Localized Infections with P. aeruginosa Strains Defective in Zinc Uptake Reveal That Zebrafish Embryos Recapitulate Nutritional Immunity Responses of Higher Eukaryotes.

The innate immune responses of mammals to microbial infections include strategies based on manipulating the local concentration of metals such as iron (Fe) and zinc (Zn), commonly described as nutritional immunity. To evaluate whether these strategies are also present in zebrafish embryos, we have conducted a series of heart cavity-localized infection experiments with Pseudomonas aeruginosa strains characterized by a different ability to acquire Zn. We have found that, 48 h after infection, the bacterial strains lacking critical components of the Zn importers ZnuABC and ZrmABCD have a reduced colonization capacity compared to the wild-type strain. This observation, together with the finding of a high level of expression of Zur-regulated genes, suggests the existence of antimicrobial mechanisms based on Zn sequestration. However, we have observed that strains lacking such Zn importers have a selective advantage over the wild-type strain in the early stages of infection. Analysis of the expression of the gene that encodes for a Zn efflux pump has revealed that at short times after infection, P. aeruginosa is exposed to high concentrations of Zn. At the same time, zebrafish respond to the infection by activating the expression of the Zn transporters Slc30a1 and Slc30a4, whose mammalian homologs mediate a redistribution of Zn in phagocytes aimed at intoxicating bacteria with a metal excess. These observations indicate that teleosts share similar nutritional immunity mechanisms with higher vertebrates, and confirm the usefulness of the zebrafish model for studying host-pathogen interactions.

Deciphering the Broad Antimicrobial Activity of Melaleuca alternifolia Tea Tree Oil by Combining Experimental and Computational Investigations.

Tea Tree Oil (TTO) is an essential oil obtained from the distillation of Melaleuca alternifolia leaves and branches. Due to its beneficial properties, TTO is widely used as an active ingredient in antimicrobial preparations for topical use or in cosmetic products and contains about 100 different compounds, with terpinen-4-ol, γ-terpinene and 1,8-cineole (or eucalyptol) being the molecules most responsible for its biological activities. In this work, the antimicrobial activity of whole TTO and these three major components was evaluated in vitro against fungi, bacteria and viruses. Molecular dynamics simulations were carried out on a bacterial membrane model and a Coxsackievirus B4 viral capsid, to propose an atomistic explanation of their mechanism of action. The obtained results indicate that the strong antimicrobial activity of TTO is attributable to the induction of an altered membrane functionality, mediated by the incorporation of its components within the lipid bilayer, and to a possible ability of the compounds to bind and alter the structural properties of the viral capsid.

New Insights into the Role of Metals in Host-Pathogen Interactions.

Almost eighty years have passed since the publication of the studies by Arthur Schade and Leona Caroline, which we can consider as the first investigations that began to disclose the importance of metals in host-pathogen interactions [...].

Salmonella Typhimurium and Pseudomonas aeruginosa Respond Differently to the Fe Chelator Deferiprone and to Some Novel Deferiprone Derivatives.

The ability to obtain Fe is critical for pathogens to multiply in their host. For this reason, there is significant interest in the identification of compounds that might interfere with Fe management in bacteria. Here we have tested the response of two Gram-negative pathogens, Salmonella enterica serovar Typhimurium (STM) and Pseudomonas aeruginosa (PAO1), to deferiprone (DFP), a chelating agent already in use for the treatment of thalassemia, and to some DFP derivatives designed to increase its lipophilicity. Our results indicate that DFP effectively inhibits the growth of PAO1, but not STM. Similarly, Fe-dependent genes of the two microorganisms respond differently to this agent. DFP is, however, capable of inhibiting an STM strain unable to synthesize enterochelin, while its effect on PAO1 is not related to the capability to produce siderophores. Using a fluorescent derivative of DFP we have shown that this chelator can penetrate very quickly into PAO1, but not into STM, suggesting that a selective receptor exists in Pseudomonas. Some of the tested derivatives have shown a greater ability to interfere with Fe homeostasis in STM compared to DFP, whereas most, although not all, were less active than DFP against PAO1, possibly due to interference of the added chemical tails with the receptor-mediated recognition process. The results reported in this work indicate that DFP can have different effects on distinct microorganisms, but that it is possible to obtain derivatives with a broader antimicrobial action.

