Influence of surfactants on the sorption of two chloroacetanilide in an Romanian chernozem soil

Pesticides have been extensively used in modern agriculture. Due to the prevalent use, there have been serious problems generated by pesticides wastes which could eventually endanger water resources and human health. The development of technologies for the decontamination of soils and waters polluted by hydrophobic organic compounds has encouraged research into the use of non-ionic surfactants as potential agents for the enhanced solubilization and removal of contaminants from soils and sediments. Sorption of two chloroacetanilide herbicides, acetochlor and metolachlor was studied on a representative chernozem soil of the Main Agricultural Research Station Ezareni belonging to the "Ion Ionescu de la Brad" University of Agriculture and Veterinary Medicine lasi, Romania, in the presence and absence of surfactants. Three different non-ionic surfactants were selected: Tween-20, Synperonic 91/5 and Silwet L-77, to verify the influence of their presence on herbicide sorption at different concentrations. Our results showed that the sorption of the studied herbicides within the soil-water-non-ionic surfactant system was influenced by the presence of non-ionic surfactants. The n values obtained were lower than 1 for all pesticide-surfactant combinations, which indicates that the amount of acetochor and metolachlor sorbed decreased with an increase in pesticide concentration. The sorption of acetochlor increased in the following order: Acetochlor+Synperonic 91/5 < Acetochlor < Acetochlor+Tween-20 < Acetochlor+Silwet L-77. In the case of metolachlor+Synperonic and metolachlor+Silwet L-77, the Kf values were significantly higher than the Kf value of metolachlor+Tween-20 on soil, where a lower Kf value could be observed with however a higher n value which indicate a higher sorption capacity at higher concentrations.     

Antagonistic and insecticidal properties of soil micromycetes

It was shown that microscopic fungi isolated in plague foci had an antagonistic effect on the plague causative agent. In the majority of the cases it was associated with their insecticidal activity against plague-transmitting fleas. It is expedient to consider the relations revealed between the burrow biocenosis components in investigation of plague enzootic aspects and development of new biological insecticides for control of the infection carriers.     

The restoration of the enzyme activity of chernozem soil after gamma-irradiation

The Influence of gamma-radiation by dozes 1, 5, 10 and 20 kGy on enzyme activity of ordinary chemozem were studied. Dynamics of the restoration of the enzyme activity after the influence of gamma-radiation in model experiments in 3, 30, 90 and 180 days was investigated. The doze 1 kGy did no statistically significant influence on the investigated enzymes. Dehydrogenase is more radiosensitive enzyme than catalase. Values of the saccharase activity differed a significant variation so in most cases it has not been registered statistically significant changes. In 90-180 days of the incubation enzymes activity was restored up to control values. Dehydrogenase activity in 180 days in variants with dozes 10 and 20 kGy was restored up to a level of the control, over variants with dozes 1 and 5 kGy--is higher than the control over 78% and 23% accordingly. Saccharase activity in 180 days after the influence of gamma-radiation with a doze 20 kGy was on 61% lower than the control.     

Succession of chitinolytic microorganisms in chernozem soil

The chitinolytic prokaryotic and eukaryotic microbial complex of chernozem soil has been investigated in the course of a succession initiated by the introduction of chitin and humidification. The dynamics of the cell numbers of chitinolytic microorganisms and of their biomass was assessed by fluorescent microscopy and by inoculation of selective media. Emission of carbon dioxide and nitrous oxide, as well as dinitrogen fixation, was assessed by gas chromatography. It was found that, when the succession was initiated by the introduction of both chitin and humidification, it resulted in greater cell numbers and biomass of chitinolytic microorganisms and higher levels of CO2 and N2O emission and of nitrogen fixation than when the succession was initiated by humidification alone. As compared to the control samples, a significant (twofold) increase in the prokaryote cell number and biomass was found on the fourth day of the succession initiated by humidification and introduction of chitin. One week after the initiation of succession, the fungal biomass and length of mycelium were twice as high as those in the control samples. These results led to the conclusion that chitin utilization in chernozem soil starts during the initial stages of succession and is performed by both prokaryotic and eukaryotic microorganisms.     

