Quantum chaotic features of the spin-orbit coupled excitons in disordered two-dimensional insulators.

We study the synergy between disorder (phenomenologically modeled by the introduction of Riesz fractional derivative in the corresponding Schrödinger equation) and spin-orbit coupling (SOC) on the exciton spectra in two-dimensional (2D) semiconductor structures. We demonstrate that the joint impact of "fractionality" and SOC considerably modifies the spectrum of corresponding "ordinary" (i.e.

Fractional quantum oscillator and disorder in the vibrational spectra.

We study the role of disorder in the vibration spectra of molecules and atoms in solids. This disorder may be described phenomenologically by a fractional generalization of ordinary quantum-mechanical oscillator problem. To be specific, this is accomplished by the introduction of a so-called fractional Laplacian (Riesz fractional derivative) to the Scrödinger equation with three-dimensional (3D) quadratic potential.

Hydrogen-uptake genes improve symbiotic efficiency in common beans (Phaseolus vulgaris L.).

Hydrogen-uptake (Hup) activity is implicated in the mitigation of energy losses associated with the biological nitrogen fixation process, and has been related to productivity increases in some legume hosts. However, in common bean (Phaseolus vulgaris L.) the expression of hydrogenase is rare.

Genomic Diversity in the Endosymbiotic Bacterium Rhizobium leguminosarum.

bv. is a soil α-proteobacterium that establishes a diazotrophic symbiosis with different legumes of the tribe. The number of genome sequences from rhizobial strains available in public databases is constantly increasing, although complete, fully annotated genome structures from rhizobial genomes are scarce.

Analysis of metal tolerance in Rhizobium leguminosarum strains isolated from an ultramafic soil.

Natural habitats containing high amounts of heavy metals provide a valuable source of bacteria adapted to deal with metal toxicity. A functional analysis of the population of legume endosymbiotic bacteria in an ultramafic soil was undertaken by studying a collection of Rhizobium leguminosarum bv viciae (Rlv) isolates obtained using pea as trap plant. One of the isolates, Rlv UPM1137, was selected on the basis of its higher tolerance to nickel and cobalt and presence of inducible mechanisms for such tolerance.

Rhizobium leguminosarum HupE is a highly-specific diffusion facilitator for nickel uptake.

Bacteria require nickel transporters for the synthesis of Ni-containing metalloenzymes in natural, low nickel habitats. In this work we carry out functional and topological characterization of Rhizobium leguminosarum HupE, a nickel permease required for the provision of this element for [NiFe] hydrogenase synthesis. Expression studies in the Escherichia coli nikABCDE mutant strain HYD723 revealed that HupE is a medium-affinity permease (apparent Km 227 ± 21 nM; Vmax 49 ± 21 pmol Ni(2+) min(-1) mg(-1) bacterial dry weight) that functions as an energy-independent diffusion facilitator for the uptake of Ni(ii) ions.

Genetic diversity of Rhizobium from nodulating beans grown in a variety of Mediterranean climate soils of Chile.

In spite of potentially being an important source of rhizobial diversity and a key determinant of common bean productivity, there is a paucity of data on Rhizobium genetic variation and species composition in the important bean producing area of Chile and only one species has been documented (Rhizobium leguminosarum). In this study, 240 Rhizobium isolates from Torcaza bean (Phaseolus vulgaris L.) nodules established in the highest bean producing area in Chile (33°34'S-70°38'W and 37°36'S-71°47'W) were characterized by PCR-RFLP markers for nodC gene, revealing eight banding patterns with the polymorphic enzyme Hinf I.

Maturation of Rhizobium leguminosarum hydrogenase in the presence of oxygen requires the interaction of the chaperone HypC and the scaffolding protein HupK.

[NiFe] hydrogenases are key enzymes for the energy and redox metabolisms of different microorganisms. Synthesis of these metalloenzymes involves a complex series of biochemical reactions catalyzed by a plethora of accessory proteins, many of them required to synthesize and insert the unique NiFe(CN)2CO cofactor. HypC is an accessory protein conserved in all [NiFe] hydrogenase systems and involved in the synthesis and transfer of the Fe(CN)2CO cofactor precursor.

