Iron, copper, zinc, and manganese transport and regulation in pathogenic Enterobacteria: correlations between strains, site of infection and the relative importance of the different metal transport systems for virulence

Bacterioplankton taxa compete for iron along the early spring-summer transition in the Arctic Ocean

Microbial assemblages under the sea ice of the Dease Strait, Canadian Arctic, were sequenced for metagenomes of a small size fraction (0.2-3 μm). The community from early March was typical for this season, with Alpha- and Gammaproteobacteria as the dominant taxa, followed by Thaumarchaeota and Bacteroidetes. Toward summer, Bacteroidetes, and particularly the genus Polaribacter, became increasingly dominant, followed by the Gammaproteobacteria. Analysis of genes responsible for microbial acquisition of iron showed an abundance of ABC transporters for divalent cations and ferrous iron. The most abundant transporters, however, were the outer membrane TonB-dependent transporters of iron-siderophore complexes. The abundance of iron acquisition genes suggested this element was essential for the microbial assemblage. Interestingly, Gammaproteobacteria were responsible for most of the siderophore synthesis genes. On the contrary, Bacteroidetes did not synthesize siderophores but accounted for most of the transporters, suggesting a role as cheaters in the competition for siderophores as public goods. This cheating ability of the Bacteroidetes may have contributed to their dominance in the summer.

Spatial distribution of trace metals and associated transport proteins during bacterial infection

Innate immune systems alter the concentrations of trace elements in host niches in response to invading pathogens during infection. This work reports the interplay between d-block metal ions and their associated biomolecules using hyphenated elemental techniques to spatially quantify both elemental distributions and the abundance of specific transport proteins. Here, lung tissues were collected for analyses from naïve and Streptococcus pneumoniae-infected mice fed on a zinc-restricted or zinc-supplemented diet. Spatiotemporal distributions of manganese (55Mn), iron (56Fe), copper (63Cu), and zinc (66Zn) were determined by quantitative laser ablation-inductively coupled plasma-mass spectrometry. The murine transport proteins ZIP8 and ZIP14, which are associated with zinc transport, were also imaged by incorporation of immunohistochemistry techniques into the analytical workflow. Collectively, this work demonstrates the potential of a single instrumental platform suitable for multiplex analyses of tissues and labelled antibodies to investigate complex elemental interactions at the host-pathogen interface. Further, these methods have the potential for broad application to investigations of biological pathways where concomitant measurement of elements and biomolecules is crucial to understand the basis of disease and aid in development of new therapeutic approaches.

Emerging Role of ABC Transporters in Glia Cells in Health and Diseases of the Central Nervous System

ATP-binding cassette (ABC) transporters play a crucial role for the efflux of a wide range of substrates across different cellular membranes. In the central nervous system (CNS), ABC transporters have recently gathered significant attention due to their pivotal involvement in brain physiology and neurodegenerative disorders, such as Alzheimer's disease (AD). Glial cells are fundamental for normal CNS function and engage with several ABC transporters in different ways. Here, we specifically highlight ABC transporters involved in the maintenance of brain homeostasis and their implications in its metabolic regulation. We also show new aspects related to ABC transporter function found in less recognized diseases, such as Huntington's disease (HD) and experimental autoimmune encephalomyelitis (EAE), as a model for multiple sclerosis (MS). Understanding both their impact on the physiological regulation of the CNS and their roles in brain diseases holds promise for uncovering new therapeutic options. Further investigations and preclinical studies are warranted to elucidate the complex interplay between glial ABC transporters and physiological brain functions, potentially leading to effective therapeutic interventions also for rare CNS disorders.

A Bis(Aquated) Mn(II)-Based MRI Contrast Agent with a Rigid Hydroquinazoline Unit: Synthesis, Characterization, and in Vivo MR Imaging Study

Since the finding of nephrogenic systemic fibrosis (NFS) in patients with renal impairment and the long-term accumulation of Gd(III) ions in the central nervous system, the search for nongadolinium ion-based MRI contrast agents made of nutrient metal ions has drawn paramount attention. In this context, the development of Mn(II)-based MRI contrast agents has been a subject of interest for the last few decades. Herein, we report a pentadentate ligand (Li2[BenzPic2]) composed of two picolinate moieties and a rigid 1,2,3,4-tetrahydroquinazoline unit and the corresponding bis(aquated) Mn(II) complex (Complex 1). The complex exhibited high thermodynamic stability (log Kcond = 11.62) and kinetic inertness similar to that of the clinically approved Gd(III)-based contrast agent Magnevist. Complex 1 exerted longitudinal relaxivity (r1) of 5.32 mM-1 s-1 at 1.41 T, 37 °C, pH 7.4, and it increased by 3.6-fold in the presence of serum albumin protein, confirming a substantial rigidifying interaction (albumin association constant KA = 1.66 × 103 M-1) between the protein and the amphiphilic (log P = -0.45) contrast agent. An intravenous dose of 0.08 mmol/kg in a healthy mouse, excellent MRI signal intensity enhancement in the vasculature of the mouse liver, and brightened images of the gallbladder, kidney, and liver were realized.

Antioxidant, antibacterial and antiviral effects of the combination of ginger and garlic extracts

Garlic and ginger are well known as safe alternatives to traditional therapies. Limited information exists regarding antioxidant, antibacterial and antiviral capabilities of the combination of ginger and garlic. Standard methodologies were employed to determine the phytochemical compositions. Antioxidant activities were evaluated through DPPH and FRAP assays. Notably, in DPPH assay, combination of ginger and garlic extracts displayed significantly higher (85.44%, p < 0.005) antioxidant activity even at lower concentrations (6 mg/ml) compared to ginger and garlic extracts alone. Similar findings were observed for FRAP assay. At low concentration of extracts (25 µg/ml), combination of ginger and garlic exhibited significant (p < 0.005) increase in reducing activity (51%) compared to ginger or garlic extracts alone. Significant antibacterial and antiviral activities were exhibited by the combination of both ginger and garlic extracts as compared to ginger and garlic extracts alone. The combined effect of garlic and ginger exhibited a synergistic effect in bacterial and viral growth inhibition. These findings suggest that the diverse phytochemical compositions of the ginger and garlic varieties contribute to their strong antioxidant properties, potentially positioning them as valuable therapeutics for bacterial and viral infections. Further analysis will be required for their widespread utilization and pharmaceutical applications.

Distinct epigenetic signatures of classical and hypervirulent Klebsiella pneumoniae

Emergence and spread of the hypervirulent pathotype of Klebsiella pneumoniae have significantly increased infection rates in community as well as healthcare settings. There is an increasing interest to identify discriminating features between classical K. pneumoniae (cKp) and hypervirulent K. pneumoniae (hvKp) to facilitate our understanding of the rapid emergence and dissemination of the hypervirulent pathotype. Here, we sought to identify unique epigenetic signatures of hvKp pathotype that differ from its classical counterpart using single-base resolution methylome analysis of native DNA sequencing on the Oxford Nanopore Technologies platform. The overall global adenine methylation in GATC motifs (i.e., Dam methylation motif) and cytosine methylation in CCWGG motifs (i.e., Dcm methylation motif) were significantly higher in hvKp isolates compared to that in cKp isolates, irrespective of their position in chromosomes or putative extra-chromosomal genetic elements. Notably, we observed significant enrichment of hypermethylated GATC and CCWGG motifs in the virulome of hvKp compared to hvKp genes not directly associated with virulence. We also observed increased methylation of GATC and CCWGG motifs in the capsule synthesis locus of hvKp isolates compared to cKp isolates. Furthermore, we identified several differentially methylated genes (DMGs) between the two pathotypes; interestingly, these DMGs include metal ion transporters, multidrug efflux pumps, transcriptional regulators of stress response, and genes associated with biofilm formation. Our results highlight hypermethylation of GATC and CCWGG motifs as unique epigenetic signatures of hvKp isolates.IMPORTANCEHypervirulent Klebsiella pneumoniae (hvKp) is a more virulent and rapidly evolving hypermucoviscous pathotype of classical K. pneumoniae (cKp). The hypervirulent pathotype is a major public health concern and is associated with high infection rates in community as well as hospital settings. With the recent emergence of multidrug-resistant hvKp, it has become imperative to investigate non-classical mechanisms such as epigenetics in addition to canonical biochemical and genetic mechanisms that delineate and differentiate the hypervirulent pathotype from its classical counterpart. Here, we identify genome-wide differences in adenine and cytosine methylation marks at well-characterized motifs between the two pathotypes. Overall, significantly higher levels of methylation were observed across chromosomal DNA and extrachromosomal elements in hvKp compared to cKp. Among hvKp isolates, the genes associated with virulence are particularly enriched for methylation marks. Our findings shed light on how epigenetic signatures may help distinguish the pathogenic potential of bacteria.

