Earthworms are soil invertebrates that play a key role in recycling organic matter in soils.In Nigeria, earthworms include Libyodrillus violaceous. Aerobic and anaerobic bacterial counts, as well as fungal counts of viable microorganisms in soils and gut sections, were made on twenty L. violaceous collected from different sites on the campus of the University of Agriculture, Abeokuta, Nigeria. The samples were collected between April and November, 2002. Numbers of microorganisms were higher in castings and gut sections than in uningested soil samples. The guts and their contents also had higher moisture and total nitrogen contents than the uningested soils. Bacteria and fungi isolated from the samples were identified by standard microbiological procedures on the bases of their morphological and biochemical characteristics. Isolated bacteria were identified as Staphylococcus, Bacillus spp., Pseudomonas aeruginosa, Streptococcus mutans, Clostridium, Spirocheata spp., Azotobacter spp., Micrococcus lylae, Acinetobacter spp., Halobacterium for bacteria. Yeast isolates were identified as Candida spp., Zygosaccharomyces spp., Pichia spp., and Saccharomyces spp while molds were identified as, Aspergillus spp., Pytium spp., Penicillium spp., Fusarium spp and Rhizopus spp. Of the five locations examined, the refuse dump area had the highest numbers of both aerobic and anaerobic organisms, followed by the arboretum while the cultivated land area recorded the lowest counts. The higher numbers of microorganisms observed in the gut sections and casts of the earthworms examined in this work reinforce the general concept that the gut and casts of earthworms show higher microbial diversity and activity than the surrounding soil. Rev. Biol. Trop. 54 (1): 49-58. Epub 2006 Mar 31.
En este trabajo se presenta, en primer lugar, una metodología de verificación y reparación de sitios Web que permite especificar requerimientos sobre el sitio Web y detectar errores en base a la especificación. Para optimizar el proceso de verificación, se definen algoritmos de cálculo de generalizaciones ecuacionales y order-sorted.
The restoration of soil microbial activities is a basic step in the reclamation of burnt soils. For this reason, the ability of municipal solid waste compost to accelerate the re-establishment of bacterial and fungal populations, as well as to re-establish physical properties in a burnt soil, was evaluated in a field experiment. Four treatments were performed by adding different doses of compost (0, 0.5, 1 and 2 kg compost m–2 soil) to a burnt Calcic Rodoxeralf soil, and the changes in microbial populations, salt content, aggregate stability and bulk density were evaluated for 1 year. Initially, the addition of compost had a negative effect on soil microbial populations, but 3 months after compost addition, the number of viable fungal propagules increased in all the amended soils. This positive effect lasted until the end of the experiment. From 30 days onwards, all the amended soils showed a greater total number of bacterial cell forming units than the unamended burnt soil. Organic amendment increased the percentage of 2- to 4-mm aggregates, although the effect on the stability of the 0.2- to 2-mm aggregates and on bulk density was less noticeable.
Atrazine is an herbicide of the s-triazine family that is used primarily as a nitrogen source by degrading microorganisms. While many catabolic pathways for xenobiotics are subjected to catabolic repression by preferential carbon sources, atrazine utilization is repressed in the presence of preferential nitrogen sources. This phenomenon appears to restrict atrazine elimination in nitrogen-fertilized soils by indigenous organisms or in bioaugmentation approaches. The mechanisms of nitrogen control have been investigated in the model strain Pseudomonas sp. ADP. Expression of atzA, atzB ad atzC, involved in the conversion of atrazine in cyanuric acid, is constitutive. The atzDEF operon, encoding the enzymes responsible for cyanuric acid mineralization, is a target for general nitrogen control. Regulation of atzDEF involves a complex interplay between the global regulatory elements of general nitrogen control and the pathway-specific LysR-type regulator AtzR. In addition, indirect evidence suggests that atrazine transport may also be a target for nitrogen regulation in this strain. The knowledge about regulatory mechanisms may allow the design of rational bioremediation strategies such as biostimulation using carbon sources or the use of mutant strains impaired in the assimilation of nitrogen sources for bioaugmentation.
