Acetate Substrate Research Articles

Expression and Characterization of a Novel Lipase from Aspergillus fumigatus with High Specific Activity

A novel lipase gene from Aspergillus fumigatus, afl1-1, was cloned and expressed with a molecular mass of 38 kDa in Escherichia coli for the first time. The recombinant lipase had a preference for short carbon chain p-nitrophenyl esters, especially toward C2 p-nitrophenyl ester and exhibited potent hydrolysis activity that had not been observed. The optimum pH and temperature of this new enzyme were 8.5 and 65 °C, respectively. The recombinant lipase (AFL1-1) is an alkaline enzyme which was stable in the pH range 6.0∼8.5 for 16 h (at 4 °C) and at 30∼50 °C for 1 h. It is an intracellular enzyme which was purified approximately 8.47-fold with an overall yield of 86.1% by single-step Ni-NTA affinity purification, with a very high specific activity of approximately 1.00 × 10(3) U mg(-1) on a standard substrate of p-nitrophenyl acetate. The Michaelis-Menten kinetic parameters V (max) and K (m) of the lipase were 1.37 mM mg(-1) min(-1) and 14.0 mM, respectively. Ca(2+) and other metal ions could not activate the lipase. According to the homology analysis and site-directed mutagenesis assay, the catalytic triad of the recombinant lipase was identified as Ser-165, Asp-260, and His-290 residues.

Template free preparation of nanoporous organically modified silica thin films on flexible substrates

We report the preparation and characterization of nanoporous organically modified silica (ormosil) thin films at room temperature and neutral pH conditions from homogeneous methyl silsesquioxane (MSQ) gels. Universally applicable and stable colloidal ormosil suspensions are prepared from the gels by sonication and coated to the substrates including glass, paper and plastics. The nanoporosity and thickness of the films can be tuned, which makes them suitable for certain applications including sensing, functional coatings, and low-dielectric materials. We demonstrate the antireflection property of the films on glass, cellulose acetate (CA) and polyetherimide (PEI) substrates. The films on CA and PEI retain their antireflection property after multiple bending cycles. Furthermore, films are intrinsically hydrophobic, over a wide pH range, with static contact angles up to 143° on paper and 123° on glass and CA. Producing nanoporous ormosil thin films on flexible substrates may expand their use in low cost electronic, optical devices and sensors, and lab-on-paper applications.

Inkjet-printed PEDOT:PSS/SWCNTs on Paper: Substrate Effects on Conductivity

ABSTRACTPoly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), or PEDOT:PSS, and single-walled carbon nanotubes (SWCNTs) were incorporated into an inkjet ink. The combination of PEDOT, a conjugated, conductive polymer, and highly conductive CNTs, yielded a conductive film after printing and curing of the ink. Several paper types were used as substrates for depositing printed patterns of the PEDOT:PSS/SWCNT ink. Wide variability in conductivity was observed for different commercial paper types, ranging from a maximum 0.9 S/cm on Epson® Premium Photo cast-coated glossy paper to 3 × 10-5 S/cm on Epson® Premium Presentation coated cardstock. Increasing the SWCNT content of the ink improved conductivity on a non-permeable cellulose acetate substrate to a point, after which the combined effects of ink filtration and jetting limited the number of nanotubes delivered to the substrate. On permeable paper, the irregularity of the substrate overcame the beneficial effects of SWCNTs as “bridges” between conductive PEDOT regions. Correlations between the substrates’ physical structure and conductivity were established for the printed sheets, with densely coated sheets presenting the highest conductivity, and porous sheets the lowest.

