Strain sensors with adjustable sensitivity by tailoring the microstructure of graphene aerogel/PDMS nanocomposites

Strain sensors with high elastic limit and high sensitivity are required to meet the rising demand for wearable electronics. Here, we present the fabrication of highly sensitive strain sensors based on nanocomposites consisting of graphene aerogel (GA) and polydimethylsiloxane (PDMS), with the primary focus being to tune the sensitivity of the sensors by tailoring the cellular microstructure through controlling the manufacturing processes. The resultant nanocomposite sensors exhibit a high sensitivity with a gauge factor of up to approximately 61.3. Of significant importance is that the sensitivity of the strain sensors can be readily altered by changing the concentration of the precursor (i.e., an aqueous dispersion of graphene oxide) and the freezing temperature used to process the GA. The results reveal that these two parameters control the cell size and cell-wall thickness of the resultant GA, which may be correlated to the observed variations in the sensitivities of the strain sensors. The higher is the concentration of graphene oxide, then the lower is the sensitivity of the resultant nanocomposite strain sensor. Upon increasing the freezing temperature from −196 to −20 °C, the sensitivity increases and reaches a maximum value of 61.3 at −50 °C and then decreases with a further increase in freezing temperature to −20 °C. Furthermore, the strain sensors offer excellent durability and stability, with their piezoresistivities remaining virtually unchanged even after 10 000 cycles of high-strain loading−unloading. These novel findings pave the way to custom design strain sensors with a desirable piezoresistive behavior.

L'acide valproïque inhibe la progression dans le cycle cellulaire chez Saccharomyces cerevisiae

L’acétylation est une modification post-traductionnelle des protéines essentielles. Elle est impliquée dans bon nombre de processus cellulaires importants comme la régulation de la structure de la chromatine et le recrutement de protéines. Deux groupes d’enzymes, soient les lysines acétyltransférases et les lysines désacétylases, régulent cette modification, autant sur les histones que sur les autres protéines. Au cours des dernières années, de petites molécules inhibitrices des désacétylases ont été découvertes. Certaines d’entre elles semblent prometteuses contre diverses maladies telles le cancer. L’acide valproïque, un inhibiteur de deux des trois classes des désacétylases, a un effet antiprolifératif chez plusieurs organismes modèles. Toutefois, les mécanismes cellulaires sous-jacents à cet effet restent encore méconnus. Ce mémoire met en lumière l’effet pH dépendant de l’acide valproïque sur différentes voies cellulaires importantes chez la levure Saccharomyces cerevisiae. Il démontre que ce composé a la capacité d’inhiber la transition entre les phases G1 et S par son action sur l’expression des cyclines de la phase G1. De plus, il inhibe l’activation de la kinase principale de la voie activée suite à un stress à la paroi cellulaire. L’acide valproïque occasionne également un arrêt dans la réplication de l’ADN sans y causer de dommage. Il s’agit là d’un effet unique qui, à notre connaissance, n’est pas observable avec d’autres agents qui inhibent la progression en phase S.

Characterization of plasmids in a human clinical strain of Lactococcus garvieae

The present work describes the molecular characterization of five circular plasmids found in the human clinical strain Lactococcus garvieae 21881. The plasmids were designated pGL1-pGL5, with molecular sizes of 4,536 bp, 4,572 bp, 12,948 bp, 14,006 bp and 68,798 bp, respectively. Based on detailed sequence analysis, some of these plasmids appear to be mosaics composed of DNA obtained by modular exchange between different species of lactic acid bacteria. Based on sequence data and the derived presence of certain genes and proteins, the plasmid pGL2 appears to replicate via a rolling-circle mechanism, while the other four plasmids appear to belong to the group of lactococcal theta-type replicons. The plasmids pGL1, pGL2 and pGL5 encode putative proteins related with bacteriocin synthesis and bacteriocin secretion and immunity. The plasmid pGL5 harbors genes (txn, orf5 and orf25) encoding proteins that could be considered putative virulence factors. The gene txn encodes a protein with an enzymatic domain corresponding to the family actin-ADP-ribosyltransferases toxins, which are known to play a key role in pathogenesis of a variety of bacterial pathogens. The genes orf5 and orf25 encode two putative surface proteins containing the cell wall-sorting motif LPXTG, with mucin-binding and collagen-binding protein domains, respectively. These proteins could be involved in the adherence of L. garvieae to mucus from the intestine, facilitating further interaction with intestinal epithelial cells and to collagenous tissues such as the collagen-rich heart valves. To our knowledge, this is the first report on the characterization of plasmids in a human clinical strain of this pathogen.