Functional characterization of a TerC family protein of Riemerella anatipestifer in manganese detoxification and virulence

Manganese (Mn) is an essential element for bacteria, but the overload of manganese is toxic. In a previous study, we showed that the cation diffusion facilitator protein MetA and the resistance-nodulation-division efflux pump MetB are responsible for Mn efflux in the bacterial pathogen Riemerella anatipestifer CH-1. However, whether this bacterium encodes additional manganese efflux proteins is unclear. In this study, we show that R. anatipestifer CH-1 encodes a tellurium resistance C (TerC) family protein with low similarity to other characterized TerC family proteins. Compared to the wild type (WT), the terC mutant of R. anatipestifer CH-1 (∆terC) is sensitive to Mn(II) intoxication. The ability of TerC to export manganese is higher than that of MetB but lower than that of MetA. Consistently, terC deletion (∆terC) led to intracellular accumulation of Mn2+ under excess manganese conditions. Further study showed that ∆terC was more sensitive than the WT to the oxidant hypoclorite but not to hydrogen peroxide. Mutagenesis studies showed that the mutant at amino acid sites of Glu116 (E116), Asp122 (D122), Glu245 (E245) Asp248 (D248), and Asp254 (D254) may be involved in the ability of TerC to export manganese. The transcription of terC was upregulated under excess manganese and downregulated under iron-limited conditions. However, this was not dependent on the manganese metabolism regulator MetR. In contrast to a strain lacking the manganese efflux pump MetA or MetB, the terC mutant is attenuated in virulence in a duckling model of infection due to increased sensitivity to duck serum. Finally, comparative analysis showed that homologs of TerC are distributed across the bacterial kingdom, suggesting that TerC exerts a conserved manganese efflux function.IMPORTANCERiemerella anatipestifer is a notorious bacterial pathogen of ducks and other birds. In R. anatipestifer, the genes involved in manganese efflux have not been completely identified, although MetA and MetB have been identified as two manganese exporters. Additionally, the function of TerC family proteins in manganese efflux is controversial. Here, we demonstrated that a TerC family protein helps prevent Mn(II) intoxication in R. anatipestifer and that the ability of TerC to export manganese is intermediate compared to that of MetA and MetB. Sequence analysis and mutagenesis studies showed that the conserved key amino sites of TerC are Glu116, Asp122, Glu245, Asp248, and Asp254. The transcription of terC was regulated by manganese excess and iron limitation. Finally, we show that TerC plays a role in the virulence of R. anatipestifer due to the increased sensitivity to duck serum, rather than the increased sensitivity to manganese. Taken together, these results expand our understanding of manganese efflux and the pathogenic mechanisms of R. anatipestifer.

Zinc acquisition and its contribution to Klebsiella pneumoniae virulence

Klebsiella pneumoniae is a World Health Organization priority pathogen and a significant clinical concern for infections of the respiratory and urinary tracts due to widespread and increasing resistance to antimicrobials. In the absence of a vaccine, there is an urgent need to identify novel targets for therapeutic development. Bacterial pathogens, including K. pneumoniae, require the d-block metal ion zinc as an essential micronutrient, which serves as a cofactor for ~6% of the proteome. During infection, zinc acquisition necessitates the use of high affinity uptake systems to overcome niche-specific zinc limitation and host-mediated nutritional immunity. Here, we report the identification of ZnuCBA and ZniCBA, two ATP-binding cassette permeases that are highly conserved in Klebsiella species and contribute to K. pneumoniae AJ218 zinc homeostasis, and the high-resolution structure of the zinc-recruiting solute-binding protein ZniA. The Znu and Zni permeases appear functionally redundant with abrogation of both systems required to reduce K. pneumoniae zinc accumulation. Disruption of both systems also exerted pleiotropic effects on the homeostasis of other d-block elements. Zinc limitation perturbed K. pneumoniae cell morphology and compromised resistance to stressors, such as salt and oxidative stress. The mutant strain lacking both systems showed significantly impaired virulence in acute lung infection models, highlighting the necessity of zinc acquisition in the virulence and pathogenicity of K. pneumoniae.

Milk microbiome in the first month of lactation and at weaning from ewes supplemented with zinc pre- and postpartum

Mastitis is an important disease with economic and welfare implications in both clinical and subclinical states. The aim of this research was to sequence the hypervariable V4 region of the 16S rRNA gene to describe the microbial diversity and taxonomy of milk from clinically healthy ewes (Rambouillet, WF = 9; Hampshire, BF = 5). Experimental ewes represented a subset of a larger study assessing the impacts of divergent dietary zinc (Zn) concentrations [1 × National Academics of Sciences, Engineering, and Medicine (NASEM) recommendations = CON or 3 × NASEM recommendations = ZnTRT] throughout late gestation and lactation. Milk was collected at four periods during early lactation (18 to 24 h, 7 d, 14 d, and 21 d postpartum) and at weaning (84 ± 14 d postpartum). Somatic cell counts (SCC) were quantified, averaged, and classed (low: < 500 × 103; medium: 500 × 103 - 100 × 104; high: > 100 × 104 cells/mL). Milk samples (n = 67) were sequenced to identify bacteria and archaea; the most abundant phyla were Actinobacteria, Bacteroidetes, Cyanobacteria, Euryarchaeota, Firmicutes, Fusobacteria, Lentisphaerae, Proteobacteria, Spirochaetes, Tenericutes, Saccharibacteria TM7, and Verrucomicrobia. Mastitis pathogens were among the most relatively abundant genera, including Staphylococcus, Mannheimia, Corynebacterium, and Pseudomonas. Effects of breed, dietary Zn concentration, SCC class, and their two-way interactions on milk microbiome diversity and taxonomy were assessed within early lactation (using a repeated measures model) and weaning samples. Alpha-diversity metrics included Pielou's evenness, Faith's phylogenetic diversity, and Shannon's entropy indices. The main and interactive effects between Zn treatment, breed, SCC class, and period were variable in early lactation and not evident in weaning samples. Milk from BF ewes had increased Faith's phylogenetic diversity and Shannon's entropy, and differed in unweighted UniFrac composition (P ≤ 0.10). Milk from CON ewes had a reduced rate of composition change through early lactation (P = 0.02) indicating greater microbiome stability than ZnTRT ewe milk. These results support that milk is not sterile, and breed, dietary Zn concentration, and SCC class variably affect the milk microbiome. Findings from the current study provide important foundational insights into the effects of increased dietary Zn supplementation on longitudinal changes in the milk microbiome and associations with mammary gland health and mastitis.

Imipenem-metal complexes: Computational analysis and toxicity studies with wastewater model microorganisms

The occurrence of antibiotic residues in diverse water sources has long been acknowledged as a potential health concern due to the emergence and spread of antibiotic-resistant bacteria and genes. However, there have been limited studies into the presence of antibiotic-metal complexes (AMCs) in real-time wastewater matrices, and their impact on wastewater microbial communities. The present work, in this regard, investigated the stability of Imipenem-metal complexes (Me = Mg (II), Ca (II), Fe (II), Cu (II), and Al (III)) with computational studies, stoichiometry with potentiometric measurements, and their antibacterial activity towards wastewater model microorganisms- Bacillus subtilis (B. subtilis) and Escherichia coli (E. Coli) by Colony Forming Unit (CFU) method. The lower energy of Imipenem-metal complexes than the parent antibiotic- Imipenem, during energy optimization using density functional (DFT) methods, revealed that metal interactions of Imipenem stabilize the drug by minimizing its energy. Further, CFU studies indicated that these complexes display higher antimicrobial activity than parent antibiotics. The electron delocalization over the entire chelated system (AMCs) reduces polarity and increases the lipophilicity of the complexes, thereby facilitating stronger interaction between AMCs and the bacterial cell membrane. Results indicate increased antibacterial activity of Imipenem-metal complexes for both E. coli and B. subtilis. The antibacterial activity, was however, more pronounced in B. subtilis, with >97% growth inhibition for metal complexes of Imipenem (at a Minimum Inhibitory Concentration of 20 nM or 6 ppb (i.e., MIC90)), for both the stoichiometric ratios (metal to ligand) ratios (M: L 1: 1 and 2: 1). All around, with increased stability and toxicity, AMCs are emerging as contaminants of concern and demand immediate attention to devise methods for their removal.

Three novel marine species of the genus Reichenbachiella exhibiting degradation of complex polysaccharides

Three novel strains designated ABR2-5T, BKB1-1T, and WSW4-B4T belonging to the genus Reichenbachiella of the phylum Bacteroidota were isolated from algae and mud samples collected in the West Sea, Korea. All three strains were enriched for genes encoding up to 216 carbohydrate-active enzymes (CAZymes), which participate in the degradation of agar, alginate, carrageenan, laminarin, and starch. The 16S rRNA sequence similarities among the three novel isolates were 94.0%-94.7%, and against all three existing species in the genus Reichenbachiella they were 93.6%-97.2%. The genome sizes of the strains ABR2-5T, BKB1-1T, and WSW4-B4T were 5.5, 4.4, and 5.0 Mb, respectively, and the GC content ranged from 41.1%-42.0%. The average nucleotide identity and the digital DNA-DNA hybridization values of each novel strain within the isolates and all existing species in the genus Reichenbachiella were in a range of 69.2%-75.5% and 17.7-18.9%, respectively, supporting the creation of three new species. The three novel strains exhibited a distinctive fatty acid profile characterized by elevated levels of iso-C15:0 (37.7%-47.4%) and C16:1 ω5c (14.4%-22.9%). Specifically, strain ABR2-5T displayed an additional higher proportion of C16:0 (13.0%). The polar lipids were phosphatidylethanolamine, unidentified lipids, aminolipids, and glycolipids. Menaquinone-7 was identified as the respiratory quinone of the isolates. A comparative genome analysis was performed using the KEGG, RAST, antiSMASH, CRISPRCasFinder, dbCAN, and dbCAN-PUL servers and CRISPRcasIdentifier software. The results revealed that the isolates harbored many key genes involved in central metabolism for the synthesis of essential amino acids and vitamins, hydrolytic enzymes, carotenoid pigments, and antimicrobial compounds. The KEGG analysis showed that the three isolates possessed a complete pathway of dissimilatory nitrate reduction to ammonium (DNRA), which is involved in the conservation of bioavailable nitrogen within the ecosystem. Moreover, all the strains possessed genes that participated in the metabolism of heavy metals, including arsenic, copper, cobalt, ferrous, and manganese. All three isolated strains contain the class 2 type II subtype C1 CRISPR-Cas system in their genomes. The distinguished phenotypic, chemotaxonomic, and genomic characteristics led us to propose that the three strains represent three novel species in the genus Reichenbachiella: R. ulvae sp. nov. (ABR2-5T = KCTC 82990T = JCM 35839T), R. agarivorans sp. nov. (BKB1-1T = KCTC 82964T = JCM 35840T), and R. carrageenanivorans sp. nov. (WSW4-B4T = KCTC 82706T = JCM 35841T).

