Anion exclusion in microbial and soil polysaccharides     

Timothy D. Hart  James M. Lynch  Anthony H. Chamberlain 《Biology and Fertility of Soils》2001,34(3):201-209

Microorganisms in soil, especially those associated with plant roots, are surrounded by envelopes of polysaccharides. These originate from both microbes and roots and are a characteristic feature of the rhizosphere. We have shown these materials to selectively restrict the diffusion of anions by the measurement of diffusion potentials. Using xanthan gum as a model microbial polysaccharide, increasing polymer concentration or polysaccharide layer thickness or the removal of acetyl and pyruvyl groups have been shown to increase the degree of anion exclusion. The anion-exclusive behaviour of xanthan has been validated independently by direct measurements of diffused ion concentrations. Data is presented showing this phenomenon to operate in KCl, KNO₃ and KH₂PO₄ systems. In all cases, the anion exclusion appears to be partial, restricting the diffusion of anions in the presence of a layer of 3% xanthan by 50-80%. By measurement of diffusion potentials, scleroglucan and polysaccharides produced by two soil bacteria, Azotobacter chroococcum and Enterobacter cloacae, were also shown to behave anion-exclusively. Ca-polygalacturonate, which has been used as a model root surface polymer, showed little ion-exclusive behaviour compared to polymers extracted from bulk soil and the rhizosphere and root surface of pea, which all showed high levels of anion exclusion. By chemical characterisation of all polymers under study, it was possible to link the presence of uronic acids within the gel to anion-exclusive behaviour. The results suggest that anion exclusion is a common property of microbial and soil polysaccharides. The ability of these materials to restrict the diffusion and thus the availability of nutrient anions at the microorganism or root cell surface may be of significance to the survival and growth of polysaccharide-producing organisms in soil.  相似文献   

Translocation of surface litter carbon into soil by Collembola     

Paul M. Chamberlain  Niall P. McNamara  Andrew W. Stott 《Soil biology & biochemistry》2006,38(9):2655-2664

Soil invertebrates are important in nutrient cycling in soils, but the degree to which mesofauna such as Collembola are responsible for the direct movement of carbon (C) from the litter layer into soil has not yet been ascertained. We used naturally occurring stable C isotopic differences between a C₄ soil and alder leaves (C₃) to examine the effect of the collembolan Folsomia candida on C translocation into soil in laboratory microcosms. Collembolan numbers greatly increased in the presence of alder, but despite large collembolan populations there were no changes in decomposition rate (measured as litter mass loss, cumulative respired CO₂ and alder C:N ratios). Small changes in the δ¹³C values of bulk soil organic matter were detected, but could not be assigned to collembolan activity. However, mean δ¹³C values of soil microbial phospholipid fatty acids (PLFAs) were significantly lower in the presence of alder and Collembola together, demonstrating that collembolan activities resulted in greater availability of litter-derived C to the soil microbial community. Additionally, the presence of Collembola resulted in the translocation of alder-derived compounds (chlorophyll and its breakdown product pheophytin) into soil, demonstrating that Collembola modify soil organic matter at the molecular level. These results are consistent with deposition of collembolan faeces in underlying soil and demonstrate that despite their small size, Collembola contribute directly to C transport in the litter-soil environment.  相似文献   

Biological management of the allergic patient     

K W Chamberlain 《The Veterinary clinics of North America》1974,4(1):65-77

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Martian atmosphere: the mariner occultation experiment     

Chamberlain JW  McElroy MB 《Science (New York, N.Y.)》1966,152(3718):21-25

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Ovarian maturation in stable flies: inhibition by 20-hydroxyecdysone   总被引：1，自引：0，他引：1  

J E Wright  W F Chamberlain  C C Barrett 《Science (New York, N.Y.)》1971,172(989):1247-1248

The steroid 20-hydroxyeedysone when given by mouth inhibits ovarian maturation in the stable fly, Stomoxys calcitrans (L.). by preventing lipid synthesis flecessary foir vitellogenlesis in the developing oocyte.  相似文献   

Invertebrate grazing affects nitrogen partitioning in the saprotrophic fungus Phanerochaete velutina     

George M. Tordoff  Paul M. Chamberlain  Thomas W. Crowther  T. Hefin Jones  Lynne Boddy 《Soil biology & biochemistry》2011,43(11):2338-2346

