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Reduced Growth Rate (reduced + growth_rate)
Selected AbstractsAmino acids Thr56 and Thr58 are not essential for elongation factor 2 function in yeastFEBS JOURNAL, Issue 20 2007Galyna Bartish Yeast elongation factor 2 is an essential protein that contains two highly conserved threonine residues, T56 and T58, that could potentially be phosphorylated by the Rck2 kinase in response to environmental stress. The importance of residues T56 and T58 for elongation factor 2 function in yeast was studied using site directed mutagenesis and functional complementation. Mutations T56D, T56G, T56K, T56N and T56V resulted in nonfunctional elongation factor 2 whereas mutated factor carrying point mutations T56M, T56C, T56S, T58S and T58V was functional. Expression of mutants T56C, T56S and T58S was associated with reduced growth rate. The double mutants T56M/T58W and T56M/T58V were also functional but the latter mutant caused increased cell death and considerably reduced growth rate. The results suggest that the physiological role of T56 and T58 as phosphorylation targets is of little importance in yeast under standard growth conditions. Yeast cells expressing mutants T56C and T56S were less able to cope with environmental stress induced by increased growth temperatures. Similarly, cells expressing mutants T56M and T56M/T58W were less capable of adapting to increased osmolarity whereas cells expressing mutant T58V behaved normally. All mutants tested were retained their ability to bind to ribosomes in vivo. However, mutants T56D, T56G and T56K were under-represented on the ribosome, suggesting that these nonfunctional forms of elongation factor 2 were less capable of competing with wild-type elongation factor 2 in ribosome binding. The presence of nonfunctional but ribosome binding forms of elongation factor 2 did not affect the growth rate of yeast cells also expressing wild-type elongation factor 2. [source] Generation and characterization of functional mutants in the translation initiation factor IF1 of Escherichia coliFEBS JOURNAL, Issue 3 2004Victor Croitoru Three protein factors IF1, IF2 and IF3 are involved in the initiation of translation in prokaryotes. No clear function has been assigned to the smallest of these three factors, IF1. Therefore, to investigate the role of this protein in the initiation process in Escherichia coli we have mutated the corresponding gene infA. Because IF1 is essential for cell viability and no mutant selection has so far been described, the infA gene in a plasmid was mutated by site-directed mutagenesis in a strain with a chromosomal infA+ gene, followed by deletion of this infA+ gene. Using this approach, the six arginine residues of IF1 were altered to leucine or aspartate. Another set of plasmid-encoded IF1 mutants with a cold-sensitive phenotype was collected using localized random mutagenesis. All mutants with a mutated infA gene on a plasmid and a deletion of the chromosomal infA copy were viable, except for an R65D alteration. Differences in growth phenotypes of the mutants were observed in both minimal and rich media. Some of the mutated infA genes were successfully recombined into the chromosome thereby replacing the wild-type infA+ allele. Several of these recombinants showed reduced growth rate and a partial cold-sensitive phenotype. This paper presents a collection of IF1 mutants designed for in vivo and in vitro studies on the function of IF1. [source] Effects of simulated browsing on growth and leaf chemical properties in Colophospermum mopane saplingsAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Edward M. Kohi Abstract Browsing intensity influences a plant's response to herbivory. Plants face a trade-off between investment in the production of secondary compounds and investment in growth. To elucidate this trade-off, we simulated four browsing intensities (0%, 50%, 75% and 100%) on mopane saplings, Colophospermum mopane (J. Kirk ex Benth.) J.Léonard, in a greenhouse experiment. This showed that, with increasing defoliation intensity, plants change their investment strategy. At intermediate levels of defoliation (50%), mopane saplings increased the synthesis of condensed tannins, so that tannin concentrations followed a hump-shaped relation with defoliation intensity, with significantly higher tannin concentration at intermediate defoliation levels. When defoliated heavily (75% and 100%), tannin concentrations dropped, and plants were carbon stressed as indicated by a reduced growth rate of the stem diameter, and leaf production and mean individual leaf mass were reduced. This suggests that, at intermediate defoliation intensity, the strategy of the plants is towards induced chemical defences. With increasing defoliation, the relative costs of the secondary metabolite synthesis become too high, and therefore, the plants change their growing strategy. Hence, browsers should be able