Bioprotection Potential of Lacticaseibacillus rhamnosus LRH01 and Lactiplantibacillus plantarum LP01 against Spoilage-Associated Penicillium Strains in Yoghurt

Penicillium spp. are considered a major spoilage fungus in dairy products. Due to the growing concerns over food safety issues and the demand for "clean label" food products from consumers, the use of lactic acid bacteria (LAB) as a bioprotective tool to control fungal spoilage of dairy products appears to be a promising alternative. Here, the antifungal activities of ten LAB cultures against five dairy-spoilage-associated Penicillium strains were studied in a model system, and the most potent bioprotective cultures were further tested in yoghurt. Lacticaseibacillus rhamnosus (L. rhamnosus) LRH01 and Lactiplantibacillus plantarum (L. plantarum) LP01 exhibited potent antifungal efficacy at low concentrations. The inhibitory effects of cell-containing fermentates (C-fermentates), cell-free fermentates (CF-fermentates), and volatiles produced by the two cultures were tested in a yoghurt serum medium. The C-fermentates showed antifungal effects, while the removal of cells from C-fermentates led to decreased antifungal activities. Volatiles alone displayed some antifungal efficiency, but less than the fermentates. In a yoghurt matrix, the specific effect of manganese depletion by the bioprotective cultures on mold growth was investigated. Here, the LAB cultures could completely suppress the growth of molds, while addition of manganese partially or fully restored the mold growth, demonstrating that manganese depletion played a key role in the antifungal activity of the tested LAB cultures in the yoghurt matrix. Both L. plantarum LP01 and L. rhamnosus LRH01 showed efficient antifungal activities in the yoghurt serum, while L. rhamnosus LRH01 exhibited the most potent inhibitory effects on Penicillium strains when added during the processing of the yoghurt with subsequent storage at 7 °C for 22 days. Our findings suggested that L. rhamnosus LRH01 could be a promising bioprotective culture for yoghurt biopreservation.

Toxins from harmful algal blooms: How copper and iron render chalkophore a predictor of microcystin production

Research on harmful algal blooms has focused on macronutrients, yet recent research increasingly indicates that understanding micronutrient roles is also important in the development of effective environmental management interventions. Here, we report results on metallophore production from mesocosms amended with copper and iron (enzymatic co-factors in photosynthetic electron transport) to probe questions of how cyanobacteria navigate the divide between copper nutrition, copper toxicity, and issues with iron bioavailability. These experiments utilized Microcystis, Chlorella and Desmodesmus spp., in mono- and mixed-cultures in lake water from a large, hypereutrophic lake (Taihu, China). To initiate experiments, copper and iron amendments were added to mesocosms containing algae that had been acclimated to achieve a state of copper and iron limitation. Mesocosms were analyzed over time for a range of analytes including algal growth parameters, algal assemblage progression, copper/iron concentrations and biomolecule production of chalkophore, siderophore and total microcystins. Community Trajectory Analysis and other multivariate methods were used for analysis resulting in our findings: 1) Microcystis spp. manage copper/iron requirements though a dynamically phased behavior of chalkophore/siderophore production according to their copper and iron limitation status (chalkophore correlates with Cu concentration, R2 = 0.99, and siderophore correlates with the sum of Cu and Fe concentrations, R2 = 0.98). 2) A strong correlation was observed between the production of chalkophore and the cyanobacterial toxin microcystin (R2 = 0.76)-Chalkophore is a predictor of microcystin production. 3) Based on our results and literature, we posit that Microcystis spp. produces microcystin in response to copper/iron availability to manage photosystem productivity and effect an energy-saving status. Results from this work underscore the importance of micronutrients in influencing harmful algal bloom progression and represents a major advance in understanding the ecological function for the cyanobacterial toxin microcystin as a hallmark of micronutrient limitation stress.

Metal Messengers: Communication in the Bacterial World through Transition-Metal-Sensing Two-Component Systems

Bacteria survive in highly dynamic and complex environments due, in part, to the presence of systems that allow the rapid control of gene expression in the presence of changing environmental stimuli. The crosstalk between intra- and extracellular bacterial environments is often facilitated by two-component signal transduction systems that are typically composed of a transmembrane histidine kinase and a cytosolic response regulator. Sensor histidine kinases and response regulators work in tandem with their modular domains containing highly conserved structural features to control a diverse array of genes that respond to changing environments. Bacterial two-component systems are widespread and play crucial roles in many important processes, such as motility, virulence, chemotaxis, and even transition metal homeostasis. Transition metals are essential for normal prokaryotic physiological processes, and the presence of these metal ions may also influence pathogenic virulence if their levels are appropriately controlled. To do so, bacteria use transition-metal-sensing two-component systems that bind and respond to rapid fluctuations in extracytosolic concentrations of transition metals. This perspective summarizes the structural and metal-binding features of bacterial transition-metal-sensing two-component systems and places a special emphasis on understanding how these systems are used by pathogens to establish infection in host cells and how these systems may be targeted for future therapeutic developments.

A Comprehensive Review on the Roles of Metals Mediating Insect-Microbial Pathogen Interactions

Insects and microbial pathogens are ubiquitous and play significant roles in various biological processes, while microbial pathogens are microscopic organisms that can cause diseases in multiple hosts. Insects and microbial pathogens engage in diverse interactions, leveraging each other's presence. Metals are crucial in shaping these interactions between insects and microbial pathogens. However, metals such as Fe, Cu, Zn, Co, Mo, and Ni are integral to various physiological processes in insects, including immune function and resistance against pathogens. Insects have evolved multiple mechanisms to take up, transport, and regulate metal concentrations to fight against pathogenic microbes and act as a vector to transport microbial pathogens to plants and cause various plant diseases. Hence, it is paramount to inhibit insect-microbe interaction to control pathogen transfer from one plant to another or carry pathogens from other sources. This review aims to succinate the role of metals in the interactions between insects and microbial pathogens. It summarizes the significance of metals in the physiology, immune response, and competition for metals between insects, microbial pathogens, and plants. The scope of this review covers these imperative metals and their acquisition, storage, and regulation mechanisms in insect and microbial pathogens. The paper will discuss various scientific studies and sources, including molecular and biochemical studies and genetic and genomic analysis.

Bioimaging tools reveal copper processing in fish cells by mitophagy

As an essential trace metal, copper (Cu) regulation, distribution and detoxification among different cellular organelles remain much unknown. In the current study, bioimaging tool was used in visualizing the locations of Cu among different organelles in fish fin cells isolated from rabbitfish Siganus fuscescens. Exposure concentration of Cu directly affected the Cu bioaccumulation and toxicity. When the exposure dosage of Cu reached 100 µM, it began to damage the cells and affect the cell viability after 10 min of exposure. Remarkably, while various Cu concentrations (50∼150 µM) initially reduced the cell viability, they did not lead to a further loss in viability over extended exposure period. Upon entry to the cells, Cu was mainly targeted to the mitochondria whose number, size and network responded immediately to the incoming Cu. However, Cu toxicity did not increase time-dependently, strongly indicating that these mitochondria damaged by Cu could be removed and its cytotoxicity could be relieved. Bioimaging results showed that lysosomes interacted with the mitochondria, which were subsequently digested within a few minutes. Meanwhile the lysosomal number increased, and the size and pH of lysosomes decreased. These reactions were in line with the observed mitophagy, suggesting that mitochondrial Cu could be detoxified, and the damaged mitochondria were removed by lysosome via mitophagy. By further purifying the cellular organelles, the mitochondrial and lysosomal Cu amounts were quantified and found to be in line with the imaging results. The present study suggested that excessive mitochondrial Cu could be removed via mitophagy to relieve the Cu toxicity.

Epistatic interactions between the high pathogenicity island and other iron uptake systems shape Escherichia coli extra-intestinal virulence

The intrinsic virulence of extra-intestinal pathogenic Escherichia coli is associated with numerous chromosomal and/or plasmid-borne genes, encoding diverse functions such as adhesins, toxins, and iron capture systems. However, the respective contribution to virulence of those genes seems to depend on the genetic background and is poorly understood. Here, we analyze genomes of 232 strains of sequence type complex STc58 and show that virulence (quantified in a mouse model of sepsis) emerged in a sub-group of STc58 due to the presence of the siderophore-encoding high-pathogenicity island (HPI). When extending our genome-wide association study to 370 Escherichia strains, we show that full virulence is associated with the presence of the aer or sit operons, in addition to the HPI. The prevalence of these operons, their co-occurrence and their genomic location depend on strain phylogeny. Thus, selection of lineage-dependent specific associations of virulence-associated genes argues for strong epistatic interactions shaping the emergence of virulence in E. coli.

In Silico Analysis of Changes in Predicted Metabolic Capabilities of Intestinal Microbiota after Fecal Microbial Transplantation for Treatment of Recurrent Clostridioides difficile Infection

IMPORTANCE

Although highly effective in treating recurrent Clostridioides difficile infection (RCDI), the mechanisms of action of fecal microbial transplantation (FMT) are not fully understood.

AIM

The aim of this study was to explore microbially derived products or pathways that could contribute to the therapeutic efficacy of FMT.

METHODS

Stool shotgun metagenomic sequencing data from 18 FMT-treated RCDI patients at 4 points in time were used for the taxonomic and functional profiling of their gut microbiome. The abundance of the KEGG orthology (KO) groups was subjected to univariate linear mixed models to assess the significance of the observed differences between 0 (pre-FMT), 1, 4, and 12 weeks after FMT.

