High Concentrations Of Divalent Cations Research Articles

Preventing acute neurotoxicity of CNS therapeutic oligonucleotides with the addition of Ca2+ and Mg2+ in the formulation

Oligonucleotide therapeutics (ASOs and siRNAs) have been explored for modulation of gene expression in the central nervous system (CNS), with several drugs approved and many in clinical evaluation. Administration of highly concentrated oligonucleotides to the CNS can induce acute neurotoxicity. We demonstrate that delivery of concentrated oligonucleotides to the CSF in awake mice induces acute toxicity, observable within seconds of injection. Electroencephalography (EEG) and electromyography (EMG) in awake mice demonstrated seizures. Using ion chromatography, we show that siRNAs can tightly bind Ca2+ and Mg2+ up to molar equivalents of the phosphodiester (PO)/phosphorothioate (PS) bonds independently of the structure or phosphorothioate content. Optimization of the formulation by adding high concentrations (above biological levels) of divalent cations (Ca2+ alone, Mg2+ alone, or Ca2+ and Mg2+) prevents seizures with no impact on the distribution or efficacy of the oligonucleotide. The data here establishes the importance of adding Ca2+ and Mg2+ to the formulation for the safety of CNS administration of therapeutic oligonucleotides.

Preventing acute neurotoxicity of CNS therapeutic oligonucleotides with the addition of Ca2+ and Mg2+ in the formulation.

Oligonucleotide therapeutics (ASOs and siRNAs) have been explored for modulation of gene expression in the central nervous system (CNS), with several drugs approved and many in clinical evaluation. Administration of highly concentrated oligonucleotides to the CNS can induce acute neurotoxicity. We demonstrate that delivery of concentrated oligonucleotides to the CSF in awake mice induces acute toxicity, observable within seconds of injection. Electroencephalography (EEG) and electromyography (EMG) in awake mice demonstrated seizures. Using ion chromatography, we show that siRNAs can tightly bind Ca2+ and Mg2+ up to molar equivalents of the phosphodiester (PO)/phosphorothioate (PS) bonds independently of the structure or phosphorothioate content. Optimization of the formulation by adding high concentrations (above biological levels) of divalent cations (Ca2+ alone, Mg2+ alone, or Ca2+ and Mg2+) prevents seizures with no impact on the distribution or efficacy of the oligonucleotide. The data here establishes the importance of adding Ca2+ and Mg2+ to the formulation for the safety of CNS administration of therapeutic oligonucleotides.

The complex effect of dissolved organic carbon on desorption of per- and poly-fluoroalkyl substances from soil under alkaline conditions

Per- and poly-fluoroalkyl substances (PFASs) are contaminants of emerging concern, yet the understanding of factors that control their leaching and release from contaminated soils remains limited. This study aimed to investigate the impact of dissolved organic carbon (DOC) on the release of PFASs—specifically, perfluorohexane sulfonate (PFHxS), perfluorooctane sulfonate (PFOS), and perfluorooctanoic acid (PFOA)from soils contaminated by aqueous film forming foam (AFFF). Batch aqueous leaching experiments were conducted on AFFF-contaminated soils under alkaline solution conditions (pH 9.5, 10.5, and 12) as it enhances leaching of both PFAS and DOC. Leaching of PFOS was significantly increased under alkaline conditions. Although the leaching of PFAS generally increased with pH, PFOS appeared to be more retained under the very alkaline pH conditions used in this study. At the same solution pH, leaching of PFOS and DOC was less in Ca(OH)2 than in NaOH. The retention of PFOS under these conditions may be attributable to the shielding of the negative charge of the soil components and colloids (e.g., DOC and clay minerals) in the leachates and/or the screening of negative charges on head groups of PFOS due to the high concentration of divalent cations. Solution chemistry affected desorption of PFOS more than PFHxS and PFOA. The study highlights that the influence of DOC on PFAS leaching and transport can be very complex, and depends on leachate chemistry (e.g., pH and cation type), PFAS chemistry, the magnitude of PFAS contamination and factors that influence the solid:liquid partitioning of organic carbon in soil.

Competition between Self-Assembly and Phase Separation Governs High-Temperature Condensation of a DNA Liquid.

