprotic ionic liquids.

Reversible light-induced solubility of disperse red 1 dye in a hydroxypropyl cellulose matrix

We present results on reversible light-induced solubility of disperse red 1 (DR1) dye in a hydroxypropyl cellulose (HPC) matrix. The samples were prepared by dissolution of both DR1 and HPC in acetone and left to dry overnight in air to form not totally uniform red coatings. It is observed that both heating and illumination of the samples with visible light promote the appearance of a dark red coloration inside the heated or illuminated regions. This new phenomenon is attributed to a dissolution of dye and/or disruption of DR1 aggregates. It is confirmed by visible light and FTIR spectroscopies. UV–Vis spectra evidence disappearance of a band at 400 nm, which is attributed to DR1 aggregates, upon illumination of the samples with visible light. FTIR spectra show new bands at 1600, 1508, and 1342 cm−1 that were assigned to symmetric and asymmetric stretching modes of NO2 of the dissolved DR1. Results evidence a dye solubilization process throughout repeated trans–cis isomery induced by visible light. This process is also a new feature of the light induced molecular movements of azo-dyes and may be used in future for the photo-command of polymer properties and/or light storage. This work opens new perspectives to use natural polymers and composites in photonic applications. It also reveals the strong potential of azo-materials as light powered molecular motors.

Fluorescence Enhancement of a Cationic Fluorene-Phenylene Conjugated Polyelectrolyte Induced by Nonionic n-Alkyl Polyoxyethylene Surfactants.

The modulation of conjugated polyelectrolyte fluorescence response by nonionic surfactants is dependent on the structures of the surfactant and polymer, polymer average molecular weight, and polyelectrolyte-surfactant interactions. In this paper, we study the effect of nonionic n-alkyl polyoxyethylene surfactants (CiEj) with different alkyl chain lengths (CiE5 with i = 6, 8, 10, and 12) and number of oxyethylene groups (C12Ej with j = 5, 7, and 9) on the photophysics and ionic conductivity of poly{[9,9-bis(6'-N,N,N-trimethylammonium)-hexyl]-2,7-fluorene-alt-1,4-phenylene}bromide (HTMA-PFP) in dimethyl sulfoxide-water 4% (v/v). Molecular dynamics simulations show that HTMA-PFP chains tend to approach as the simulation evolves. However, the minimum distance between the polymer centers of mass increases upon addition of the surfactant and grows with both the surfactant alkyl chain length and the number of oxyethylene groups, although there are no specific polymer-surfactant interactions. A significant increase in the polymer emission intensity has been observed at surfactant concentrations around their critical micelle concentrations (cmcs), which is attributed to polymer aggregate disruption. However, an increase in the solution conductivity for concentrations above the C12E5 cmc has only been observed for the HTMA-PFP/C12E5 system. The enhancement of fluorescence emission intensity and conductivity upon surfactant addition increases with polymer average molecular weights and seems to be controlled by the polymer-surfactant proximity, which is maximum for C10E5 and C12E5.

Urea induced changes in self-assembly and aggregate microstructures of amphiphilic star block copolymers with widely different hydrophobicity

The presence of excess of denaturants like urea unfolds proteins and disfavours micellization of surfactants; the mode of interaction of urea has always been a matter of debate. Inspired by this need, the effect of urea on the monolayer and micellar characteristics of three polyethylene oxide/propylene oxide (PEO/PPO) starblock copolymers Tetronics® viz. T1301, T1304 and T1307 (with almost same molecular weight of PPO but varying% PEO as 10, 40 and 70%, respectively) in aqueous urea solutions was investigated through scattering/spectral technique and Langmuir film balance.The three copolymers showed markedly different behaviour. In the absence of urea, the most hydrophobic T1301 forms vesicular structures (few hundred nm), T1304 with moderate hydrophobicity forms spherical micelles (∼10–20nm) with low polydispersity while very hydrophilic T1307 exists as a highly polydispersed system with unimers (∼3–5nm), loose aggregates (∼10–20nm) and clusters (with few hundred nm size). However, the addition of urea (0–8M) to these copolymer solutions leads to the disruption of any loose aggregates formed which is probably due to its binding with the copolymer chains that enhances the solubility of Tetronics® and overall polydispersity of the copolymer solutions. In support to our hypothesis, the binding of urea was validated using fluorescence measurements/Langmuir film balance and it was established that urea follows the direct mechanism (as proposed in earlier reports) and the intercalation of urea between the PEO chains leads to the extended conformations as observed by Langmuir film balance. Although, urea had a common denaturing effect on all the three copolymers, the hydrating effect of urea was most evident for copolymers with more hydrophilic character.