Increased amylosucrase activity and specificity, and identification of regions important for activity, specificity and stability through molecular evolution

Amylosucrase is a transglycosidase which belongs to family 13 of the glycoside hydrolases and transglycosidases, and catalyses the formation of amylose from sucrose. Its potential use as an industrial tool for the synthesis or modification of polysaccharides is hampered by its low catalytic efficiency on sucrose alone, its low stability and the catalysis of side reactions resulting in sucrose isomer formation. Therefore, combinatorial engineering of the enzyme through random mutagenesis, gene shuffling and selective screening (directed evolution) was applied, in order to generate more efficient variants of the enzyme. This resulted in isolation of the most active amylosucrase (Asn387Asp) characterized to date, with a 60% increase in activity and a highly efficient polymerase (Glu227Gly) that produces a longer polymer than the wild-type enzyme. Furthermore, judged from the screening results, several variants are expected to be improved concerning activity and/or thermostability. Most of the amino acid substitutions observed in the totality of these improved variants are clustered around specific regions. The secondary sucrose-binding site and beta strand 7, connected to the important Asp393 residue, are found to be important for amylosucrase activity, whereas a specific loop in the B-domain is involved in amylosucrase specificity and stability.     

Occurrence of itraconazole-tolerant micromycetes in the soil and food products

Unexpected pathogens from the environment represent considerable risk for humans with impaired health. We examined the occurrence of itraconazole tolerant micromycetes in soil and in maize products. Five concentrations of itraconazole (2.5–12.5 μg/mL) selected according to known treatment schedules for human patients were incorporated into Sabouraud agar with chloramphenicol and Rose Bengal and diluted samples were inoculated onto the agar surface. After 7-d growth at 22°C colonies ofAlternaria sp.,Aspergillus clavatus. A. glaucus group,A. flavus. A, fumigatus, A. niger group,A. ochraceus group,A. ochraceus, Chœtomium sp.,Cladosporium cladosporioides. Cylindrocarpon sp.Doratomyces sp.,Fusarium sp.,F. moniliforme. F. oxysporum. F. solani, F. subglutinans. Marianaea elegans, Mortierella sp.,Mucor sp.,Myrothecium sp.,Penicillium sp.,Rhizopus sp.,Scopulariopsis brevicaulis. Sepedonium sp.,Stachybotrys chartarum. Stemphylium sp.,Torula humicola andTrichoderma viride were isolated.     

Site-directed mutagenesis of an alkaline phytase: influencing specificity, activity and stability in acidic milieu

Site-directed mutagenesis of a thermostable alkaline phytase from Bacillus sp. MD2 was performed with an aim to increase its specific activity and activity and stability in an acidic environment. The mutation sites are distributed on the catalytic surface of the enzyme (P257R, E180N, E229V and S283R) and in the active site (K77R, K179R and E227S). Selection of the residues was based on the idea that acid active phytases are more positively charged around their catalytic surfaces. Thus, a decrease in the content of negatively charged residues or an increase in the positive charges in the catalytic region of an alkaline phytase was assumed to influence the enzyme activity and stability at low pH. Moreover, widening of the substrate-binding pocket is expected to improve the hydrolysis of substrates that are not efficiently hydrolysed by wild type alkaline phytase. Analysis of the phytase variants revealed that E229V and S283R mutants increased the specific activity by about 19% and 13%, respectively. Mutation of the active site residues K77R and K179R led to severe reduction in the specific activity of the enzyme. Analysis of the phytase mutant-phytate complexes revealed increase in hydrogen bonding between the enzyme and the substrate, which might retard the release of the product, resulting in decreased activity. On the other hand, the double mutant (K77R-K179R) phytase showed higher stability at low pH (pH 2.6-3.0). The E227S variant was optimally active at pH 5.5 (in contrast to the wild type enzyme that had an optimum pH of 6) and it exhibited higher stability in acidic condition. This mutant phytase, displayed over 80% of its initial activity after 3 h incubation at pH 2.6 while the wild type phytase retained only about 40% of its original activity. Moreover, the relative activity of this mutant phytase on calcium phytate, sodium pyrophosphate and p-nitro phenyl phosphate was higher than that of the wild type phytase.     

