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Lag Period (lag + period)
Selected AbstractsFactors affecting biodegradation of 2-chlorophenol by Alcaligenes sp. in aerobic reactorsENVIRONMENTAL TOXICOLOGY, Issue 4 2001A. Gallego Abstract The influence of variations in carbon source concentration, cell inocula, pH, presence of other substrates, and other organisms on the biodegradation of 2-chlorophenol (2-CP) was studied for Alcaligenes sp. isolated from natural sources. Assays of biodegradation were performed in batch and continuous-flow fluidized-bed aerobic reactors. Evaluation of biodegradation was performed by determining total phenols, chemical oxygen demand (COD), and 2-CP by ultraviolet (UV) spectrophotometry. Measurement of microbial growth was carried out by the plate count method. Bioassays of acute toxicity were performed to evaluate detoxification by using Daphnia magna. Results obtained show that under batch conditions with initial inocula of 106 cells/mL the strain grew exponentially with 100, 200, and 300 mg/L of 2-CP within 48 hr. A lag period was observed with low cell density inocula (105 cells/mL). The strain showed marked delay in the biodegradation of 2-CP at pH 5. Removal of target substrate from mixtures containing other carbon sources demonstrated the possibility of concurrent growth. Mineralization of 2-CP was assessed by gas chromatography carried out at the end of the batch assays and at the exit of the continuous-flow reactor. The presence of other organisms (bacteria, rotifers, ciliate, and algae) that developed in the fluidized-bed reactor did not affect the efficacy of the biodegradation of 2-CP. The removal of 2-CP in the two assayed systems was over 97% in all cases. Toxicity was not detected at the exit of the continuous reactor. © 2001 John Wiley & Sons, Inc. Environ Toxicol 16: 306,313, 2001 [source] Hydrolysis of the amyloid ,-peptide (A,) 1,40 between Asp23,Val24 produces non-aggregating fragments.JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2005An electrospray mass spectrometric study Abstract The aggregation of full-length (residues 1,40) amyloid ,-peptide (A,) and fragments corresponding to residues 1,23 and 24,40 was studied by electrospray mass spectrometry, using gramicidin as a non-aggregating reference. Following a lag period, A,(1,40) at 140 µM concentration aggregates with apparent first-order kinetics. Under acidic conditions A,(1,40) undergoes spontaneous cleavage between Asp23,Val24 and to a lesser extent also at two other Asp,X motifs. Incubation in acidic H218O showed incorporation of 18O in fragment A,(1,23), confirming that the Asp23,Val24 peptide bond had been hydrolyzed. Incubation of synthetic A,(1,23) and A,(24,40) peptides with A,(1,40) showed that A,(24,40) remained in solution for several months, that A,(1,23) partly disappeared from solution, whereas A,(1,40) completely disappeared. Further, treatment of sedimentable aggregates formed after co-incubation of the three peptides with hexafluoro-2-propanol or formic acid recovered the intensity of A,(1,40). These data support previous studies showing that the region of A, encompassing residues 16,24 is necessary for aggregation into amyloid fibrils. Copyright © 2005 John Wiley & Sons, Ltd. [source] Oxidative stress and neurodegeneration: where are we now?JOURNAL OF NEUROCHEMISTRY, Issue 6 2006Barry Halliwell Abstract The brain and nervous system are prone to oxidative stress, and are inadequately equipped with antioxidant defense systems to prevent ,ongoing' oxidative damage, let alone the extra oxidative damage imposed by the neurodegenerative diseases. Indeed, increased oxidative damage, mitochondrial dysfunction, accumulation of oxidized aggregated proteins, inflammation, and defects in protein clearance constitute complex intertwined pathologies that conspire to kill neurons. After a long lag period, therapeutic and other interventions based on a knowledge of redox biology are on the horizon for at least some of the neurodegenerative diseases. [source] Close dependence of fibroblast proliferation on collagen scaffold matrix stiffnessJOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE, Issue 2 2009E. Hadjipanayi Abstract Human dermal fibroblasts (HDFs) in free-floating collagen matrices show minimal proliferation, although