Biochemical and spectroscopic properties of Brucella microti glutamate decarboxylase, a key component of the glutamate-dependent acid resistance system

In orally acquired bacteria, the ability to counteract extreme acid stress (pH < 2.5) ensures survival during transit through the animal host stomach. In several neutralophilic bacteria, the glutamate-dependent acid resistance system (GDAR) is the most efficient molecular system in conferring protection from acid stress. In Escherichia coli its structural components are either of the two glutamate decarboxylase isoforms (GadA, GadB) and the antiporter, GadC, which imports glutamate and exports γ-aminobutyrate, the decarboxylation product. The system works by consuming protons intracellularly, as part of the decarboxylation reaction, and exporting positive charges via the antiporter. Herein, biochemical and spectroscopic properties of GadB from Brucella microti (BmGadB), a Brucella species which possesses GDAR, are described. B. microti belongs to a group of lately described and atypical brucellae that possess functional gadB and gadC genes, unlike the most well-known "classical" Brucella species, which include important human pathogens. BmGadB is hexameric at acidic pH. The pH-dependent spectroscopic properties and activity profile, combined with in silico sequence comparison with E. coli GadB (EcGadB), suggest that BmGadB has the necessary structural requirements for the binding of activating chloride ions at acidic pH and for the closure of its active site at neutral pH. On the contrary, cellular localization analysis, corroborated by sequence inspection, suggests that BmGadB does not undergo membrane recruitment at acidic pH, which was observed in EcGadB. The comparison of GadB from evolutionary distant microorganisms suggests that for this enzyme to be functional in GDAR some structural features must be preserved

Le Condizioni di Esistenza dell' Arco fra Carboni

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The Glutaminase-dependent system confers extreme acid resistance to new species and atypical strains of Brucella

Neutralophilic bacteria have developed specific mechanisms to cope with the acid stress encountered in environments such as soil, fermented foods, and host compartments. In Escherichia coli, the glutamate decarboxylase (Gad)-dependent system is extremely efficient: it requires the concerted action of glutamate decarboxylase (GadA/GadB) and of the glutamate (Glu)/γ-aminobutyrate antiporter, GadC. Notably, this system is operative also in new strains/species of Brucella, among which Brucella microti, but not in the "classical" species, with the exception of marine mammals strains. Recently, the glutaminase-dependent system (named AR2_Q), relying on the deamination of glutamine (Gln) into Glu and on GadC activity, was described in E. coli. In Brucella genomes, a putative glutaminase (glsA)-coding gene is located downstream of the gadBC genes. We found that in B. microti these genes are expressed as a polycistronic transcript. Moreover, using a panel of Brucella genus-representative strains, we show that the AR2_Q system protects from extreme acid stress (pH =2.5), in the sole presence of Gln, only the Brucella species/strains predicted to have functional glsA and gadC. Indeed, mutagenesis approaches confirmed the involvement of glsA and gadC of B. microti in AR2_Q and that the acid-sensitive phenotype of B. abortus can be ascribed to a Ser248Leu substitution in GlsA, leading to loss of glutaminase activity. Furthermore, we found that the gene BMI_II339, of unknown function and downstream of the gadBC-glsA operon, positively affects Gad- and GlsA-dependent AR. Thus, we identified novel determinants that allow newly discovered and marine mammals Brucella strains to be better adapted to face hostile acidic environments. As for significance, this work may contribute to the understanding of the host preferences of Brucella species and opens the way to alternative diagnostic targets in epidemiological surveillance of brucellosis

Biochemical characterization of predicted Precambrian RuBisCO

The antiquity and global abundance of the enzyme, RuBisCO, attests to the crucial and longstanding role it has played in the biogeochemical cycles of Earth over billions of years. The counterproductive oxygenase activity of RuBisCO has persisted over billions of years of evolution, despite its competition with the carboxylase activity necessary for carbon fixation, yet hypotheses regarding the selective pressures governing RuBisCO evolution have been limited to speculation. Here we report the resurrection and biochemical characterization of ancestral RuBisCOs, dating back to over one billion years ago (Gyr ago). Our findings provide an ancient point of reference revealing divergent evolutionary paths taken by eukaryotic homologues towards improved specificity for CO2, versus the evolutionary emphasis on increased rates of carboxylation observed in bacterial homologues. Consistent with these distinctions, in vivo analysis reveals the propensity of ancestral RuBisCO to be encapsulated into modern-day carboxysomes, bacterial organelles central to the cyanobacterial CO2 concentrating mechanism

Spontaneous orbital polarization in the nematic phase of FeSe

The origin of nematicity in FeSe remains a critical outstanding question towards understanding unconventional superconductivity in proximity to nematic order. To understand what drives the nematicity, it is essential to determine which electronic degree of freedom admits a spontaneous order parameter independent from the structural distortion. Here, we use X-ray linear dichroism at the Fe K pre-edge to measure the anisotropy of the 3d orbital occupation as a function of in situ applied stress and temperature across the nematic transition. Along with X-ray diffraction to precisely quantify the strain state, we reveal a lattice-independent, spontaneously-ordered orbital polarization within the nematic phase, as well as an orbital polarizability that diverges as the transition is approached from above. These results provide strong evidence that spontaneous orbital polarization serves as the primary order parameter of the nematic phase.Comment: Main: 22 pages, 4 figures. Supp: 32 pages, 18 figure