RESULTS

Of the 59,987 KO groups identified by shotgun metagenomic sequencing, 27 demonstrated a statistically significant change after FMT. These KO groups are involved in many cellular processes, including iron homeostasis, glycerol metabolism, and arginine regulation, all of which have been implicated to play important roles in bacterial growth and virulence in addition to modulating the intestinal microbial composition.

CONCLUSION

Our findings suggest potential changes in key KO groups post-FMT, which may contribute to FMT efficacy beyond the restored microbial composition/diversity and metabolism of bile acids and short-chain fatty acids. Future larger studies that include a fecal metabolomics analysis combined with animal model validation work are required to further elucidate the molecular mechanisms.

Metal manipulators and regulators in human pathogens: A comprehensive review on microbial redox copper metalloenzymes "multicopper oxidases and superoxide dismutases"

The chemistry of metal ions with human pathogens is essential for their survival, energy generation, redox signaling, and niche dominance. To regulate and manipulate the metal ions, various enzymes and metal chelators are present in pathogenic bacteria. Metalloenzymes incorporate transition metal such as iron, zinc, cobalt, and copper in their reaction centers to perform essential metabolic functions; however, iron and copper have gained more importance. Multicopper oxidases have the ability to perform redox reaction on phenolic substrates with the help of copper ions. They have been reported from Enterobacteriaceae, namely Salmonella enterica, Escherichia coli, and Yersinia enterocolitica, but their role in virulence is still poorly understood. Similarly, superoxide dismutases participate in reducing oxidative stress and allow the survival of pathogens. Their role in virulence and survival is well established in Salmonella typhimurium and Mycobacterium tuberculosis. Further, to ensure survival against stress, like metal starvation or metal toxicity, redox metalloenzymes and metal transportation systems of pathogens actively participate in metal homeostasis. Recently, the omics and protein structure biology studies have helped to predict new targets for regulation the colonization potential of the pathogenic strains. The current review is focused on the major roles of redox metalloenzymes, especially MCOs and SODs of human pathogenic bacteria.

Manganese Efflux Achieved by MetA and MetB Affects Oxidative Stress Resistance and Iron Homeostasis in Riemerella anatipestifer

In bacteria, manganese homeostasis is controlled by import, regulation, and efflux. Here, we identified 2 Mn exporters, MetA and MetB (manganese efflux transporters A and B), in Riemerella anatipestifer CH-1, encoding a putative cation diffusion facilitator (CDF) protein and putative resistance-nodulation-division (RND) efflux pump, respectively. Compared with the wild type (WT), ΔmetA, ΔmetB, and ΔmetAΔmetB exhibited sensitivity to manganese, since they accumulated more intracellular Mn2+ than the WT under excess manganese conditions, while the amount of iron in the mutants was decreased. Moreover, ΔmetA, ΔmetB, and ΔmetAΔmetB were more sensitive to the oxidant NaOCl than the WT. Further study showed that supplementation with iron sources could alleviate manganese toxicity and that excess manganese inhibited bacterial cell division. RNA-Seq showed that manganese stress resulted in the perturbation of iron metabolism genes, further demonstrating that manganese efflux is critical for iron homeostasis. metA transcription was upregulated under excess manganese but was not activated by MetR, a DtxR family protein, although MetR was also involved in manganese detoxification, while metB transcription was downregulated under iron depletion conditions and in fur mutants. Finally, homologues of MetA and MetB were found to be mainly distributed in members of Flavobacteriaceae. Specifically, MetB represents a novel manganese exporter in Gram-negative bacteria. IMPORTANCE Manganese is required for the function of many proteins in bacteria, but in excess, manganese can mediate toxicity. Therefore, the intracellular levels of manganese must be tightly controlled. Manganese efflux transporters have been characterized in some other bacteria; however, their homologues could not be found in the genome of Riemerella anatipestifer through sequence comparison. This indicated that other types of manganese efflux transporters likely exist. In this study, we characterized 2 transporters, MetA and MetB, that mediate manganese efflux in R. anatipestifer in response to manganese overload. MetA encodes a putative cation diffusion facilitator (CDF) protein, which has been characterized as a manganese transporter in other bacteria, while this is the first observation of a putative resistance-nodulation-division (RND) transporter contributing to manganese export in Gram-negative bacteria. In addition, the mechanism of manganese toxicity was studied by observing morphological changes and by transcriptome sequencing. Taken together, these results are important for expanding our understanding of manganese transporters and revealing the mechanism of manganese toxicity.

The action of phytochemicals in biofilm control

Covering: 2009 to 2021Antimicrobial resistance is now rising to dangerously high levels in all parts of the world, threatening the treatment of an ever-increasing range of infectious diseases. This has becoming a serious public health problem, especially due to the emergence of multidrug-resistance among clinically important bacterial species and their ability to form biofilms. In addition, current anti-infective therapies have low efficacy in the treatment of biofilm-related infections, leading to recurrence, chronicity, and increased morbidity and mortality. Therefore, it is necessary to search for innovative strategies/antibacterial agents capable of overcoming the limitations of conventional antibiotics. Natural compounds, in particular those obtained from plants, have been exhibiting promising properties in this field. Plant secondary metabolites (phytochemicals) can act as antibiofilm agents through different mechanisms of action from the available antibiotics (inhibition of quorum-sensing, motility, adhesion, and reactive oxygen species production, among others). The combination of different phytochemicals and antibiotics have revealed synergistic or additive effects in biofilm control. This review aims to bring together the most relevant reports on the antibiofilm properties of phytochemicals, as well as insights into their structure and mechanistic action against bacterial pathogens, spanning December 2008 to December 2021.

Heavy Metals Concentration in Sardina pilchardus (Walbaum, 1792) from the Moroccan Mediterranean Coast and Potential Human Health Risk Assessment

Due to their toxicity, long persistence, bioaccumulative nature, and biomagnification in the food chain, heavy metals pose a serious hazard. The aim of this study was to evaluate the health risks associated with the consumption of Sardina pilchardus (Walbaum, 1792) and to study the spatiotemporal dynamics of four potentially toxic metallic elements. Three hundred and sixty specimens of sardine were collected between December 2020 and October 2021 at three Mediterranean coast sites, Beni-Ensar, Ras el Ma, and El-Houceima, in the northeast region of Morocco. The toxic metallic elements were evaluated by assessing the contamination level of cadmium (Cd), mercury (Hg), lead (Pb), and arsenic (As) in the muscle, liver, and gills of sardine from the Mediterranean Moroccan coast. The results showed a significant effect of the study area, organ, and season ( $p>0.05$ ) on Moroccan Mediterranean sardine heavy metal contamination levels. Regardless the location and season, the liver presents the higher concentration of the studied metals ( $p<0.05$ ). The highest heavy metal concentrations of Cd (0.408 μg·g−1 wet weight (ww)), Hg (0.044 μg·g−1 ww), and As (6.74 μg·g−1 ww) were found in winter while the concentration of Pb was the highest in autumn (0.056 μg·g−1 ww). Furthermore, the lowest contamination of metal levels was found in the spring. El-Houceima region contains the highest values for Hg (0.093 μg·g−1 ww), Pb (0.018 μg·g−1 ww), and As (7.73 μg·g−1 ww). However, the highest values for Cd (0.172 μg·g−1 ww) were recorded in Beni-Ensar. Regarding the assessment of possible risks to human health, the results showed that the indices are below the established safety values in the case of estimated weekly intake, and target hazard quotient (THQ). In contrast, the carcinogenic risk index and total THQ were above the threshold limits and thus represented a potential carcinogenic risk to human health.

Divalent metal ion binding to Staphylococcus aureus FeoB transporter regions

Transition metal ions such as iron, copper, zinc, manganese or, nickel are essential in many biological processes. Bacteria have developed a number of mechanisms for their acquisition and transport, in which numerous of proteins and smaller molecules are involved. One of the representatives of these proteins is FeoB, which belongs to the Feo (ferrous ion transporter) family. Although ferrous iron transport system is widespread among microorganisms, it is still poorly described in Gram-positive pathogens, such as Staphylococcus aureus. In this work, combined potentiometric and spectroscopic studies (UV-Vis, CD and EPR) were carried out to determine Cu(II), Fe(II) and Zn(II) binding modes to FeoB fragments (Ac-IDYHKLMK-NH₂, Ac-ETSHDKY-NH₂, and Ac-SFLHMVGS-NH₂). For the first time iron(II) complexes with peptides were characterized by potentiometry. All studied ligands are able to form a variety of thermodynamically stable complexes with transition metal ions. It was concluded that among the studied systems, the most effective metal ion binding is observed for the Ac-ETSHDKY-NH₂ peptide. Moreover, comparing preferences of all ligands towards different metal ions, copper(II) complexes are the most stable ones at physiological pH.

Comparative genomic analysis provides insight into the phylogeny and potential mechanisms of adaptive evolution of Sphingobacterium sp. CZ-2

Sphingobacterium is a class of Gram-negative, non-fermentative bacilli that have received widespread attention due to their broad ecological distribution and oil degradation ability, but are rarely involved in infections. In this manuscript, a novel Sphingobacterium strain isolated from wildfire-infected tobacco leaves was named Sphingobacterium sp. CZ-2. NGS and TGS sequencing results showed a whole genome of 3.92 Mb with 40.68 mol% GC content and containing 3,462 protein-coding genes, 9 rRNA-coding genes and 50 tRNA-coding genes. Phylogenetic analysis, ANI and dDDH calculations all supported that Sphingobacterium sp. CZ-2 represented a novel species of the genus Sphingobacterium. Analysis of the specific genes of Sphingobacterium sp. CZ-2 by comparative genomics revealed that metal transport proteins encoded by the troD and cusA genes could maintain the balance of heavy metal ion concentrations in the internal environment of bacteria and avoid heavy metal toxicity while meeting the needs of growth and reproduction, and transport proteins encoded by the malG gene could keep nutrients required for the survival of bacteria. Synteny and genome evolutionary analyses of Sphingobacterium strains implicated that the gene family contraction as a major process in genome evolution, with insertional sequences leading to mutations, deletions and reversals of genes that help bacteria to withstand complex environmental changes. Complete genome sequencing and systematic comparative genomic analysis will contribute new insights into the adaptive evolution of this novel species and the genus Sphingobacterium.