The heterogeneity of nutrients in forest soils is governed by many biotic and abiotic factors. The significance of nutrient patchiness in determining soil processes remains poorly understood. Some saprotrophic basidiomycete fungi influence nutrient heterogeneity by forming large mycelial networks that enable translocation of nutrients between colonized patches of dead organic matter. The effect of mycophagous soil fauna on these networks and subsequent nutrient redistribution has, however, been little studied. We used a soil microcosm system to investigate the potential effects of a mycophagous collembola, Protaphorura armata, on nutrient transfer within, and nutrient loss from, the mycelium of a saprotrophic basidiomycete fungus, Phanerochaete velutina. A ¹⁵N label, added to central mycelium, was used to track nitrogen movement within the microcosms across 32 days. Although collembola grazing had little impact on δ¹⁵N values, it did alter the partitioning of ¹⁵N between different regions of mycelia. Less ¹⁵N was transferred to new mycelial growth in grazed systems than in ungrazed systems, presumably because collembola reduced fungal growth rate and altered mycelial morphology. Surprisingly, collembola grazing did not increase the mineralization of N from mycelium into the bulk soil. Overall, our results suggest that mycophagous soil fauna can alter nutrient flux and partitioning within fungal mycelium; this has the potential to affect the dynamics and spatial heterogeneity of forest floor nutrients.  相似文献   

Myristicin in cigarette smoke     

Schmeltz I  Stedman RL  Ard JS  Chamberlain WJ 《Science (New York, N.Y.)》1966,151(3706):96-97

The pharmacologically active aromatic ether, myristicin, was isolated from the smoke of commercial cigarettes. The compound was identified by spectrometry (infrared, ultraviolet, and mass) and gas chromatography. The amount of myristicin in smoke is relatively low, and its contribution, if any, to the physiological action of cigarette smoke is unknowvn.  相似文献   

Size Dependence of Structural Metastability in Semiconductor Nanocrystals     

CC Chen  AB Herhold  CS Johnson  AP Alivisatos 《Science (New York, N.Y.)》1997,276(5311):398-401

The kinetics of a first-order, solid-solid phase transition were investigated in the prototypical nanocrystal system CdSe as a function of crystallite size. In contrast to extended solids, nanocrystals convert from one structure to another by single nucleation events, and the transformations obey simple unimolecular kinetics. Barrier heights were observed to increase with increasing nanocrystal size, although they also depend on the nature of the nanocrystal surface. These results are analogous to magnetic phase transitions in nanocrystals and suggest general rules that may be of use in the discovery of new metastable phases.  相似文献   

Orbitofrontal dysfunction in patients with obsessive-compulsive disorder and their unaffected relatives     

Chamberlain SR  Menzies L  Hampshire A  Suckling J  Fineberg NA  del Campo N  Aitken M  Craig K  Owen AM  Bullmore ET  Robbins TW  Sahakian BJ 《Science (New York, N.Y.)》2008,321(5887):421-422

Obsessive-compulsive disorder (OCD) is characterized by repetitive thoughts and behaviors associated with underlying dysregulation of frontostriatal circuitry. Central to neurobiological models of OCD is the orbitofrontal cortex, a neural region that facilitates behavioral flexibility after negative feedback (reversal learning). We identified abnormally reduced activation of several cortical regions, including the lateral orbitofrontal cortex, during reversal learning in OCD patients and their clinically unaffected close relatives, supporting the existence of an underlying previously undiscovered endophenotype for this disorder.  相似文献   

Measurement of Parity Nonconservation and an Anapole Moment in Cesium     

CS Wood  SC Bennett  D Cho  BP Masterson  JL Roberts  CE Tanner  CE Wieman 《Science (New York, N.Y.)》1997,275(5307):1759-1763

The amplitude of the parity-nonconserving transition between the 6S and 7S states of cesium was precisely measured with the use of a spin-polarized atomic beam. This measurement gives Im(E1pnc)/beta = -1.5935(56) millivolts per centimeter and provides an improved test of the standard model at low energy, including a value for the S parameter of -1.3(3)exp (11)theory. The nuclear spin-dependent contribution was 0.077(11) millivolts per centimeter; this contribution is a manifestation of parity violation in atomic nuclei and is a measurement of the long-sought anapole moment.  相似文献