In many biopolymer solutions, attractive interactions that stabilize finite-sized clusters at low concentrations also promote phase separation at high concentrations. Here we study a model biopolymer system that exhibits the opposite behavior, whereby self-assembly of DNA oligonucleotides into finite-sized, stoichiometric clusters tends to inhibit phase separation. We first use microfluidics-based experiments to map a novel phase transition in which the oligonucleotides condense as the temperature increases at high concentrations of divalent cations. We then show that a theoretical model of competition between self-assembly and phase separation quantitatively predicts changes in experimental phase diagrams arising from DNA sequence perturbations. Our results point to a general mechanism by which self-assembly shapes phase boundaries in complex biopolymer solutions.

Effects of cation valence on swelling power, solubility, pasting, gel strength characteristics of potato starch

The objective of this study was to investigate the effects of monovalent, divalent and trivalent cations on the physicochemical properties of potato starch. Cations decreased the water absorption in potato starch granules to cause lower swelling power, especially 0.02–0.04 mmol/g Fe3+ or 0.01–0.04 mmol/g Al3+, but 0.01 mmol/g trivalent cation led more amylose dissolving into the water to cause higher solubility. High concentration of divalent or trivalent cations markedly decreased the viscosity in potato starch paste during further heating and cooling, resulting in the decreases of the trough and finial viscosity, especially 0.04 mmol/g Fe3+. Higher valence of cations decreased the gel strength in potato starch, especially 0.02–0.04 mmol/g Fe3+ or Al3+. Higher valence of cations decreased the starch gel binding with the water and caused lower water holding capacity. In general, a higher valence of cations caused more changes in the physicochemical characteristics of potato starch.

Metagenomic Analysis of a Concrete Bridge Reveals a Microbial Community Dominated by Halophilic Bacteria and Archaea.

Concrete hosts a small but diverse microbiome that changes over time. Shotgun metagenomic sequencing would enable assessment of both the diversity and function of the microbial community in concrete, but a number of unique challenges make this difficult for concrete samples. The high concentration of divalent cations in concrete interferes with nucleic acid extraction, and the extremely low biomass in concrete means that DNA from laboratory contamination may be a large fraction of the sequence data. Here, we develop an improved method for DNA extraction from concrete, with higher yield and lower laboratory contamination. To show that this method provides DNA of sufficient quality and quantity to do shotgun metagenomic sequencing, DNA was extracted from a sample of concrete obtained from a road bridge and sequenced with an Illumina MiSeq system. This microbial community was dominated by halophilic Bacteria and Archaea, with enriched functional pathways related to osmotic stress responses. Although this was a pilot-scale effort, we demonstrate that metagenomic sequencing can be used to characterize microbial communities in concrete and that older concrete structures may host different microbes than recently poured concrete. IMPORTANCE Prior work on the microbial communities of concrete focused on the surfaces of concrete structures such as sewage pipes or bridge pilings, where thick biofilms were easy to observe and sample. Because the biomass inside concrete is so low, more recent analyses of the microbial communities inside concrete used amplicon sequencing methods to describe those communities. However, to understand the activity and physiology of microbes in concrete, or to develop living infrastructure, we must develop more direct methods of community analysis. The method developed here for DNA extraction and metagenomic sequencing can be used for analysis of microbial communities inside concrete and can likely be adapted for other cementitious materials.

Novel Chimeric Amino Acid-Fatty Alcohol Ester Amphiphiles Self-Assemble into Stable Primitive Membranes in Diverse Geological Settings.