Intermolecular Coulombic Decay in Endohedral Fullerene at the 4d→4f Resonance.

Intermolecular processes offer unique decay mechanisms for complex systems to internally relax. Here, we report the observation of an intermolecular Coulombic decay channel in an endohedral fullerene, a holmium nitride complex (Ho_{3}N) embedded within a C_{80} fullerene, between neighboring holmium ions, and between the holmium complex and the carbon cage. By measuring the ions and the electrons in coincidence after XUV photoabsorption, we can isolate the different decay channels, which are found to be more prevalent relative to intra-atomic Auger decay.

Growth of Pseudomonas aeruginosa in zinc poor environments is promoted by a nicotianamine-related metallophore.

Previous studies have suggested that P. aeruginosa possesses redundant zinc uptake systems. To identify uncharacterized zinc transporters, we analyzed the genome-wide transcriptional responses of P. aeruginosa PA14 to zinc restriction. This approach led to the identification of an operon (zrmABCD) regulated by the zinc uptake regulator Zur, that encodes for a metallophore-mediated zinc import system. This operon includes the genes for an uncharacterized TonB-dependent Outer Membrane Protein (ZrmA) and for a putative nicotianamine synthase (ZrmB). The simultaneous inactivation of the ZnuABC transporter and of one of these two genes markedly decreases the ability of P. aeruginosa to grow in zinc-poor media and compromises intracellular zinc accumulation. Our data demonstrate that ZrmB is involved in the synthesis of a metallophore which is released outside the cell and mediates zinc uptake through the ZrmA receptor. We also show that alterations in zinc homeostasis severely affect the ability of P. aeruginosa to cause acute lung and systemic infections in C57BL/6 mice, likely due to the involvement of zinc in the expression of several virulence traits. These findings disclose a hitherto unappreciated role of zinc in P. aeruginosa pathogenicity and reveal that this microorganism can obtain zinc through a strategy resembling siderophore-mediated iron uptake.

Salmonella enterica serovar Typhimurium growth is inhibited by the concomitant binding of Zn(II) and a pyrrolyl-hydroxamate to ZnuA, the soluble component of the ZnuABC transporter.

BACKGROUND: Under conditions of Zn(II) deficiency, the most relevant high affinity Zn(II) transport system synthesized by many Gram-negative bacteria is the ZnuABC transporter. ZnuABC is absent in eukaryotes and plays an important role in bacterial virulence. Consequently, ZnuA, the periplasmic component of the transporter, appeared as a good target candidate to find new compounds able to contrast bacterial growth by interfering with Zn(II) uptake. METHODS: Antibacterial activity assays on selected compounds from and in-house library against Salmonella enterica serovar Typhimurium ATCC14028 were performed. The X-ray structure of the complex formed by SeZnuA with an active compound was solved at 2.15Å resolution. RESULTS: Two di-aryl pyrrole hydroxamic acids differing in the position of a chloride ion, RDS50 ([1-[(4-chlorophenyl)methyl]-4-phenyl-1H-pyrrol-3-hydroxamic acid]) and RDS51 (1-[(2-chlorophenyl)methyl]-4-phenyl-1H-pyrrol-3-hydroxamic acid) were able to inhibit Salmonella growth and its invasion ability of Caco-2 cells. The X-ray structure of SeZnuA containing RDS51 revealed its presence at the metal binding site concomitantly with Zn(II) which is coordinated by protein residues and the hydroxamate moiety of the compound. CONCLUSIONS: Two molecules interfering with ZnuA-mediated Zn(II) transport in Salmonella have been identified for the first time. The resolution of the SeZnuA-RDS51 X-ray structure revealed that RDS51 is tightly bound both to the protein and to Zn(II) thereby inhibiting its release. These features pave the way to the rational design of new Zn(II)-binding drugs against Salmonella. GENERAL SIGNIFICANCE: The data reported show that targeting the bacterial ZnuABC transporter can represent a good strategy to find new antibiotics against Gram-negative bacteria.

