It has been established for more than 35 years that homopolymer melts can exhibit thermorheological complexity, i.e., different relaxation processes which contribute to viscoelasticity have different ...temperature dependences. In particular, segmental and terminal relaxation processes are known to have different temperature dependences for polystyrene, poly(vinyl acetate), polypropylene glycol, poly(phenylmethylsiloxane), polyisoprene, and polyisobutylene. Atactic polypropylene (aPP) is an interesting model polymer for understanding melt dynamics, being the simplest vinyl polymer which is completely amorphous. The purpose of this communication is to show the relationship between recent NMR and dielectric relaxation results on aPP with earlier light scattering, creep, and dynamic mechanical measurements. The combined data set covers 15 decades of segmental relaxation times and 10 orders of magnitude in terminal relaxation shift factors.
In a previous study, we evaluated the degree of virulence of Mycobacterium avium subsp. paratuberculosis (Map) strains isolated from cattle in Argentina in a murine model. This assay allowed us to ...differentiate between high-virulent MapARG1347 and low-virulent MapARG1543 strains. To corroborate whether the differences in virulence could be attributed to genetic differences between the strains, we performed Whole Genome Sequencing and compared the genomes and gene content between them and determined the differences related to the reference strain MapK10. We found 233 SNPs/INDELS in one or both strains relative to Map K10. The two strains share most of the variations, but we found 15 mutations present in only one of the strains. Considering NS-SNP/INDELS that produced a severe effect in the coding sequence, we focus the analysis on four predicted proteins, putatively related to virulence. Survival of MapARG1347 strain in bMDM was higher than MapARG1543 and was more resistant to acidic pH and H2O2 stresses than MapK10. The genomic differences between the two strains found in genes MAP1203 (a putative peptidoglycan hydrolase), MAP0403 (a putative serine protease) MAP1003c (a member of the PE-PPE family) and MAP4152 (a putative mycofactocin binding protein) could contribute to explain the contrasting phenotype previously observed in mice models.
•WGS of Argentinian isolates with contrasting pathogenic phenotypes.•Phylogenetic analysis with whole genome sequences available from GenBank.•Identification of NS-SNP and INDELS by comparative genomic analysis.
The exported repetitive protein (erp) gene encodes a secreted 36-kDa protein with a central domain containing several proline-glycine-leucine-threonine-serine (PGLTS) repeats. It has been ...demonstrated that erp is a virulence-associated factor since the disruption of this gene impairs the growth of Mycobacterium bovis and Mycobacterium tuberculosis in mice.
In order to elucidate the function of Erp we searched for Erp-binding proteins from M. tuberculosis by using a bacterial two-hybrid system. Our results indicate that Erp interacts specifically with two putative membrane proteins, Rv1417 and Rv2617c. Further analysis revealed that the latter two interact with each other, indicating that Rv1417, Rv2617c and Erp are connected through multiple interactions. While Rv1417 is disseminated in several Actinomycetales genera, orthologues of Rv2617c are exclusively present in members of the M. tuberculosis complex (MTC). The central and amino-terminal regions of Erp were determined to be involved in the interaction with Rv1417 and Rv2627c. Erp forms from Mycobacterium smegmatis and Mycobacterium leprae were not able to interact with Rv2617c in two-hybrid assays. Immunolocalization experiments showed that Rv1417 and Rv2617c are found on the cell membrane and Erp on the bacterial cell wall. Finally, comparative genomics and expression studies revealed a possible role of Rv1417 in riboflavin metabolism.
We identified interactive partners of Erp, an M. tuberculosis protein involved in virulence, which will be the focus of future investigation to decipher the function of the Erp family protein.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
mce3 is one of the four mce operons in Mycobacterium tuberculosis that encode exported proteins with a probable role in the virulence of this bacterium. Upstream of mce3 there is a putative ...regulatory gene (Rv1963) that harbours a double tetR-family signature. To study the role of this putative regulatory gene in the transcriptional regulation of the mce3 operon, Mycobacterium smegmatis mc(2)155 and M. tuberculosis H37Rv strains that harboured gene fusions between the mce3 promoter region and the Escherichia coli lacZ gene, either containing or not containing the Rv1963 gene, were used. The presence of the Rv1963 gene in the strains greatly reduced beta-galactosidase activity, suggesting that the Rv1963-encoded protein is a transcriptional repressor of the mce3 operon. Expression of mce3 by recombinant M. tuberculosis was increased when it was grown in a macrophage-like cell line (J774), compared to the level of expression seen when the recombinant bacterium was grown under in vitro conditions. However, no lifting of repression was induced. The mce3 promoter was defined by deletion and cloning of the Rv1963-Rv1964 intergenic region in a 200 bp DNA fragment harbouring the region upstream of the Rv1964 start codon. Gel-shift experiments determined that the Rv1963-binding site was located in this region. These results indicate that the mce3 operon is transcriptionally regulated and that under certain, unknown, conditions repression of gene expression could be lifted.