Surfactant enhanced lipase containing films characterized by confocal laser scanning microscopy

Confocal laser scanning microscopy (CLSM) in combination with a fluorescently labeling enzyme dye, LavaPurple™, was demonstrated as a technique for the visualization of Thermomyces ( Humicola) lanuginosa lipase (LIP HLL) and Candida antarctica lipase A (LIP CA) within a transparent latex coating. Addition of Teric Surfactants (C 16 non-ionic Teric 475, 1.8% (w/w) or C 10 non-ionic Teric 460, 2.0% (w/w)) significantly increased the accumulation of both LIP HLL and LIP CA to the surface of a latex coating. An α-naphthyl acetate substrate assay was used to quantify the accumulated lipase. The results derived from the acetate assay correlated with the enzyme accumulation (at the surface) observed in the CLSM images of the latex coating. This correlation demonstrated that the increased enzyme accumulation within the top 2 μm of the latex film was responsible for the increase in surface enzymatic activity. The combination of CLSM imagery and quantifiable image analysis provided a valuable tool for the optimization of surfactant concentrations for maximizing the activity of an enzyme (and potentially other additives) within a latex coating.

Purification and characterisation of an alkaliphilic esterase from a culinary medicinal mushroom, Sparassis crispa

In this study, we found that the fruiting body of the medicinal and edible mushroom Sparassis crispa produces an alkaliphilic esterase. The substrate specificity of this esterase was high for a p-nitrophenyl acetate substrate. The S. crispa esterase was purified using ammonium sulphate precipitation, anion exchange and gel filtration chromatography. The recovery and purification yields of the enzyme were 15–17% and 70–73 folds from six different strains of S. crispa, respectively. The molecular weight of the purified enzyme was approximately 60 kDa, as determined by SDS–PAGE. A zymogram analysis using a tributyrin substrate revealed that this enzyme is an esterase. The optimum pH and temperature were 8.0 and 50 °C, respectively. The pH and temperature stability profiles show that this enzyme is more stable under alkaline conditions and at 30–40 °C. K m and V max for this esterase enzyme acting on p-nitrophenyl acetate were 0.2 mM and 0.5 U/mg proteins, respectively.

Optimal control of hydrogen production in a continuous anaerobic fermentation bioreactor

This paper addresses the problem of optimization of hydrogen production in continuous anaerobic digesters using a model predictive control (MPC) strategy. The process is described by a dynamic nonlinear model. The influent concentration of molasses together with the effluent substrate and product concentrations of acetate, propionate, butyrate and biomass were estimated by an asymptotic online observer from measurements of gas composition in H 2 and CO 2 and gas flow rate. The observer was tested experimentally before to apply MPC online. The combined strategy (MPC and observer) was used in order to optimize a bioreactor of 2 L. The hydrogen production was increased by 75% up to 8 . 27 mL H 2 L − 1 min − 1 , using the influent flow rate as the main control variable while keeping the conversion of the influent concentration higher than 95% and maintaining the temperature at 37 °C and pH at 5.5.

Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) Inkjet Inks Doped with Carbon Nanotubes and a Polar Solvent: The Effect of Formulation and Adhesion on Conductivity

A conductive aqueous polymer suspension of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), or PEDOT:PSS, was used as the basis for an inkjet-printable and translucent conductive material. Several types of surfactants were used to achieve suitable particle sizes for inkjet printing, with Zonyl™ FS-300 non-ionic surfactant providing suitable surface tension, stability and dispersion. Viscosity was controlled using water and glycerol. Glycerol was also included as a humectant. 10 w/w% polar solvent (dimethyl sulfoxide) was used to increase conductivity, as a co-solvent and as a viscosity modifier. Carbon nanotubes, both single- and multi-walled, were dispersed in the ink to further improve its conductivity. The optimized ink was printed onto coated photo-paper and cellulose acetate (CA) substrates and characterized for ink layer thickness and conductivity. The effect of paper folding and peeling of an adhesive strip from the ink surface on the conductivity of the printed samples was also characterized. Optical microscopy showed that the conductive ink was contained almost entirely in the pores of the photo-paper coating layer and fibres, but remained as a film on the CA surface. In the case of photo-paper, failure occurred primarily at the coating–paper interface. The cohesive failure compromised the conductivity of the PEDOT:PSS layer contained in the coating. In the case of CA (within the coating layer), the PEDOT:PSS film's conductivity was not significantly affected by folding or peeling. This suggests that PEDOT:PSS is a robust conductive material well-suited to applications requiring significant flexibility.