Prime-boost vaccination with attenuated Salmonella Typhimurium ΔznuABC and inactivated Salmonella Choleraesuis is protective against Salmonella Choleraesuis challenge infection in piglets.

BACKGROUND: Salmonella enterica serovar Choleraesuis (S. Choleraesuis) infection causes a systemic disease in pigs. Vaccination could represent a solution to reduce prevalence in farms. In this study, we aimed to assess the efficacy of an attenuated strain of Salmonella enterica serovar Typhimurium (S. Typhimurium ΔznuABC) against S. Choleraesuis infection. The vaccination protocol combined priming with attenuated S. Typhimurium ΔznuABC vaccine and boost with an inactivated S. Choleraesuis vaccine and we compared the protection conferred to that induced by an inactivated S. Choleraesuis vaccine. METHODS: The first group of piglets was orally vaccinated with S. Typhimurium ΔznuABC and boosted with inactivated S. Choleraesuis, the second one was intramuscularly vaccinated with S. Choleraesuis inactivated vaccine and the third group of piglets was unvaccinated. All groups of animals were challenged with a virulent S. Choleraesuis strain at day 35 post vaccination. RESULTS: The results showed that the vaccination protocol, priming with S. Typhimurium ΔznuABC and boosted with inactivated S. Choleraesuis, applied to group A was able to limit weight loss, fever and organs colonization, arising from infection with virulent S. Choleraesuis, more effectively, than the prime-boost vaccination with homologous S. Choleraesuis inactivated vaccine (group B). CONCLUSION: In conclusion, these research findings extend the validity of attenuated S. Typhimurium ΔznuABC strain as a useful mucosal vaccine against S. Typhimurium and S. Choleraesuis pig infection. The development of combined vaccination protocols can have a diffuse administration in field conditions because animals are generally infected with different concomitant serovars.

Experimental setups for FEL-based four-wave mixing experiments at FERMI.

The recent advent of free-electron laser (FEL) sources is driving the scientific community to extend table-top laser research to shorter wavelengths adding elemental selectivity and chemical state specificity. Both a compact setup (mini-TIMER) and a separate instrument (EIS-TIMER) dedicated to four-wave-mixing (FWM) experiments has been designed and constructed, to be operated as a branch of the Elastic and Inelastic Scattering beamline: EIS. The FWM experiments that are planned at EIS-TIMER are based on the transient grating approach, where two crossed FEL pulses create a controlled modulation of the sample excitations while a third time-delayed pulse is used to monitor the dynamics of the excited state. This manuscript describes such experimental facilities, showing the preliminary results of the commissioning of the EIS-TIMER beamline, and discusses original experimental strategies being developed to study the dynamics of matter at the fs-nm time-length scales. In the near future such experimental tools will allow more sophisticated FEL-based FWM applications, that also include the use of multiple and multi-color FEL pulses.

The Salmonella enterica ZinT structure, zinc affinity and interaction with the high-affinity uptake protein ZnuA provide insight into the management of periplasmic zinc.