In the dairy industry, the characterization of Streptococcus thermophilus phage types is very important for the selection and use of efficient starter cultures. The aim of this study was to develop a characterization system useful in phage control programs in dairy plants. A comparative study of phages of different origins was initially performed based on their morphology, DNA restriction profiles, DNA homology, structural proteins, packaging mechanisms, and lifestyles and on the presence of a highly conserved DNA fragment of the replication module. However, these traditional criteria were of limited industrial value, mainly because there appeared to be no correlation between these variables and host ranges. We therefore developed a PCR method to amplify VR2, a variable region of the antireceptor gene, which allowed rapid detection of S. thermophilus phages and classification of these phages. This method has a significant advantage over other grouping criteria since our results suggest that there is a correlation between typing profiles and host ranges. This association could be valuable for the dairy industry by allowing a rational starter rotation system to be established and by helping in the selection of more suitable starter culture resistance mechanisms. The method described here is also a useful tool for phage detection, since specific PCR amplification was possible when phage-contaminated milk was used as a template (detection limit, 105 PFU ml–1).
El caracol Pala, Strombus gigas (Strombidae), es de gran importancia ecológica y socioeconómica en el área caribeña colombiana. Sin embargo, es una especie catalogada como "vulnerable" y existe muy poca información referente a las especies bacterianas asociadas al caracol que puedan ser importantes para el desarrollo, manejo productivo y de seguridad acuícola de estos gastrópodos. En este trabajo, nosotros empleamos un estudio microbiológico y molecular de la región intergénica entre los genes 16S y 23S rDNA, análisis del gen rDNA 16S y secuenciación, para analizar las bacterias asociadas al caracol Pala (S. gigas). La composición de bacterias cultivables asociadas fue evaluada por su capacidad para crecer en agar marino y en medios de cultivos selectivos. De un total de 28 muestras analizadas encontramos que el número de bacterias cultivadas en condiciones aerobias fue de alrededor 10(6) ufc mL-1 donde las bacterias pertenecientes a la familia Vibrionacea fueron las más abundantes, cerca de >10(5) ufc mL-1. El análisis molecular de la región intergénica entre los genes 16S y 23S rDNA de las diferentes muestras, reveló una gran complejidad bacteriana asociada a S. gigas. Las secuencias de los amplificados del gen rDNA 16S identificó Pseudoalteromonas sp., Halomonas sp., Psycrobacter sp., Cobetia sp., Pseudomonas sp. y Vibrios sp. Nuestros resultados podrían sugerir un rol importante de estas bacterias como componentes de la comunidad asociada al S. gigas. Esta información puede complementar los estudios que se están implementando en los procesos para la conservación y repoblamiento de las poblaciones de S. gigas en Colombia.
This study describes a new type of taphonomic alteration of fossil bone that occurred in a continental carbonate
palaeolake environment at the reference Spanish Miocene site of Cerro de la Garita (Concud, Teruel). Scanning
electron microscopy showed this type of alteration to be characterized by microtunnels that penetrate inward
from the bone surface and by a branching-meandering arrangement of microchannels on the bone surface.
These microtunnels had a highly electron dense inner wall, seen as a characteristic rim in transverse section.
Microspheres were seen inside the microtunnels. Both this electron dense layer and these microspheres were
found to be composed of calcium phosphate. These taphonomic modifications bear some similarities to, but
also differs from, those caused by bacterial attack on bone and enamel in marine and terrestrial environments,
suggesting the present process to be a new type of bioerosion. The microspheres inside the microtunnels were
similar in size, shape and composition to the fossilized bacteria covering fossils from Fossil-Lagersttäten
palaeolake sites, such as Libros (Teruel, Spain) and Messel (Germany). Under the transmission electron
microscope these structures showed an apparent cell wall, suggesting them to be fossilized coccoid bacteria.
