The formation of bacterial biofilms is initiated by cells transitioning from the free-swimming mode of growth to a surface. This review is aimed at highlighting the common themes that have emerged in ...recent research regarding the key components, signals, and cues that aid in the transition and those involved in establishing a more permanent surface association during initial attachment.
The important human pathogen Pseudomonas aeruginosa has been linked to numerous biofilm-related chronic infections. Here, we demonstrate that biofilm formation following the transition to the surface ...attached lifestyle is regulated by three previously undescribed two-component systems: BfiSR (PA4196-4197) harboring an RpoD-like domain, an OmpR-like BfmSR (PA4101-4102), and MifSR (PA5511-5512) belonging to the family of NtrC-like transcriptional regulators. These two-component systems become sequentially phosphorylated during biofilm formation. Inactivation of bfiS, bfmR, and mifR arrested biofilm formation at the transition to the irreversible attachment, maturation-1 and -2 stages, respectively, as indicated by analyses of biofilm architecture, and protein and phosphoprotein patterns. Moreover, discontinuation of bfiS, bfmR, and mifR expression in established biofilms resulted in the collapse of biofilms to an earlier developmental stage, indicating a requirement for these regulatory systems for the development and maintenance of normal biofilm architecture. Interestingly, inactivation did not affect planktonic growth, motility, polysaccharide production, or initial attachment. Further, we demonstrate the interdependency of this two-component systems network with GacS (PA0928), which was found to play a dual role in biofilm formation. This work describes a novel signal transduction network regulating committed biofilm developmental steps following attachment, in which phosphorelays and two sigma factor-dependent response regulators appear to be key components of the regulatory machinery that coordinates gene expression during P. aeruginosa biofilm development in response to environmental cues.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Dispersion enables biofilm bacteria to transit from the biofilm to the planktonic growth state and to spawn novel communities in new locales. Although the chemotaxis protein BdlA plays a role in the ...dispersion of Pseudomonas aeruginosa biofilms in response to environmental cues, little is known about regulation of BdlA activity or how BdlA modulates the dispersion response. Here, we demonstrate that BdlA in its native form is inactive and is activated upon nonprocessive proteolysis at a ClpP-protease-like cleavage site located between the Per Arnt Sim (PAS) sensory domains PASa and PASb. Activation of BdlA to enable biofilm dispersion requires phosphorylation at tyrosine-238 as a signal, elevated c-di-GMP levels, the chaperone ClpD, and the protease ClpP. The resulting truncated BdlA polypeptide chains directly interact and are required for P. aeruginosa biofilms to disperse. Our results provide a basis for understanding the mechanism of biofilm dispersion that may be applicable to a large number of biofilm-forming pathogenic species. Insights into the mechanism of BdlA function have implications for the control of biofilm-related infections.
Although little is known regarding the mechanism of biofilm dispersion, it is becoming clear that this process coincides with alteration of cyclic di-GMP (c-di-GMP) levels. Here, we demonstrate that ...dispersion by Pseudomonas aeruginosa in response to sudden changes in nutrient concentrations resulted in increased phosphodiesterase activity and reduction of c-di-GMP levels compared to biofilm and planktonic cells. By screening mutants inactivated in genes encoding EAL domains for nutrient-induced dispersion, we identified in addition to the previously reported ΔrbdA mutant a second mutant, the ΔdipA strain (PA5017 dispersion-induced phosphodiesterase A), to be dispersion deficient in response to glutamate, nitric oxide, ammonium chloride, and mercury chloride. Using biochemical and in vivo studies, we show that DipA associates with the membrane and exhibits phosphodiesterase activity but no detectable diguanylate cyclase activity. Consistent with these data, a ΔdipA mutant exhibited reduced swarming motility, increased initial attachment, and polysaccharide production but only somewhat increased biofilm formation and c-di-GMP levels. DipA harbors an N-terminal GAF (cGMP-specific phosphodiesterases, adenylyl cyclases, and FhlA) domain and two EAL motifs within or near the C-terminal EAL domain. Mutational analyses of the two EAL motifs of DipA suggest that both are important for the observed phosphodiesterase activity and dispersion, while the GAF domain modulated DipA function both in vivo and in vitro without being required for phosphodiesterase activity. Dispersion was found to require protein synthesis and resulted in increased dipA expression and reduction of c-di-GMP levels. We propose a role of DipA in enabling dispersion in P. aeruginosa biofilms.