BACKGROUND: In Gram-negative bacteria the ZnuABC transporter ensures adequate zinc import in Zn(II)-poor environments, like those encountered by pathogens within the infected host. Recently, the metal-binding protein ZinT was suggested to operate as an accessory component of ZnuABC in periplasmic zinc recruitment. Since ZinT is known to form a ZinT-ZnuA complex in the presence of Zn(II) it was proposed to transfer Zn(II) to ZnuA. The present work was undertaken to test this claim. METHODS: ZinT and its structural relationship with ZnuA have been characterized by multiple biophysical techniques (X-ray crystallography, SAXS, analytical ultracentrifugation, fluorescence spectroscopy). RESULTS: The metal-free and metal-bound crystal structures of Salmonella enterica ZinT show one Zn(II) binding site and limited structural changes upon metal removal. Spectroscopic titrations with Zn(II) yield a KD value of 22±2nM for ZinT, while those with ZnuA point to one high affinity (KD<20nM) and one low affinity Zn(II) binding site (KD in the micromolar range). Sedimentation velocity experiments established that Zn(II)-bound ZinT interacts with ZnuA, whereas apo-ZinT does not. The model of the ZinT-ZnuA complex derived from small angle X-ray scattering experiments points to a disposition that favors metal transfer as the metal binding cavities of the two proteins face each other. CONCLUSIONS: ZinT acts as a Zn(II)-buffering protein that delivers Zn(II) to ZnuA. GENERAL SIGNIFICANCE: Knowledge of the ZinT-ZnuA relationship is crucial for understanding bacterial Zn(II) uptake.

EIS: the scattering beamline at FERMI.

The Elastic and Inelastic Scattering (EIS) beamline at the free-electron laser FERMI is presented. It consists of two separate end-stations: EIS-TIMEX, dedicated to ultrafast time-resolved studies of matter under extreme and metastable conditions, and EIS-TIMER, dedicated to time-resolved spectroscopy of mesoscopic dynamics in condensed matter. The scientific objectives are discussed and the instrument layout illustrated, together with the results from first exemplifying experiments.

Practical way to avoid spurious geometrical contributions in Brillouin light scattering experiments at variable scattering angles.

In this Letter, we present a simple method to avoid the well-known spurious contributions in the Brillouin light scattering (BLS) spectrum arising from the finite aperture of collection optics. The method relies on the use of special spatial filters able to select the scattered light with arbitrary precision around a given value of the momentum transfer (Q). We demonstrate the effectiveness of such filters by analyzing the BLS spectra of a reference sample as a function of scattering angle. This practical and inexpensive method could be an extremely useful tool to fully exploit the potentiality of Brillouin acoustic spectroscopy, as it will easily allow for effective Q-variable experiments with unparalleled luminosity and resolution.

Determination of dynamical parameters in liquids by homodyne transient grating spectroscopy at large angles.

We report on the possibility of extracting fast dynamical relaxation times from homodyne transient grating measurements. We demonstrate the validity of our approach by experimental measurements on liquid acetonitrile and by comparison with literature. This approach would be of tremendous help in the case of free-electron-laser-based transient grating experiments due to the overcoming of technical difficulties, such as large-angle geometries.

Deregulation of transition metals homeostasis is a key feature of cadmium toxicity in Salmonella.

Cadmium is a highly toxic metal whose presence in the environment represents a challenge for all forms of life. To improve our knowledge on cadmium toxicity, we have explored Salmonella Typhimurium responses to this metal. We have found that cadmium induces the concomitant expression of the cation efflux pump ZntA and of the high affinity zinc import system ZnuABC. This observation suggests that cadmium accumulation within the cell induces a condition of apparent zinc starvation, possibly due to the ability of this metal to compete with zinc for the metal binding site of proteins. This hypothesis is supported by the finding that strains lacking ZntA or ZnuABC are hyper-susceptible to cadmium and that the cadmium-induced growth defect of a znuABC mutant strain is largely relieved by zinc supplementation. A similar growth defect was observed for a mutant with impaired ability to acquire iron, whereas cadmium does not affect growth of a strain defective in manganese import. Cadmium also influences the expression and activity of the two cytoplasmic superoxide dismutases FeSOD and MnSOD, which are required to control cadmium-mediate oxidative stress. Exposure to cadmium causes a reduction of FeSOD activity in Salmonella wild type and the complete abrogation of its expression in the strain defective in iron import. In contrast, although MnSOD intracellular levels increase in response to cadmium, we observed discrepancies between protein levels and enzymatic activity which are suggestive of incorporation of non-catalytic metals in the active site or to cadmium-mediated inhibition of manganese import. Our results indicate that cadmium interferes with the ability of cells to manage transition metals and highlight the close interconnections between the homeostatic mechanisms regulating the intracellular levels of different metals.

