A combination of three mutations, dcd, pyrH, and cdd, establishes thymidine (Deoxyuridine) auxotrophy in thyA+ strains of Salmonella typhimurium

The dum gene of Salmonella typhimurium was originally identified as a gene involved in dUMP synthesis (C. F. Beck et al., J. Bacteriol. 129:305-316, 1977). In the genetic background used in their selection, the joint acquisition of a dcd (dCTP deaminase) and a dum mutation established a condition of thymidine (deoxyuridine) auxotrophy. In this study, we show that dum is identical to pyrH, the gene encoding UMP kinase. The level of UMP kinase activity in the dum mutant was found to be only 30% of that observed for the dum+ strain. Thymidine prototrophy was restored to the original dum dcd mutant (KP1361) either by transduction using a pyrH+ donor or by complementation with either of two pyrH+-carrying plasmids. Thymidine auxotrophy could be reconstructed in the dum+ derivative (KP1389) by the introduction of a mutant pyrH allele. To define the minimal mutational complement necessary to produce thymidine auxotrophy in thyA+ strains, a dcd::Km null mutation was constructed. In the wild-type background, dcd::Km alone or in combination with a pyrH (dum) mutation did not result in a thymidine requirement. A third mutation, cdd (cytidine-deoxycytidine deaminase), was required together with the dcd and pyrH mutations to impart thymidine auxotrophy.     

Preferential Flow in a Reclamation Cover: Hydrological and Geochemical Response

Evapotranspirative covers used for waste containment or land reclamation strategies are intended to function in perpetuity. Pedogenesis of the cover materials caused by biophysical processes may lead to the development of macroporosity (i.e., preferential flow paths), which will alter the hydrological response from the intended design function. Hydrometric and geochemical data were used in this study to examine the contribution of preferential flow to the hydrological response of a reclamation cover on saline-sodic shale mine overburden, in a cold semiarid environment. The hydrometric data suggest that infiltration occurs along preferential flow paths when the ground is frozen or when wet antecedent soil moisture conditions develop prior to precipitation events. Interflow is initiated during the spring snowmelt when the cover thaws and water migrates from the preferential flow paths into the soil matrix, causing a perched water table to form on the cover-shale interface. The cessation of interflow coincides with a recession of the perched water table and an increase in matric suction within the cover in response to elevated evapotranspiration demands. The chemistry and stable isotope signature of the interflow demonstrates that these waters are initially composed of fresher snowmelt water, flowing along preferential flow paths, which then transition to pre-event water dominated by higher concentration water from within the soil matrix. A numerical simulation demonstrates that macroporosity imposes a significant control on the discharge rate and cumulative volume of interflow.     

Analyzing Xyloglucan Endotransglycosylases by Incorporating Synthetic Oligosaccharides into Plant Cell Walls

The plant cell wall is a cellular exoskeleton consisting predominantly of a complex polysaccharide network that defines the shape of cells. During growth, this network can be loosened through the action of xyloglucan endotransglycosylases (XETs), glycoside hydrolases that “cut and paste” xyloglucan polysaccharides through a transglycosylation process. We have analyzed cohorts of XETs in different plant species to evaluate the substrate specificities of xyloglucan acceptors by using a set of synthetic oligosaccharides obtained by automated glycan assembly. The ability of XETs to incorporate the oligosaccharides into polysaccharides printed as microarrays and into stem sections of Arabidopsis thaliana, beans, and peas was assessed. We found that single xylose substitutions are sufficient for transfer, and xylosylation of the terminal glucose residue is not required by XETs, independent of plant species. To obtain information on the potential xylosylation pattern of the natural acceptor of XETs, that is, the nonreducing end of xyloglucan, we further tested the activity of xyloglucan xylosyl transferase (XXT) 2 on the synthetic xyloglucan oligosaccharides. These data shed light on inconsistencies between previous studies towards determining the acceptor substrate specificities of XETs and have important implications for further understanding plant cell wall polysaccharide synthesis and remodeling.     

Third-party perceptions of a layoff: Procedural, derogation, and retributive aspects of justice.

Third-party observers (N?=?123) learned about a layoff from a newspaper article developed for this study. Two aspects of the layoff procedure were manipulated in the article: (a) the level of input (voice) by layoff victims in the layoff procedure and (b) how the layoff was communicated to the victims. Both variables predicted observers' perceptions of the procedural justice of the layoff. Victim derogation was positively related to observers' procedural fairness of the layoff. Victim derogation also moderated the relationship between the justice manipulations and fairness. Procedural fairness predicted observers' behavioral intentions both as a customer and potential employee. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of beef cow winter feeding systems, pen manure and compost on soil nitrogen and phosphorous amounts and distribution, soil density, and crop biomass

A field experiment was conducted on continuous barley to evaluate the effects of 3 beef cattle winter feeding systems (bale grazing (BG); swath grazing (SG); straw–chaff grazing (STCH)) and pen manure and compost application on soil N and P amounts and distribution, soil density and barley crop biomass. Cattle winter feeding systems were managed during the winter of 2005–2006. Effects of extensive winter feeding system on soil nutrients and soil density were determined in the spring of 2006 after winter feeding. Nitrate nitrogen (NO₃–N) amounts at the low slope position in the 0–15 cm depth were 53% higher (P < 0.10) on BG sites than STCH sites. This may be attributed to the larger concentration of feed, thus feed nutrients, in the BG wintering system. Phosphorus amounts on the BG wintering sites at high slope were 34% higher (P < 0.10) than amounts at the same slope on the SG or STCH sites. Soil density was 21% greater (P < 0.10) where cows BG compared to where cows grazed straw–chaff piles, indicating differences in soil strength and resistance to penetration by roots. Soil density decreased on compost and raw manure sites in comparison to where no manure was applied, thus validating the benefits of manure on soil structure. Crop biomass measured on BG sites was consistent with soil nutrients captured, resulting in a 15% greater (P < 0.10) total biomass compared to STCH and SG wintering sites. Soil nutrient and crop biomass distribution was consistent among winter feeding sites with the STCH sites having the most uniform distribution of nutrients and crop biomass, and the BG sites having the least. Managing manure nutrients from winter feeding systems can be beneficial when followed by an annual cropping system.