Biochemical studies of two forensically important insects in Egypt which had colonized rabbit carrions treated with organophosphorus compound

The objective of this study is to elucidate the effect of Pirimiphos-methyl (Organophosphorus insecticide) on protein profile of insects that found in/above or around treated rabbit (Oryctolagus cunicullus domesticus L.) carrions. Additionally, an esterase analysis was performed to clarify the effect of this insecticide on necrophagous insects. Biochemical studies were carried out on collected adult Dermestes maculatus De-Geer and pupae of Chrysomya albiceps (Weidemann) for their forensic importance. Four protein fractions observed only in the treated beetles and one unique band for the control group. Treated Chrysomya albiceps pupae exhibited 14 specific bands whereas two bands were only exhibited by the control. Genetic distances calculated for treated and control insects were 0.38 and 0.42 for adult Dermestes maculatus and pupae of Chrysomya albiceps, respectively. Variations in protein bands may be interpreted that some pesticides enhance the transcription of certain sequences which are probably related to resistance and /or detoxification mechanisms. Esterase pattern analysis using α-naphthyl acetate reflected 4 characteristic bands for treated beetles. However, using β-naphthyl acetate yielded 4 specific bands for the control group. For Chrysomya albiceps pupae, conduction of α- naphthyl acetate yielded one common band for both treated and control groups and one specific band for the control group. Whereas, using of β- naphthyl acetate substrate yielded two common bands shared by both groups and one specific band for the control group. Forensically important insects such as Chrysomya albiceps Weidemann and Dermestes maculatus De-Geer have an active esterase system.

Preparation and thermal characterization of films containing liquid crystals in a cellulose acetate substrate for externally regulated applications

Two different series of polymer dispersed liquid crystal (PDLC) films were prepared for their future use as externally controlled electrolytes in direct methanol fuel cells (DMFC). The liquid crystals used in this work were commercial cholesteryl oleyl carbonate (COC) and n-(4-methoxybencylidine)-4-butylanilyne (MBBA); cellulose acetate (CA) was used as the polymer substrate. All the films were characterized by differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA) to analyze the existence of interactions between the components, the modification of the liquid crystal behavior and the thermal stability of the films. The two series of films exhibited very different behaviors. While the films containing CA and COC maintained most of the properties characteristic of the pure components, including the COC mesomorphism, the analysis of films containing CA and MBBA revealed the existence of strong interactions between the components that promoted the inhibition of the MBBA mesomorphic behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effects of crude feruloyl and acetyl esterase solutions of Neocallimastix sp. YQ1 and Anaeromyces sp. YQ3 isolated from Holstein steers on hydrolysis of Chinese wildrye grass hay, wheat bran, maize bran, wheat straw and corn stalks

Neocallimastix sp. YQ1 and Anaeromyces sp. YQ3 were isolated from rumen fluids of Holstein steers using a modification of the roll-tube technique of Hungate (1969). After a 9-day incubation for YQ1, and a 4-day incubation for YQ3, with optimal carbon and N supply in cultures, crude enzyme solutions of both fungi were prepared by centrifuging cultures for 10 min at 1000 × g at 4 °C. Enzymological characteristics of ferulic acid esterase and acetyl esterase were measured in the crude enzyme solution. The Michaelis constants ( K m ) and maximum velocities ( V max ) of ferulic acid esterase against methyl ferulate at pH 6.0 and 39 °C were 30 μM and 8.05 mU for YQ1 and 129 μM and 3.15 mU for YQ3, respectively. With substrate of p-nitrophenyl acetate, the K m and V max of AE at pH 6.0 and 39 °C were 0.21 mM and 336 mU for YQ1 and 5.26 mM and 854 mU for YQ3. Enzymatic release of reducing sugar, ferulic acid, and p-coumaric acid from complex fibre-rich feedstuffs was evaluated, and YQ3 released more reducing sugars from wheat straw, but less from the other plant materials especially maize bran and corn stalks. YQ3 liberated much more hydroxycinnamic acids from corn stalks, and YQ1 liberated much more hydroxycinnamic acids from maize bran. Anaerobic rumen fungi showed species diversity of enzymological characteristics of ferulic acid esterase and acetyl ester esterase, and exhibited a strong capability to release ferulic acid and p-coumaric acid from complex fibre-rich feedstuffs. Therefore anaerobic fungi, especially their FAE, should not be neglected in studies on biodegradation of plant cell walls in the rumen as well as on industrial processes developed to release ferulic acid and p-coumaric acid from agricultural by-products with potential commercial industrial applications, such as precursors of natural vanillin, natural antioxidants, food preservative agents, anti-inflammatory agents and photoprotectants.