Investigation of Zur-regulated metal transport systems reveals an unexpected role of pyochelin in zinc homeostasis.

Limiting the availability of transition metals at infection sites serves as a critical defense mechanism employed by the innate immune system to combat microbial infections. Pseudomonas aeruginosa exhibits a remarkable ability to thrive in zinc-deficient environments, facilitated by intricate cellular responses governed by numerous genes regulated by the zinc-responsive transcription factor Zur. Many of these genes have unknown functions, including those within the predicted PA2911-PA2914 and PA4063-PA4066 operons. A structural bioinformatics investigation revealed that PA2911-PA2914 comprises a TonB-dependent outer membrane receptor and inner membrane ABC-permeases responsible for importing metal-chelating molecules, whereas PA4063-PA4066 contains genes encoding a MacB transporter, likely involved in the export of large molecules. Molecular genetics and biochemical experiments, feeding assays, and intracellular metal content measurements support the hypothesis that PA2911-PA2914 and PA4063-PA4066 are engaged in the import and export of the pyochelin-cobalt complex, respectively. Notably, cobalt can reduce zinc demand and promote the growth of P. aeruginosa strains unable to import zinc, highlighting pyochelin-mediated cobalt import as a novel bacterial strategy to counteract zinc deficiency. These results unveil an unexpected role for pyochelin in zinc homeostasis and challenge the traditional view of this metallophore exclusively as an iron transporter. IMPORTANCE: The mechanisms underlying the remarkable ability of Pseudomonas aeruginosa to resist the zinc sequestration mechanisms implemented by the vertebrate innate immune system to control bacterial infections are still far from being fully understood. This study reveals that the Zur-regulated gene clusters PA2911-2914 and PA4063-PA4066 encode systems for the import and export of cobalt-bound pyochelin, respectively. This proves to be a useful strategy to counteract conditions of severe zinc deficiency since cobalt can replace zinc in many proteins. The discovery that pyochelin may contribute to cellular responses to zinc deficiency leads to a reevaluation of the paradigm that pyochelin is a siderophore involved exclusively in iron acquisition and suggests that this molecule has a broader role in modulating the homeostasis of multiple metals.

Oxidative stress and antioxidant therapy in cystic fibrosis.

Cystic fibrosis is a lethal autosomal recessive condition caused by a defect of the transmembrane conductance regulator gene that has a key role in cell homeostasis. A dysfunctional cystic fibrosis transmembrane conductance regulator impairs the efflux of cell anions such as chloride and bicarbonate, and also that of other solutes such as reduced glutathione. This defect produces an increased viscosity of secretions together with other metabolic defects of epithelia that ultimately promote the obstruction and fibrosis of organs. Recurrent pulmonary infections and respiratory dysfunction are main clinical consequences of these pathogenetic events, followed by pancreatic and liver insufficiency, diabetes, protein-energy malnutrition, etc. This complex comorbidity is associated with the extensive injury of different biomolecular targets by reactive oxygen species, which is the biochemical hallmark of oxidative stress. These biological lesions are particularly pronounced in the lung, in which the extent of oxidative markers parallels that of inflammatory markers between chronic events and acute exacerbations along the progression of the disease. Herein, an abnormal flux of reactive oxygen species is present by the sustained activation of neutrophils and other cystic fibrosis-derived defects in the homeostatic processes of pulmonary epithelia and lining fluids. A sub-optimal antioxidant protection is believed to represent a main contributor to oxidative stress and to the poor control of immuno-inflammatory pathways in these patients. Observed defects include an impaired reduced glutathione metabolism and lowered intake and absorption of fat-soluble antioxidants (vitamin E, carotenoids, coenzyme Q-10, some polyunsaturated fatty acids, etc.) and oligoelements (such as Se, Cu and Zn) that are involved in reactive oxygen species detoxification by means of enzymatic defenses. Oral supplements and aerosolized formulations of thiols have been used in the antioxidant therapy of this inherited disease with the main aim of reducing the extent of oxidative lesions and the rate of lung deterioration. Despite positive effects on laboratory end points, poor evidence was obtained on the side of clinical outcome so far. These aspects examined in this critical review of the literature clearly suggest that further and more rigorous trials are needed together with new generations of pharmacological tools to a more effective antioxidant and anti-inflammatory therapy of cystic fibrosis patients. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Zinc ion coordination as a modulating factor of the ZnuA histidine-rich loop flexibility: a molecular modeling and fluorescence spectroscopy study.