Primitive cells are believed to have been self-assembled vesicular structures with minimal metabolic components, that were capable of self-maintenance and self-propagation in early Earth geological settings. The coevolution and self-assembly of biomolecules, such as amphiphiles, peptides, and nucleic acids, or their precursors, were essential for protocell emergence. Here, we present a novel class of amphiphiles-amino acid-fatty alcohol esters-that self-assemble into stable primitive membrane compartments under a wide range of geochemical conditions. Glycine n-octyl ester (GOE) and isoleucine n-octyl ester (IOE), the condensation ester products of glycine or isoleucine with octanol (OcOH), are expected to form at a mild temperature by wet-dry cycles. The GOE forms micelles in acidic aqueous solutions (pH 2-7) and vesicles at intermediate pH (pH 7.3-8.2). When mixed with cosurfactants (octanoic acid [OcA]; OcOH, or decanol) in different mole fractions [XCosurfactant = 0.1-0.5], the vesicle stability range expands significantly to span the extremely acidic to mildly alkaline (pH 2-8) and extremely alkaline (pH 10-11) regions. Only a small mole fraction of cosurfactant [XCosurfactant = 0.1] is needed to make stable vesicular structures. Notably, these GOE-based vesicles are also stable in the presence of high concentrations of divalent cations, even at low pHs and in simulated Hadean seawater composition (without sulfate). To better understand the self-assembly behavior of GOE-based systems, we devised complementary molecular dynamics computer simulations for a series of mixed GOE/OcA systems under simulated acidic pHs. The resulting calculated critical packing parameter values and self-assembly behavior were consistent with our experimental findings. The IOE is expected to show similar self-assembly behavior. Thus, amino acid-fatty alcohol esters, a novel chimeric amphiphile class composed of an amino acid head group and a fatty alcohol tail, may have aided in building protocell membranes, which were stable in a wide variety of geochemical circumstances and were conducive to supporting replication and self-maintenance. The present work contributes to our body of work supporting our hypothesis for synergism and coevolution of (proto)biomolecules on early Earth.

Manipulating polydispersity of lens β-crystallins using divalent cations demonstrates evidence of calcium regulation

Crystallins comprise the protein-rich tissue of the eye lens. Of the three most common vertebrate subtypes, β-crystallins exhibit the widest degree of polydispersity due to their complex multimerization properties in situ. While polydispersity enables precise packing densities across the concentration gradient of the lens for vision, it is unclear why there is such a high degree of structural complexity within the β-crystallin subtype and what the role of this feature is in the lens. To investigate this, we first characterized β-crystallin polydispersity and then established a method to dynamically disrupt it in a process that is dependent on isoform composition and the presence of divalent cationic salts (CaCl2 or MgCl2). We used size-exclusion chromatography together with dynamic light scattering and mass spectrometry to show how high concentrations of divalent cations dissociate β-crystallin oligomers, reduce polydispersity, and shift the overall protein surface charge-properties that can be reversed when salts are removed. While the direct, physiological relevance of these divalent cations in the lens is still under investigation, our results support that specific isoforms of β-crystallin modulate polydispersity through multiple chemical equilibria and that this native state is disrupted by cation binding. This dynamic process may be essential to facilitating the molecular packing and optical function of the lens.

Outstanding Enrofloxacin Removal Using an Unmodified Low-Cost Sorbent Prepared from the Leaves of Pyracantha koidzumii.

Increasing discharges of synthetic antimicrobial agents from industrial and municipal sewage, as well as from agricultural runoffs into water bodies, is still a global challenge. Here, an unmodified low-cost sorbent was prepared in an ecofriendly manner from Pyracantha koidzumii leaves for the removal of enrofloxacin (ENR). Sorbent characterization was accomplished using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), BET surface area, zeta potential, and point of zero charge. Biosorption assays were carried out via batch mode concerning the impact of adsorbent dosage, contact time, solution pH, solution ionic strength, adsorbate concentration, and temperature. In general, ENR adsorption was significantly correlated with pH and ionic strength. At a neutral pH, the sorbent had a theoretical maximal ENR uptake of 138.89 mg/g. However, the adsorption capacity was significantly affected by the presence of high concentrations of divalent cations (Ca2+ and Mg2+). The findings from the kinetics and isotherms showed that the pseudo-second-order kinetic and Langmuir isotherm models best fit the experimental data. Electrostatic interactions, hydrogen bonding, and π-π stacking were the most important mechanisms of adsorption of ENR onto the P. koidzumii sorbent. Overall, this study suggests the promising application of this agricultural residue for the efficient removal of ENR from water.

High Concentrations of Divalent Cations in Extracellular Environments Reduce in vitro Antibiotic Activity of Tigecycline

Tigecycline is known to form a complex with divalent cations such as Mg2+ and Ca2+, which is essential for a mode of action of tigecycline. In this study, we investigated the effects of levels of divalent cations on the in vitro antibacterial activity of tigecycline against two strains each of Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii. When Mg2+ or Ca2+ was added to be tantamount to criteria levels of severe hypermagnesemia or hypercalcemia in Mueller-Hinton II broth, minimum inhibitory concentrations were increased 2- to 4-fold in all strains. In media containing high concentrations of Mg2+ or Ca2+, bacterial survival rates increased significantly after 24-hour exposure to tigecycline for all strains except one K. pneumoniae strain. Thus, levels of divalent cations in extracellular condition might affect tigecycline activity. While testing on humans is still required, our results suggest that caution should be exercised when using tigecycline to treat infected patients with hypermagnesemia and hypercalcemia.