to benefit from earlier browsing by either adopting a low or a relatively high browsing pressure. Résumé La réponse d'une plante à sa consommation dépend de l'intensité de ce phénomène. Les plantes sont confrontées à un compromis entre un investissement dans la production de composants secondaires et un investissement dans leur croissance. Pour élucider ce compromis, nous avons simulé quatre intensités de consommation (0%, 50%, 75% et 100%) sur des jeunes mopanes, Colophospermum mopane (J. Kirk ex Benth.) J.Leonard, lors d'expériences sous serre. Ceci a montré que, lorsque la défoliation s'intensifie, les plantes changent leur stratégie d'investissement. À des niveaux de défoliation intermédiaires (50%), les jeunes plants de mopanes augmentaient la synthèse de tanins condensés, de sorte que les concentrations en tanins suivaient une courbe en cloche (hump-shaped) selon l'intensité de la défoliation; elles étaient significativement plus élevées aux niveaux de défoliation intermédiaires. Lorsque les plantes sont fortement défoliées (75% et 100%), leurs concentrations en tanins chutent, et elles sont en stress carbone comme le montre le taux de croissance réduit du diamètre du tronc; la production de feuilles et la masse moyenne de feuilles par individu sont aussi réduites. Cela suggère que, quand l'intensité de défoliation est intermédiaire, la stratégie des plants va vers une défense chimique induite. Lorsque la défoliation augmente, le coût relatif de la synthèse du métabolite secondaire devient trop élevé et le plant change de stratégie de croissance. Donc, les herbivores qui les consomment devraient pouvoir bénéficier d'une consommation antérieure en adoptant une pression de consommation faible ou relativement élevée. [source] Role of phosphoglucosamine mutase on virulence properties of Streptococcus mutansMOLECULAR ORAL MICROBIOLOGY, Issue 4 2009X. D. Liu Introduction:,Streptococcus mutans has been strongly implicated as the principal etiological agent in dental caries. As a gram-positive bacterium, S. mutans has a thick and compact cell wall to maintain the cell shape and protect the cells against mechanical or osmotic damage. Previous studies have proved that peptidoglycan is the main component of the cell wall involved in the autolysis or biofilm formation processes. Methods:, In this study, we investigated the gene SMU.1426c in the amino-sugar metabolism pathway of S. mutans UA159, which encodes phosphoglucosamine mutase (GlmM). The glmM gene that functions in the biosynthesis of peptidoglycan has been well investigated in Escherichia coli. Here a glmM mutant strain of S. mutans UA159 was constructed and several virulence properties were investigated. Results:, The mutant devoid of the glmM gene displayed long chains, reduced growth rate and increased autolysis. Biofilm formation by the mutant was found to be attenuated. Conclusion:, These results proved that peptidoglycan biosynthesis plays an important part in a series of bacterial morphologies. The glmM gene may have a constructive role in the virulence properties of S. mutans. [source] The Lmgpi15 gene, encoding a component of the glycosylphosphatidylinositol anchor biosynthesis pathway, is required for morphogenesis and pathogenicity in Leptosphaeria maculansNEW PHYTOLOGIST, Issue 4 2008Estelle Remy Summary ,,Random insertional mutagenesis was used to investigate pathogenicity determinants in Leptosphaeria maculans. One tagged nonpathogenic mutant, termed m20, was analysed in detail here. ,,The mutant phenotype was investigated by microscopic analyses of infected plant tissues and in vitro growth assays. Complementation and silencing experiments were used to identify the altered gene. Its function was determined by bioinformatics analyses, cell biology experiments and functional studies. ,,The mutant was blocked at the invasive growth phase after an unaffected initial penetration stage, and displayed a reduced growth rate and an aberrant hyphal morphology in vitro. The T-DNA insertion occurred in the intergenic region between two head-to-tail genes, leading to a complex deregulation of their expression. The unique gene accounting for the mutant phenotype was suggested to be the orthologue of the poorly conserved Saccharomyces cerevisiae gpi15, which encodes for one component of the glycosylphosphatidylinositol (GPI) anchor biosynthesis pathway. Consistent with this predicted function, a functional translational fusion with the green fluorescent protein (GFP) was targeted to the endoplasmic reticulum. Moreover, the mutant exhibited an altered cell wall and addition of glucosamine relieved growth defects. ,,It is concluded that the GPI anchor biosynthetic pathway is required for morphogenesis, cell wall integrity and pathogenicity in Leptosphaeria maculans. [source] Optimizing the internal quantum efficiency of GaInN SQW structures for green light emittersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006D. Fuhrmann