ZnuA is the soluble component of the high-affinity ZnuABC zinc transporter belonging to the ATP-binding cassette-type periplasmic Zn-binding proteins. The zinc transporter ZnuABC is composed by three proteins: ZnuB, the membrane permease, ZnuC, the ATPase component and ZnuA, the soluble periplasmic metal-binding protein which captures Zn and delivers it to ZnuB. The ZnuA protein contains a charged flexible loop, rich in histidines and acidic residues, showing significant species-specific differences. Various studies have established that this loop contributes to the formation of a secondary zinc binding site, which has been proposed to be important in the acquisition of periplasmic Zn for its delivery to ZnuB or for regulation of zinc uptake. Due to its high mobility the structure of the histidine-rich loop has never been solved by X-ray diffraction studies. In this paper, through a combined use of molecular modeling, mutagenesis and fluorescence spectroscopy, we confirm the presence of two zinc binding sites characterized by different affinities for the metal ion and show that the flexibility of the loop is modulated by the binding of the zinc ions to the protein. The data obtained by fluorescence spectroscopy have then be used to validate a 3D model including the unsolved histidine-rich loop.

TRAP1 S-nitrosylation as a model of population-shift mechanism to study the effects of nitric oxide on redox-sensitive oncoproteins.

S-nitrosylation is a post-translational modification in which nitric oxide (NO) binds to the thiol group of cysteine, generating an S-nitrosothiol (SNO) adduct. S-nitrosylation has different physiological roles, and its alteration has also been linked to a growing list of pathologies, including cancer. SNO can affect the function and stability of different proteins, such as the mitochondrial chaperone TRAP1. Interestingly, the SNO site (C501) of TRAP1 is in the proximity of another cysteine (C527). This feature suggests that the S-nitrosylated C501 could engage in a disulfide bridge with C527 in TRAP1, resembling the well-known ability of S-nitrosylated cysteines to resolve in disulfide bridge with vicinal cysteines. We used enhanced sampling simulations and in-vitro biochemical assays to address the structural mechanisms induced by TRAP1 S-nitrosylation. We showed that the SNO site induces conformational changes in the proximal cysteine and favors conformations suitable for disulfide bridge formation. We explored 4172 known S-nitrosylated proteins using high-throughput structural analyses. Furthermore, we used a coarse-grained model for 44 protein targets to account for protein flexibility. This resulted in the identification of up to 1248 proximal cysteines, which could sense the redox state of the SNO site, opening new perspectives on the biological effects of redox switches. In addition, we devised two bioinformatic workflows ( https://github.com/ELELAB/SNO_investigation_pipelines ) to identify proximal or vicinal cysteines for a SNO site with accompanying structural annotations. Finally, we analyzed mutations in tumor suppressors or oncogenes in connection with the conformational switch induced by S-nitrosylation. We classified the variants as neutral, stabilizing, or destabilizing for the propensity to be S-nitrosylated and undergo the population-shift mechanism. The methods applied here provide a comprehensive toolkit for future high-throughput studies of new protein candidates, variant classification, and a rich data source for the research community in the NO field.