A Manganese-independent Aldolase Enables Staphylococcus aureus To Resist Host-imposed Metal Starvation

The preferred carbon source of Staphylococcus aureus and many other pathogens is glucose, and its consumption is critical during infection. However, glucose utilization increases the cellular demand for manganese, a nutrient sequestered by the host as a defense against invading pathogens. Therefore, bacteria must balance glucose metabolism with the increasing demand that metal-dependent processes, such as glycolysis, impose upon the cell. A critical regulator that enables S. aureus to resist nutritional immunity is the ArlRS two-component system. This work revealed that ArlRS regulates the expression of FdaB, a metal-independent fructose 1,6-bisphosphate aldolase. Further investigation revealed that when S. aureus is metal-starved by the host, FdaB functionally replaces the metal-dependent isozyme FbaA, thereby allowing S. aureus to resist host-imposed metal starvation in culture. Although metal-dependent aldolases are canonically zinc-dependent, this work uncovered that FbaA requires manganese for activity and that FdaB protects S. aureus from manganese starvation. Both FbaA and FdaB contribute to the ability of S. aureus to cause invasive disease in wild-type mice. However, the virulence defect of a strain lacking FdaB was reversed in calprotectin-deficient mice, which have defects in manganese sequestration, indicating that this isozyme contributes to the ability of this pathogen to overcome manganese limitation during infection. Cumulatively, these observations suggest that the expression of the metal-independent aldolase FdaB allows S. aureus to alleviate the increased demand for manganese that glucose consumption imposes, and highlights the cofactor flexibility of even established metalloenzyme families. IMPORTANCE Staphylococcus aureus and other pathogens consume glucose during infection. Glucose utilization increases the demand for transition metals, such as manganese, a nutrient that the host limits as a defense mechanism against invading pathogens. Therefore, pathogenic bacteria must balance glucose and manganese requirements during infection. The two-component system ArlRS is an important regulator that allows S. aureus to adapt to both glucose and manganese starvation. Among the genes regulated by ArlRS is the metal-independent fructose 1,6-bisphosphate aldolase fdaB, which functionally substitutes for the metal-dependent isoenzyme FbaA and enables S. aureus to survive host-imposed manganese starvation. Unexpectedly, and differing from most characterized metal-dependent aldolases, FbaA requires manganese for activity. Cumulatively, these findings reveal a new mechanism for overcoming nutritional immunity as well as the cofactor plasticity of even well-characterized metalloenzyme families.

Fur functions as an activator of T6SS-mediated bacterial dominance and virulence in Aeromonas hydrophila

Aeromonas hydrophila, a ubiquitous bacterium in aquatic habitats with broad host ranges, has earned the nickname of a 'Jack-of-all-trades'. However, there is still a limited understanding of the mechanism of how this bacterium fit the competition with other species in dynamic surroundings. The type VI secretion system (T6SS) is macromolecular machinery found in Gram-negative bacteria's cell envelope that is responsible for bacterial killing and/or pathogenicity toward different host cells. In this study, the depression of A. hydrophila T6SS under iron-limiting conditions was detected. The ferric uptake regulator (Fur) was then found to act as an activator of T6SS by directly binding to the Fur box region in vipA promoter in the T6SS gene cluster. The transcription of vipA was repressed in Δfur. Moreover, the inactivation of Fur resulted in considerable defects in the interbacterial competition activity and pathogenicity of A. hydrophila in vitro and in vivo. These findings provide the first direct evidence that Fur positively regulates the expression and functional activity of T6SS in Gram-negative bacteria and will help to understand the fascinating mechanism of competitive advantage for A. hydrophila in different ecological niches.

Radiometal chelators for infection diagnostics

Infection of native tissues or implanted devices is common, but clinical diagnosis is frequently difficult and currently available noninvasive tests perform poorly. Immunocompromised individuals (for example transplant recipients, or those with cancer) are at increased risk. No imaging test in clinical use can specifically identify infection, or accurately differentiate bacterial from fungal infections. Commonly used [18F]fluorodeoxyglucose (18FDG) positron emission computed tomography (PET/CT) is sensitive for infection, but limited by poor specificity because increased glucose uptake may also indicate inflammation or malignancy. Furthermore, this tracer provides no indication of the type of infective agent (bacterial, fungal, or parasitic). Imaging tools that directly and specifically target microbial pathogens are highly desirable to improve noninvasive infection diagnosis and localization. A growing field of research is exploring the utility of radiometals and their chelators (siderophores), which are small molecules that bind radiometals and form a stable complex allowing sequestration by microbes. This radiometal-chelator complex can be directed to a specific microbial target in vivo, facilitating anatomical localization by PET or single photon emission computed tomography. Additionally, bifunctional chelators can further conjugate therapeutic molecules (e.g., peptides, antibiotics, antibodies) while still bound to desired radiometals, combining specific imaging with highly targeted antimicrobial therapy. These novel therapeutics may prove a useful complement to the armamentarium in the global fight against antimicrobial resistance. This review will highlight current state of infection imaging diagnostics and their limitations, strategies to develop infection-specific diagnostics, recent advances in radiometal-based chelators for microbial infection imaging, challenges, and future directions to improve targeted diagnostics and/or therapeutics.

A Fur-regulated type VI secretion system contributes to oxidative stress resistance and virulence in Yersinia pseudotuberculosis

The type VI secretion system (T6SS) is a widespread protein secretion apparatus deployed by many Gram-negative bacterial species to interact with competitor bacteria, host organisms, and the environment. Yersinia pseudotuberculosis T6SS4 was recently reported to be involved in manganese acquisition; however, the underlying regulatory mechanism still remains unclear. In this study, we discovered that T6SS4 is regulated by ferric uptake regulator (Fur) in response to manganese ions (Mn2+), and this negative regulation of Fur was proceeded by specifically recognizing the promoter region of T6SS4 in Y. pseudotuberculosis. Furthermore, T6SS4 is induced by low Mn2+ and oxidative stress conditions via Fur, acting as a Mn2+-responsive transcriptional regulator to maintain intracellular manganese homeostasis, which plays important role in the transport of Mn2+ for survival under oxidative stress. Our results provide evidence that T6SS4 can enhance the oxidative stress resistance and virulence for Y. pseudotuberculosis. This study provides new insights into the regulation of T6SS4 via the Mn2+-dependent transcriptional regulator Fur, and expands our knowledge of the regulatory mechanisms and functions of T6SS from Y. pseudotuberculosis.

Alterations of the intestinal microbiota in age-related macular degeneration

Purpose

Age-related macular degeneration (AMD) is the leading cause of vision loss in those over the age of 50. Recently, intestinal microbiota has been reported to be involved in the pathogenesis of ocular diseases. The purpose of this study was to discover more about the involvement of the intestinal microbiota in AMD patients.

Methods

Fecal samples from 30 patients with AMD (AMD group) and 17 age- and sex-matched healthy controls (control group) without any fundus disease were collected. DNA extraction, PCR amplification, and 16S rRNA gene sequencing of the samples were performed to identify intestinal microbial alterations. Further, we used BugBase for phenotypic prediction and PICRUSt2 for KEGG Orthology (KO) as well as metabolic feature prediction.

Results

The intestinal microbiota was found to be significantly altered in the AMD group. The AMD group had a significantly lower level of Firmicutes and relatively higher levels of Proteobacteria and Bacteroidota compared to those in the control group. At the genus level, the AMD patient group showed a considerably higher proportion of Escherichia-Shigella and lower proportions of Blautia and Anaerostipes compared with those in the control group. Phenotypic prediction revealed obvious differences in the four phenotypes between the two groups. PICRUSt2 analysis revealed KOs and pathways associated with altered intestinal microbiota. The abundance of the top eight KOs in the AMD group was higher than that in the control group. These KOs were mainly involved in lipopolysaccharide biosynthesis.

Conclusion

The findings of this study indicated that AMD patients had different gut microbiota compared with healthy controls, and that AMD pathophysiology might be linked to changes in gut-related metabolic pathways. Therefore, intestinal microbiota might serve as non-invasive indicators for AMD clinical diagnosis and possibly also as AMD treatment targets.

Resistance Mechanism and Physiological Effects of Microcin Y in Salmonella enterica subsp. enterica Serovar Typhimurium

Salmonella bacteria pose a significant threat to animal husbandry and human health due to their virulence and multidrug resistance. The lasso peptide MccY is a recently discovered antimicrobial peptide that acts against various serotypes of Salmonella. In this study, we further explore the resistance mechanism and activity of MccY. Mutants of Ton system genes, including tonB, exbB, and exbD, in Salmonella enterica subsp. enterica serovar Typhimurium were constructed, and the MICs to MccY exhibited significant increases in these deletion mutants compared to the MIC of the parent strain. Subsequently, MccY resistance was quantitatively analyzed, and these mutants also showed greatly reduced rates of killing, even with a high concentration of MccY. In addition, a minimal medium with low iron environment enhanced the sensitivity of these mutants to MccY. Measurements of a series of physiological indicators, including iron utilization, biofilm formation, and motility, demonstrated that MccY may decrease the virulence of S. Typhimurium. Transcriptomic analysis showed that iron utilization, biofilm formation, flagellar assembly, and virulence-related genes were downregulated to varying degrees when S. Typhimurium was treated with MccY. In conclusion, deletion of Ton system genes resulted in resistance to MccY and the susceptibility of these mutants to MccY was increased and differed under a low-iron condition. This lasso peptide can alter multiple physiological properties of S. Typhimurium. Our study will contribute to improve the knowledge and understanding of the mechanism of MccY resistance in Salmonella strains. IMPORTANCE The resistance of Salmonella to traditional antibiotics remains a serious challenge. Novel anti-Salmonella drugs are urgently needed to address the looming crisis. The newly identified antimicrobial peptide MccY shows broad prospects for development and application because of its obvious antagonistic effect on various serotypes of Salmonella. However, our previous study showed that the peptide could confer resistance to Salmonella by disrupting the receptor gene fhuA. In this study, we further explored the potential resistance mechanism of MccY and demonstrated the importance of the Salmonella Ton complex for MccY transport. Disruption in Ton system genes resulted in S. Typhimurium resistance to this peptide, and MccY could alter multiple bacterial physiological properties. In summary, this study further explored the resistance mechanism and antibacterial effect of MccY in S. Typhimurium and provided a scientific basis for its development and application.