Abstract GaxIn1,xN/GaN single quantum well (QW) structures emitting in the range of 450 nm to 620 nm have been grown by MOVPE. Temperature and excitation power dependent photoluminescence (PL) was used to determine the internal quantum efficiency (IQE) for these structures. For the blue emitting QWs high IQE values on the order of 60% were achieved. Due to a reduced growth temperature, reduced growth rate and increased V/III ratio we obtained QWs with good morphology and high In content above 25%. Thinner QWs with high In content showed a clear improvement of IQE compared to QW-structures with larger thickness but smaller In-content emitting at the same wavelength. Between ,peak = 460 nm and 530 nm we observed a slight reduction in IQE with values of 58% at 490 nm and 40% at 525 nm. But towards ,peak = 620 nm IQE decreased due to the electric field induced separation of the electron and hole wavefunction down to 1%. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High resolution near-field spectroscopy investigation of tilted InGaN quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003F. Hitzel Abstract We studied the emission wavelength dependence of InGaN quantum wells on surface tilt. A sample was prepared by overgrowing an SiC substrate with etched trenches and was investigated by a high resolution near field optical spectroscope (spectroscopy SNOM). We found out that emission wavelength on tilted surfaces is strongly blue shifted even by small surface tilts of about 1 degree. Possible explanations for the blue shift are a reduced growth rate and therefore a reduced quantum well thickness, a reduced piezoelectric field or a different In incorporation during growth. The significance of each of these effects are discussed in this paper. [source] The plasma membrane Na+/H+ antiporter SOS1 is essential for salt tolerance in tomato and affects the partitioning of Na+ between plant organsPLANT CELL & ENVIRONMENT, Issue 7 2009RAQUEL OLÍAS ABSTRACT We have identified a plasma membrane Na+/H+ antiporter gene from tomato (Solanum lycopersicum), SlSOS1, and used heterologous expression in yeast to confirm that SlSOS1 was the functional homolog of AtSOS1. Using post-transcriptional gene silencing, we evaluated the role played by SlSOS1 in long-distance Na+ transport and salt tolerance of tomato. Tomato was used because of its anatomical structure, more complex than that of Arabidopsis, and its agricultural significance. Transgenic tomato plants with reduced expression of SlSOS1 exhibited reduced growth rate compared to wild-type (WT) plants in saline conditions. This sensitivity correlated with higher accumulation of Na+ in leaves and roots, but lower contents in stems of silenced plants under salt stress. Differential distribution of Na+ and lower net Na+ flux were observed in the xylem sap in the suppressed plants. In addition, K+ concentration was lower in roots of silenced plants than in WT. Our results demonstrate that SlSOS1 antiporter is not only essential in maintaining ion homeostasis under salinity, but also critical for the partitioning of Na+ between plant organs. The ability of tomato plants to retain Na+ in the stems, thus preventing Na+ from reaching the photosynthetic tissues, is largely dependent on the function of SlSOS1. [source] A gel-free quantitative proteomics approach to investigate temperature adaptation of the food-borne pathogen Cronobacter turicensis 3032PROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 18 2010Paula Carranza Abstract The opportunistic food-borne pathogen Cronobacter sp. causes rare but significant illness in neonates and is capable to grow at a remarkably wide range of temperatures from 5.5 to 47°C. A gel-free quantitative proteomics approach was employed to investigate the molecular basis of the Cronobacter sp. adaptation to heat and cold-stress. To this end the model strain Cronobacter turicensis 3032 was grown at 25, 37, 44, and 47°C, and whole-cell and secreted proteins were iTRAQ-labelled and identified/quantified by 2-D-LC-MALDI-TOF/TOF-MS. While 44°C caused only minor changes in C. turicensis growth rate and protein profile, 47°C affected the expression of about 20% of all 891 identified proteins and resulted in a reduced growth rate and rendered the strain non-motile and filamentous. Among the heat-induced proteins were heat shock factors, transcriptional and translational proteins, whereas proteins affecting cellular morphology, proteins involved in motility, central metabolism and energy production were down-regulated. Notably, numerous potential virulence factors were found to be up-regulated at higher temperatures, suggesting an elevated pathogenic potential of Cronobacter sp. under these growth conditions. Significant alterations in the protein expression profile and growth rate of C. turicensis exposed to 25°C indicate that at this temperature the organism is cold-stressed. Up-regulated gene products