Effects of media composition on substrate removal by pure and mixed bacterial cultures

Continuous culture experiments with identical experimental designs were run with a mixed microbial community of activated sludge origin and an axenic bacterial culture derived from it. Each culture received 2-chlorophenol (2-CP) at a concentration of 160 mg/L as COD and L-lysine at a concentration of 65 mg/L as COD. A factorial experimental design was employed with dilution rate and media composition as the two controlled variables. Three dilution rates were studied: 0.015, 0.0325, and 0.05 h^–1. Media composition was changed by adding four biogenic compounds (butyric acid, thymine, glutamic acid and lactose) in equal COD proportions at total concentrations of 0, 34, 225, and 1462 mg/L as COD. The measured variables were the effluent concentrations of 2-CP as measured by the 4-aminoantipyrene test and lysine as measured by the o-diacetylbenzene procedure. The results suggest that community structure and substrate composition play important roles in the response of a microbial community to mixed substrates. The addition of more biogenic substrates to the axenic culture had a deleterious effect on the removal of both lysine and 2-CP, although the effect was much larger on lysine removal. In contrast, additional substrates had a positive effect on the removal of 2-CP by the mixed community and much less of a negative effect on the removal of lysine. The dilution rate at which the cultures were growing had relatively little impact on the responses to the additional substrates.Abbreviations COD chemical oxygen demand - 2-CP 2-chlorophenol - DOC dissolved organic carbon - MDL method detection limit - SS suspended solids     

Model misspecification and bias for inverse probability weighting estimators of average causal effects

Commonly used semiparametric estimators of causal effects specify parametric models for the propensity score (PS) and the conditional outcome. An example is an augmented inverse probability weighting (IPW) estimator, frequently referred to as a doubly robust estimator, because it is consistent if at least one of the two models is correctly specified. However, in many observational studies, the role of the parametric models is often not to provide a representation of the data-generating process but rather to facilitate the adjustment for confounding, making the assumption of at least one true model unlikely to hold. In this paper, we propose a crude analytical approach to study the large-sample bias of estimators when the models are assumed to be approximations of the data-generating process, namely, when all models are misspecified. We apply our approach to three prototypical estimators of the average causal effect, two IPW estimators, using a misspecified PS model, and an augmented IPW (AIPW) estimator, using misspecified models for the outcome regression (OR) and the PS. For the two IPW estimators, we show that normalization, in addition to having a smaller variance, also offers some protection against bias due to model misspecification. To analyze the question of when the use of two misspecified models is better than one we derive necessary and sufficient conditions for when the AIPW estimator has a smaller bias than a simple IPW estimator and when it has a smaller bias than an IPW estimator with normalized weights. If the misspecification of the outcome model is moderate, the comparisons of the biases of the IPW and AIPW estimators show that the AIPW estimator has a smaller bias than the IPW estimators. However, all biases include a scaling with the PS-model error and we suggest caution in modeling the PS whenever such a model is involved. For numerical and finite sample illustrations, we include three simulation studies and corresponding approximations of the large-sample biases. In a dataset from the National Health and Nutrition Examination Survey, we estimate the effect of smoking on blood lead levels.     

Copper Toxicity in Maize: The Severity of the Stress is Reduced Depending on the Applied Fe-Chelating Agent

Journal of Plant Growth Regulation - The wide use of copper (Cu)-based fungicide has caused a stepwise accumulation of Cu in the environment increasing the occurrence of phytotoxicity in crops. To...     

A MACROMUTATION IN TRIPSACUM DACTYLOIDES (POACEAE): CONSEQUENCES FOR SEED SIZE,GERMINATION, AND SEEDLING ESTABLISHMENT

A recessive allele of a gene in Tripsacum dactyloides L. (eastern gamagrass) changes staminate florets to pistillate or hermaphrodite, and restores fertility to suppressed florets. There were ten to 25 times more seeds in the mutant pistillate form, and these were 0.32 to 0.59 times smaller than seeds from the normal form. Seeds from pistillate plants had significantly lower germination rates (22% vs. 50%), and seedlings grew 20% slower than those of normal plants in a greenhouse experiment. Pistillate seedling survival rates were lower in both high- (18.8% vs. 62.6%) and low- (52.8% vs. 72.6%) competition environments in a field experiment, and surviving seedlings were smaller. The maternal parent of volunteer seedlings next to a plantation of normal and pistillate plants was determined by dissecting the attached fruitcases of 1,313 seedlings. Pistillate plants in the plantation produced 90% of all seeds falling on the site but only 29% of the volunteer seedlings. The pistillate macromutation is not likely to spread in the wild due to morphological constraints on seed size and packaging.     

High-resolution solution structure of two members of a conformationally homogeneous combinatorial peptide library based on the classical zinc-finger motif

Summary We describe the high-resolution structure by NMR of two peptides that belong to a combinatorial library based on the zinc-finger motif. The library represents, to the best of our knowledge, the first example of a conformationally homogeneous peptide library and was obtained by introducing random residues in five positions of the -helical portion of a 26-residue consensus peptide (CP1) belonging to the Cys²-Hys² zinc-finger family. The result was shown to be a highly homogeneous -helical library (Bianchi et al., 1995). The structures of the parent compound (CP1) and of a representative member (CP1m) that was selected by screening the library with a monoclonal antibody are compared in detail as an example of the very high stability of the zinc-finger scaffold upon sequence variability. The two peptides exhibit an extremely high degree of structural similarity. The use of this type of conformationally constrained combinatorial library might represent a step forward in the design of peptidomimetics, as it considerably accelerates the process of the identification of the spatial relationship among the pharmacophoric groups.Abbreviations t-Bu tert-butyloxycarbonyl - Fmoc 9-fluorenylmethoxycarbonyl     

Purification and properties of DNA topoisomerase II from Daucus carota cells

Topoisomerase II was partially purified from Daucus carota cellsby a procedure including ammonium sulphate fractionation, ion-exchange,and affinity chromatography steps. The type II enzyme, identifiedfor its ability to unknot knotted P4 DNA and decatenate Trypanosomacruzi kDNA, requires ATP and Mg²⁺ for activity. The unknottingactivity was sensitive to an inhibitor of the mammalian typeII enzyme, the drug VP16 (IC₅₀ 32 mmol m^–3), whereas inhibitorsof DNA gyrase showed a limited effect on activity. The SDS-PAGEanalysis of the dsDNA cellulose fraction revealed the presenceof four polypeptides of apparent molecular masses of 72, 71,34, and 33 kDa among which only a polypeptide of about 70 kDacrossreacted with antibodies against yeast topoisomerase II.Immunoprecipitation experiments with monoclonal antibodies tothe and ß isoforms of the human enzyme confirmedthe recognition of a polypeptide of 70 kDa. The sedimentationcoefficient (S) of the topoisomerase II in the phosphocellulosefraction, calculated by analytical glycerol gradient, was 6.1corresponding to a molecular mass of about 123 kDa. Resultssuggest the presence in carrot of a protein of molecular massof 70 kDa having the typical properties of an eukaryotic topoisomeraseII and carrying epitopes recognized by MoAbs to both human and ß enzymes. The 70 kDa polypeptide might then representthe monomer of a homodimer enzyme of 123 kDa. Key words: Daucus carota, topoisomerase II, immunoprecipitation