Showing papers by "University of Oklahoma published in 2002"

Initial sequencing and comparative analysis of the mouse genome.

Abstract: The sequence of the mouse genome is a key informational tool for understanding the contents of the human genome and a key experimental tool for biomedical research. Here, we report the results of an international collaboration to produce a high-quality draft sequence of the mouse genome. We also present an initial comparative analysis of the mouse and human genomes, describing some of the insights that can be gleaned from the two sequences. We discuss topics including the analysis of the evolutionary forces shaping the size, structure and sequence of the genomes; the conservation of large-scale synteny across most of the genomes; the much lower extent of sequence orthology covering less than half of the genomes; the proportions of the genomes under selection; the number of protein-coding genes; the expansion of gene families related to reproduction and immunity; the evolution of proteins; and the identification of intraspecies polymorphism.

Leading creative people: Orchestrating expertise and relationships

Abstract: Global competition, new production techniques, and rapid technological change have placed a premium on creativity and innovation. Although many variables influence creativity and innovation in organizational settings, there is reason to suspect that leaders and their behavior represent a particularly powerful influence. In the present article, we review the available literature examining leadership behaviors contributing to creativity and innovation in organizational settings. Based on the findings obtained in these studies, we argue that the leadership of creative people requires expertise. Moreover, the successful leader must employ a number of direct and indirect influence tactics—tactics consistent with the needs of creative people working in an organizational environment. The implications of these observations for theory and practice are discussed.

Corporate social responsibility in europe and the u.s.: insights from businesses self-presentations

Abstract: The paper compares the extent and content of businesses’ communications about corporate social responsibility (CSR) in France, the Netherlands, the U.K., and the U.S. In particular, the study investigates the nature of CSR principles, processes, and stakeholder issues discussed in web pages. The results show that businesses in the four countries do not display the same eagerness to appear as socially responsible and employ diverse means to convey social responsibility images.

Toward a Theory of Entrepreneurial Cognition: Rethinking the People Side of Entrepreneurship Research:

Abstract: The failure of past “entrepreneurial personality”—based research to clearly distinguish the unique contributions to the entrepreneurial process of entrepreneurs as people, has created a vacuum with...

Genome sequence of Streptococcus mutans UA159, a cariogenic dental pathogen

Abstract: Streptococcus mutans is the leading cause of dental caries (tooth decay) worldwide and is considered to be the most cariogenic of all of the oral streptococci. The genome of S. mutans UA159, a serotype c strain, has been completely sequenced and is composed of 2,030,936 base pairs. It contains 1,963 ORFs, 63% of which have been assigned putative functions. The genome analysis provides further insight into how S. mutans has adapted to surviving the oral environment through resource acquisition, defense against host factors, and use of gene products that maintain its niche against microbial competitors. S. mutans metabolizes a wide variety of carbohydrates via nonoxidative pathways, and all of these pathways have been identified, along with the associated transport systems whose genes account for almost 15% of the genome. Virulence genes associated with extracellular adherent glucan production, adhesins, acid tolerance, proteases, and putative hemolysins have been identified. Strain UA159 is naturally competent and contains all of the genes essential for competence and quorum sensing. Mobile genetic elements in the form of IS elements and transposons are prominent in the genome and include a previously uncharacterized conjugative transposon and a composite transposon containing genes for the synthesis of antibiotics of the gramicidin/bacitracin family; however, no bacteriophage genomes are present.

Neck Dissection Classification Update: Revisions Proposed by the American Head and Neck Society and the American Academy of Otolaryngology–Head and Neck Surgery

Abstract: Since the first description of the radical neck dissection by George Crile almost a century ago, many variations and modifications of the procedure have been added. These include the functional neck dissection, the modified radical neck dissection, and various selective neck dissections. In response to the need for an organized approach in describing these operations, the Committee for Head and Neck Surgery and Oncology of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) in 1988 initiated an effort to develop a standardized classification system for neck dissection (Table 1). During this process, input was obtained from the Education Committee of the American Society for Head and Neck Surgery (ASHNS) and its Council. The final product, endorsed by the ASHNS and the AAO-HNS, was published in the ARCHIVES 1 and as a monograph 2 by the AAO-HNS in 1991.