High Concentrations of Divalent Cations in Extracellular Environments Reduce in vitro Antibiotic Activity of Tigecycline

Tigecycline is known to form a complex with divalent cations such as Mg2+ and Ca2+, which is essential for a mode of action of tigecycline. In this study, we investigated the effects of levels of divalent cations on the in vitro antibacterial activity of tigecycline against two strains each of Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii. When Mg2+ or Ca2+ was added to be tantamount to criteria levels of severe hypermagnesemia or hypercalcemia in Mueller-Hinton II broth, minimum inhibitory concentrations were increased 2- to 4-fold in all strains. In media containing high concentrations of Mg2+ or Ca2+, bacterial survival rates increased significantly after 24-hour exposure to tigecycline for all strains except one K. pneumoniae strain. Thus, levels of divalent cations in extracellular condition might affect tigecycline activity. While testing on humans is still required, our results suggest that caution should be exercised when using tigecycline to treat infected patients with hypermagnesemia and hypercalcemia.

Application of Amine Modified Magnetic Nanoparticles as an Efficient and Reusable Nanofluid for Removal of Ba2+ in High Saline Waters

This study describes an investigation on the application of functionalized nanoparticles used as a sorbent for extraction and removal of barium ions from high saline waters. Magnetic recyclable Fe3O4@SiO2 nanoparticles with amine groups were developed and those surface and structural properties were investigated using TEM, FT-IR, XRD, DLS and zeta-potential measurements. Fe3O4@SiO2@NH2 nano adsorbent exhibited good capability to remove Ba2+ from high saline water, resulting from making interaction between Ba2+ and surface amino groups of the prepared magnetic nanopartciles. The performance of the modified nanoparticles is slightly affected due to high concentration of divalent cations (Ca2+). Magnetic nanoparticles are easily recovered from aqueous solution by magnetic separation and regenerated easily by acid treatment. Results of the present study show that recyclable amino functionalized magnetic nanoparticles can be used as a reusable particle to remove barium from produced formation water.

New Factors for Protoplast-Callose-Fiber Formation in Salt-Tolerant Mangrove Plants, Avicennia alba and Bruguiera sexangula and Analysis of Fiber Substructures

Elongated and spiral β-1,3-glucan (callose) fibers were obtained by new factors from protoplasts cultured in liquid medium from suspension cultured cells of two salt-tolerant mangrove species; Avicennia alba and Bruguiera sexangula. Differences in salt factor for protoplast-fiber formation were compared with those of the callose fibers developed from protoplasts of non-mangrove tree plants, Larix leptolepis and Betula platyphylla, which high concentrations of divalent cations, Mg2+ (50 mM) or Ca2+ (100 mM), were stimulatory. In the halophilic A. alba protoplasts, whose cell division was stimulated by up to 400 mM NaCl, addition of Mg2+, Ca2+, K+ ions inhibited protoplast-fiber formation. In B. sexangula, protoplast-fibers were rapidly and efficiently formed only by another new factor, electric cell fusion treatment of protoplasts. Spiral fibers developed from mangrove protoplasts were detected under an inverted microscope, and their specific blue-green color for callose after staining with Aniline Blue dye was detected under a fluorescence microscope. Enzymatic certification of callose was further performed with laminarinase, specific for callose, in comparison with cellulase CBH1, specific for cellulose. Differences in sub-structures, fibrils and sub-fibrils of two mangrove protoplast-fibers were analyzed using laser confocal scanning microscopy, atomic force microscopy and image J analysis. Tube-like fine structure was observed using transmission electron microscopy in single protoplast-fiber of B. sexangula selected with a micromanipulator.

Cobalt ion interaction with TMEM16A calcium-activated chloride channel: Inhibition and potentiation.