CzcR Is Essential for Swimming Motility in Pseudomonas aeruginosa during Zinc Stress

Two-component system (TCS) plays a vital role in modulating target gene expression in response to the changing environments. Pseudomonas aeruginosa is a ubiquitous opportunistic pathogen that can survive under diverse stress conditions. The great adaptability of P. aeruginosa relies heavily on the abundant TCSs encoded by its genome. However, most TCSs in P. aeruginosa have not been well-characterized. CzcS/CzcR is a metal responsive TCS which displays multiple regulatory functions associated with metal hemostasis, quorum sensing activity and antibiotic resistance. In this study, we found that swimming motility of P. aeruginosa was completely abolished during zinc (Zn2+) stress when the czcR gene from the TCS CzcS/CzcR was deleted. Noticeably, CzcR was dispensable for swimming without the stress of Zn2+ excess. CzcR was shown to be activated by Zn2+ stress possibly through inducing its expression level and triggering its phosphorylation to positively regulate swimming which was abolished by Zn2+ stress in a CzcR-independent manner. Further TEM analyses and promoter activity examinations revealed that CzcR was required for the expression of genes involved in flagellar biosynthesis during Zn2+ stress. In vitro protein-DNA interaction assay showed that CzcR was capable of specifically recognizing and binding to the promoters of operons flgBCDE, flgFGHIJK, and PA1442/FliMNOPQR/flhB. Together, this study demonstrated a novel function of CzcR in regulating flagellar gene expression and motility in P. aeruginosa when the pathogen encounters Zn2+ stress conditions. IMPORTANCE The fitness of bacterial cells depends largely on their ability to sense and respond quickly to the changing environments. P. aeruginosa expresses a great number of signal sensing and transduction systems that enable the pathogen to grow and survive under diverse stress conditions and cause serious infections at different sites in many hosts. In addition to the previously characterized functions to regulate metal homeostasis, quorum sensing activity, and antibiotic resistance, here we report that CzcR is a novel regulator essential for flagellar gene expression and swimming motility in P. aeruginosa during Zn2+ stress. Since swimming motility is important for the virulence of P. aeruginosa, findings in this study might provide a new target for the treatment of P. aeruginosa infections with Zn2+-based antimicrobial agents in the future.

Fungal Zinc Homeostasis and Its Potential as an Antifungal Target: A Focus on the Human Pathogen Aspergillus fumigatus

Aspergillus fumigatus is an opportunistic airborne fungus that causes severe invasive aspergillosis in immunocompromised patients. Zinc is an essential micronutrient for the growth of A. fumigatus and even for all microorganisms. An increasing number of studies have reported that fungal zinc acquisition ability plays a key role in fungal survival in hosts with an extremely zinc-limited microenvironment. The ability to fight scarcity and excess of zinc are tightly related to fungal virulence and may be used as new potential targets. Because the regulation of zinc homeostasis is important, a thorough understanding of the functional genes involved in the regulatory network for zinc homeostasis is required for fungal pathogens. The current mini-review summarized potential zinc homeostasis regulators in A. fumigatus and classified these regulators according to localization and function, which were identified or predicted based on A. fumigatus or deduced from homologs in model yeasts. Future perspectives for zinc homeostasis regulators as potential antifungal targets to treat invasive aspergillosis are also discussed.

Pathogenicity Islands in Uropathogenic Escherichia coli Clinical Isolate of the Globally Disseminated O25:H4-ST131 Pandemic Clonal Lineage: First Report from Egypt

Uropathogenic Escherichia coli (UPEC) is the main etiological agent of urinary tract infections (UTIs). The pathogenesis of UTIs relies upon UPEC's acquisition of virulence determinants that are commonly inserted into large chromosomal blocks which are termed 'pathogenicity islands' (PAIs). In this study, we investigated the virulence-associated genes embedded in the chromosome of a UPEC Egyptian strain, EC14142. Additionally, we present a detailed characterization of the PAIs in the EGY_EC14142 chromosome. The isolate displayed a multidrug-resistant phenotype, and whole genome sequencing indicated that it belonged to the globally disseminated O25:H4-ST131 pandemic lineage and the H30-Rx clade. EGY_EC14142 carried genes that are responsible for resistance to aminoglycosides, fluoroquinolones, extended-spectrum β-lactams, macrolides, folate pathway antagonists, and tetracyclines. It encoded five PAIs with a high similarity to PAI II536, PAI IV536, PAI V536, PAI-536-icd, and PAIusp. The genome analysis of EGY_EC14142 with other closely related UPEC strains revealed that they have a high nucleotide sequence identity. The constructed maximum-likelihood phylogenetic tree showed the close clonality of EGY_EC14142 with the previously published ST131 UPEC international isolates, thus endorsing the broad geographical distribution of this clone. This is the first report characterizing PAIs in a UPEC Egyptian strain belonging to the globally disseminated pandemic clone O25:H4-ST131.

Modulation of immune cell function, IDO expression and kynurenine production by the quorum sensor 2-heptyl-3-hydroxy-4-quinolone (PQS)

Many invasive micro-organisms produce 'quorum sensor' molecules which regulate colony expansion and may modulate host immune responses. We have examined the ability of Pseudomonas Quorum Sensor (PQS) to influence cytokine expression under conditions of inflammatory stress. The administration of PQS in vivo to mice with collagen-induced arthritis (CIA) increased the severity of disease. Blood and inflamed paws from treated mice had fewer regulatory T cells (Tregs) but normal numbers of Th17 cells. However, PQS (1μM) treatment of antigen-stimulated lymph node cells from collagen-immunised mice in vitro inhibited the differentiation of CD4+IFNγ+ cells, with less effect on CD4+IL-17+ cells and no change in CD4+FoxP3+Tregs. PQS also inhibited T cell activation by anti-CD3/anti-CD28 antibodies. PQS reduced murine macrophage polarisation and inhibited expression of IL1B and IL6 genes in murine macrophages and human THP-1 cells. In human monocyte-derived macrophages, IDO1 gene, protein and enzyme activity were all inhibited by exposure to PQS. TNF gene expression was inhibited in THP-1 cells but not murine macrophages, while LPS-induced TNF protein release was increased by high PQS concentrations. PQS is known to have iron scavenging activity and its suppression of cytokine release was abrogated by iron supplementation. Unexpectedly, PQS decreased the expression of indoleamine-2, 3-dioxygenase genes (IDO1 and IDO2), IDO1 protein expression and enzyme activity in mouse and human macrophages. This is consistent with evidence that IDO1 inhibition or deletion exacerbates arthritis, while kynurenine reduces its severity. It is suggested that the inhibition of IDO1 and cytokine expression may contribute to the quorum sensor and invasive actions of PQS.

Zn2+-Induced Conformational Change Affects the SAM Binding in a Mycobacterial SAM-Dependent Methyltransferase

Zinc is a cofactor for enzymes involved in DNA replication, peptidoglycan hydrolysis, and pH maintenance, in addition to the transfer of the methyl group to thiols. Here, we discovered a new role of Zn²⁺ as an inhibitor for S-adenosyl methionine (SAM) binding in a mycobacterial methyltransferase. Rv1377c is annotated as a putative methyltransferase that is upregulated upon the mitomycin C treatment of Mycobacterium tuberculosis. Sequence analysis and experimental validation allowed the identification of distinct motifs responsible for SAM binding. A detailed analysis of the AlphaFold-predicted structure of Rv1377c revealed four cysteine residues capable of coordinating a Zn²⁺ ion located in proximity to the SAM-binding site. Further, experimental studies showed distinct conformational changes upon Zn²⁺ binding to the protein, which compromised its ability to bind SAM. This is the first report wherein Zn²⁺-driven conformational changes in a methyltransferase undermines its ability to bind SAM.