Isolation and Characterization of a GDSL Esterase from the Metagenome of a Marine Sponge-associated Bacteria

Using a metagenome library constructed from a bacterial associated with a marine sponge Hyrtios erecta, we identified a novel esterase that belongs to the SGNH hydrolase superfamily of esterases. The substrate specificity of EstHE1 was determined using p-nitrophenyl (pNP) ester (C2: acetate, C4: butylate, C6: caproate, C12: laurate, C16: palmitate). EstHE1 exhibited activity against C2 (5.6 U/mg), C4 (5.1 U/mg), and C6 (2.8 U/mg) substrates. The optimal temperature for EstHE1 esterase activity of the pNP acetate substrate was 40 degrees C, and EstHE1 retained 60% of its enzymatic activity in the 30-50 degrees C range. This esterase showed moderate thermostability, retaining 58% of its activity even after preincubation for 12 h at 40 degrees C. EstHE1 also maintained activity in high concentrations of NaCl, indicating that this esterase is salt-tolerant. Thus, EstHE1 has the thermal stability and salt tolerance necessary for use as an industrial enzyme.

Practical Synthesis of Linear α-Iodo/Bromo-α,β-unsaturated Aldehydes/Ketones from Propargylic Alcohols via Au/Mo Bimetallic Catalysis

An efficient synthesis of alpha-iodo/bromo-alpha,beta-unsaturated aldehydes/ketones directly from propargylic alcohols is described. This reaction is catalyzed collaboratively by two metal complexes, Ph(3)PAuNTf(2) and MoO(2)(acac)(2), and Ph(3)PO as an additive helps suppress undesired enone/enal formation. Notable features of this method include low catalyst loadings, mild reaction conditions, and mostly good to excellent diastereoselectivity. In comparison with our previously developed method based on propargylic acetate substrates, this chemistry omits the need to prepare acetate derivatives and, moreover, has a much broader substrate scope.

Feruloyl and acetyl esterase production of an anaerobic rumen fungus Neocallimastix sp. YQ2 effected by glucose and soluble nitrogen supplementations and its potential in the hydrolysis of fibrous feedstuffs