this may increase when the matrix is ,under tension'. We have investigated the detailed mechanics underlying one of the possible controls of this important cell behaviour, in particular the hypothesis that this is a response to substrate stiffness. Hyperhydrated collagen gels were plastic-compressed (PC) to give a predetermined collagen density and stiffness. Mechanical properties were tested using a dynamic mechanical analyser; cell number by Alamar blue assay. In the stiffest PC matrices, cell proliferation was rapid and seeding density-dependent, with a population doubling time of 2 days. In contrast, compliant attached matrices showed a 4 day lag period and a doubling time of 6 days. HDF growth was directly related to matrix stiffness, such that increasing stiffness using a range of compression levels (0,75% fluid removal) supported increasing proliferation rate, doubling times and matrix elastic modulus. HDF quiescence in compliant matrices was reversible, such that increasing stiffness in situ by compression at 1 and 5 days initiated proliferation. We conclude that collagen matrix stiffness regulates proliferation of fibroblasts (a duro-response), with important implications for understanding fibroblast,matrix feedback controls during wound healing and the design and regulation of engineered connective tissues based on collagen and other hydrogel-based scaffolds. Copyright © 2008 John Wiley & Sons, Ltd. [source] Cellular location and temperature-dependent assembly of IncHI1 plasmid R27-encoded TrhC-associated conjugative transfer protein complexesMOLECULAR MICROBIOLOGY, Issue 3 2001Matthew W. Gilmour Conjugal transfer of IncHI plasmid DNA between Gram-negative bacteria is temperature sensitive, as mating is optimal between 22°C and 30°C but is inhibited at 37°C. R27, isolated from Salmonella enterica serovar Typhi, is an IncHI1 plasmid of 180 kbp that has been sequenced completely. The gene encoding green fluorescent protein (GFP) was inserted into R27 in frame with trhC. TrhC is a mating pair formation (Mpf) protein that is essential for plasmid transfer and H-pilus production. Fluorescence microscopy allowed visualization of the TrhC,GFP fusion protein, and Escherichia coli cells were examined for the subcellular localization and temperature-dependent production of TrhC,GFP. At 27°C, TrhC,GFP was found at the periphery of cells as discrete foci, indicating an association of TrhC within protein complexes in the bacterial cell membrane, whereas at 37°C, little fluorescence was detected. These foci probably represent the intracellular position of protein complexes involved in conjugative transfer, as the formation of foci was dependent upon the presence of other Mpf proteins. During temperature shift experiments from 37°C to 27°C, a long lag period was required for generation of GFP foci. Conversely, during short shifts from 27°C to 37°C, the GFP foci remained stable. These results suggest that the expression of transfer genes in the Tra2 region of R27 is temperature dependent. Subcellular localization of TrhC was verified by cellular fractionation. Expression patterns of TrhC,GFP were confirmed with immunoblot analysis and reverse transcriptase,polymerase chain reaction (RT,PCR). These results allow us to propose mechanisms to explain the temperature-sensitive transfer of R27. [source] The Political Economy of Polarization: The Italian Case, 1963,1987POLITICS & POLICY, Issue 1 2003Riccardo Pelizzo Economic voting in Italy has received scant attention in the literature, and the few studies available show little or no empirical support for economic voting hypotheses as applied to Italy. We argue that this dearth of results is primarily due to poor operationalization and study design. In contrast to previous studies that focused on the relationship between the state of the economy and the electoral performance of individual parties, we investigate the impact of prices, employment, and economic output on the polarization of the party system. Using data on seven Italian national elections covering the period 1963,87, we show that polarization is, in fact, closely related to macroeconomic performance. Additionally, in contrast to past studies of Italy, the results are robust with respect to the lag period of the economic variables. [source] Identification