Transduction with Integration-Defective Mutants of Salmonella typhimurium Bacteriophage KB1

Phage KB1 has gained use as a generalized transducing phage for Salmonella typhimurium, including strains resistant to phage P22. Integration-defective mutants of KB1 have now been isolated; one of these, int-1, is recommended for transduction when nonlysogenic recombinants are desired.     

Mechanical effects on endothelial cell morphology: In vitro assessment

Summary Endothelial cells are subjected to fluid mechanical forces which accompany blood flow. These cells become elongated and orient their long axes parallel to the direction of shear stress when the cultured cells are subjected to flow in an in vitro circulatory system. When the substrate is compliant and cyclically deformed, to simulate effects of pressure in the vasculature, the cells elongate an orient perpendicular to the axis of deformation. Cell shape changes are reflected in the alignment of microtubule networks. The systems described provide tools for assessing the individual roles of shear stress, pressure, and mechanical strain on vascular cell structure and function. This work was partially supported by grants HL 17437, HL 18072, and HL 23016 from the National Institutes of Health, Bethesda, MD, and grant C-938 from the Robert A. Welch Foundation.     

The finO gene of antibiotic resistance plasmid R100

Lambda phages carrying the R100 finO gene have been isolated from an R100:: lambda cointegrate in which lambda was inserted into the R100 traD gene at kb coordinate 72.1. Physical analyses of these phages place the finO gene within R100 SalI fragment D, near kb coordinate 82.0. Analysis of proteins synthesized by the phages did not identify the finO gene product, although a constitutive protein of m.w. 30,100 was encoded by R100 DNA between kb coordinates 78.7 and 81.2.     

Transfer-deficient cointegrates of Flac and lambda prophage

Summary Twelve transfer-deficient mutants of the plasmid Flac were obtained by insertion of prophage lambda into secondary attachment sites within the transfer region. Insertions into eight different tra genes were identified. These mutations were strongly polar on expression of tra genes previously mapped downstream, and thus confirmed that the genes traA through traD form a single operon. However, some continued expression of traI suggested that this was transcribed in part from a promoter located between traD and tral, and in part from the transfer operon promoter. One insertion early in the transfer operon produced a plasmid-specific tra mutation not complemented by R100-1 or R1-19: this insertion was into a new gene (traY), located before traA as the first member of the transfer operon. Partial tra deletion mutants were obtained as 42° C — survivors from several of the Flac tra:: ED4 plasmids, and their properties are described.     

Treatment of metal-contaminated water using bacterial sulfate reduction: results from pilot-scale reactors

Simple anaerobic reactors were installed to treat metal-contaminated water in an underground coal mine and at a smelting residues dump in Pennsylvania. The reactors consisted of barrels and tanks filled with spent mushroom compost, within which bacterial sulfate reduction became established. Concentrations of Al, Cd, Fe, Mn, Ni, and Zn were typically lowered by over 95% as contaminated water flowed through the reactors. Cadmium, Fe, Ni, and some Zn were retained as insoluble metal sulfides following their reaction with bacterially generated H(2)S. Aluminum, Mn, and some Zn hydrolyzed and were retained as insoluble hydroxides or carbonates. Reactor effluents were typically circumneutral in pH and contained net alkalinity. The principal sources of alkalinity in the reactors were bacterial sulfate reduction and limestone dissolution. This article examines the chemistry of the reactor systems and the opportunities for enhancing their metal-retaining and alkalinity-generating potential. (c) 1992 John Wiley & Sons, Inc.     

Shear sensitivity of hybridoma cells in batch, fed-batch, and continuous cultures.

Previously, we observed that CRL-8018 hybridoma cells were more sensitive to well-defined viscometric shear during the lag and stationary phases than during the exponential phase of batch cultures. Some potential hypotheses for explaining the increase in shear sensitivity are (1) nutrient limitations that result in a decrease in production of specific cellular components responsible for the mechanical strength of the cell, (2) nutrient limitations that lead to synchronization of the culture in a cell cycle phase that is more sensitive to shear, or (3) a link between cell growth and shear sensitivity, such that slowly growing cells are more sensitive to shear. Here, the duration of the exponential phase was increased with use of fed-batch, and the effect on shear sensitivity of the cultures was measured with a viscometric technique. Extension of exponential growth resulted in an increased period during which the cells were insensitive to shear. Additionally, the shear sensitivity of the cells was constant over a wide range of growth rates and metabolic yields in chemostat cultures. These observations suggest that as long as the cells are actively (exponentially) growing, their shear sensitivity does not depend on the growth rate or metabolic state of the cell as expressed by metabolic yields. Thus, hypothesis 3 above can be dismissed.     

Targeting viral infection by microRNA inhibition

An inhibitor of microRNA-122 reduces viral load in chimpanzees that are chronically infected with hepatitis C virus, suggesting that such an approach might have therapeutic potential in humans.     

Structure and function of wildfire and mountain pine beetle forest boundaries

Landscape boundaries, in particular those created by natural disturbances, are fundamental structures in landscape functioning. At the stand scale, forest boundaries show a wide range of characteristics varying from sharp to diffuse, wavy to straight, enclosed areas (patches) to open ones; all of these have different effects of forest vegetation. The objectives of this study were 1) to characterize the structure of forest boundaries (width, steepness, heterogeneity) and 2) to investigate forest vegetation functional response in the boundary zones created by wildfires and mountain pine beetle (MPB) outbreaks. We studied 11 mountain pine beetle and 7 wildfire boundary zones (4–7 y since disturbance) using field‐based two‐dimensional grids in southern central British Columbia (Canada). Boundary zone delineation was determined through spatially constrained clustering algorithms at three sampling unit resolutions (5×5 m, 10×10 m, and 20×20 m). Then, to characterize boundary width and shape, we developed two new boundary indexes (maximized and minimized boundary zones). The identified boundary widths ranged from 0 to 127 m with a mean width of 51 m at the 20×20 m resolution for both fire and MPB. Although the widths were comparable between disturbance types, fires generally had steeper boundaries (more pronounced) than MPB, largely due to higher peak tree mortality within the disturbances (89 vs 43%). Most of the forest vegetation response variables (understory vegetation diversity, plot‐level species richness, evenness, and multivariate community measures) in the boundary zones tended not to be intermediate in value between the intact forest and disturbance area, in spite of intermediate tree mortality. Tree mortality heterogeneity in the boundary zones was often highest in fires and was equal to the internal heterogeneity in MPB disturbances. Using historical natural disturbance patterns as a conservation strategy, this study proposes that forest management should create boundary complexity (width and shape), thereby creating landscape heterogeneity similar to landscapes influenced primarily by natural disturbances.