Dynamics of an oligosporous actinomycete population in chernozem soil

Investigation of the dynamics of an oligosporous actinomycete population in chernozem soil in the course of succession induced by soil wetting allowed us to reveal the time intervals and conditions optimal for the isolation of particular oligosporous actinomycetes. Saccharopolysporas and microbisporas proved to be best isolated in the early and late stages of succession, whereas actinomycetes of the subgroupActinomadura and saccharomonosporas could be best isolated in the early and intermediate stages of succession     

Use of micromycetes Trichoderma for soil bioremediation in tree nurseries

Data were obtained on the improvement of soil microbiocenoses in artificial ecosystems after the introduction of micromycetes Trichoderma. Application of biologically active substances released by some of aboriginal microbial strains can solve bioremediation problems in a given region at a low cost.     

Phytotoxic effects of (+/-)-catechin in vitro, in soil, and in the field

Background

Exploring the residence time of allelochemicals released by plants into different soils, episodic exposure of plants to allelochemicals, and the effects of allelochemicals in the field has the potential to improve our understanding of interactions among plants.

Methodology/Principal Findings

We conducted experiments in India and the USA to understand the dynamics of soil concentrations and phytotoxicity of (±)-catechin, an allelopathic compound exuded from the roots of Centaurea maculosa, to other plants in vitro and in soil. Experiments with single and pulsed applications into soil were conducted in the field. Experimental application of (±)-catechin to soils always resulted in concentrations that were far lower than the amounts added but within the range of reported natural soil concentrations. Pulses replenished (±)-catechin levels in soils, but consistently at concentrations much lower than were applied, and even pulsed concentrations declined rapidly. Different natural soils varied substantially in the retention of (±)-catechin after application but consistent rapid decreases in concentrations over time suggested that applied experimental concentrations may overestimate concentrations necessary for phytotoxicity by over an order of magnitude. (±)-Catechin was not phytotoxic to Bambusa arundinacea in natural Indian soil in a single pulse, but soil concentrations at the time of planting seeds were either undetectable or very low. However, a single dose of (±)-catechin suppressed the growth of bamboo in sand, in soil mixed with organic matter, and Koeleria macrantha in soils from Montana and Romania, and in field applications at 40 µg l⁻¹. Multiple pulses of (±)-catechin were inhibitory at very low concentrations in Indian soil.

Conclusions/Significance

Our results demonstrate that (±)-catechin is highly dynamic in natural soils, but is phytotoxic well below natural concentrations measured in some soils and applied at low concentrations in the field. However, there is substantial conditionality in the effects of the allelochemical.     

PNA-DNA triplexes: stability and specificity

The review considers the properties and some applications of complexes formed by peptide nucleic acid (PNA) molecules with complementary DNA sites, with emphasis on the structure and properties of PNA2/DNA triplexes.     

碳添加下黑钙土胞内、胞外脲酶活性变化及其机制

土壤脲酶作为能够催化尿素水解的最重要酶类,对草地生态系统氮素供应具有重要作用。目前探讨不同碳添加对草地土壤胞外脲酶影响的研究报道相对较多,但碳添加对土壤胞内脲酶的影响,以及胞内和胞外脲酶对碳添加的响应是否一致等尚需深入研究。本研究依托额尔古纳森林草原过渡带生态系统研究站开展的碳添加野外试验平台(以葡萄糖为碳源),选取无碳添加(C₀)、250(C₂₅₀)和500(C₅₀₀) kg C·hm^-2·a^-1处理为供试对象,探讨碳添加下黑钙土胞内、胞外脲酶活性响应及其与土壤性质的关系。结果表明: 碳添加显著提高了土壤胞内脲酶活性,增加了土壤胞内脲酶活性占总脲酶活性的比例,但对土壤胞外脲酶活性没有显著影响。土壤胞内脲酶活性与微生物生物量具有显著正相关关系,表明胞内脲酶活性增加主要是由微生物生物量增加引起的。结构方程模型(SEM)分析表明,碳添加通过影响土壤微生物生物量间接提高了土壤胞内脲酶活性。     