L'acide valproïque inhibe la progression dans le cycle cellulaire chez Saccharomyces cerevisiae

L’acétylation est une modification post-traductionnelle des protéines essentielles. Elle est impliquée dans bon nombre de processus cellulaires importants comme la régulation de la structure de la chromatine et le recrutement de protéines. Deux groupes d’enzymes, soient les lysines acétyltransférases et les lysines désacétylases, régulent cette modification, autant sur les histones que sur les autres protéines. Au cours des dernières années, de petites molécules inhibitrices des désacétylases ont été découvertes. Certaines d’entre elles semblent prometteuses contre diverses maladies telles le cancer. L’acide valproïque, un inhibiteur de deux des trois classes des désacétylases, a un effet antiprolifératif chez plusieurs organismes modèles. Toutefois, les mécanismes cellulaires sous-jacents à cet effet restent encore méconnus. Ce mémoire met en lumière l’effet pH dépendant de l’acide valproïque sur différentes voies cellulaires importantes chez la levure Saccharomyces cerevisiae. Il démontre que ce composé a la capacité d’inhiber la transition entre les phases G1 et S par son action sur l’expression des cyclines de la phase G1. De plus, il inhibe l’activation de la kinase principale de la voie activée suite à un stress à la paroi cellulaire. L’acide valproïque occasionne également un arrêt dans la réplication de l’ADN sans y causer de dommage. Il s’agit là d’un effet unique qui, à notre connaissance, n’est pas observable avec d’autres agents qui inhibent la progression en phase S.

The Sinorhizobium meliloti EmrR Regulator Is Required for Efficient Colonization of Medicago sativa Root Nodules

The nitrogen-fixing bacterium Sinorhizobium meliloti must adapt to diverse conditions encountered during its symbiosis with leguminous plants. We characterized a new symbiotically relevant gene, emrR (SMc03169), whose product belongs to the TetR family of repressors and is divergently transcribed from emrAB genes encoding a putative major facilitator superfamily-type efflux pump. An emrR deletion mutant produced more succinoglycan, displayed increased cell-wall permeability, and exhibited higher tolerance to heat shock. It also showed lower tolerance to acidic conditions, a reduced production of siderophores, and lower motility and biofilm formation. The simultaneous deletion of emrA and emrR genes restored the mentioned traits to the wild-type phenotype, except for survival under heat shock, which was lower than that displayed by the wild-type strain. Furthermore, the ΔemrR mutant as well as the double ΔemrAR mutant was impaired in symbiosis with Medicago sativa; it formed fewer nodules and competed poorly with the wild-type strain for nodule colonization. Expression profiling of the ΔemrR mutant showed decreased expression of genes involved in Nod-factor and rhizobactin biosynthesis and in stress responses. Expression of genes directing the biosynthesis of succinoglycan and other polysaccharides were increased. EmrR may therefore be involved in a regulatory network targeting membrane and cell wall modifications in preparation for colonization of root hairs during symbiosis.

HydroxyprolineO-arabinosyltransferase mutants oppositely alter tip growth inArabidopsis thalianaandPhyscomitrella patens

Hydroxyproline O-arabinosyltransferases (HPATs) are members of a small, deeply conserved family of plant-specific glycosyltransferases that add arabinose sugars to diverse proteins including cell wall-associated extensins and small signaling peptides. Recent genetic studies in flowering plants suggest that different HPAT homologs have been co-opted to function in diverse species-specific developmental contexts. However, nothing is known about the roles of HPATs in basal plants. We show that complete loss of HPAT function in Arabidopsis thaliana and the moss Physcomitrella patens results in a shared defect in gametophytic tip cell growth. Arabidopsis hpat1/2/3 triple knockout mutants suffer from a strong male sterility defect as a consequence of pollen tubes that fail to fully elongate following pollination. Knocking out the two HPAT genes of Physcomitrella results in larger multicellular filamentous networks due to increased elongation of protonemal tip cells. Physcomitrella hpat mutants lack cell-wall associated hydroxyproline arabinosides and can be rescued with exogenous cellulose, while global expression profiling shows that cell wall-associated genes are severely misexpressed, implicating a defect in cell wall formation during tip growth. Our findings point to a major role for HPATs in influencing cell elongation during tip growth in plants.

