1,434 research outputs found
State transition and electrocaloric effect of BaZrTiO: simulation and experiment
The electrocaloric effect (ECE) of BaZrTiO (BZT) is closely
related to the relaxor state transition of the materials. This work presents a
systematic study on the ECE and the state transition of the BZT, using a
combined canonical and microcanonical Monte Carlo simulations based a
lattice-based on a Ginzburg-Landau-type Hamiltonian. For comparison and
verification, experimental measurements have been carried on BTO and BZT
( and ) samples, including the ECE at various temperatures, domain
patterns by Piezoresponse Force Microscopy at room temperature, and the P-E
loops at various temperatures. Results show that the dependency of BZT behavior
of the Zr-concentration can be classified into three different stages. In the
composition range of , ferroelectric domains are visible,
but ECE peak drops with increasing Zr-concentration harshly. In the range of , relaxor features become prominent, and the decrease of
ECE with Zr-concentration is moderate. In the high concentration range of , the material is almost nonpolar, and there is no ECE peak visible.
Results suggest that BZT with certain low range of Zr-concentration around
can be a good candidate with relatively high ECE and
simutaneously wide temperature application range at rather low temperature
The Small RNA ErsA of Pseudomonas aeruginosa Contributes to Biofilm Development and Motility through Post-transcriptional Modulation of AmrZ
The small RNA ErsA of Pseudomonas aeruginosa was previously suggested to be involved in biofilm formation via negative post-transcriptional regulation of the algC gene that encodes the virulence-associated enzyme AlgC, which provides sugar precursors for the synthesis of several polysaccharides. In this study, we show that a knock-out ersA mutant strain forms a flat and uniform biofilm, not characterized by mushroom-multicellular structures typical of a mature biofilm. Conversely, the knock-out mutant strain showed enhanced swarming and twitching motilities. To assess the influence of ErsA on the P. aeruginosa transcriptome, we performed RNA-seq experiments comparing the knock-out mutant with the wild-type. More than 160 genes were found differentially expressed in the knock-out mutant. Parts of these genes, important for biofilm formation and motility regulation, are known to belong also to the AmrZ transcriptional regulator regulon. Here, we show that ErsA binds in vitro and positively regulates amrZ mRNA at post-transcriptional level in vivo suggesting an interesting contribution of the ErsA-amrZ mRNA interaction in biofilm development at several regulatory levels
55 Investigation of the RetS–GacAS regulatory network in clinical Pseudomonas aeruginosa isolates reveals evolutionary adaptation
Digitalitzat per Artypla
Proteins to Order Use of Synthetic DNA to Generate Site-Specific Mutations
The ability to cause specific changes in the amino acid
sequences of proteins would greatly advance studies on the
influence of protein structure on biochemical function. If
the desired changes can once be made in the nucleic acid
which encodes the protein, one can use cloning in an appropriate microorganism to produce essentially limitless
quantities of the mutant protein. We describe here the
application of oligonucleotide-directed site-specific mutagenesis to accomplish this objective for the enzyme
B-lactamase, the gene for which is contained in the plasmid
pBR322. The method uses a procedure to screen for mutant clones which depends on the DNA in the various colonies and not on the properties of the mutant protein; the method can, therefore, be widely applied and does not require, in each separate case, the development of a screening procedure which depends on some phenotypic difference between mutant and wild-type protein
The effect of local thermal fluctuations on the folding kinetics: a study from the perspective of the nonextensive statistical mechanics
Protein folding is a universal process, very fast and accurate, which works
consistently (as it should be) in a wide range of physiological conditions. The
present work is based on three premises, namely: () folding reaction is a
process with two consecutive and independent stages, namely the search
mechanism and the overall productive stabilization; () the folding kinetics
results from a mechanism as fast as can be; and () at nanoscale
dimensions, local thermal fluctuations may have important role on the folding
kinetics. Here the first stage of folding process (search mechanism) is focused
exclusively. The effects and consequences of local thermal fluctuations on the
configurational kinetics, treated here in the context of non extensive
statistical mechanics, is analyzed in detail through the dependence of the
characteristic time of folding () on the temperature and on the
nonextensive parameter .The model used consists of effective residues
forming a chain of 27 beads, which occupy different sites of a D infinite
lattice, representing a single protein chain in solution. The configurational
evolution, treated by Monte Carlo simulation, is driven mainly by the change in
free energy of transfer between consecutive configurations. ...Comment: 19 pages, 3 figures, 1 tabl
The influence of quintessence on the motion of a binary system in cosmology
We employ the metric of Schwarzschild space surrounded by quintessential
matter to study the trajectories of test masses on the motion of a binary
system. The results, which are obtained through the gradually approximate
approach, can be used to search for dark energy via the difference of the
azimuth angle of the pericenter. The classification of the motion is discussed.Comment: 7 pages, 1 figur
Diversity, Prevalence, and Longitudinal Occurrence of Type II Toxin-Antitoxin Systems of Pseudomonas aeruginosa Infecting Cystic Fibrosis Lungs
Type II toxin-antitoxin (TA) systems are most commonly composed of two genes encoding a stable toxin, which harms the cell, and an unstable antitoxin that can inactivate it. TA systems were initially characterized as selfish elements, but have recently gained attention for regulating general stress responses responsible for pathogen virulence, formation of drug-tolerant persister cells and biofilms—all implicated in causing recalcitrant chronic infections. We use a bioinformatics approach to explore the distribution and evolution of type II TA loci of the opportunistic pathogen, Pseudomonas aeruginosa, across longitudinally sampled isolates from cystic fibrosis lungs. We identify their location in the genome, mutations, and gain/loss during infection to elucidate their function(s) in stabilizing selfish elements and pathogenesis. We found (1) 26 distinct TA systems, where all isolates harbor four in their core genome and a variable number of the remaining 22 on genomic islands; (2) limited mutations in core genome TA loci, suggesting they are not under negative selection; (3) no evidence for horizontal transmission of elements with TA systems between clone types within patients, despite their ability to mobilize; (4) no gain and limited loss of TA-bearing genomic islands, and of those elements partially lost, the remnant regions carry the TA systems supporting their role in genomic stabilization; (5) no significant correlation between frequency of TA systems and strain ability to establish as chronic infection, but those with a particular TA, are more successful in establishing a chronic infection
The paranasal sinuses are focus for colonisation and chronic biofilm lung infection in CF patients
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Long-term evolution of antibiotic tolerance in Pseudomonas aeruginosa lung infections
Pathogenic bacteria respond to antibiotic pressure with the evolution of resistance but survival can also depend on their ability to tolerate antibiotic treatment, known as tolerance. While a variety of resistance mechanisms and underlying genetics are well characterized in vitro and in vivo, an understanding of the evolution of tolerance, and how it interacts with resistance in situ is lacking. We assayed for tolerance and resistance in isolates of Pseudomonas aeruginosa from chronic cystic fibrosis lung infections spanning up to 40 years of evolution, with 3 clinically relevant antibiotics: meropenem, ciprofloxacin, and tobramycin. We present evidence that tolerance is under positive selection in the lung and that it can act as an evolutionary stepping stone to resistance. However, by examining evolutionary patterns across multiple patients in different clone types, a key result is that the potential for an association between the evolution of resistance and tolerance is not inevitable, and difficult to predict
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