TMEM16A, a Ca2+-sensitive Cl- channel, plays key roles in many physiological functions related to Cl- transport across lipid membranes. Activation of this channel is mediated via binding intracellular Ca2+ to the channel with a relatively high apparent affinity, roughly in the sub-μM to low μM concentration range. Recently available high-resolution structures of TMEM16 molecules reveal that the high-affinity Ca2+ activation sites are formed by several acidic amino acids, using their negatively charged sidechain carboxylates to coordinate the bound Ca2+. In this study, we examine the interaction of TMEM16A with a divalent cation, Co2+, which by itself cannot activate current in TMEM16A. This divalent cation, however, has two effects when applied intracellularly. It inhibits the Ca2+-induced TMEM16A current by competing with Ca2+ for the aforementioned high-affinity activation sites. In addition, Co2+ also potentiates the Ca2+-induced current with a low affinity. This potentiation effect requires high concentration (mM) of Co2+, similar to our previous findings that high concentrations (mM) of intracellular Ca2+ ([Ca2+]i) can induce more TMEM16A current after the Ca2+-activation sites are saturated by tens of μM [Ca2+]i. The degrees of potentiation by Co2+ and Ca2+ also roughly correlate with each other. Interestingly, mutating a pore residue of TMEM16A, Y589, alters the degree of potentiation in that the smaller the sidechain of the replaced residue, the larger the potentiation induced by divalent cations. We suggest that the Co2+ potentiation and the Ca2+ potentiation share a similar mechanism by increasing Cl- flux through the channel pore, perhaps due to an increase of positive pore potential after the binding of divalent cations to phospholipids in the pore. A smaller sidechain of a pore residue may allow the pore to accommodate more phospholipids, thus enhancing the current potentiation caused by high concentrations of divalent cations.

Biophysical characterization of a series of novel non‐RAFT copolymers with improved buffer behavior

Synthetic amphipathic polymers present an invaluable tool for excision and liberation of superstructures of membrane proteins (MPs) and their surrounding annular membrane bilayer in donut‐shaped nanoparticles or discs. Styrene‐co‐maleic acid polymers (SMAs) have demonstrated most efficiency for the structural characterization of membrane proteins. However, some drawbacks such as sensitivity to acidic pH and high concentration of divalent cations, interference with the spectroscopic profiles of proteins, high polydispersity index (PDI) and nonspecific interaction with protein surface have hindered the ultimate optimal utilization of SMA polymers for functional characterization of MPs in lipid bilayer and hence for drug discovery purposes. We have developed multiple series of novel non‐RAFT amphipathic polymers that demonstrate improved behaviors in acidic pH and high concentration of calcium. Some of these unique amphipathic polymers display exemplary polydispersity (PDI ~1), strict alternation (a well‐defined sequence of comonomers) and distinct spectrophotometric profiles. We further characterized the application of these novel polymeric detergents for purification of a model integral beta‐barrel MP, PagP, from the outer membrane of E. coli.

Motility of the Labial Palps in Feeding Behavior and its Innervation in the Marine Mussel, Mytilus galloprovincialis.

The labial palps of bivalves are thought to be involved in suspension feeding. However, the function of their muscular movements and neural regulation are still unclear. In semi-intact preparations of Mytilus, in which one valve was removed, suspended particles were removed from the labial palps following two kinds of compound movements: torsional and rotational. Both of these compound movements are therefore thought to function in rejection during feeding. These movements were observed in reduced preparations of isolated labial palps with intact cerebral ganglia, and were maintained even after removal of the cerebral ganglia, suggesting that they are generated by the peripheral neural network. Stimulation of the anterior pallial nerve elicited tetanic contraction of the labial palp, followed by secondary responses, including torsional movement. Secondary responses were dramatically reduced by a high concentration of divalent cations, in which polysynaptic pathways were inhibited. Hence, the cerebral ganglia may play an excitatory role within the peripheral neural network and the labial palp musculature via the anterior pallial nerve. Administration of serotonin induced repetitive muscular movements, whereas dopamine did not induce muscular movements. Serotonin-induced muscular movements were not elicited under a high concentration of divalent cation condition. In histochemical experiments, both the serotonergic and dopaminergic neural processes and cell body-like structures were widely observed inside the labial palp, the anterior pallial nerve, and the cerebral ganglia. Serotonin may thus contribute to activation of polysynaptic peripheral pathways, which are involved in regulating compound movements.