The periplasmic domain of the barrel assembly machinery protein A (BamA) from Escherichia coli assists folding of outer membrane protein A

The assembly of outer membranes of the cell wall of Gram-negative bacteria and of various organelles of eukaryotic cells requires the evolutionarily conserved β-barrel-assembly machinery (BAM) complex. This thesis describes the biochemical and biophysical properties of the periplasmic domain of the β-barrel assembly machinery protein A (PD-BamA) of the E. coli BAM complex, its effect on insertion and folding of the Outer membrane protein A (OmpA) into lipid bilayers and the identification of regions of PD-BamA that may be involved in protein-protein interactions. The secondary structure of PD-BamA in mixed lipid bilayers, analyzed by Circular dichroism (CD) spectroscopy, contained less β-sheet at an increased content of phosphatidylglycerol (PG) in the lipid membrane. This result showed membrane binding, albeit only in the presence of negatively charged lipids. Fluorescence spectroscopy demonstrated that PD-BamA only binds to lipid bilayers containing the negatively charged DOPG, confirming the results of CD spectroscopy. PD-BamA did not bind to zwitterionic but overall neutral lipid bilayers. PD-BamA bound to OmpA at a stoichiometry of 1:1. PD-BamA strongly facilitated insertion and folding of OmpA into lipid membranes. Kinetics of PD-BamA mediated folding of OmpA was well described by two parallel folding processes, a fast folding process and a slow folding process, differing by 2-3 orders of magnitude in their rate constants. The folding yields of OmpA depended on the concentration of lipid membranes and also on the lipid head groups. The presence of PD-BamA resulted in increased folding yields of OmpA in negatively charged DOPG, but PD-BamA did not affect the folding kinetics of OmpA into bilayers of zwitterionic but overall neutral lipids. The efficiency of folding and insertion of OmpA into lipid bilayers strongly depended on the ratio PD-BamA/OmpA and was optimal at equimolar concentrations of PD-BamA and OmpA. To examine complexes of unfolded OmpA with PD-BamA in more detail, site-directed spectroscopy was used to explore contact regions in both, PD-BamA and OmpA. Similarly, contact regions were also investigated for another protein complex formed by PD-BamA and the lipoprotein BamD. The obtained data suggest, that the site of interaction on PD-BamA for OmpA might be oriented towards the exterior environment away from the preceding POTRA domains, but that PD-BamA is oriented with its short α-helix α1 of POTRA domain 5 towards the C-terminal end of BamD.

Changes in enzymatic activity, accumulation of proteins and softening of persimmon (Diospyros kaki Thunb.) flesh as a function of pre-cooling acclimatization.

One of the major causes of ?Fuyu? persimmon loss after cold storage (CS) is the breakdown of its flesh, which results in the production of a translucent fruit (a water-soaked fruit). It is believed that the cause of this disturbance is linked to disorganization of the cytoskelet and endomembrane system, which changes the synthesis and transport of proteins and metabolites, resulting in incomplete ripening. To test this hypothesis, ?Fuyu? persimmon was subjected to three different postharvest treatments (T): Control ? harvested and kept at 23±3 ◦C and relative humidity (RH) of 85±5% (room temperature, RT) for 12 days, T1 ? harvested and kept under cold storage (CS) (1±1 ◦C and RH of 85±5%) for 30 days followed by RT storage for 2 days, T2 ? kept under RT for 2 days (acclimatization) followed by CS for 30 days. Control and T2 resulted in fruit with decreased flesh firmness (FF), and increased soluble solids (SS) and ascorbic acid (AA) contents. In these fruit the activity of endo-1,4-ß-glucanase (endo-1,4-ß-gluc), pectin methylesterase (PME), polygalacturonase (PG) and ß-galactosidase (ß-gal) increased. T1 resulted in translucent fruit with decreased FF, without any enzymatic activity changes, probably due to the physical disruption of the cytoskeleton. Further, there was an increased content of proteins corresponding to expansins in fruit kept under Control and T2 conditions, which suggests that these conditions do contribute to the synthesis and/or transport of proteins involved in the process of solubilization of the cell wall. In these fruit, there was also a major accumulation of gene transcripts corresponding to heat shock proteins (HSPs) of organelles related to endomembrane, which suggests participation of these genes in the prevention of damage caused by cold conditions. These data proved the hypotheses that acclimatization contributes to the expression of HSPs, and synthesis and transportat of proteins involved in the solubilization of the cell wall. The expression of these genes results in the normal ripening of the persimmon, as confirmed by the evolution of ethylene production.