Kinetic Modeling of Hardwood Prehydrolysis. Part II. Xylan Removal by Dilute Hydrochloric Acid Prehydrolysis

Knowledge of prehydrolysis kinetics has applicability to the design, development, and modeling of processes to separate wood into its basic chemical constituents (i.e., cellulose, hemicellulose, and lignin). The kinetics of xylan hemicellulose removal with 0.10 M HC1 at 120 C from quaking aspen, paper birch, American elm, red maple, and southern red oak was studied. The mathematical model developed in Part I to describe the kinetics of xylan removal by water prehydrolysis of these species could be used to model xylan removal with dilute hydrochloric acid. Xylan removal could thus be modeled as the sum of two parallel first-order reactions—one fast and one slow. However, unlike the case with water prehydrolysis where the rate constants for the fast (kf) and slow (ks) reaction processes could be correlated with each other, they could not be correlated for HC1 prehydrolysis. Instead the kf and ks values determined for each species clustered about average kf and ks values for all the species as a whole. A single set of parameters determined from a nonlinear least squares fit of the experimental prehydrolysis data for all the species as a whole to the model could be used to reasonably describe the course of xylan removal from all the species. The fact that one set of parameters could be used suggests that the same reactions are taking place on prehydrolysis and that the chemical structure and physical morphology of the xylan hemicellulose were essentially the same in the species studied and probably in all temperate hardwood species. The model thus provides a good approximation of xylan removal from any temperate hardwood with dilute hydrochloric acid at the reaction conditions studied

Mycobacteria in Nail Salon Whirlpool Footbaths, California

In 2000, an outbreak of Mycobacterium fortuitum furunculosis affected customers using whirlpool footbaths at a nail salon. We swabbed 30 footbaths in 18 nail salons from 5 California counties and found mycobacteria in 29 (97%); M. fortuitum was the most common. Mycobacteria may pose an infectious risk for pedicure customers

Carbohydrate antigens in nipple aspirate fluid predict the presence of atypia and cancer in women requiring diagnostic breast biopsy

<p>Abstract</p> <p>Background</p> <p>The goal of this prospective study was to determine (a) concentrations of the carbohydrate biomarkers Thomsen Friedenreich (TF) antigen and its precursor, Tn antigen, in nipple discharge (ND) collected from women requiring biopsy because of a suspicious breast lesion; and (b) if concentration levels predicted pathologic diagnosis.</p> <p>Methods</p> <p>Adult women requiring biopsy to exclude breast cancer were enrolled and ND obtained. The samples from 124 women were analyzed using an anti-TF and anti-Tn monoclonal antibodies in direct immunoassay.</p> <p>Results</p> <p>The highest median concentration in ND for TF and Tn was in women with ductal carcinoma <it>in situ </it>(DCIS). TF was higher in women with 1) cancer (DCIS or invasive) vs. either no cancer (atypia or benign pathology, p = .048), or benign pathology (p = .018); and 2) abnormal (atypia or cancer) versus benign pathology (p = .016); and was more predictive of atypia or cancer in post- compared to premenopausal women. Tn was not predictive of disease. High TF concentration and age were independent predictors of disease, correctly classifying either cancer or abnormal vs. benign pathology 83% of the time in postmenopausal women.</p> <p>Conclusions</p> <p>TF concentrations in ND were higher in women with precancer and cancer compared to women with benign disease, and TF was an independent predictor of breast atypia and cancer. TF may prove useful in early breast cancer detection.</p

Heterosis Is Prevalent for Multiple Traits in Diverse Maize Germplasm

BACKGROUND: Heterosis describes the superior phenotypes observed in hybrids relative to their inbred parents. Maize is a model system for studying heterosis due to the high levels of yield heterosis and commercial use of hybrids. METHODS: The inbred lines from an association mapping panel were crossed to a common inbred line, B73, to generate nearly 300 hybrid genotypes. Heterosis was evaluated for seventeen phenotypic traits in multiple environments. The majority of hybrids exhibit better-parent heterosis in most of the hybrids measured. Correlations between the levels of heterosis for different traits were generally weak, suggesting that the genetic basis of heterosis is trait-dependent. CONCLUSIONS: The ability to predict heterosis levels using inbred phenotype or genetic distance between the parents varied for the different traits. For some traits it is possible to explain a significant proportion of the heterosis variation using linear modeling while other traits are more difficult to predict

The effect of artificial selection on phenotypic plasticity in maize

Remarkable productivity has been achieved in crop species through artificial selection and adaptation to modern agronomic practices. Whether intensive selection has changed the ability of improved cultivars to maintain high productivity across variable environments is unknown. Understanding the genetic control of phenotypic plasticity and genotype by environment (G × E) interaction will enhance crop performance predictions across diverse environments. Here we use data generated from the Genomes to Fields (G2F) Maize G × E project to assess the effect of selection on G × E variation and characterize polymorphisms associated with plasticity. Genomic regions putatively selected during modern temperate maize breeding explain less variability for yield G × E than unselected regions, indicating that improvement by breeding may have reduced G × E of modern temperate cultivars. Trends in genomic position of variants associated with stability reveal fewer genic associations and enrichment of variants 0–5000 base pairs upstream of genes, hypothetically due to control of plasticity by short-range regulatory elements

A Robust, Simple Genotyping-by-Sequencing (GBS) Approach for High Diversity Species

Advances in next generation technologies have driven the costs of DNA sequencing down to the point that genotyping-by-sequencing (GBS) is now feasible for high diversity, large genome species. Here, we report a procedure for constructing GBS libraries based on reducing genome complexity with restriction enzymes (REs). This approach is simple, quick, extremely specific, highly reproducible, and may reach important regions of the genome that are inaccessible to sequence capture approaches. By using methylation-sensitive REs, repetitive regions of genomes can be avoided and lower copy regions targeted with two to three fold higher efficiency. This tremendously simplifies computationally challenging alignment problems in species with high levels of genetic diversity. The GBS procedure is demonstrated with maize (IBM) and barley (Oregon Wolfe Barley) recombinant inbred populations where roughly 200,000 and 25,000 sequence tags were mapped, respectively. An advantage in species like barley that lack a complete genome sequence is that a reference map need only be developed around the restriction sites, and this can be done in the process of sample genotyping. In such cases, the consensus of the read clusters across the sequence tagged sites becomes the reference. Alternatively, for kinship analyses in the absence of a reference genome, the sequence tags can simply be treated as dominant markers. Future application of GBS to breeding, conservation, and global species and population surveys may allow plant breeders to conduct genomic selection on a novel germplasm or species without first having to develop any prior molecular tools, or conservation biologists to determine population structure without prior knowledge of the genome or diversity in the species

Comparative genomics reveals insights into avian genome evolution and adaptation

Birds are the most species-rich class of tetrapod vertebrates and have wide relevance across many research fields. We explored bird macroevolution using full genomes from 48 avian species representing all major extant clades. The avian genome is principally characterized by its constrained size, which predominantly arose because of lineage-specific erosion of repetitive elements, large segmental deletions, and gene loss. Avian genomes furthermore show a remarkably high degree of evolutionary stasis at the levels of nucleotide sequence, gene synteny, and chromosomal structure. Despite this pattern of conservation, we detected many non-neutral evolutionary changes in protein-coding genes and noncoding regions. These analyses reveal that pan-avian genomic diversity covaries with adaptations to different lifestyles and convergent evolution of traits