Green mawbyite, PbFe3+Fe2+0.4Zn0.6(AsO4)2OH(H2O), from the Lagoa mine, northern Portugal

An occurrence of an unusual, green-coloured mawbyite was found coating arsenopyrite in a specimen from the Lagoa mine, Northern Portugal. Electron microprobe analyses combined with a single-crystal structure refinement gives the formula as PbFe3+ Fe2+ 0.4 Zn 0.6 (AsO 4) 2 O H(H2O). The change of color from the usual bright red or orange color of mawbyite is attributed to the high concentration of divalent cations, Fe2+ and Zn, in the metal atom site.

Study of Surfactant–Polymer Flooding in High-Temperature and High-Salinity Carbonate Rocks

Secondary waterflood processes have low oil recovery in carbonate reservoirs as a result of their oil-wetness and heterogeneity. Surfactants in combination with polymer solutions can improve the oil recovery significantly from these reservoirs through ultralow interfacial tension (IFT), mobility control, and wettability alteration. However, application of surfactant–polymer (SP) flooding in high-salinity and high-temperature carbonate reservoirs is constrained by the thermal stability of polymers at elevated temperatures, compatibility of surfactants with a high concentration of divalent cations present in formation brines, and geochemical interactions with carbonate minerals. This research is focused on understanding surfactant and polymer interactions with formation brines containing high concentrations of divalent cations and thermal stability and transport of polymers in carbonate rocks at a high temperature (80 °C). Surfactant phase behavior experiments (with and without polymer) were performed to id...

Effect of divalent cations in low salinity water flooding in sandstone reservoirs

The never ending challenge for petroleum engineers is to improve recovery from existing reservoirs. One promising and relatively low cost method for improving recovery is low salinity (LS) waterflooding. Previously [1], we studied the effects that divalent cations (Ca2+ and Mg2+) in formation water (FW) have on LS water EOR tests, and we found that higher concentrations of divalent cations generally and specifically Ca2+ in FW lowered the performance of LS water EOR. In this study, we probe the significance of the Ca2+ and Mg2+ concentrations in the injected LS water. We also measured the wettability index to investigate the wettability alteration resulted after changing the divalent cations concentrations. Berea sandstone cores were saturated with oil and connate FW. Each core was flooded with two pore volumes (PV) of FW followed by two PVs of various LS waters at reservoir temperature (90 °C). During flooding, aqueous samples of the effluent were analyzed for pH, Ca2+ and Mg2+ concentration. Six LS water flood cases were investigated: (a) 3× dilution of Ca2+ with original Ca2+ concentration; (b) 3× dilution of Mg2+ with original Mg2+; (c) 3× dilution of both Ca2+ and Mg2+; (d) 10× dilution of Ca2+ with original Ca2+ concentration; (e) 10× dilution of Mg2+ with original Mg2+; (f) 10× dilution of both Ca2+ and Mg2+. Overall, both Ca2+ dilution cases achieved a positive LS effect (higher incremental oil recovery), with the 10× Ca2+ dilution producing a larger effect than the 3× dilution. The Mg2+ dilution cases produced either zero or small LS effects. When both Ca2+ and Mg2+ were diluted, there was a positive LS effect but less than for just Ca2+. The presence of Mg2+ inhibited the full benefit of the Ca2+ dilution.

Defining the regulatory mechanism of NikR, a nickel-responsive transcriptional regulator, in Brucella abortus.

Metals are essential micronutrients for virtually all forms of life, but metal acquisition is a double-edged sword, because high concentrations of divalent cations can be toxic to the cell. Therefore, the genes involved in metal acquisition, storage and efflux are tightly regulated. The present study characterizes a nickel-responsive transcriptional regulator in the intracellular mammalian pathogen, Brucella abortus. Deletion of bab2_0432 (nikR) in B. abortus led to alterations in the nickel-responsive expression of the genes encoding the putative nickel importer NikABCDE and, moreover, NikR binds directly to a specific DNA sequence within the promoter region of nikA in a metal-dependent manner to control gene expression. While NikR is involved in controlling the expression of nikA, nikR is not required for the infection of macrophages or mice by B. abortus. Overall, this work characterizes the role of NikR in nickel-responsive gene expression, as well as the dispensability of nikR for Brucella virulence.