To obtain an optimal feruloyl and acetyl esterase production of an anaerobic Neocallimastix sp. YQ2 grown on either Chinese wildrye grass hay (CW) or alfalfa hay (AH) or corn stalk (CS), three simultaneous 2 × 4 factorial experiments of 10-day pure cultures were applied with two levels of glucose (G +: glucose added at a level of 1.0 g/L and G −: without glucose) and four levels of N source (N1: 1.0 g/L yeast extract, 1.0 g/L tryptone and 0.5 g/L (NH 4) 2SO 4; N2: 2.8 g/L yeast extract and 0.5 g/L (NH 4) 2SO 4; N3: 1.6 g/L tryptone and 0.5 g/L (NH 4) 2SO 4; N4: 1.4 g/L yeast extract, 1.7 g/L tryptone). Optimal combinations of glucose and N supplements for YQ2 to produce ferulic acid esterase, acetyl esterase, xylanase, carboxymethyl cellulase and avicelase were G +N2 for CS, G −N3 for CW, G −N3 for CW, G +N2 for CS, and G +N2 for CW, respectively. These five kinds of fibrolytic enzyme had different variation tendencies and maximum activity at different times of incubation. The fungus produced more total volatile fatty acids, and less propionic acids and iso-valeric acids, when CS was used as growth substrate, as well as more acetic acids when CW was used than when AH was used ( P<0.05). As for the enzymological characteristics of feruloyl and acetyl esterase, Michaelis constants ( K m) and maximum velocities ( V max) of ferulic acid esterase against methyl ferulate at pH 6.0 and 39 °C were 90 μM and 1.15 mU, and the Michaelis constants and maximum velocities of acetyl esterase at pH 7.0 and 39 °C were 2.97 mM and 294 mU with specific substrate of p-nitrophenyl acetate. The crude enzyme preparation of the fungi grown on CS with the G +N1 combination had higher potential to release ferulic acid, and p-coumaric acid in CS up to 129.8 g/kg the alkali-extractable ferulic acid and 88.1 g/kg the alkali-extractable p-coumaric acid, respectively ( P<0.05). The strong capability to hydrolyse plant materials by the fungus can be used to understand the degradation of fibre-rich feedstuffs in the rumen and also open prospects for development of direct fed feed enzyme products for ruminants.

The lack of floral synthesis and emission of isoeugenol in Petunia axillaris subsp. parodii is due to a mutation in the isoeugenol synthase gene.

Floral scent has been extensively investigated in plants of the South American genus Petunia. Flowers of Petunia integrifolia emit mostly benzaldehyde, while flowers of Petunia axillaris subsp. axillaris emit a mixture of volatile benzenoid and phenylpropanoid compounds that include isoeugenol and eugenol. Flowers of the artificial hybrid Petunia hybrida, a cross between P. integrifolia and P. axillaris, emit a similar spectrum of volatiles as P. axillaris subsp. axillaris. However, the flowers of P. axillaris subsp. parodii emit neither isoeugenol nor eugenol but contain high levels of dihydroconiferyl acetate in the petals, the main scent-synthesizing and scent-emitting organs. We recently showed that both isoeugenol and eugenol in P. hybrida are biosynthesized from coniferyl acetate in reactions catalyzed by isoeugenol synthase (PhIGS1) and eugenol synthase (PhEGS1), respectively, via a quinone methide-like intermediate. Here we show that P. axillaris subsp. parodii has a functional EGS gene that is expressed in flowers, but its IGS gene contains a frame-shift mutation that renders it inactive. Despite the presence of active EGS enzyme in P. axillaris subsp. parodii, in the absence of IGS activity the coniferyl acetate substrate is converted by an as yet unknown enzyme to dihydroconiferyl acetate. By contrast, suppressing the expression of PhIGS1 in P. hybrida by RNA interference also leads to a decrease in isoeugenol biosynthesis, but instead of the accumulation of dihydroconiferyl acetate, the flowers synthesize higher levels of eugenol.

Effect of choline and acetate substrates on bifurcation and chaotic behavior of acetylcholine neurocycle and Alzheimer's and Parkinson's diseases

In this work a novel two-enzyme–two-compartment model is developed in order to explore the dynamics, bifurcation, and chaotic characteristics of the acetylcholine neurocycle. The model takes into consideration the physiological events of the choline uptake into the presynaptic neuron and choline release in the postsynaptic neuron. The effects of feed choline concentrations, feed acetate concentrations as bifurcation parameters are studied. It was found that feed choline concentrations play an important role and have a direct effect on the acetylcholine neurocycle through a certain important range of parameters. The feed acetate concentrations have less effect. A detailed bifurcation analysis over a wide range of parameters is carried out in order to uncover some important features of the system, such as static bifurcation, dynamic bifurcation and chaotic behavior. These findings are related to the real phenomena occurring in the neurons, like periodic stimulation of neural cells and non-regular functioning of acetylcholine receptors. The results are compared to the results of physiological experiments and other published models. As there is strong evidence that cholinergic brain diseases like Alzheimer's disease and Parkinson's disease are related to the concentration of acetylcholine, the present findings are useful for uncovering some of the characteristics of these diseases and encouraging more well-directed physiological research coupled to useful mathematical modeling. It is concluded from the results in this paper that feed choline is more important factor than feed acetate in ACh processes.