Soil organic carbon stocks and fractionation under different land uses in the Peruvian high-Andean Puna

Soil organic C (SOC), the largest terrestrial C pool, has been shown to be sensitive to agricultural disturbance. In the Andean Puna, agricultural expansion is thought to be jeopardizing the large SOC stock sequestered in its soils. In this paper, we assessed the impact changes in land use have on C sequestration, fractionation and δ13C natural abundance featuring two case studies in the Peruvian Central Puna. We found SOC stocks greater than average temperate grassland soils (between 123±4 and 136±4MgCha−1 in the 0–30cm soil profile); however, they did not differ between land uses. In the first case study, depletion of δ13C in mineral associated C in long fallow (>7yr) and maca (Lepidium meyenii Walpers) croplands was hypothesized to be caused by disruption of soil aggregates due to tillage and initial greater SOC concentration in maca plots. In addition, SOC loss was found in long fallow plots, and was correlated to steep and low plant cover plots; evidencing that soil degradation does not occur during cropping activity but due to erosion after land abandonment. In the second case study, a long-established perennial ryegrass (Lolium perenne L.) - white clover (Trifolium repens L.) association (>40yr) was studied. We did not find an increase in SOC stock under the cultivated pasture. However, we found a better soil aggregation and an increase of 17.3 and 12.2gCkg−1WSA in particulate organic C, and SOC within small macroaggregates in cultivated pasture soils. Soil δ13C natural abundance was about 1‰ depleted in all measured C fractions of cultivated pastures when compared to native grasslands, suggesting that pasture-fixed C forms labile and recalcitrant SOC fractions.

Temporal variations of organic matter fractions of different lability in an Entic Haplustoll

Stable and labile soil organic compounds play different roles in the soil. It is a question of how far soil organic matter (SOM) fractions with different labilities vary as a function of climatic and management conditions. In order to answer this question stable (organic C -C-, total N -N-, organic P -Po-), and labile SOM fractions (total carbohydrates -CHt- and hot water soluble carbohydrates -CHw-) were measured monthly for two years in the 10-cm soil top-layer of an Entic Haplustoll, under conventional tillage (CT), vertical tillage (VT) and no-till (NT). Results showed that contents of all analyzed organic fractions were higher in NT than in VT and CT in almost all sampling dates. All organic compounds were less variable with time in NT and VT than in CT, in agreement with the smaller soil disturbance of NT and VT compared to CT. The more labile fractions varied as a function of short term changes in the climatic conditions, mainly temperature. Under soil disturbing tillage systems, the most stable fractions tended to decrease and the more labile to increase with time. This was attributed to the transformation of the more stable into the more labile fractions, possibly due to the disruption of aggregates produced by tillage that favored SOM mineralization. Po was the less variable compound, even under the most disturbing tillage conditions. The quotients C/N, CHt/C and CHw/C evolved similarly in all tillage systems, indicating that that tillage systems change the amount but not the quality of SOM.