The linear viscoelastic properties of 1,4-polyisoprene (PI; M W = 504 000) were measured by combined mechanical and dielectric spectroscopies. For local segmental motion, the respective mechanical ...and dielectric relaxation times, although differing substantially in magnitude, have identical temperature dependencies. The shape of the segmental relaxation function itself was sensitive to temperature. The data, obtained over a 160 degree range of temperatures, could be reduced to yield ostensibly satisfactory master curves; however, detailed analysis reveals the usual breakdown of time−temperature superpositioning in the glass transition zone. Given the near equivalence of the respective breadths of its terminal and segmental dispersions, thermorheological complexity in PI is unanticipated by theory. In the plateau zone, the mechanical spectrum of PI exhibits power law behavior, with an exponent (0.21) close to a proposed universal value.
Comparisons were made of the fragility (
T
g-normalized temperature dependence of segmental relaxation times) derived from mechanical and dielectric measurements to the same quantity determined from ...the activation energy for enthalpy relaxation as measured by differential scanning calorimetry (DSC). For linear polystyrenes of varying molecular weight, as well as for several other polymers, there was near quantitative agreement between the two measures of fragility. However, for poly(vinylethylene) (PVE) networks, whose normalized temperature dependence by either method increased with increasing crosslink density, the relationship was not quantitative. In contrast to the assessment of fragility, the shape (breadth) of the relaxation function cannot be reliably obtained from DSC measurements. The analysis yields results which depend on thermal history, contradicting the method’s assumption of thermorheological simplicity.
Electromechanical, mechanical, and volumetric measurements on vinylidene fluoride terpolymers with trifluoroethylene and trichlorofluoroethylene are reported. One purpose of the investigation was to ...assess the contribution of an electric field-induced crystal phase transformation to the large electrostrictive coefficient (43 nm2 V-2 at 1 Hz, parallel to the field). Such a crystal transformation is evidenced by the change in the Curie transition enthalpy after application of an electric field. Using the volume change at the Curie transition, along with X-ray diffraction data, we quantify the amount of the ferroelectric and paraelectric crystalline forms. From this, we conclude that, for electric fields up to 10 MV/m, the strain resulting from the field-induced crystal phase change is too small to account for the large electrostriction observed in the terpolymer. The transition from the α to the β-crystalline form is also induced by hydrostatic pressure, with the β-crystals formed at elevated pressures stable at ambient pressure. The Curie transition in the terpolymer, similar to the behavior of the copolymer, is accompanied by changes in both the shear and bulk moduli. The Curie transition exhibits significant hysteresis during thermal cycling, implying that both the electrostriction and the mechanical properties will be sensitive to processing.
The segmental dynamics in 1,2-polybutadiene was studied over a broad range of temperature and pressure using dielectric spectroscopy. The glass transition temperature was found to be strongly ...dependent on pressure (dT g/dP = 240 K/GPa). Moreover, while no appreciable change in the shape of the relaxation function with pressure was observed for spectra compared at a fixed value of the relaxation time, the fragility (T g-normalized temperature dependence) increased with pressure. From the ratio of the isochronal to isobaric expansivities, and consistently from the ratio of the isochoric and isobaric activation energies, temperature was found to exert a stronger influence on the dynamics than does the volume. This is similar to results for other polymers as well as small molecule glass-formers (when the latter lack hydrogen bonds). Finally, a comparison was made of the properties of 1,2-PBD with those of other vinyl polymers having different pendent groups. The different segmental dynamics reflect the manner in which local relaxation is governed by intermolecular cooperativity. Consistent with this interpretation, 1,2-PBD exhibits an activation volume more than 9 times the molar volume of its repeat unit; this is significantly larger than the values for the other vinyl polymers.
Mycobacterium avium sp. avium (MAA), M. avium sp. hominissuis (MAH), and M. avium sp. paratuberculosis (MAP) are the main members of the M. avium complex (MAC) causing diseases in several hosts. The ...aim of this study was to describe the genetic diversity of MAC isolated from different hosts. Twenty-six MAH and 61 MAP isolates were recovered from humans and cattle, respectively. GenoType CM® and IS1311-PCR were used to identify Mycobacterium species. The IS901-PCR was used to differentiate between MAH and MAA, while IS900-PCR was used to identify MAP. Genotyping was performed using a mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) scheme (loci: 292, X3, 25, 47, 3, 7, 10, 32) and patterns (INMV) were assigned according to the MAC-INMV database (http://mac-inmv.tours.inra.fr/). Twenty-two (22/26, 84·6%) MAH isolates were genotyped and 16 were grouped into the following, INMV 92, INMV 121, INMV 97, INMV 103, INMV 50, and INMV 40. The loci X3 and 25 showed the largest diversity (D: 0·5844), and the global discriminatory index (Hunter and Gaston discriminatory index, HGDI) was 0·9300. MAP (100%) isolates were grouped into INMV 1, INMV 2, INMV 11, INMV 8, and INMV 5. The HGDI was 0·6984 and loci 292 and 7 had the largest D (0·6980 and 0·5050). MAH presented a higher D when compared with MAP. The MIRU-VNTR was a useful tool to describe the genetic diversity of both MAH and MAP as well as to identify six new MAH patterns that were conveniently reported to the MAC-INMV database. It was also demonstrated that, in the geographical region studied, human MAC cases were produced by MAH as there was no MAA found among the human clinical samples.
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