C−H Bond Functionalization via Hydride Transfer: Lewis Acid Catalyzed Alkylation Reactions by Direct Intramolecular Coupling of sp3 C−H Bonds and Reactive Alkenyl Oxocarbenium Intermediates

C-H bond functionalization enables strategically new approaches to the synthesis of complex organic molecules including biologically active compounds, research probes and functional organic materials. To address the shortcomings of transition metal catalyzed processes, we have developed a new approach to direct coupling of sp(3) C-H bonds and alkenes based on Lewis acid-promoted hydride transfer. Activation of alpha,beta-unsaturated aldehydes and ketones with Lewis acid triggers intramolecular hydride transfer, leading to a zwitterionic intermediate, which in turn undergoes ionic cyclization to afford the cyclic alkylation product. The scope of this method is expanded by the generation of alkenyl-oxocarbenium species as highly activated alkene intermediates capable of abstracting a hydride from unreactive carbon centers, including benzyl-, allyl-, and crotyl-ethers, as well as primary alkyl ethers, at room temperature. The alkenyl acetal and ketal substrates show dramatically faster rates of cyclization, as well as improved chemical yield and diastereoselectivity, compared to the corresponding carbonyl compounds. Furthermore, the use of boron trifluoride etherate as the Lewis acid and ethylene glycol as the organocatalyst provides a highly active catalytic system, presumably via the in situ formation of alkenyl-oxocarbenium intermediates, which eliminates the need for expensive transition metal Lewis acids or the preparation of ketal substrates. This binary catalytic system greatly improves the efficiency of the hydride transfer-initiated alkylation reactions.

Multiple forms of esterase in the larvae of Pectinophora gossypiella treated with three volatile oils.

In the present work, polyacrylamide gel electrophoresis were used for detection the forms of esterase in the last larval instar of Pectinophora gossypiella. The larvae were treated as newly hatched larvae with sublethal concentration(LC50) of three volatile oils (Petroselinum sativum, Coriandrum sativum and Cymbapoyon citratus). The larval tissues showed response towards α - naphthyl acetate and βnaphthyl acetate substrates. The esterase bands have been classified according to their reaction with three specific inhibitors (Eserine, Chlorphrifos and Fenitrothion). The results were showed great differences in number of zones of esterase activity and in substrate specificity between treated and untreated samples. Five, four, seven and six esterase bands in untreated and (P. sativum, C. sativum and C. citrates) treated samples respectively, show activity towards α- naphthyl acetate. Six, five, seven and seven esterases were able to hydrolyze β- naphthyl acetate in previous samples arrangement. In the case of α - naphthyl acetate, volatile oils caused the increasing of arylestrases and carboxylestrases activities, while cholinesterase activity was inhibited.

The effect of organo clay and adsorbed FeO 3 nanoparticles on cells cultured on Ethylene Vinyl Acetate substrates and fibers

Nanocomposites of Ethylene Vinyl Acetate (EVA 260) with Cloisite 20A organo clay and Cloisite 20A organo clay impregnated with Fe(CO) 5 were produced in a twin-screw extruder. Dynamic mechanical analysis (DMA) measurements indicated that the moduli increased monotonically for the Cloisite, up to a concentration of 10%, after which the modulus decreased. Adult human dermal fibroblasts (AHDF) were plated on these surfaces and the cell growth was found to be maximal on the nanocomposites containing 10% Cloisite. AHDFs cultured on substrates with higher Cloisite content had low surface area, poor growth curves, and misshaped actin fibers. Compounding EVA with Fe(CO) 5 soaked Cloisite did not enhance the modulus even at a loading of 10%. TEM images indicate nanoparticles form and coat the Cloisite platelet surfaces, possibly interfering with the exfoliation process. On the other hand, cell culture of MC3T3 osteoblasts proliferated on the Fe containing nanocomposites, the largest effect being observed when cultured in a constant magnetic field. These results indicate how the chemical nature of the Cloisite 20A organo clay can also play a major role. Finally, since natural ECM is fibrillar, these EVA nanocomposites were also electrospun into micron thick fibers. MC3T3s proliferated well on these fibers and the MC3T3 proliferation was maximized by culture on electrospun aligned fibers in a constant magnetic field.

