Iron metabolism in pathogenic bacteria

<p>Ferritin Degradation by Pneumococcal HtrA, RadA and ClpP Serine Proteases : A Probable Way For Releasing and Acquisition Of Iron</p>

Purpose

Iron is a necessary element for the growth of bacteria; however, there are limited iron sources known for these microorganisms yet. Intracellular iron is stored as ferritin from, which releases iron in a gradual and controlled manner. The present study aimed to characterize ferritin-binding proteins (FBPs) of Streptococcus pneumoniae.

Material and Methods

S. pneumoniae species were cultured in BHI broth containing ferritin (1094 ng/mL) for 4h at 37°C. Ferritin level was measured using ELISA assay. Bacterial proteome was electrophoresed on SDS-PAGE and then transferred on PVDF nitrocellulose membrane. Afterward, the PVDF membranes were incubated with a ferritin solution. Identification of ferritin binding proteins was performed using anti-ferritin monoclonal antibody conjugated with HRP enzyme. Molecular docking was used to assess the interaction between pneumococcal proteases and FBPs applying phenylmethylsulfonyl fluoride (PMSF) as a protease inhibitor.

Results

No FBPs were identified in S. pneumoniae proteome. Moreover, ferritin levels have significantly (p<0.05) decreased following the growth of S. pneumoniae in ferritin-rich BHI medium. Also, molecular docking showed that RadA protease, ClpP hydrolase, and HtrA protease can potentially interact with PMSF protease inhibitors. On the other hand, the addition of the PMSF to the culture of S. pneumoniae prevented the reduction of ferritin, which indicates a potential role of RadA, ClpP, and HtrA proteases in ferritin degradation.

Conclusion

Our results suggest that S. pneumoniae produces no FBPs and also cannot directly use ferritin as an iron source. However, ferritin may be degraded through a protease-mediated mode.

Characterization of anti-BCG benz[α]anthraquinones and new siderophores from a Xinjiang desert-isolated rare actinomycete Nocardia sp. XJ31

Abstract

The current global demand for novel anti-TB drugs has drawn urgent attention on the discovery of natural product compounds with anti-TB activity. Lots of efforts have emphasized on environmental samples from unexplored or underexplored natural habits and identified numerous rare actinomycete taxa producing structurally diverse bioactive natural products. Herein, we report a survey of the rare actinobacteria diversity in Xinjiang region together with the discovery of anti-TB active natural products from these strains. We have collected 17 soil samples at different sites with different environmental conditions, from which 39 rare actinobacteria were identified by using a selective isolation strategy with 5 media variations. Among those isolated strains, XJ31 was identified as a new Nocardia sp. based on 16S rRNA gene analysis. Through one strain-many compounds (OSMAC) strategy combined with anti-Bacillus Calmette-Guérin bioassay-guided isolation, two groups of compounds were identified. They were twelve siderophores (nocardimicins, 1-12) and two anthraquinones (brasiliquinones, 13 and 14) and ten of them were identified as new compounds. The structures of the purified compounds were elucidated using HR-ESI-MS, 1D NMR, and 2D NMR techniques. The anti-TB bioassays revealed that the two benz[α]anthraquinones have potent activity against BCG (MICs = 25 μM), which can be used as a promising start point for further anti-TB drug development.

Key points

• Ten new natural products were identified from Nocardia sp. XJ31.

• Brasiliquinones13and14showed moderate anti-BCG activity.

Electronic supplementary material

The online version of this article (10.1007/s00253-020-10842-2) contains supplementary material, which is available to authorized users.

Iron-Uptake Systems of Chicken-Associated Salmonella Serovars and Their Role in Colonizing the Avian Host

Iron is an essential micronutrient for most bacteria. Salmonella enterica strains, representing human and animal pathogens, have adopted several mechanisms to sequester iron from the environment depending on availability and source. Chickens act as a major reservoir for Salmonella enterica strains which can lead to outbreaks of human salmonellosis. In this review article we summarize the current understanding of the contribution of iron-uptake systems to the virulence of non-typhoidal S. enterica strains in colonizing chickens. We aim to address the gap in knowledge in this field, to help understand and define the interactions between S. enterica and these important hosts, in comparison to mammalian models.