and comparison of aerobic and denitrifying polyphosphate-accumulating organismsBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2003Raymond J. Zeng Abstract Two laboratory-scale sequencing batch reactors (SBRs) were operated for enhanced biological phosphorus removal (EBPR) in alternating anaerobic,aerobic or alternating anaerobic,anoxic modes, respectively. Polyphosphate-accumulating organisms (PAOs) were enriched in the anaerobic,aerobic SBR and denitrifying PAOs (DPAOs) were enriched in the anaerobic,aerobic SBR. Fluorescence in situ hybridization (FISH) demonstrated that the well-known PAO, "Candidatus Accumulibacter phosphatis" was abundant in both SBRs, and post-FISH chemical staining with 4,6-diamidino-2-phenylindol (DAPI) confirmed that they accumulated polyphosphate. When the anaerobic,anoxic SBR enriched for DPAOs was converted to anaerobic,aerobic operation, aerobic uptake of phosphorus by the resident microbial community occurred immediately. However, when the anaerobic,aerobic SBR enriched for PAOs was exposed to one cycle with anoxic rather than aerobic conditions, a 5-h lag period elapsed before phosphorus uptake proceeded. This anoxic phosphorus-uptake lag phase was not observed in the subsequent anaerobic,aerobic cycle. These results demonstrate that the PAOs that dominated the anaerobic,aerobic SBR biomass were the same organisms as the DPAOs enriched under anaerobic,anoxic conditions. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 83: 140,148, 2003. [source] Calorimetric Studies on Dry Pectinlyase Preparations: Impact of Glass Transition on Inactivation KineticsBIOTECHNOLOGY PROGRESS, Issue 4 2001Viviana M. Taragano The glass transition temperature (Tg) of a dry ultrafiltrated pectinlyase (PL) preparation decreased from 56 to 24 °C when water content increased to 20%. The thermal transition temperature (Tp) for protein denaturation decreased greatly up to 40% moisture; above 40% no further changes in Tp were observed. In the glassy state, a lag period of approximately 7 days with no PL activity loss was observed; after that, PL activity was lost. Above Tg, the rates of PL inactivation greatly increased. In the glassy state Ea was 16.6 kJ/mol. When the system was in a higher mobility state (rubbery), Ea increased to 66.5 kJ/mol. [source] Cell proliferation of human bone marrow mesenchymal stem cells on biodegradable microcarriers enhances in vitro differentiation potentialCELL PROLIFERATION, Issue 5 2010L.-Y. Sun Objectives:, For reasons of provision of highly-specific surface area and three-dimensional culture, microcarrier culture (MC) has garnered great interest for its potential to expand anchorage-dependent stem cells. This study utilizes MC for in vitro expansion of human bone marrow mesenchymal stem cells (BMMSCs) and analyses its effects on BMMSC proliferation and differentiation. Materials and methods:, Effects of semi-continuous MC compared to control plate culture (PC) and serial bead-to-bead transfer MC (MC bead-T) on human BMMSCs were investigated. Cell population growth kinetics, cell phenotypes and differentiation potential of cells were assayed. Results:, Maximum cell density and overall fold increase in cell population growth were similar between PCs and MCs with similar starting conditions, but lag period of BMMSC growth differed substantially between the two; moreover, MC cells exhibited reduced granularity and higher CXCR4 expression. Differentiation of BMMSCs into osteogenic and adipogenic lineages was enhanced after 3 days in MC. However, MC bead-T resulted in changes in cell granularity and lower osteogenic and adipogenic differentiation potential. Conclusions:, In comparison to PC, MC supported expansion of BMMSCs in an up-scalable three-dimensional culture system using a semi-continuous process, increasing potential for stem cell homing ability and osteogenic and adipogenic differentiation. [source] Neutrophil regeneration precedes healing of tissue destruction, as indicated by serum C-reactive protein, in children with cancer recovering from neutropenic feverACTA PAEDIATRICA, Issue 8 2002K Vettenranta Aim: To evaluate the relationship between absolute neutrophil count and C-reactive protein (CRP) in the recovery phase of neutropenic fever among paediatric patients with cancer. Methods: A