Bacterioplankton have the potential to significantly affect the cycling of organic matter in the ocean; however, little is known about the linkage between bacterial assemblage structure and carbon metabolism. In this study, we investigated whether changes in the phylogenetic composition of bacterioplankton were associated with changes in bacterial carbon processing (bacterial production, respiration and biomass) in the subtropical NE Atlantic Ocean. We found consistent differences in the composition of the bacterial assemblage, as revealed by denaturing gradient gel electrophoresis (DGGE) and catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH), along a gradient from the NW African upwelling to the oligotrophic North Atlantic Subtropical Gyre. The percent contribution of Bacteroidetes, Roseobacter and Gammaproteobacteria significantly increased towards more productive waters, whereas the SAR11 clade of the Alphaproteobacteria remained relatively constant (average 28% of DAPI-stained cells) throughout the area. Changes in the composition of the bacterial assemblage detected by DGGE were weakly but significantly correlated with changes in carbon processing variables. The abundances of Roseobacter and Gammaproteobacteria were highly correlated with the concentration of particulate organic carbon and chlorophyll a, reflecting the affinity of these groups to nutrient-enriched conditions. The abundance of Roseobacter was also positively correlated with heterotrophic bacterial production, suggesting their active participation in carbon processing.
A novel microporous templated carbon material doped with nitrogen is synthesized by using a two-step nanocasting process using acrylonitrile (AN) and propylene as precursors, and Na-Y zeolite as a scaffold. Liquid-phase impregnation and in situ polymerization of the nitrogenated precursor inside the nanochannels of the inorganic scaffold, followed by gas-phase impregnation with propylene, enables pore-size control and functionality tuning of the resulting carbon material. The material thereby obtained has a narrow pore-size distribution (PSD), within the micropore range, and a large amount of heteroatoms (i.e., oxygen and nitrogen). In addition, the carbon material inherits the ordered structure of the inorganic host. Such features simultaneously present in the carbon result in it being ideal for use as an electrode in a supercapacitor. Although presenting a moderately developed specific surface area (S_BET = 1680 m2 g-1), the templated carbon material displays a large gravimetric capacitance (340 F g-1) in aqueous media because of the combined electrochemical activity of the heteroatoms and the accessible porosity. This material can operate at 1.2 V in an aqueous medium with good cycleability - beyond 10 000 cycles - and is extremely promising for use in the development of high-energy-density supercapacitors.
This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.
The spatial scale and the magnitude of carbon and nitrogen translocation was examined in 5 tropical (Cymodocea serrulata, Halophila stipulacea, Halodule uninervis, Thalassodendron ciliatum, Thalassia hemprichii) and 3 temperate (Cymodocea nodosa, Posidonia oceanica, Zostera noltii) seagrass species using Carbon-13 (C-13) and Nitrogen-15 (N-15) as tracers in experiments conducted in situ. Seagrass leaf and rhizome production during the study period varied from <0.001 to 0.015 gDW shoot-1 d-1 and 0.002 to 0.017 gDW rhizomeapex-1 d-1, respectively. Based on measured leaf and rhizome growth rates, the demand of resources for leaf production varied from 0.19 to 4.99 mgC shoot-1 d-1, and from 0.01 to 0.24 mgN shoot-1 d-1, while the demand for rhizome production varied from 0.62 to 5.57 mgC rhizome apex-1 d-1 and from 0.02 to 0.12 mgN rhizomeapex-1 d-1. Seagrass leaves incorporated the isotopes at rates ranging from 0.04 to 0.63 µg C-13 gDW-1 h-1, and <0.01 to 0.35 µg N-15 g DW-1 h-1. After 4 d, all incubated shoots had shared part of the incorporated C-13 and N-15 with ramets placed at maximum distances ranging from 2.7 (H. stipulacea) to 81 cm (C. nodosa), indicating that seagrass clonal integration may be maintained between 1.6 d (H. stipulacea) and 5.4 yr (P. oceanica). Resource translocation within seagrass clones was stimulated towards horizontal rhizome apices. Seagrass ramets, in 4 d, shared with their neighbours between 0.37 and 390 µg C-13 and between 0.02 and 178 µg N-15. During the study period, resource translocation would supply <5% and up to 40% of the leaf carbon and nitrogen
required by a neighbouring developing ramet, respectively, and <5% and up to 36% of the carbon and nitrogen required for rhizome growth; provided that the incorporated resources over 1 d were mobilised at similar rates over 4 d. These results conclusively demonstrate physiological integration between seagrass ramets, and that resource translocation may be an important mechanism for young seagrass ramets to acquire resources and for seagrass clones to expand and persist.