B-type esterases in the snail Xeropicta derbentina: An enzymological analysis to evaluate their use as biomarkers of pesticide exposure

The study was prompted to characterize the B-type esterase activities in the terrestrial snail Xeropicta derbentina and to evaluate its sensitivity to organophosphorus and carbamate pesticides. Specific cholinesterase and carboxylesterase activities were mainly obtained with acetylthiocholine (K(m)=77.2 mM; V(max)=38.2 mU/mg protein) and 1-naphthyl acetate (K(m)=222 mM, V(max)=1095 mU/mg protein) substrates, respectively. Acetylcholinesterase activity was concentration-dependently inhibited by chlorpyrifos-oxon, dichlorvos, carbaryl and carbofuran (IC50=1.35x10(-5)-3.80x10(-8) M). The organophosphate-inhibited acetylcholinesterase activity was reactivated in the presence of pyridine-2-aldoxime methochloride. Carboxylesterase activity was inhibited by organophosphorus insecticides (IC50=1.20x10(-5)-2.98x10(-8) M) but not by carbamates. B-esterase-specific differences in the inhibition by organophosphates and carbamates are discussed with respect to the buffering capacity of the carboxylesterase to reduce pesticide toxicity. These results suggest that B-type esterases in X. derbentina are suitable biomarkers of pesticide exposure and that this snail could be used as sentinel species in field monitoring of Mediterranean climate regions.

Microbiological characterization and specific methanogenic activity of anaerobe sludges used in urban solid waste treatment

This study presents the microbiological characterization of the anaerobic sludge used in a two-stage anaerobic reactor for the treatment of organic fraction of urban solid waste (OFUSW). This treatment is one alternative for reducing solid waste in landfills at the same time producing a biogas (CH(4) and CO(2)) and an effluent that can be used as biofertilizer. The system was inoculated with sludge from a wastewater treatment plant (WWTP) (Río Frío Plant in Bucaramanga-Colombia) and a methanogenic anaerobic digester for the treatment of pig manure (Mesa de los Santos in Santander). Bacterial populations were evaluated by counting groups related to oxygen sensitivity, while metabolic groups were determined by most probable number (MPN) technique. Specific methanogenic activity (SMA) for acetate, formate, methanol and ethanol substrates was also determined. In the acidogenic reactor (R1), volatile fatty acids (VFA) reached values of 25,000 mg L(-1) and a concentration of CO(2) of 90%. In this reactor, the fermentative population was predominant (10(5)-10(6)MPN mL(-1)). The acetogenic population was (10(5)MPN mL(-1)) and the sulphate-reducing population was (10(4)-10(5)MPN mL(-1)). In the methanogenic reactor (R2), levels of CH(4) (70%) were higher than CO(2) (25%), whereas the VFA values were lower than 4000 mg L(-1). Substrate competition between sulphate-reducing (10(4)-10(5)MPN mL(-1)) and methanogenic bacteria (10(5)MPN mL(-1)) was not detected. From the SMA results obtained, acetoclastic (2.39 g COD-CH(4)g(-1)VSS(-1)day(-1)) and hydrogenophilic (0.94 g COD-CH(4)g(-1)VSS(-1)day(-1)) transformations as possible metabolic pathways used by methanogenic bacteria is suggested from the SMA results obtained. Methanotrix sp., Methanosarcina sp., Methanoccocus sp. and Methanobacterium sp. were identified.