total of 102 paediatric oncology patients with 177 episodes of fever and neutropenia was studied prospectively in a two-centre setting. Antimicrobial therapy was discontinued 9 d (mean) post-initiation with a mean absolute neutrophil count of 1.8 ± 109l -1 and CRP of 32 mg l -1. Results: The mean level of CRP below 20 mg l -1 was reached on day 12. The level of CRP peaked on the day following the commencement of antimicrobial therapy. Throughout the episodes of fever and neutropenia higher levels of CRP were associated with a lower absolute neutrophil count. Following defervescence the pace of marrow recovery as evidenced by an increasing absolute neutrophil count to < 0.2 and < 0.5 ± 109l -1 was more rapid than the normalization of serum CRP. There was a 2,3 d lag period between absolute neutrophil count exceeding the level of 200 ± 106l -1 and the return of CRP to a baseline level. All episodes were treated successfully and there were no fatalities. Conclusion: Among patients recovering from neutropenia and fever the signs of marrow recovery remain the key criterion in evaluating the safety of discontinuing antimicrobial therapy, with serum CRP remaining more of an indicator of ongoing tissue repair. [source] Extracellular phosphatase activity of natural plankton studied with ELF97 phosphate: fluorescence quantification and labelling kineticsENVIRONMENTAL MICROBIOLOGY, Issue 6 2003í Nedoma Summary ELF®97 phosphate (ELFP) is a phosphatase substrate which produces ELF®97 alcohol (ELFA), a fluorescent water-insoluble product, upon hydrolysis. We studied the kinetics of ELFA precipitation in freshwater samples at levels of total plankton and single phytoplankton cells, and tested the suitability of ELFP for measurement of surface-bound algal extracellular phosphatases. Samples from acidic Ple,né Lake (pH , 5; high phosphatase activity) and eutrophic ,ímov reservoir (pH ,7,10; moderate phosphatase activity) were incubated with ELFP for 5,300 min, fixed with HgCl2 and filtered through polycarbonate filters. Relative fluorescence of filter-retained ELFA precipitates was quantified with image analysis. Time-courses of ELFA formation exhibited lag periods followed by finite periods of linear increase. In Ple,né Lake, lag-times were shorter (1,18 min) and rates of increase in ELFA fluorescence higher (by ,2 orders of magnitude) than in ,ímov reservoir (lag-times 30,200 min). Similar patterns of ELFA formation kinetics were also observed in Ple,né Lake samples in cuvette spectrofluorometer measurements (which failed in ,ímov reservoir). Linear regression of seasonal data on rates of increase in ELFA fluorescence from image cytometry and spectrofluorometry (r2 = 0.65, n = 10) allowed for calibration of image cytometry in terms of amount of cell-associated ELFA. Preliminary measurements of extracellular phosphatase activities of several algae resulted in rates (10,2260 fmol cell,1 h,1) which are comparable to data reported in the literature for algal cultures. [source] Elucidating the factors influencing the biodegradation of cylindrospermopsin in drinking water sourcesENVIRONMENTAL TOXICOLOGY, Issue 3 2008Maree J. Smith Abstract The cyanotoxin cylindrospermopsin (CYN) is produced by several species of cyanobacteria and can be persistent in drinking waters supplies, which is of major concern to water authorities because of its potential to severely compromise human health. Consequently, there is a need to fully understand the persistence of CYN in water supplies, in particular, to determine whether this toxin is readily degraded by endemic aquatic organisms. This study provides insights into the environmental factors that can influence the biodegradation of this toxin in Australian drinking water supplies. Biodegradation of CYN was only evident in water supplies that had a history of toxic Cylindrospermopsis raciborskii blooms. In addition, lag periods were evident prior to the onset of biodegradation; however, repeated exposure of the endemic organisms to CYN resulted in substantial decreases in the lag periods. Furthermore, the concentration of CYN was shown to influence biodegradation with a near linear relationship (R2 of 0.9549) existing between the biodegradation rate and the initial CYN concentration. Temperature was also shown to affect the biodegradation