New insights into microbial interactions and putative competitive mechanisms during the hydrogen production from tequila vinasses

This study aimed to characterize the prokaryotic community and putative microbial interactions involved in hydrogen (H₂) production during the dark fermentation (DF) process, applying principal components analysis (PCA) to correlate changes in operational, physicochemical, and biological variables. For this purpose, a continuous stirred-tank reactor-type digester fed with tequila vinasses was operated at 24, 18, and 12 h of hydraulic retention times (HRTs) to apply organic loading rates of 20, 36, and 54 g-COD L^-1 d^-1, corresponding to stages I, II, and III, respectively. Results indicated high population dynamics for Archaea during the DF process toward a decrease in total sequences from 6299 to 99. Concerning the Bacteria community, lactic acid bacteria (LAB) were dominant reaching a relative abundance of 57.67%, while dominant H₂-producing bacteria (HPB) decreased from 25.76% to 21.06% during stage III. Putative competitive exclusion mechanisms such as competition for substrates, bacteriocins production, and micronutrient depletion carried out by Archaea and non-H₂-producing bacteria (non-HPB), especially LAB, could negatively impact the dominance of HPB such as Ethanoligenens harbinense and Clostridium tyrobutyricum. As a consequence, low maximal volumetric H₂ production rate (672 mL-H₂ L^-1 d^-1) and yield (3.88 mol-H₂ assimilated sugars^-1) were obtained. The global scenario obtained by PCA correlations suggested that C. tyrobutyricum positively impacted H₂ molar yield through butyrate fermentation using the butyryl-CoA:acetate CoA transferase pathway, while the most abundant HPB E. harbinense decreased its relative abundance at the shortest HRT toward the dominance of non-HPB. This study provides new insights into the microbial interactions and helps to better understand the DF performance for H₂ production using tequila vinasses as substrate. KEY POINTS: • E. harbinense and C. tyrobutyricum were responsible for H₂ production. • Clostridiales used acetate and butyrate fermentations for H₂ production. • LAB won the competition for sugars against Clostridiales during DF. • Putative bacteriocins production and micronutrients depletion could favor LAB.

Enhancers of Host Immune Tolerance to Bacterial Infection Discovered Using Linked Computational and Experimental Approaches

Current therapeutic strategies against bacterial infections focus on reduction of pathogen load using antibiotics; however, stimulation of host tolerance to infection in the presence of pathogens might offer an alternative approach. Computational transcriptomics and Xenopus laevis embryos are used to discover infection response pathways, identify potential tolerance inducer drugs, and validate their ability to induce broad tolerance. Xenopus exhibits natural tolerance to Acinetobacter baumanii, Klebsiella pneumoniae, Staphylococcus aureus, and Streptococcus pneumoniae bacteria, whereas Aeromonas hydrophila and Pseudomonas aeruginosa produce lethal infections. Transcriptional profiling leads to definition of a 20-gene signature that discriminates between tolerant and susceptible states, as well as identification of a more active tolerance response to gram negative compared to gram positive bacteria. Gene pathways associated with active tolerance in Xenopus, including some involved in metal ion binding and hypoxia, are found to be conserved across species, including mammals, and administration of a metal chelator (deferoxamine) or a HIF-1α agonist (1,4-DPCA) in embryos infected with lethal A. hydrophila increased survival despite high pathogen load. These data demonstrate the value of combining the Xenopus embryo infection model with computational multiomics analyses for mechanistic discovery and drug repurposing to induce host tolerance to bacterial infections.

Inflammatory bowel disease biomarkers

Inflammatory bowel disease (IBD) is characterized as chronic inflammation in the gastrointestinal tract, which includes two main subtypes, Crohn's disease and ulcerative colitis. Endoscopy combined with biopsy is the most effective way to establish IBD diagnosis and disease management. Imaging techniques have also been developed to monitor IBD. Although effective, the methods are expensive and invasive, which leads to pain and discomfort. Alternative noninvasive biomarkers are being explored as tools for IBD prognosis and disease management. This review focuses on novel biomarkers that have emerged in recent years. These serological biomarkers and microRNAs could potentially be used for disease management in IBD, thereby decreasing patient discomfort and morbidity.

Less is more: Enterobactin concentration dependency in copper tolerance and toxicity

The ability of siderophores to play roles beyond iron acquisition has been recently proven for many of them and evidence continues to grow. An earlier work showed that the siderophore enterobactin is able to increase copper toxicity by reducing Cu²⁺ to Cu⁺, a form of copper that is more toxic to cells. Copper toxicity is multifaceted. It involves the formation of reactive oxygen species (ROS), mismetallation of enzymes and possibly other mechanisms. Given that we previously reported on the capacity of enterobactin to alleviate oxidative stress caused by various stressors other than copper, we considered the possibility that the siderophore could play a dual role regarding copper toxicity. In this work, we show a bimodal effect of enterobactin on copper toxicity (protective and harmful) which depends on the siderophore concentration. We found that the absence of enterobactin rendered Escherichia coli cells more sensitive to copper, due to the reduced ability of those cells to cope with the metal-generated ROS. Consistently, addition of low concentrations of the siderophore had a protective effect by reducing ROS levels. We observed that in order to achieve this protection, enterobactin had to enter cells and be hydrolyzed in the cytoplasm. Further supporting the role of enterobactin in oxidative stress protection, we found that both oxygen and copper, induced the expression of the siderophore and also found that copper strongly counteracted the well-known downregulation effect of iron on enterobactin synthesis. Interestingly, when enterobactin was present in high concentrations, cells became particularly sensitive to copper most likely due to the Cu²⁺ to Cu⁺ reduction, which increased the metal toxicity leading to cell death.

The impacts of viral infection and subsequent antimicrobials on the microbiome-resistome of growing pigs

BACKGROUND

Antimicrobials are used in food-producing animals for purposes of preventing, controlling, and/or treating infections. In swine, a major driver of antimicrobial use is porcine reproductive and respiratory syndrome (PRRS), which is caused by a virus that predisposes infected animals to secondary bacterial infections. Numerous antimicrobial protocols are used to treat PRRS, but we have little insight into how these treatment schemes impact antimicrobial resistance (AMR) dynamics within the fecal microbiome of commercial swine. The aim of this study was to determine whether different PRRS-relevant antimicrobial treatment protocols were associated with differences in the fecal microbiome and resistome of growing pigs. To accomplish this, we used a metagenomics approach to characterize and compare the longitudinal wean-to-market resistome and microbiome of pigs challenged with PRRS virus and then exposed to different antimicrobial treatments, and a group of control pigs not challenged with PRRS virus and having minimal antimicrobial exposure. Genomic DNA was extracted from pen-level composite fecal samples from each treatment group and subjected to metagenomic sequencing and microbiome-resistome bioinformatic and statistical analysis. Microbiome-resistome profiles were compared over time and between treatment groups.

RESULTS

Fecal microbiome and resistome compositions both changed significantly over time, with a dramatic and stereotypic shift between weaning and 9 days post-weaning (dpw). Antimicrobial resistance gene (ARG) richness and diversity were significantly higher at earlier time points, while microbiome richness and diversity were significantly lower. The post-weaning shift was characterized by transition from a Bacteroides-dominated enterotype to Lactobacillus- and Streptococcus-dominated enterotypes. Both the microbiome and resistome stabilized by 44 dpw, at which point the trajectory of microbiome-resistome maturation began to diverge slightly between the treatment groups, potentially due to physical clustering of the pigs. Challenge with PRRS virus seemed to correspond to the re-appearance of many very rare and low-abundance ARGs within the feces of challenged pigs. Despite very different antimicrobial exposures after challenge with PRRS virus, resistome composition remained largely similar between the treatment groups. Differences in ARG abundance between the groups were mostly driven by temporal changes in abundance that occurred prior to antimicrobial exposures, with the exception of ermG, which increased in the feces of treated pigs, and was significantly more abundant in the feces of these pigs compared to the pigs that did not receive post-PRRS antimicrobials.

CONCLUSIONS

The fecal microbiome-resistome of growing pigs exhibited a stereotypic trajectory driven largely by weaning and physiologic aging of the pigs. Events such as viral illness, antimicrobial exposures, and physical grouping of the pigs exerted significant yet relatively minor influence over this trajectory. Therefore, the AMR profile of market-age pigs is the culmination of the life history of the individual pigs and the populations to which they belong. Disease status alone may be a significant driver of AMR in market-age pigs, and understanding the interaction between disease processes and antimicrobial exposures on the swine microbiome-resistome is crucial to developing effective, robust, and reproducible interventions to control AMR. Video Abstract.

Offense and Defense in Granulomatous Inflammation Disease

Granulomatous inflammation (GI) diseases are a group of chronic inflammation disorders characterized by focal collections of multinucleated giant cells, epithelioid cells and macrophages, with or without necrosis. GI diseases are closely related to microbes, especially virulent intracellular bacterial infections are important factors in the progression of these diseases. They employ a range of strategies to survive the stresses imposed upon them and persist in host cells, becoming the initiator of the fighting. Microbe-host communication is essential to maintain functions of a healthy host, so defense capacity of hosts is another influence factor, which is thought to combine to determine the result of the fighting. With the development of gene research technology, many human genetic loci were identified to be involved in GI diseases susceptibility, providing more insights into and knowledge about GI diseases. The current review aims to provide an update on the most recent progress in the identification and characterization of bacteria in GI diseases in a variety of organ systems and clinical conditions, and examine the invasion and escape mechanisms of pathogens that have been demonstrated in previous studies, we also review the existing data on the predictive factors of the host, mainly on genetic findings. These strategies may improve our understanding of the mechanisms underlying GI diseases, and open new avenues for the study of the associated conditions in the future.

Manganese Utilization in Salmonella Pathogenesis: Beyond the Canonical Antioxidant Response

The metal ion manganese (Mn²⁺) is equally coveted by hosts and bacterial pathogens. The host restricts Mn²⁺ in the gastrointestinal tract and Salmonella-containing vacuoles, as part of a process generally known as nutritional immunity. Salmonella enterica serovar Typhimurium counteract Mn²⁺ limitation using a plethora of metal importers, whose expression is under elaborate transcriptional and posttranscriptional control. Mn²⁺ serves as cofactor for a variety of enzymes involved in antioxidant defense or central metabolism. Because of its thermodynamic stability and low reactivity, bacterial pathogens may favor Mn²⁺-cofactored metalloenzymes during periods of oxidative stress. This divalent metal catalyzes metabolic flow through lower glycolysis, reductive tricarboxylic acid and the pentose phosphate pathway, thereby providing energetic, redox and biosynthetic outputs associated with the resistance of Salmonella to reactive oxygen species generated in the respiratory burst of professional phagocytic cells. Combined, the oxyradical-detoxifying properties of Mn²⁺ together with the ability of this divalent metal cation to support central metabolism help Salmonella colonize the mammalian gut and establish systemic infections.