Conflicting Voices: The Effects of Institutional Ownership Heterogeneity and Internal Governance on Corporate Innovation Strategies

Abstract: Examining the relationship between governance and corporate innovation strategies, we found, in opposition to the assumption that owners have a unified voice, differences among governance constitue

The Effect of Customers' Emotional Responses to Service Failures on Their Recovery Effort Evaluations and Satisfaction Judgments

Abstract: This study examines the role of customer emotions in the context of service failure and recovery encounters. It investigates how customers' emotional responses to service failures influence their satisfaction judgments after accounting for cognitive antecedents of satisfaction. The study also considers how customers' emotional responses to service failures influence how they evaluate an organization's recovery efforts. The research is conducted by surveying customers about their satisfaction judgments in two service settings, restaurants and hotels. The results suggest that customers' emotional responses to service failures will influence their recovery effort evaluations and satisfaction judgments in some circumstances and that the effects of emotion vary across industry settings. This study identifies the types of efforts that are most effective in helping customers “recover” from the negative emotions caused by service failures.

Apolipoprotein E polymorphism and cardiovascular disease: a HuGE review.

Abstract: This review examines the association between the apolipoprotein (apo) var epsilon gene polymorphism (or its protein product (apo E)), metabolic regulation of cholesterol, and cardiovascular disease. The apo var epsilon gene is located at chromosome 19q13.2. Among the variants of this gene, alleles (*) epsilon2, (*) epsilon3, and (*) epsilon4 constitute the common polymorphism found in most populations. Of these variants, apo (*) epsilon3 is the most frequent (>60%) in all populations studied. The polymorphism has functional effects on lipoprotein metabolism mediated through the hepatic binding, uptake, and catabolism of chylomicrons, chylomicron remnants, very low density lipoprotein (VLDL), and high density lipoprotein subspecies. Apo E is the primary ligand for two receptors, the low density lipoprotein (LDL) receptor (also known as the B/E receptor) found on the liver and other tissues and an apo E-specific receptor found on the liver. The coordinate interaction of these lipoprotein complexes with their receptors forms the basis for the metabolic regulation of cholesterol. Allelic variation in apo var epsilon is consistently associated with plasma concentrations of total cholesterol, LDL cholesterol, and apo B (the major protein of LDL, VLDL, and chylomicrons). Apo var epsilon has been studied in disorders associated with elevated cholesterol levels or lipid derangements (i.e., hyperlipoproteinemia type III, coronary heart disease, strokes, peripheral artery disease, and diabetes mellitus). The apo var epsilon genotype yields poor predictive values when screening for clinically defined atherosclerosis despite positive, but modest associations with plaque and coronary heart disease outcomes. In addition to genotype-phenotype associations with vascular disease, the alleles and isoforms of apo var epsilon have been related to dementias, most commonly Alzheimer's disease.

Minimal neuropsychological assessment of MS patients: a consensus approach.

Abstract: Cognitive impairment is common in multiple sclerosis (MS), yet patients seen in MS clinics and neurologic practices are not routinely assessed neuropsychologically. In part, poor utilization of NP services may be attributed to a lack of consensus among neuropsychologists regarding the optimal approach for evaluating MS patients. An expert panel composed of neuropsychologists and psychologists from the United States, Canada, United Kingdom, and Australia was convened by the Consortium of MS Centers (CMSC) in April, 2001. Our objectives were to: (a) propose a minimal neuropsychological (NP) examination for clinical monitoring of MS patients and research, and (b) identify strategies for improving NP assessment of MS patients in the future. The panel reviewed pertinent literature on MS-related cognitive dysfunction, considered psychometric factors relevant to NP assessment, defined the purpose and optimal characteristics of a minimal NP examination in MS, and rated the psychometric and practical properties of 36 candidate NP measures based on available literature. A 90-minute NP battery, the Minimal Assessment of Cognitive Function in MS (MACFIMS), emerged from this discussion. The MACFIMS is composed of seven neuropsychological tests, covering five cognitive domains commonly impaired in MS (processing speed/working memory, learning and memory, executive function, visual-spatial processing, and word retrieval). It is supplemented by a measure of estimated premorbid cognitive ability. Recommendations for assessing other factors that may potentially confound interpretation of NP data (e.g., visual/sensory/motor impairment, fatigue, and depression) are offered, as well as strategies for improving NP assessment of MS patients in the future.