Diversity of Salmonella spp. serovars isolated from the intestines of water buffalo calves with gastroenteritis.

BACKGROUND: Salmonellosis in water buffalo (Bubalus bubalis) calves is a widespread disease characterized by severe gastrointestinal lesions, profuse diarrhea and severe dehydration, occasionally exhibiting a systemic course. Several Salmonella serovars seem to be able to infect water buffalo, but Salmonella isolates collected from this animal species have been poorly characterized. In the present study, the prevalence of Salmonella spp. in water buffalo calves affected by lethal gastroenteritis was assessed, and a polyphasic characterization of isolated strains of S. Typhimurium was performed. RESULTS: The microbiological analysis of the intestinal contents obtained from 248 water buffalo calves affected by lethal gastroenteritis exhibited a significant prevalence of Salmonella spp. (25%), characterized by different serovars, most frequently Typhimurium (21%), Muenster (11%), and Give (11%). The 13 S. Typhimurium isolates were all associated with enterocolitis characterized by severe damage of the intestine, and only sporadically isolated with another possible causative agent responsible for gastroenteritis, such as Cryptosporidium spp., Rotavirus or Clostridium perfringens. Other Salmonella isolates were mostly isolated from minor intestinal lesions, and often (78% of cases) isolated with other microorganisms, mainly toxinogenic Escherichia coli (35%), Cryptosporidium spp. (20%) and Rotavirus (10%). The S. Typhimurium strains were characterized by phage typing and further genotyped by polymerase chain reaction (PCR) detection of 24 virulence genes. The isolates exhibited nine different phage types and 10 different genetic profiles. Three monophasic S. Typhimurium (B:4,12:i:-) isolates were also found and characterized, displaying three different phage types and three different virulotypes. The molecular characterization was extended to the 7 S. Muenster and 7 S. Give isolates collected, indicating the existence of different virulotypes also within these serovars. Three representative strains of S. Typhimurium were tested in vivo in a mouse model of mixed infection. The most pathogenic strain was characterized by a high number of virulence factors and the presence of the locus agfA, coding for a thin aggregative fimbria. CONCLUSIONS: These results provide evidence that Salmonella is frequently associated with gastroenteritis in water buffalo calves, particularly S. Typhimurium. Moreover, the variety in the number and distribution of different virulence markers among the collected S. Typhimurium strains suggests that within this serovar there are different pathotypes potentially responsible for different clinical syndromes.

Impairment of the Zn/Cd detoxification systems affects the ability of Salmonella to colonize Arabidopsis thaliana.

Salmonella capacity to colonize different environments depends on its ability to respond efficiently to fluctuations in micronutrient availability. Among micronutrients, Zn, besides playing an essential role in bacterial physiology, is a key element whose concentration can influence bacterial survival in a particular niche. Plant colonization by Salmonella enterica was described for several years, and some molecular determinants involved in this host-pathogen interaction have started to be characterized. However, it is still unclear if Zn plays a role in the outcome of this interaction, as well established for animal hosts that employ nutritional immunity strategies to counteract pathogens infections. In this study, we have investigated the involvement of Salmonella Typhimurium main effectors of zinc homeostasis in plant colonization, using Arabidopsis thaliana as a model host. The results show that to colonize plant tissues, Salmonella takes advantage of its ability to export excess metal through the efflux pumps ZntA and ZitB. In fact, the deletion of these Zn/Cd detoxification systems can affect bacterial persistence in the shoots, depending on metal availability in the plant tissues. The importance of Salmonella ability to export excess metal was enhanced in the colonization of plants grown in high Zn conditions. On the contrary, the bacterial disadvantage related to Zn detoxification impairment can be abrogated if the plant cannot efficiently translocate Zn to the shoots. Overall, our work highlights the role of Zn in Salmonella-plant interaction and suggests that modulation of plant metal content through biofortification may be an efficient strategy to control pathogen colonization.