•Mg-Zn ferrites prepared by autocombustion, co-precipitation, spray pyrolysis.•Influence of structural features on magnetic properties of ferrites is determined.•The highest magnetization is achieved ...for Mg0.5Zn0.5Fe2O4 nanoparticles.
Structural characteristics and magnetic properties of MgxZn1–xFe2O4 (x = 0.25; 0.5; 0.7) nanomaterials prepared by autocombustion, co-precipitation and spray pyrolysis methods were studied. Different characterization techniques are used to study the structural formation of the generated nanoparticles, namely X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), infrared spectroscopy (FT-IR) and vibrating sample magnetometery (VSM). In case of citrate autocombustion and co-precipitation methods, the magnetization goes through a maximum at Mg0.5Zn0.5Fe2O4 composition, while the dependence on the composition is subtle for spray pyrolysis. An increase in temperature and duration of heat treatment during the synthesis process leads to a particle size growth and to a cation redistribution between spinel sub-lattices. These resulted in a significant increase in the specific magnetization of the particles generated by citrate autocombustion method. The nanoparticles synthesized by co-precipitation method exhibit superparamagnetic behavior with no coercivity at room temperature. Nonetheless, the materials prepared by spray pyrolysis and citrate autocombustion methods are found to possess small coercivity of 30–80 Oe. The highest specific magnetization at room temperature is referring to Mg0.5Zn0.5Fe2O4 nanoparticles obtained by citrate autocombustion method (30 emu/g). The revealed correlations can be used to synthesize spinel ferrite nanoparticles with well-defined collective properties for a wide spectrum of applications.
Context.
Shock-induced changes in ordinary chondrite meteorites related to impacts or planetary collisions are known to be capable of altering their optical properties. Thus, one can hypothesize that ...a significant portion of the ordinary chondrite material may be hidden within the observed dark C/X asteroid population.
Aims.
The exact pressure-temperature conditions of the shock-induced darkening are not well constrained. Thus, we experimentally investigate the gradual changes in the chondrite material optical properties as a function of the shock pressure.
Methods.
A spherical shock experiment with Chelyabinsk LL5 was performed in order to study the changes in its optical properties. The spherical shock experiment geometry allows for a gradual increase of shock pressure from ~15 GPa at a rim toward hundreds of gigapascals in the center.
Results.
Four distinct zones were observed with an increasing shock load. The optical changes are minimal up to ~50 GPa. In the region of ~50–60 GPa, shock darkening occurs due to the troilite melt infusion into silicates. This process abruptly ceases at pressures of ~60 GPa due to an onset of silicate melting. At pressures higher than ~150 GPa, recrystallization occurs and is associated with a second-stage shock darkening due to fine troilite-metal eutectic grains. The shock darkening affects the ultraviolet, visible, and near-infrared region while changes to the MIR spectrum are minimal.
Conclusions.
Shock darkening is caused by two distinct mechanisms with characteristic pressure regions, which are separated by an interval where the darkening ceases. This implies a reduced amount of shock-darkened material produced during the asteroid collisions.
In the framework of the effective field theory approach to heavy supersymmetry radiative corrections in the Higgs sector of the minimal supersymmetric standard model (MSSM) for the effective ...potential decomposition up to the dimension-six operators are calculated. Symbolic expressions for the threshold corrections induced by F- and D-soft supersymmetry breaking terms are derived, and the Higgs boson mass spectrum respecting the condition mh=125 GeV for the lightest CP-even scalar is evaluated.
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