of CYN, which is important since CYN is now being detected in more temperate climates. The presence of copper-based algicides inhibited CYN degradation, which has significant implications since copper-based algicides are commonly used to control cyanobacterial growth in water bodies. The results from this study indicate that the biodegradation of CYN in natural water bodies is a complex process that can be influenced by many environmental factors, some of which include CYN concentration, temperature, and the presence of copper-based algicides. © 2008 Wiley Periodicals, Inc. Environ Toxicol, 2008. [source] Assessing in situ rates of anaerobic hydrocarbon bioremediationMICROBIAL BIOTECHNOLOGY, Issue 2 2009Lisa M. Gieg Summary Identifying metabolites associated with anaerobic hydrocarbon biodegradation is a reliable way to garner evidence for the intrinsic bioremediation of problem contaminants. While such metabolites have been detected at numerous sites, the in situ rates of anaerobic hydrocarbon decay remain largely unknown. Yet, realistic rate information is critical for predicting how long individual contaminants will persist and remain environmental threats. Here, single-well push,pull tests were conducted at two fuel-contaminated aquifers to determine the in situ biotransformation rates of a suite of hydrocarbons added as deuterated surrogates, including toluene- d8, o -xylene- d10, m -xylene- d10, ethylbenzene- d5 (or - d10), 1, 2, 4-trimethylbenzene- d12, 1, 3, 5-trimethylbenzene- d12, methylcyclohexane- d14 and n -hexane- d14. The formation of deuterated fumarate addition and downstream metabolites was quantified and found to be somewhat variable among wells in each aquifer, but generally within an order of magnitude. Deuterated metabolites formed in one aquifer at rates that ranged from 3 to 50 µg l,1 day,1, while the comparable rates at another aquifer were slower and ranged from 0.03 to 15 µg l,1 day,1. An important observation was that the deuterated hydrocarbon surrogates were metabolized in situ within hours or days at both sites, in contrast to many laboratory findings suggesting that long lag periods of weeks to months before the onset of anaerobic biodegradation are typical. It seems clear that highly reduced conditions are not detrimental to the intrinsic bioremediation of fuel-contaminated aquifers. [source] A cohort mortality study of chemical laboratory workers at Department of Energy Nuclear Plants,AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 9 2008Travis Kubale PhD Abstract Objective This study evaluates the mortality experience of 6,157 chemical laboratory workers employed at United States Department of Energy facilities. Methods All cause, all cancer and cause-specific standardized mortality ratios were calculated. Cox regression analyses were conducted to further evaluate the relation between chemical exposure and mortality risk due to selected cancers. Results The mortality due to all causes combined and all cancers combined were below expectation for the cohort. There were no statistically significant elevations reported among males for any specific cancer or non-cancer outcome. There no statistically significant elevations among females for any specific non-cancer and most specific cancers; however, multiple myeloma deaths were significantly elevated (SMR,=,3.56; 95% CI,=,1.43,7.33; number of observed deaths, n,=,7). Statistically significant elevations were seen among workers employed 20+ years for leukemia using both 2- and 5-year lag periods. Also, a statistically significant positive trend of elevated lung cancer mortality with increasing employment duration was seen using both 5- and 10-year lags. A similar trend was seen for smoking related cancers among men. Conclusion While lymphatic and hematopoietic cancer mortality was below expectation, a significant elevation of multiple myeloma deaths among females and an elevation of leukemia among workers employed 20+ years (possibly due to radiation and benzene exposure) were observed. A NIOSH case,control study is underway to examine more closely the relation between multiple myeloma and a variety of chemical exposures among workers employed at the Oak Ridge K-25 facility. Am. J. Ind. Med. 51:656,667, 2008. Published 2008 Wiley-Liss, Inc. [source] | |||||||||||||