Composite coatings made of nanocrystalline TiC (nc-TiC) particles and amorphous carbon (a-C) have been prepared in a double magnetron sputtering system using graphite and titanium targets under Ar bombardment. Chemical composition and microstructure of coatings were studied by transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and x-ray diffraction (XRD) for a set of samples prepared varying the ratio and intensity of power applied to each magnetron. Changes in coatings microstructure, from a quasipolycrystalline TiC to a nanocomposite formed by nanocrystals of TiC embedded in an amorphous matrix of carbon (nc-TiC/a-C), are observed depending on the synthesis conditions. Tribological and mechanical properties of coatings were tested using a pin-on-disk tribometer and an ultramicrohardness indenter, respectively. Coatings with moderate hardness (7–27 GPa), low friction (0.1–0.2), and low wear rates (k~10–7 mm3/N m) were obtained. A percentage between 15% and 30% of TiC is found as an optimum value to get a good compromise between good mechanical and tribological properties. Finally, a mapping of the mechanical and tribological properties of the nc-TiC/a-C system is presented for the synthesis conditions employed.
Este trabajo tiene como objetivo identificar factores de éxito para el sector artesanal mexicano, utilizando la habilidad de los negocios para adquirir y coordinar sus recursos y capacidades. En la literatura abundan las propuestas de factores de éxito para empresas muy consolidadas, mientras que los negocios de artesanía basan sus expectativas en las preferencias del consumidor, tienen gran variabilidad en su organización, en la formalidad y en la flexibilidad de su estructura, lo que dificulta la utilización de esos factores. Para la obtención de datos se empleó una entrevista estructurada en 337 negocios de artesanía, se realizó en 8 estados de la República Mexicana : Guanajuato, Jalisco, Michoacán, Estado de México, Guerrero, Oaxaca, Puebla y Veracruz. Se utilizó el análisis de regresión lineal múltiple para determinar los factores de éxito. Como resultado se obtuvieron nueve factores de éxito: innovación administrativa, impacto del financiamiento, tecnología de producción, tecnología en administración, capacidad en el manejo del proceso, del empaque, diferenciación e información. Se proponen ecuaciones que pueden ser aplicadas en el manejo del éxito del negocio, para cuando el éxito se mida como satisfacción con el negocio, o por ingresos en ventas, el crecimiento del negocio, o por el tamaño del negocio.
We report a tip-based nanofabrication method to generate carbon nanopatterns. The process uses the field-induced transformation of carbon dioxide gas into a solid material. It requires the application of low-to-moderate voltages ∼ 10–40 V. The method allow us to fabricated sub-25 nm dots and it can be up scaled to pattern square centimeter areas. Photoemission spectroscopy shows that the carbon is the dominating atomic species of the fabricated structures. The formation of carbon nanostructures and oxides by atomic force microscope nanolithography expands its potential by providing patterns on the same sample with different chemical composition.
A study based on a total of 41 nanoporous carbons shows that there exists a good correlation between the limiting gravimetric capacitances Co at low current densities j (1 mA cm−2) measured in aprotic (1 M (C2H5)4 NBF4 in acetonitrile) and in acidic (2 M aqueous H2SO4) electrolytes. The comparison of the surface-related capacitances (F m−2) of well characterized samples with the amount of thermodesorbed CO suggests a strong contribution of CO generating surface groups to charge storage in the acidic electrolyte, but a negligible contribution in the aprotic medium. It also appears that the decrease of the capacitance with current density is similar in both electrolytes. This confirms that the average micropore width and the CO2 generating surface groups are the main factors which limit the ionic mobility in both electrolytes.
In the context of gold extraction, leaching is the dissolution of the metal or even a mineral in a liquid phase.
Thus, it is of a primary concern the dissolution of gold in an aqueous solution, operation which requires both a
complexant and an oxidant to achieve acceptable leaching rates and yields. A limited number of ligands form
complexes of sufficient stability and at a suitable rate for their use in gold leaching operations. Cyanide is mostly
used because of its relatively low cost and great efficiency for gold dissolution. The main disadvantage associated
with its use is the extremely toxic character of the reagent. Thus, several other ligands had been considered for gold
extraction from ores, regarding to environmental pressures and even restrictions to the use of cyanide, potential of
having faster gold leaching kinetics than cyanide, possibility of their use in acidic media, which is suitable in the
treatment of refractory ores, and a greater degree of selectivity than cyanide for gold over other metals. Nevertheless,
some of them presented some disadvantages which limited their practical use. Ammoniacal thiosulfate leaching has
a considerable potential as an effective and less hazardous procedure (than cyanide) for gold extraction from
auriferous ores. Once gold is dissolved, separation of the precious metal from the solution can be achieved using
different procedures (i.e. adsorption onto activated carbon). In the present investigation, up to fivel models were
used to correlate the adsorption of gold onto the carbon, being the Fleming model the one which best fit the
experimental results on gold adsorption.