NIR light and enzyme dual stimuli-responsive amphiphilic diblock copolymer assemblies

Using atom transfer radical polymerization (ATRP) and macromolecular azo coupling reaction, both o-nitrobenzyl (ONB) group and azobenzene group were efficiently incorporated into the center of the amphiphilic diblock copolymer chain. The prepared diblock copolymer was well characterized by UV–vis, 1H NMR, and GPC methods. Self-assembly of the amphiphilic copolymer in selected solvents can result in uniform self-assembly aggregates. In the presence of external stimuli [upconversion nanoparticles (UCNPs)/NIR light or enzyme], the amphiphilic diblock copolymer chain could be broken by the cleavage of ONB or azobenzene group, which would lead to the disruption of the self-assembly aggregates. This photo- and enzyme-triggered disruption process was proved by using transmission electron microscopy (TEM) and GPC method. Fluorescence emission spectra measurements indicated that the release of Nile red, a hydrophobic dye, encapsulated by the self-assembly aggregates, could be successfully realized under the NIR light and enzyme stimuli. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2450–2457

Anti-amyloid aggregation activity of novel carotenoids: implications for Alzheimer's drug discovery.

Alzheimer’s disease (AD) is the leading cause of dementia, affecting approximately 33.5 million people worldwide. Aging is the main risk factor associated with AD. Drug discovery based on nutraceutical molecules for prevention and treatment of AD is a growing topic. In this sense, carotenoids are phytochemicals present mainly in fruits and vegetables with reported benefits for human health. In this research, the anti-amyloidogenic activity of three carotenoids, cryptocapsin, cryptocapsin-5,6-epoxide, and zeaxanthin, was assessed. Cryptocapsin showed the highest bioactivity, while cryptocapsin-5,6-epoxide and zeaxanthin exhibited similar activity on anti-aggregation assays. Molecular modeling analysis revealed that the evaluated carotenoids might follow two mechanisms for inhibiting Aβ aggregation: by preventing the formation of the fibril and through disruption of the Aβ aggregates. Our studies provided evidence that cryptocapsin, cryptocapsin-5,6-epoxide, and zeaxanthin have anti-amyloidogenic potential and could be used for prevention and treatment of AD.

Avidity for Polypeptide Binding by Nucleotide-Bound Hsp104 Structures.

Recent Hsp104 structural studies have reported both planar and helical models of the hexameric structure. The conformation of Hsp104 monomers within the hexamer is affected by nucleotide ligation. After nucleotide-driven hexamer formation, Hsp104-catalyzed disruption of protein aggregates requires binding to the peptide substrate. Here, we examine the oligomeric state of Hsp104 and its peptide binding competency in the absence of nucleotide and in the presence of ADP, ATPγS, AMPPNP, or AMPPCP. Surprisingly, we found that only ATPγS facilitates avid peptide binding by Hsp104. We propose that the modulation between high- and low-peptide affinity states observed with these ATP analogues is an important component of the disaggregation mechanism of Hsp104.

Expansion of 3D human induced pluripotent stem cell aggregates in bioreactors: Bioprocess intensification and scaling-up approaches

Human induced pluripotent stem cells (hiPSC) are attractive tools for drug screening and disease modeling and promising candidates for cell therapy applications. However, to achieve the high numbers of cells required for these purposes, scalable and clinical-grade technologies must be established.In this study, we use environmentally controlled stirred-tank bioreactors operating in perfusion as a powerful tool for bioprocess intensification of hiPSC production. We demonstrate the importance of controlling the dissolved oxygen concentration at low levels (4%) and perfusion at 1.3day−1 dilution rate to improve hiPSC growth as aggregates in a xeno-free medium. This strategy allowed for increased cell specific growth rate, maximum volumetric concentrations (4.7×106cell/mL) and expansion factors (approximately 19 in total cells), resulting in a 2.6-fold overall improvement in cell yields. Extensive cell characterization, including whole proteomic analysis, was performed to confirm that cells’ pluripotent phenotype was maintained during culture.A scalable protocol for continuous expansion of hiPSC aggregates in bioreactors was implemented using mechanical dissociation for aggregate disruption and cell passaging. A total expansion factor of 1100 in viable cells was obtained in 11days of culture, while cells maintained their proliferation capacity, pluripotent phenotype and potential as well as genomic stability after 3 sequential passages in bioreactors.