Characterization of the Bacteriophage BUCT603 and Therapeutic Potential Evaluation Against Drug-Resistant Stenotrophomonas maltophilia in a Mouse Model

Stenotrophomonas maltophilia (S. maltophilia) is a common opportunistic pathogen that is resistant to many antibiotics. Bacteriophages are considered to be an effective alternative to antibiotics for the treatment of drug-resistant bacterial infections. In this study, we isolated and characterized a phage, BUCT603, infecting drug-resistant S. maltophilia. Genome sequencing showed BUCT603 genome was composed of 44,912 bp (32.5% G + C content) with 64 predicted open reading frames (ORFs), whereas no virulence-related genes, antibiotic-resistant genes or tRNA were identified. Whole-genome alignments showed BUCT603 shared 1% homology with other phages in the National Center for Biotechnology Information (NCBI) database, and a phylogenetic analysis indicated BUCT603 can be classified as a new member of the Siphoviridae family. Bacteriophage BUCT603 infected 10 of 15 S. maltophilia and used the TonB protein as an adsorption receptor. BUCT603 also inhibited the growth of the host bacterium within 1 h in vitro and effectively increased the survival rate of infected mice in a mouse model. These findings suggest that bacteriophage BUCT603 has potential for development as a candidate treatment of S. maltophilia infection.

Zinc Essentiality, Toxicity, and Its Bacterial Bioremediation: A Comprehensive Insight

Zinc (Zn) is one of the most abundantly found heavy metals in the Earth's crust and is reported to be an essential trace metal required for the growth of living beings, with it being a cofactor of major proteins, and mediating the regulation of several immunomodulatory functions. However, its essentiality also runs parallel to its toxicity, which is induced through various anthropogenic sources, constant exposure to polluted sites, and other natural phenomena. The bioavailability of Zn is attributable to various vegetables, beef, and dairy products, which are a good source of Zn for safe consumption by humans. However, conditions of Zn toxicity can also occur through the overdosage of Zn supplements, which is increasing at an alarming rate attributing to lack of awareness. Though Zn toxicity in humans is a treatable and non-life-threatening condition, several symptoms cause distress to human activities and lifestyle, including fever, breathing difficulty, nausea, chest pain, and cough. In the environment, Zn is generally found in soil and water bodies, where it is introduced through the action of weathering, and release of industrial effluents, respectively. Excessive levels of Zn in these sources can alter soil and aquatic microbial diversity, and can thus affect the bioavailability and absorption of other metals as well. Several Gram-positive and -negative species, such as Bacillus sp., Staphylococcus sp., Streptococcus sp., and Escherichia coli, Pseudomonas sp., Klebsiella sp., and Enterobacter sp., respectively, have been reported to be promising agents of Zn bioremediation. This review intends to present an overview of Zn and its properties, uses, bioavailability, toxicity, as well as the major mechanisms involved in its bioremediation from polluted soil and wastewaters.

Assessment of Metal Accumulation by Arthrospira platensis and Its Adaptation to Iterative Action of Nickel Mono- and Polymetallic Synthetic Effluents

Cyanobacteria-mediated wastewater remediation is an economical, efficient, and eco-friendly technology. The present work deals with the bioaccumulation performance of Arthrospira platensis (Spirulina) grown for four cycles in a medium containing nickel mono- and polymetallic synthetic effluents. The metal uptake by spirulina biomass was evaluated using neutron activation analysis. The effects of effluents on biomass production, protein, and phycobiliprotein content were assessed. Metal accumulation in the biomass depended on the effluent composition and metal ion concentrations. Nickel accumulation in the biomass was directly proportional to its concentration in effluents, and maximum uptake (1310 mg/kg) was attained in the Ni/Cr/Fe system. In the same system, biomass accumulated 110 times more chromium and 4.7 times more iron than control. The highest accumulation of copper (2870 mg/kg) was achieved in the Ni/Cu/Zn/Mo system and zinc (1860 mg/kg)—in the Ni/Cu/Zn/Sr system. In biomass grown in the media loaded with nickel and also chromium, iron, copper, strontium, zinc, and molybdenum, a decrease in productivity (on average by 10%) during the first cycle of cultivation and moderate reduction of protein content (by 15–27%) was observed. The presence of metals in the cultivation media inhibited phycobiliprotein synthesis, especially of phycocyanin, and promoted the synthesis of allophycocyanin. The maximum reduction of phycocyanin content was 77%, and the increase of allophycocyanin content—by 45%. Arthrospira platensis may be deemed as bioremediation of nickel-polluted wastewaters of complex composition.

Particle-Bound Hg(II) is Available for Microbial Uptake as Revealed by a Whole-Cell Biosensor

Particle-bound mercury (Hg_P), ubiquitously present in aquatic environments, can be methylated into highly toxic methylmercury, but it remains challenging to assess its bioavailability. In this study, we developed anEscherichia coli-based whole-cell biosensor to probe the microbial uptake of inorganic Hg(II) and assess the bioavailability of Hg_P sorbed on natural and model particles. This biosensor can quantitatively distinguish the contribution of dissolved Hg(II) and Hg_P to intracellular Hg. Results showed that the microbial uptake of Hg_P was ubiquitous in the environment, as evidenced by the bioavailability of sorbed-Hg(II) onto particulate matter and model particles (Fe₂O₃, Fe₃O₄, Al₂O₃, and SiO₂). In both oxic and anoxic environments, Hg_P was an important Hg(II) source for microbial uptake, with enhanced bioavailability under anoxic conditions. The composition of particles significantly affected the microbial uptake of Hg_P, with higher bioavailability being observed for Fe₂O₃ and lower for Al₂O₃ particles. The bioavailability of Hg_P varied also with the size of particles. In addition, coating with humic substances and model organic compound (cysteine) on Fe₂O₃ particles decreased the bioavailability of Hg_P. Overall, our findings highlight the role of Hg_P in Hg biogeochemical cycling and shed light on the enhanced Hg-methylation in settling particles and sediments in aquatic environments.

Ferric Citrate Uptake Is a Virulence Factor in Uropathogenic Escherichia coli

More than half of women will experience a urinary tract infection (UTI), with uropathogenic Escherichia coli (UPEC) causing ~80% of uncomplicated cases. Iron acquisition systems are essential for uropathogenesis, and UPEC strains encode highly diverse iron acquisition systems, underlining their importance. However, a recent UPEC clinical isolate, HM7, lacks this diversity and instead encodes the synthesis pathway for a sole siderophore, enterobactin. To determine if HM7 possesses unidentified iron acquisition systems, we performed RNA sequencing under iron-limiting conditions and demonstrated that the ferric citrate uptake system (fecABCDE and fecIR) was highly upregulated. Importantly, there are high levels of citrate within urine, some of which is bound to iron, and the fec system is enriched in UPEC isolates compared to fecal strains. Therefore, we hypothesized that HM7 and other similar strains use the fec system to acquire iron in the host. Deletion of both enterobactin biosynthesis and ferric citrate uptake (ΔfecA/ΔentB) abrogates use of ferric citrate as an iron source, and fecA provides an advantage in human urine in the absence of enterobactin. However, in a UTI mouse model, fecA is a fitness factor independent of enterobactin production, likely due to the action of host lipocalin-2 chelating ferrienterobactin. These findings indicate that ferric citrate uptake is used as an iron source when siderophore efficacy is limited, such as in the host during UTI. Defining these novel compensatory mechanisms and understanding the nutritional hierarchy of preferred iron sources within the urinary tract are important in the search for new approaches to combat UTI.

Iron-Deficiency in Atopic Diseases: Innate Immune Priming by Allergens and Siderophores

Although iron is one of the most abundant elements on earth, about a third of the world's population are affected by iron deficiency. Main drivers of iron deficiency are beside the chronic lack of dietary iron, a hampered uptake machinery as a result of immune activation. Macrophages are the principal cells distributing iron in the human body with their iron restriction skewing these cells to a more pro-inflammatory state. Consequently, iron deficiency has a pronounced impact on immune cells, favoring Th2-cell survival, immunoglobulin class switching and primes mast cells for degranulation. Iron deficiency during pregnancy increases the risk of atopic diseases in children, while both children and adults with allergy are more likely to have anemia. In contrast, an improved iron status seems to protect against allergy development. Here, the most important interconnections between iron metabolism and allergies, the effect of iron deprivation on distinct immune cell types, as well as the pathophysiology in atopic diseases are summarized. Although the main focus will be humans, we also compare them with innate defense and iron sequestration strategies of microbes, given, particularly, attention to catechol-siderophores. Similarly, the defense and nutritional strategies in plants with their inducible systemic acquired resistance by salicylic acid, which further leads to synthesis of flavonoids as well as pathogenesis-related proteins, will be elaborated as both are very important for understanding the etiology of allergic diseases. Many allergens, such as lipocalins and the pathogenesis-related proteins, are able to bind iron and either deprive or supply iron to immune cells. Thus, a locally induced iron deficiency will result in immune activation and allergic sensitization. However, the same proteins such as the whey protein beta-lactoglobulin can also transport this precious micronutrient to the host immune cells (holoBLG) and hinder their activation, promoting tolerance and protecting against allergy. Since 2019, several clinical trials have also been conducted in allergic subjects using holoBLG as a food for special medical purposes, leading to a reduction in the allergic symptom burden. Supplementation with nutrient-carrying lipocalin proteins can circumvent the mucosal block and nourish selectively immune cells, therefore representing a new dietary and causative approach to compensate for functional iron deficiency in allergy sufferers.