We employ electrostatic force microscopy to study the electrostatic environment of graphene sheets prepared with the micromechanical exfoliation technique. We detect the electric dipole of residues left from the adhesive tape during graphene preparation, as well as the dipole of water molecules adsorbed on top of graphene. Water molecules form a dipole layer that can generate an electric field as large as ~10^9 V m−1. We expect that water molecules can significantly modify the electrical properties of graphene devices.
A combined study of the crystalline structure, the chemical interaction, and diffusion processes of the substrate/layer interface of amorphous-carbon hard coatings is presented. The structure of the coatings and their gradient layer interface to a chromium buffer layer has been investigated on two substrates [Si(100) and tool steel] using x-ray diffraction (XRD). Chemical interaction and diffusion processes at the interfaces and within the layers were analyzed by Auger electron spectroscopy and x-ray photoemission spectroscopy depth profiles. The chromium buffer layer revealed similar textured structure on both substrates. The subsequent gradient layer was determined (within XRD limits) to be amorphous and composed of an amorphous-carbon and chromium-carbide composite. The chromium carbide maintains the same stoichiometry (Cr3C2), regardless of the gradually changing chromium content. No large-scale interdiffusion was measured, either between or within the layers.
Data from several years of monthly samplings are combined with a 1-year detailed study of carbon flux through bacteria at a NW Mediterranean coastal site to delineate the bacterial role in carbon use and to assess whether environmental factors or bacterial assemblage composition affected the in situ rates of bacterial carbon processing. Leucine (Leu) uptake rates [as an estimate of bacterial heterotrophic production (BHP)] showed high interannual variability but, on average, lower values were found in winter (around 50 pM Leu−1 h−1) as compared to summer (around 150 pM Leu−1 h−1). Leu-to-carbon conversion factors ranged from 0.9 to 3.6 kgC mol Leu−1, with generally higher values in winter. Leu uptake was only weakly correlated to temperature, and over a full-year cycle (in 2003), Leu uptake peaked concomitantly with winter chlorophyll a (Chl a) maxima, and in periods of high ectoenzyme activities in spring and summer. This suggests that both low molecular weight dissolved organic matter (DOM) released by phytoplankton, and high molecular weight DOM in periods of low Chl a, can enhance BHP. Bacterial respiration (BR, range 7–48 μg C l−1 d−1) was not correlated to BHP or temperature, but was significantly correlated to DOC concentration. Total bacterial carbon demand (BHP plus BR) was only met by dissolved organic carbon produced by phytoplankton during the winter period. We measured bacterial growth efficiencies by the short-term and the long-term methods and they ranged from 3 to 42%, increasing during the phytoplankton blooms in winter (during the Chl a peaks), and in spring. Changes in bacterioplankton assemblage structure (as depicted by denaturing gradient gel electrophoresis fingerprinting) were not coupled to changes in ecosystem functioning, at least in bacterial carbon use.
Inorganic carbon removal through acidification is a common practice prior to isotopic analysis of macroinvertebrate samples. We have experimentally tested the effect of acidification on the elemental and isotopic composition of a range of beach arthropod species. Acidification resulted in a significant depletion of 7.7 % and 1.2 % in average for carbon and nitrogen, respectively. This highlights that acid washing affects other body compounds apart from carbonates. With a few exceptions, 13C and 15N showed no changes following the 1N HCl attack. Our results strongly suggest that samples with a presumable high CaCO3 content, result impoverished in 13C as a consequence of acidification, while those suspected to be carbonate-free are not significantly affected. Regarding 15N values, it seemed that only high carbonate species may be 15N impoverished when treated with HCl. It is recommended to acidify only carbonate-rich samples prior 13C analyses as a standard protocol.