Analyses of the cag pathogenicity island of Helicobacter pylori

Abstract: Most strains of Helicobacter pylori from patients with peptic ulcer disease or intestinal-type gastric cancer carry cagA, a gene that encodes an immunodominant protein of unknown function, whereas many of the strains from asymptomatically infected persons lack this gene Recent studies showed that the cagA gene lies near the right end of a approximately 37kb DNA segment (a pathogenicity island, or PAI) that is unique to cagA+ strains and that the cag PAI was split in half by a transposable element insertion in the reference strain NCTC11638 In complementary experiments reported here, we also found the same cag PAI, and sequenced a 39 kb cosmid clone containing the left 'cagII' half of this PAI Encoded in cagII were four proteins each with homology to four components of multiprotein complexes of Bordetella pertussis ('Ptl'), Agrobacterium tumefaciens ('Vir'), and conjugative plasmids ('Tra') that help deliver pertussis toxin and T (tumour inducing) and plasmid DNA, respectively, to target eukaryotic or prokaryotic cells, and also homologues of eukaryotic proteins that are involved in cytoskeletal structure To the left of cagII in this cosmid were genes for homologues of HsIU (heat-shock protein) and Era (essential GTPase); to the right of cagII were homologues of genes for a type I restriction endonuclease and ion transport functions Deletion of the cag PAI had no effect on synthesis of the vacuolating cytotoxin, but this deletion and several cag insertion mutations blocked induction of synthesis of proinflammatory cytokine IL-8 in gastric epithelial cells Comparisons among H pylori strains indicated that cag PAI gene content and arrangement are rather well conserved We also identified two genome rearrangements with end-points in the cag PAI One, in reference strain NCTC11638, involved IS605, a recently described transposable element (as also found by others) Another rearrangement, in 3 of 10 strains tested (including type strain NCTC11637), separated the normally adjacent cagA and picA genes and did not involve IS605 Our results are discussed in terms of how cag-encoded proteins might help trigger the damaging inflammatory responses in the gastric epithelium and possible contributions of DNA rearrangements to genome evolution

Review: power and information technology research: a metatriangulation review

Abstract: This study uses a metatriangulation approach to explore the relationships between power and information technology impacts, development or deployment, and management or use in a sample of 82 articles from 12 management and MIS journals published between 1980 and 1999. We explore the multiple paradigms underlying this research by applying two sets of lenses to examine the major findings from our sample. The technological imperative, organizational imperative, and emergent perspectives (Markus and Robey 1988) are used as one set of lenses to better understand researchers' views regarding the causal structure between IT and organizational power. A second set of lenses, which includes the rational, pluralist, interpretive, and radical perspectives (Bradshaw-Camball and Murray 1991), is used to focus on researchers' views of the role of power and different IT outcomes. We apply each lens separately to describe patterns emerging from the previous power and IT studies. In addition, we discuss the similarities and differences that occur when the two sets of lenses are simultaneously applied. We draw from this discussion to develop metaconjectures, (i.e., propositions that can be interpreted from multiple perspectives), and to suggest guidelines for studying power in future research.

A review of non-DLVO interactions in environmental colloidal systems

Abstract: The interaction and behavior of surfaces orcolloids is of quantitative significance inunderstanding the transport and fate ofcompounds and microorganisms in environmentalsystems. Historically, the DLVO model ofcolloid stability has described theseinteractions. This model finds its basis in aforce (energy) balance that comprisesattractive van der Waals and repulsiveelectrostatic interactions. Recently, the DLVOmodel has been found unable to fully describebiotic and abiotic colloidal behavior inaqueous media. The suspending phase (commonlywater) is often treated as a force (energy)transmitting or propagating medium. It isreasonable to believe that the structure ofwater may participate in a more significantfashion. Moreover, other moieties (sorbed anddissolved) may also have non-DLVO effects. Significant work has been focused on extendingthe precepts of the traditional DLVO model toaccommodate these non-DLVO forces (energies). This paper reviews many of the interactionsthat play a role in environmental systems andare not commonly subsumed by the traditionalDLVO model: e.g., hydrogen bonding and thehydrophobic effect, hydration pressure,non-charge transfer Lewis acid baseinteractions, and steric interactions.