Shaken or stirred?: Comparison of methods for dispersion of Mycoplasma pneumoniae aggregates for persistence in vivo

BackgroundMycoplasma pneumoniae (Mpn), one of the smallest self-replicating prokaryotes, is known to readily adhere to host cells and to form aggregates in suspension. Having only one cell membrane and no cell wall, mycoplasmas present questions as to optimal aggregate disruption method while minimizing cell death in vitro. We compared conventional vortex mixing with other methods for disruption of bacterial aggregates and for its effect on cell viability. MethodsStrain UAB PO1, a clinical Mpn isolate, was dispersed using a conventional vortex mixer with or without nonionic detergent (0.1% and 0.01% Tween-20), a probe-type ultrasonicator, or repeated passage through a 27-gauge needle. The resulting suspensions were assayed for recoverable colony-forming units (CFU). Flow cytometric assays were carried out to examine particle size and membrane integrity with the transmembrane potential dye DiBAC4. Wet Scanning Transmission Electron Microscopy (Wet-STEM) was performed for high resolution imaging of the resultant cell suspensions. Additional Mpn strains and other human mollicute species were assayed in a similar manner. Mice were infected with either vortexed or sonicated UAB PO1 and bacterial persistence was examined via Mpn-specific 16S qPCR. ResultsComparison between dispersion methods showed a 10-fold enrichment of recoverable Mpn CFU with sonication compared to other methods. Time-course analysis showed significantly lower bacterial CFU with vortexing compared to sonication at all time points. Flow cytometric analysis showed increased cellular membrane damage via DiBAC4 staining in sonicated suspensions, but a decreased particle size. Wet-STEM imaging showed markedly improved dispersion with sonication compared to conventional vortex treatment, and surprisingly vortexing for 30s produced up to a 100-fold drop in CFU. Results similar to UAB PO1 were obtained with three additional Mpn strains and other Mollicutes species, although they exhibited differential susceptibilities to disaggregation by sonication. Finally, increased persistence of the organism in a mouse model of infection was observed using sonicated suspensions for initial infection. ConclusionsSonication is superior to vortexing with or without nonionic detergent or repeated 27-gauge needle passage for dispersion of Mpn aggregates while preserving cell viability. Preparation of Mpn suspensions for in vivo experiments is best accomplished using brief sonication due to the dramatic increase in CFU produced by sonication. Dispersion methods may affect the final experimental results and should be an important consideration for future research involving mycoplasma species.

Using ultrasonic energy to elucidate the effects of decomposing plant residues on soil aggregation

Water-stable soil aggregates are generally formed following the addition of organic materials in soils. This process is mediated by the interaction between microbes and soil organic matter in ways that are still not completely understood. To get insight into the effects of decomposing plant residues on aggregate dynamics, a clay soil with an inherently low soil organic carbon (SOC) content, was amended with two different sources of organic matter (alfalfa, C:N=16.7 and barley straw, C:N=95.6) at different input levels (0, 10, 20, & 30gCkg−1 soil). These were incubated for a period of 3 months over which soil respiration was assessed using the NaOH capture method, water aggregate stability was determined with the mean weight diameter (MWD) by wet sieving, and the relative strength of aggregates exposed to ultrasonic agitation was modelled using the aggregate disruption characteristic curve (ADCC) and soil dispersion characteristic curve (SDCC). As expected, the quality and quantity of organic matter added controlled the respiration rate, with alfalfa (0.457g CO2Cg−1C for total respiration rate) being greater than barley amended samples (0.178g CO2Cg−1C) at any C input rate. Both residue quality and quantity of organic matter input also influenced the amount of aggregates formed and their relative strength. The MWD of soils amended with alfalfa residues was greater than that of barley straw at lower input rates and early in the incubation (e.g. at 28 days of incubation and at a rate of 10gCkg−1 soil, MWD was 575μm and 731μm for barley straw and alfalfa, respectively). However, in the longer term (84 days of incubation), the use of ultrasonic energy revealed that barley straw resulted in stronger aggregates, especially at higher input rates despite showing similar MWD as alfalfa. The use of ultrasonic agitation, where we quantify the energy required to liberate and disperse aggregates allowed us to differentiate the effects of C inputs on the size of stable aggregates and their relative strength.