Dual role of HupF in the biosynthesis of [NiFe] hydrogenase in Rhizobium leguminosarum.

Background: [NiFe] hydrogenases are enzymes that catalyze the oxidation of hydrogen into protons and electrons, to use H₂ as energy source, or the production of hydrogen through proton reduction, as an escape valve for the excess of reduction equivalents in anaerobic metabolism. Biosynthesis of [NiFe] hydrogenases is a complex process that occurs in the cytoplasm, where a number of auxiliary proteins are required to synthesize and insert the metal cofactors into the enzyme structural units. The endosymbiotic bacterium Rhizobium leguminosarum requires the products of eighteen genes (hupSLCDEFGHIJKhypABFCDEX) to synthesize an active hydrogenase.

Rhizobium leguminosarum hupE encodes a nickel transporter required for hydrogenase activity.

Synthesis of the hydrogen uptake (Hup) system in Rhizobium leguminosarum bv. viciae requires the function of an 18-gene cluster (hupSLCDEFGHIJK-hypABFCDEX). Among them, the hupE gene encodes a protein showing six transmembrane domains for which a potential role as a nickel permease has been proposed.

Host-dependent expression of Rhizobium leguminosarum bv. viciae hydrogenase is controlled at transcriptional and post-transcriptional levels in legume nodules.

The legume host affects the expression of Rhizobium leguminosarum hydrogenase activity in root nodules. High levels of symbiotic hydrogenase activity were detected in R. leguminosarum bacteroids from different hosts, with the exception of lentil (Lens culinaris).

Symbiotic hydrogenase activity in Bradyrhizobium sp. (Vigna) increases nitrogen content in Vigna unguiculata plants.

Bradyrhizobium sp. (Lupinus) and Bradyrhizobium sp. (Vigna) mutants in which hydrogenase (hup) activity was affected were constructed and analyzed.

Control of the Ralstonia solanacearum Type III secretion system (Hrp) genes by the global virulence regulator PhcA.

Expression of several virulence factors in the plant pathogen bacterium Ralstonia solanacearum is controlled by a complex regulatory network, at the center of which is PhcA. We provide genetic evidence that PhcA also represses the expression of hrp genes that code for the Type III protein secretion system, a major pathogenicity determinant in this bacterium. The repression of hrp genes in complete medium is relieved in a phcA mutant and two distinct signals, a quorum-sensing signal and complex nitrogen sources, appear to trigger this PhcA-dependent repression.

Molecular and functional characterization of the Azorhizobium caulinodans ORS571 hydrogenase gene cluster.

In this work, we report the cloning and sequencing of the Azorhizobium caulinodans ORS571 hydrogenase gene cluster. Sequence analysis revealed the presence of 20 open reading frames hupTUVhypFhupSLCDFGHJK hypABhupRhypCDEhupE. The physical and genetic organization of A.

Characterization of a new internal promoter (P3) for Rhizobium leguminosarum hydrogenase accessory genes hupGHIJ.

Synthesis of the Rhizobium leguminosarum [NiFe] hydrogenase requires the participation of 16 accessory genes (hupCDEFGHIJKhypABFCDEX) besides the genes encoding the structural proteins (hupSL). Transcription of hupSL is controlled by a -24/-12-type promoter (P(1)), located upstream of hupS and regulated by NifA. In this work, a second -24/-12-type promoter (P(3)), located upstream of the hupG gene and transcribing hupGHIJ genes in R.

Diversity and evolution of hydrogenase systems in rhizobia.

Uptake hydrogenases allow rhizobia to recycle the hydrogen generated in the nitrogen fixation process within the legume nodule. Hydrogenase (hup) systems in Bradyrhizobium japonicum and Rhizobium leguminosarum bv. viciae show highly conserved sequence and gene organization, but important differences exist in regulation and in the presence of specific genes.

A signal transfer system through three compartments transduces the plant cell contact-dependent signal controlling Ralstonia solanacearum hrp genes.

Ralstonia solanacearum hrp genes encode a type III secretion system required for disease development in host plants and for hypersensitive response elicitation on non-hosts. hrp genes are expressed in the presence of plant cells through the HrpB regulator. This activation, which requires physical interaction between the bacteria and the plant cell, is sensed by the outer membrane receptor PrhA.