Negative Thermal Expansion Near the Precipice of Structural Stability in Open Perovskites

Negative thermal expansion (NTE) describes the anomalous propensity of materials to shrink when heated. Since its discovery, the NTE effect has been found in a wide variety of materials with an array of magnetic, electronic and structural properties. In some cases, the NTE originates from phase competition arising from the electronic or magnetic degrees of freedom but we here focus on a particular class of NTE which originates from intrinsic dynamical origins related to the lattice degrees of freedom, a property we term structural negative thermal expansion (SNTE). Here we review some select cases of NTE which strictly arise from anharmonic phonon dynamics, with a focus on open perovskite lattices. We find that NTE is often present close in proximity to competing structural phases, with structural phase transition lines terminating near T=0 K yielding the most prominent displays of the SNTE effect. We further provide a theoretical model to make precise the proposed relationship among the signature behavior of SNTE, the proximity of these systems to structural quantum phase transitions and the effects of phase fluctuations near these unique regions of the structural phase diagram. The effects of compositional disorder on NTE and structural phase stability in perovskites are discussed

Probing magnetism in exfoliated VI3 layers with magnetotransport

We perform magnetotransport experiments on exfoliated multilayers of $\rm{VI_3}$, a 2D magnetic semiconductor reported to exhibit Ising ferromagnetism both in bulk and 2D form. Measurements of the magnetoconductance performed on field-effect transistors and tunnel barriers consistently show that the Curie temperature is $T_C~=~57~K$ (significantly larger than in the bulk; $T_C^{\rm bulk}~=~50~K$), irrespective of thickness (between 7 and 20~nm), in agreement with recent magneto-optical experiments. Measurements on tunnel barriers allow magnetism to be probed down to temperatures much lower than $T_C$. They show that below $T~\simeq~40$ K the magnetoconductance in a perpendicular magnetic field becomes negative, and that a pronounced hysteresis appears when the field is applied parallel to the planes. These phenomena, which have no observable counterpart in magneto-optical measurements, indicate an evolution of the magnetic state that deviates from that expected from a simple Ising ferromagnet. We attribute the effect to the large in-plane component of the magnetization, which we suggest to point in different directions in different $\rm{VI_3}$ layers. Our results provide new information about magnetism in exfoliated $\rm{VI_3}$ crystals and illustrate the complementarity of magnetotransport and magneto-optical measurements to probe the state of atomically thin 2D magnets.Comment: 10 pages, 5 figure

DPO multiplex PCR as an alternative to culture and susceptibility testing to detect Helicobacter pylori and its resistance to clarithromycin

<p>Abstract</p> <p>Background</p> <p>Macrolide resistance in <it>Helicobacter pylori </it>is the major risk factor for treatment failure when using a proton pump inhibitor-clarithromycin containing therapy. Macrolide resistance is due to a few mutations on the 23S ribomosal subunit encoded by the 23S rRNA gene. The present study aimed at investigating the performance of the dual priming oligonucleotide (DPO)-PCR kit named Seeplex^®ClaR-<it>H. pylori </it>ACE detection designed to detect <it>H. pylori </it>and two types of point mutations causing clarithromycin resistance in <it>H. pylori</it>.</p> <p>Methods</p> <p>The performance of Seeplex^®ClaR-<it>H. pylori </it>ACE detection was evaluated on 127 gastric biopsies in comparison to conventional bacterial culture followed by the determination of susceptibility to clarithromycin by E-test, as well as by an in-house real-time PCR using a fluorescence resonance energy transfer (FRET) technology.</p> <p>Results</p> <p>Considering culture as the reference test, the sensitivity of DPO-PCR and real-time FRET-PCR was 97.7% and 100% while specificity was 83.1% and 80.7%, respectively. However, both PCR were concordant in detecting 14 <it>H. pylori </it>positive cases which were negative by culture. Globally, E-test and DPO-PCR were concordant with regard to clarithromycin susceptibility in 95.3% of the cases (41/43), while real-time FRET-PCR and DPO-PCR were concordant in 95% (57/60).</p> <p>Conclusion</p> <p>The DPO-PCR is an interesting tool to detect <it>H. pylori </it>on gastric biopsies and to study its susceptibility to clarithromycin in laboratories that cannot perform real-time PCR assays.</p

Experimental realization of a single-layer multiferroic

Multiferroic materials have garnered wide interest for their exceptional static and dynamical magnetoelectric properties. Intrinsic type-II multiferroics exhibit an inversion-symmetry-breaking magnetic order which directly induces a ferroelectric lattice distortion through mechanisms such as the inverse Dzyaloshinskii-Moriya interaction. This direct coupling between the magnetic and structural order parameters results in record-strength magnetoelectric effects. Two-dimensional materials possessing such intrinsic multiferroic properties have been long sought for harnessing magnetoelectric coupling in nanoelectronic devices. Here, we report the discovery of type-II multiferroic order in a single atomic layer of transition metal-based van der Waals material NiI2. Using a combination of optical birefringence, second harmonic generation, and Raman spectroscopy in bulk NiI2, we first identified multiple independent and robust signatures of the multiferroic state. Subsequently, we studied the evolution of the optical signatures as a function of temperature and layer number, to find that the multiferroic state is robust down to monolayer NiI2. These observations establish NiI2 as a new platform for studying emergent multiferroic phenomena, chiral magnetic textures and ferroelectricity in the two-dimensional limit