Enterococcus faecalis produces extracellular superoxide and hydrogen peroxide that damages colonic epithelial cell DNA.

Abstract: Enterococcus faecalis is a commensal microorganism of the human intestinal tract that produces substantial extracellular superoxide (O(-)(2)), and derivative reactive oxygen species such as H(2)O(2) and hydroxyl radical, through autoxidation of membrane-associated demethylmenaquinone. Because these oxidants may be important as a cause of chromosomal instability (CIN) associated with sporadic adenomatous polyps and colorectal cancer, the ability of E.faecalis to damage eukaryotic cell DNA was examined using the alkaline lysis single cell gel electrophoresis (comet) assay. Both Chinese hamster ovary and HT-29 intestinal epithelial cells showed increased DNA damage after co-incubation with wild-type E. faecalis strain OG1RF, but not a transposon-inactivated mutant with attenuated extracellular O(-)(2) production. E. faecalis-mediated DNA damage was prevented by catalase, but not manganese superoxide dismutase, indicating H(2)O(2) arising from O(-)(2) was the genotoxin. In a rat model of intestinal colonization, OG1RF resulted in significantly higher stool concentrations of H(2)O(2) and 5,5-dimethyl-1-pyrroline N-oxide adducts of hydroxyl and thiyl radicals, as identified by electron spin resonance-spin trapping, compared with rats colonized with a mutant strain having attenuated O(-)(2) production. Using the comet assay, luminal cells from the colon of rats colonized with O(-)(2)-producing E. faecalis showed significantly increased DNA damage compared with control rats colonized with the mutant. These findings suggest a potentially profound role for extracellular free radical production by E. faecalis in promoting CIN associated with sporadic adenomatous polyps and colorectal cancer.

Water Solubilization of Single-Walled Carbon Nanotubes by Functionalization with Glucosamine

Abstract: Water solubilization of single-walled carbon nanotubes (SWNTs) has been achieved by functionalizing the SWNT with glucosamine. The grafting of glucosamine to the nanotubes was attained by producing acyl chloride on the carboxylic groups associated with the nanotubes. Subsequently, amide bonds were formed between the glucosamine and the SWNT. This grafting results in solubility of SWNT in water, which ranges from 0.1 to 0.3 mg/mL, depending on temperature.

Nucleation of Polypropylene Crystallization by Single-Walled Carbon Nanotubes

Abstract: Nonisothermal and isothermal crystallization experiments were performed on polypropylene mixed with carbon nanotubes produced by disproportionation of CO on Co-Mo catalysts. Functionalization of the nanotubes with octadecylamine made the tubes hydrophobic and allowed the tubes to be solubilized in an organic solvent. Mixing of the nanotubes with the polymer was accomplished by adding the nanotubes to a Decalin solution that contained dissolved polypropylene, followed by evaporation of the solvent. Dynamic mechanical analysis indicated very little difference in the small-strain mechanical properties between filled and unfilled polymers at the very low solid levels that were tested. By contrast, the crystallization behavior of the filled and unfilled polymer was quite different. Nanotubes promoted growth of the less-preferred beta form of crystalline polypropylene at the expense of the alpha form. In nonisothermal crystallization, the total amount of crystalline material in the sample was the same for the filled and unfilled materials. However, for isothermal crystallization experiments, the percent crystallinity in the filled materials was slightly higher. Most importantly, the rate of crystallization was substantially higher in the filled system. The results presented in this paper clearly show that carbon nanotubes nucleate crystallinity in polypropylene.