Relationships between the stereochemistry and biological activity of fungal phytotoxins

Toxins produced by phytopathogenic fungi assume great importance because of their involvement in several plant diseases. Although such pathogens are known to have seriously damaged crops, forest, and environmental resources, they represent a very important tool to develop new environmentally friendly herbicides and fungicides. This review deals with the relationships between the biological activity of some phytotoxins produced by pathogenic fungi for major forest plants and for damaging weeds and their stereochemistry. In particular, the methods used to determine their relative and/or absolute configuration will be illustrated. These include the application of Mosher's and Murata's methods, X-ray diffractometric analysis, circular dichroism, and the use of computational methods to determine the theoretical optical rotatory power as well as the CD spectrum. The importance of determining the absolute configuration to achieve the total synthesis of some phytotoxins, interesting for their potential practical application, is also discussed.     

Causation in biology: stability,specificity, and the choice of levels of explanation

This paper attempts to elucidate three characteristics of causal relationships that are important in biological contexts. Stability has to do with whether a causal relationship continues to hold under changes in background conditions. Proportionality has to do with whether changes in the state of the cause “line up” in the right way with changes in the state of the effect and with whether the cause and effect are characterized in a way that contains irrelevant detail. Specificity is connected both to David Lewis’ notion of “influence” and also with the extent to which a causal relation approximates to the ideal of one cause–one effect. Interrelations among these notions and their possible biological significance are also discussed.     

Phytotoxic activity of Cachrys pungens Jan,a mediterranean species: separation,identification and quantification of potential allelochemicals

In continuous research for bioactive compounds obtained from plants to use for weed control in sustainable agriculture, the aerial parts of Cachrys pungens Jan (Umbelliferae) were extracted with methanol and then fractionated using hexane, chloroform (CHCl₃) and ethyl acetate (AcOEt). The potential phytotoxicity of total methanolic extract and each fraction was assayed in vitro on seed germination and root elongation of lettuce (Lactuca sativa L.) and the most active fractions were assayed on three of the most common weeds (Lolium perenne, Amaranthus retroflexus, Echinochloa crus-galli). Non linear regression that allowed to obtain the ED₅₀ index for both physiological processes was applied. The fraction bioassays indicated the following hierarchy of phytotoxicity for both processes: CHCl₃ ≥ AcOEt > hexane. Moreover, in the present work was chemically characterized for the first time (through HPTLC) the polar fraction of this species pointing out the high presence of flavonoids and phenolic acids. In particular six of them have been chemically characterized and quantified (naringin, quercetin, catechin, caffeic acid, ferulic acid and gallic acid). These results make C. pungens Jan a potential source of natural compounds employable for an eco-friendly agriculture.     

Induction of polarity in mouse 8-cell blastomeres: specificity, geometry, and stability

We studied the cellular mechanisms underlying the induction of polarity in individual blastomeres of the 8-cell mouse embryo. The ability to induce polarity is lacking in the membranes of unfertilized and newly fertilized mouse eggs, then develops during the 2-cell stage, and is present in membranes of cells from 4-, 8-, and 16-cell stages. The axis of polarity takes 3-5 h to become established and thereafter appears to be stable. Multiple cell contacts affect the orientation of the axis of polarity, and no polarity develops in cells which are totally surrounded. Polarized cells show evidence of an limited capacity for slight adjustments in their position relative to other cells. The implications of these results for the mechanisms by which a blastocyst is generated are discussed briefly.