comprised cold-shock, DNA-binding and ribosomal proteins, factors that support protein folding and proteins opposing cold-induced decrease in membrane fluidity, whereas down-regulated proteins were mainly involved in central metabolism. [source] Comparison of stress responses in wild and captive winter flounder (Pseudopleuronectes americanus Walbaum) broodstockAQUACULTURE RESEARCH, Issue 10 2003S Plante Abstract Chronic stress is responsible for many problems occurring in fish holding facilities, such as increased susceptibility to disease, reduced growth rate and suppression of the immune response. The goal of this study was to verify if wild winter flounder (Pseudopleuronectes americanus Walbaum) suffer from chronic stress when kept several months in captivity. We hypothesized that winter flounder not subjected to chronic stress in captivity would have similar or higher condition indices and similar stress response compared to fish from the wild. Our results showed that the condition index of winter flounder kept in captivity was higher (1.50) than those from the wild (1.33) even after one year of captivity. The intensity of the acute stress response following short-term exposure to air was similar between wild and captive fish (no significant interaction between the factors ,stress' and ,origin of the fish'). Body water content (an indicator of energy reserves) was lower (76.1%) compared to wild fish (79.8%) after one year of captivity, suggesting that the winter fast had been less energetically demanding in captive fish. These results indicate that no chronic stress was present in captive fish. On the other hand, the mortality during captivity was around 30%, which is high for the aquaculture industry. Further work to address this problem is required. [source] Multifrequency permittivity measurements enable on-line monitoring of changes in intracellular conductivity due to nutrient limitations during batch cultivations of CHO cellsBIOTECHNOLOGY PROGRESS, Issue 1 2010Sven Ansorge Abstract Lab and pilot scale batch cultivations of a CHO K1/dhfr, host cell line were conducted to evaluate on-line multifrequency permittivity measurements as a process monitoring tool. The ,-dispersion parameters such as the characteristic frequency (fC) and the permittivity increment (,,max) were calculated on-line from the permittivity spectra. The dual-frequency permittivity signal correlated well with the off-line measured biovolume and the viable cell density. A significant drop in permittivity was monitored at the transition from exponential growth to a phase with reduced growth rate. Although not reflected in off-line biovolume measurements, this decrease coincided with a drop in OUR and was probably caused by the depletion of glutamine and a metabolic shift occurring at the same time. Sudden changes in cell density, cell size, viability, capacitance per membrane area (CM), and effects caused by medium conductivity (,m) could be excluded as reasons for the decrease in permittivity. After analysis of the process data, a drop in fC as a result of a fall in intracellular conductivity (,i) was identified as responsible for the observed changes in the dual-frequency permittivity signal. It is hypothesized that the ,-dispersion parameter fC is indicative of changes in nutrient availability that have an impact on intracellular conductivity ,i. On-line permittivity measurements consequently not only reflect the biovolume but also the physiological state of mammalian cell cultures. These findings should pave the way for a better understanding of the intracellular state of cells and render permittivity measurements an important tool in process development and control. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Tolerance of Soil Flagellates to Increased NaCl levelsTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 4 2002FLEMMING EKELUND ABSTRACT. The ability of heterotrophic flagellates to survive and adapt to increasing salinities was investigated in this study. Whole soil samples were subjected to salinities corresponding to marine conditions and clonal cultures were used to perform growth and adaptation experiments at a wide range of different salinities (0,50 ppm). More morphotypes tolerant to elevated NaCl levels were found in road verge soil that was heavily exposed to de-icing salt than in less exposed soils, though there were fewer tolerant than intolerant morphotypes in all soils examined. Heterotrophic flagellates isolated on a freshwater medium from a non-exposed soil were unable to thrive at salinities above 15 ppt, and showed reduced growth rates even at low salt salinities (1,5 ppt). The findings suggest that heterotrophic soil flagellates are less tolerant to NaCl than their aquatic relatives, possibly due to their long evolutionary history in soil, and support the idea that identical morphospecies may differ considerably with respect to physiology [source] | |||||||||||||