Structural Basis of Gating by the Outer Membrane Transporter FecA

Abstract: Siderophore-mediated acquisition systems facilitate iron uptake. We present the crystallographic structure of the integral outer membrane receptor FecA from Escherichia coli with and without ferric citrate at 2.5 and 2.0 angstrom resolution. FecA is composed of three distinct domains: the barrel, plug, and NH2-terminal extension. Binding of ferric citrate triggers a conformational change of the extracellular loops that close the external pocket of FecA. Ligand-induced allosteric transitions are propagated through the outer membrane by the plug domain, signaling the occupancy of the receptor in the periplasm. These data establish the structural basis of gating for receptors dependent on the cytoplasmic membrane protein TonB. By compiling available data for this family of receptors, we propose a mechanism for the energy-dependent transport of siderophores.

Quantitative tools for perfecting species lists

Abstract: A substantial body of literature has accumulated on the topic of the estimation of species richness by extrapolation. However, most of these methods rely on an objective sampling of nature. This condition is difficult to meet and seldom achieved for large regions. Furthermore, scientists conducting biological surveys often already have preliminary but subjectively gathered species lists, and would like to assess the completeness of such lists, and/or to find a way to perfect them. We propose several strategies for utilizing external data (such as might be obtained using GIS) to aid in the completion of species lists. These include: (i) using existing species lists to develop predictive models; (ii) using the uniqueness of the environment as a guide to find underrepresented species; (iii) using spectral heterogeneity to locate environmentally heterogeneous regions; (iv) combining surveys with statistical model-building in an iterative manner. We demonstrate the potential of these approaches using simulation and case studies from Oklahoma. Copyright © 2002 John Wiley & Sons, Ltd.

Direct surface thermodynamic observations within the rear-flank downdrafts of nontornadic and tornadic supercells

Abstract: Despite the long-surmised importance of the hook echo and rear-flank downdraft (RFD) in tornadogenesis, only a paucity of direct observations have been obtained at the surface within hook echoes and RFDs. In this paper, in situ surface observations within hook echoes and RFDs are analyzed. These “mobile mesonet” data have unprecedented horizontal spatial resolution and were obtained from the Verifications of the Origins of Rotation in Tornadoes Experiment (VORTEX) and additional field experiments conducted since the conclusion of VORTEX. The surface thermodynamic characteristics of hook echoes and RFDs associated with tornadic and nontornadic supercells are investigated to address whether certain types of hook echoes and RFDs are favorable (or unfavorable) for tornadogenesis. Tornadogenesis is more likely and tornado intensity and longevity increase as the surface buoyancy, potential buoyancy (as measured by the convective available potential energy), and equivalent potential temperature in the R...

Creditor Rights, Enforcement, and Debt Ownership Structure: Evidence from the Global Syndicated Loan Market

Abstract: This paper examines the relation between legal risk - defined as the strength and enforcement of creditors' rights - and debt ownership concentration to understand the various governance roles played by banks as large creditors. Using a sample of 495 project finance loan tranches (worth $151 billion) to borrowers in 61 different countries, we document high absolute levels of debt ownership concentration: the largest single bank holds 20.3% while the top five banks collectively hold 61.2% of a typical loan tranche. We also show that syndicates in countries with weak creditor rights and poor legal enforcement are larger and more diffuse. Based on this finding, we conclude that lenders structure loan syndicates to facilitate monitoring and low-cost re-contracting in countries where creditors have strong and enforceable legal rights. In contrast, lenders attempt to deter strategic defaults by creating larger and more diffuse syndicates when they cannot resort to legal enforcement mechanisms to protect their claims.

Providing a Rationale in an Autonomy-Supportive Way as a Strategy to Motivate Others During an Uninteresting Activity

Abstract: When motivating others during uninteresting activities, people typically use extrinsic contingencies that promote controlling forms of extrinsic motivation. In contrast, we investigated a motivational strategy that could support another person’s capacity to personally endorse and value the effort he or she put forth during the uninteresting activity. That strategy is the provision of an externally provided rationale when communicated in an autonomy-supportive way. In two studies, we tested and found support for a motivational mediation model, based on selfdetermination theory, in which the presence of such a rationale (vs. its absence) adds to participants’ identification with the task’s personal value which, in turn, explains participants’ subsequent effort. These studies suggest that extrinsically motivated behaviors can become self-determined through the process of identification and that the promotion of this identification experience depends on the presence of a rationale that is communicated in an autonomy-supportive way.

The Chemical Composition and Age of the Metal-poor Halo Star BD +17°3248*

Abstract: We have combined new high-resolution spectra obtained with the Hubble Space Telescope (HST )a nd ground-based facilities to make a comprehensive new abundance analysis of the metal-poor, halo star BD +17 � 3248. We have detected the third r-process peak elements osmium, platinum, and (for the first time in a metal-poor star) gold, elements whose abundances can only be reliably determined using HST. Our observations illustrate a pattern seen in other similar halo stars with the abundances of the heavier neutron capture elements, including the third r-process peak elements, consistent with a scaled solar system r-process distribution. The abundances of the lighter neutron capture elements, including germanium and silver, fall below that same scaled solar r-process curve, a result similar to that seen in the ultra–metal-poor star CS 22892-052. A single site with two regimes or sets of conditions, or perhaps two different sites for the lighter and heavier neutron capture elements, might explain the abundance pattern seen in this star. In addition, we have derived a

Combustion of hydrogen-enriched methane in a lean premixed swirl-stabilized burner

Abstract: The combustion characteristics of a premixed, swirl-stabilized flame were studied to determine the effects of enriching methane with hydrogen under fuel-lean conditions. The burner consisted of a center-body with an annular, premixed fuel-air jet. Swirl was introduced to the flow using 45-degree swirl vanes. The combustion occurred within an air-cooled quartz chamber at atmospheric pressure. Flame stability and blowout maps were obtained for different amount of hydrogen addition at several fuel-air flow rates. Gas probe measurements were obtained to demonstrate reductions in CO concentration with hydrogen addition, without adversely affecting the NO x emissions. The flame structure near the lean stability limit was described by direct luminous photographs and planar laser-induced fluorescence measurements of the OH radical. Results show that the addition of a moderate amount of hydrogen to the methane/air mixture increased the peak OH concentration. Hydrogen addition resulted in a significant change in the flame structure, indicated by a shorter and more robust appearing flame. The observed trends concur with the strained opposed premixed flame analysis using RUN-1DL. The computations revealed that enriching the methane with hydrogen increased the strain resistance of the flame as well as the OH levels in the flame.

Gout and hyperuricemia.

Abstract: Gout continues to be a health problem around the world despite the availability of effective therapies Although the prevalence is influenced by genetic factors, the associations of alcohol consumption, obesity, and hypertension appear to be partially responsible for the increased prevalence of gout and hyperuricemia in African and Oriental countries The association between hyperuricemia and cardiovascular disease seems linked to insulin resistance This relation, in part, explains the common coexistence of hyperlipidemia and glucose intolerance in patients with gout Accordingly, it is recommended that one pay more attention to dietary manipulation in patients with gout in addition to managing hypertension, obesity, and other medical problems Although acute gout attacks can be treated, eliminating gout requires effective removal of urate from the body Allopurinol remains a dominant urate-lowering agent, however its use may be limited by allergic reactions Uricosuric agents are also effective urate-lowering agents and provide an alternative to allopurinol Strategies to treat patients who are sensitive to allopurinol continue to evolve

SWNT-Filled Thermoplastic and Elastomeric Composites Prepared by Miniemulsion Polymerization

Abstract: SWNT-filled polystyrene (SWNT-PS) and styrene−isoprene (SWNT-SI) composites prepared by miniemulsion polymerization showed distinctive physical features such as uniform black coloration, high solubility in toluene as well as in tetrahydrofuran (THF), and semiconductor to ohmic electrical behavior. Raman spectra for both hybrid materials suggested a reduced vibrational freedom of the polymer chains as a consequence of the nanotube incorporation. An adsorbed polymer layer on the nanotube bundles contributes to a better dispersion of the inorganic nanoreinforcement.

A note on the judgmental effects of the balanced scorecard's information organization

Abstract: We examine judgmental effects of the balanced scorecard’s organization. The balanced scorecard contains a large number of performance measures divided into four categories. We examine whether the scorecard’s organization results in managerial performance evaluation judgments consistent with a recognition of the potential relations (i.e. nonindependence) of measures within a category. Supporting this idea, we find that performance evaluations are affected by organizing the measures into the balanced scorecard categories when multiple below-target (or above-target) measures are contained within a category but that evaluations are not affected when the above/below-target measures are distributed across the scorecard’s four categories. # 2002 Elsevier Science Ltd. All rights reserved.

Polypropylene fibers reinforced with carbon nanotubes

Abstract: The strength properties of polypropylene fibers were enhanced with single-wall carbon nanotubes (SWNTs) Solvent processing was used to disperse SWNTs in a commodity polypropylene After the solvent was removed, the solid polymer was melt-spun and postdrawn into fibers of unusual strength For a 1-wt % loading of nanotubes, the fiber tensile strength increased 40% (from 90 to 131 g/denier) At the same time, the modulus increased 55% (from 60 to 93 g/denier) © 2002 Wiley Periodicals, Inc J Appl Polym Sci 86: 2079–2084, 2002

Changes in microclimate induced by experimental warming and clipping in tallgrass prairie

Abstract: In order to facilitate interpretation and comparison of warming effects on ecosystems across various habitats, it is imperative to quantify changes in microclimate induced by warming facilities. This paper reports observed changes in air temperature, soil temperature and soil-moisture content under experimental warming and clipping in a tallgrass prairie in the Great Plains, USA. We used a factorial design with warming as the primary factor nested with clipping as the secondary factor. Infrared heater was used in order to simulate climatic warming and clipping to mimic mowing for hay or grazing. The warming treatment significantly increased daily mean and minimum air temperatures by 1.1 and 2.3 °C, respectively, but had no effect on daily maximum air temperature, resulting in reduced diurnal air-temperature range. Infrared heaters substantially increased daily maximum (2.5 and 3.5 °C), mean (2.0 and 2.6 °C) and minimum (1.8 and 2.1 °C) soil temperatures in both the unclipped and clipped subplots. Clipping also significantly increased daily maximum (3.4 and 4.3 °C) and mean (0.6 and 1.2 °C) soil temperatures, but decreased daily minimum soil temperature (1.0 and 0.6 °C in the control and warmed plots, respectively). Daily maximum, mean and minimum soil temperatures in the clipped, warmed subplots were 6.8, 3.2 and 1.1 °C higher than those in the unclipped, control subplots. Infrared heaters caused a reduction of 11.0% in soil moisture in the clipped subplots, but not in the unclipped subplots. Clipping reduced soil-moisture content by 17.7 and 22.7% in the control and warmed plots, respectively. Experimental warming and clipping interacted to exacerbate soil-moisture loss (26.7%). Overall, infrared heaters simulated climate warming well by enhancing downward infrared radiation and by reducing the diurnal air-temperature range.

Gene expression profiling of Escherichia coli growth transitions: an expanded stringent response model.

Abstract: When conditions cause bacterial growth to stop, extensive reprogramming of physiology and gene expression allows for the cell's survival. We used whole-genome DNA arrays to determine the system response in Escherichia coli cells experiencing transient growth arrest caused by glucose-lactose diauxie and H2O2 treatment, and also entry into stationary phase. The results show that growth-arrested cells induce stringent control of several gene systems. The vast majority of genes encoding the transcription and translation apparatus immediately downregulate, followed by a global return to steady state when growth resumes. Approximately one-half of the amino acid biosynthesis genes downregulate during growth arrest, with the notable exception of the his operon, which transiently upregulates in the diauxie experiment. Nucleotide biosynthesis downregulates, a result that is again consistent with the stringent response. Likewise, aerobic metabolism downregulates during growth arrest, and the results led us to suggest a model for stringent control of the ArcA regulon. The stationary phase stress response fully induces during growth arrest, whether transient or permanent, in a manner consistent with known mechanisms related to stringent control. Cells similarly induce the addiction module anti-toxin and toxin genes during growth arrest; the latter are known to inhibit translation and DNA replication. The results indicate that in all aspects of the response cells do not distinguish between transient and potentially permanent growth arrest (stationary phase). We introduce an expanded model for the stringent response that integrates induction of stationary phase survival genes and inhibition of transcription, translation and DNA replication. Central to the model is the reprogramming of transcription by guanosine tetraphosphate (ppGpp), which provides for the cell's rapid response to growth arrest and, by virtue of its brief half-life, the ability to quickly resume growth as changing conditions allow.