The Serratia marcescens Siderophore Serratiochelin Is Necessary for Full Virulence during Bloodstream Infection

Serratia marcescens is a bacterium frequently found in the environment, but over the last several decades it has evolved into a concerning clinical pathogen, causing fatal bacteremia. To establish such infections, pathogens require specific nutrients; one very limited but essential nutrient is iron. We sought to characterize the iron acquisition systems in S. marcescens isolate UMH9, which was recovered from a clinical bloodstream infection. Using RNA sequencing (RNA-seq), we identified two predicted siderophore gene clusters (cbs and sch) that were regulated by iron. Mutants were constructed to delete each iron acquisition locus individually and in conjunction, generating both single and double mutants for the putative siderophore systems. Mutants lacking the sch gene cluster lost their iron-chelating ability as quantified by the chrome azurol S (CAS) assay, whereas the cbs mutant retained wild-type activity. Mass spectrometry-based analysis identified the chelating siderophore to be serratiochelin, a siderophore previously identified in Serratia plymuthica Serratiochelin-producing mutants also displayed a decreased growth rate under iron-limited conditions created by dipyridyl added to LB medium. Additionally, mutants lacking serratiochelin were significantly outcompeted during cochallenge with wild-type UMH9 in the kidneys and spleen after inoculation via the tail vein in a bacteremia mouse model. This result was further confirmed by an independent challenge, suggesting that serratiochelin is required for full S. marcescens pathogenesis in the bloodstream. Nine other clinical isolates have at least 90% protein identity to the UMH9 serratiochelin system; therefore, our results are broadly applicable to emerging clinical isolates of S. marcescens causing bacteremia.

VuuB and IutB reduce ferric-vulnibactin in Vibrio vulnificus M2799

Vibrio vulnificus, a pathogenic bacterium that causes serious infections in humans, requires iron for growth. Clinical isolate, V. vulnificus M2799, secretes a catecholate siderophore, namely, vulnibactin, to capture iron (III) from the environment. Growth experiments using a deletion mutant indicated that VuuB, a member of the FAD-containing siderophore-interacting protein family, plays a crucial role in Fe³⁺-vulnibactin reduction. IutB, a member of the ferric-siderophore reductase family, stands a substitute for VuuB in its absence. It remained unclear why V. vulnificus M2799 has two proteins with relevant functions. Here we biochemically characterized VuuB and IutB using purified recombinant proteins. Purified VuuB, a flavoprotein, catalyzed the reduction of Fe³⁺-nitrilotriacetic acid as its electron acceptor, in the presence of NADH as its electron donor and FAD as its cofactor. IutB catalyzed the reduction of Fe³⁺-nitrilotriacetic acid, in the presence of NADH, NADPH, or reduced glutathione as its electron donor. The optimal pH values and temperatures of VuuB and IutB were 7.0 and 37 °C, and 8.5 and 45 °C, respectively. On analyzing their ferric-chelate reductase activities, both VuuB and IutB were found to catalyze the reduction of Fe³⁺-aerobactin, Fe³⁺-vibriobactin, and Fe³⁺-vulnibactin. When the biologically relevant substrate, Fe³⁺-vulnibactin, was used, the levels of ferric-chelate reductase activities were similar between VuuB and IutB. Finally, the mRNA levels were quantified by qRT-PCR in M2799 cells cultivated under low-iron conditions. The number of vuuB mRNA was 8.5 times greater than that of iutB. The expression ratio correlated with the growth of their mutants in the presence of vulnibactin.

Siderophore and indolic acid production by Paenibacillus triticisoli BJ-18 and their plant growth-promoting and antimicrobe abilities

Paenibacillus triticisoli BJ-18, a N2-fixing bacterium, is able to promote plant growth, but the secondary metabolites that may play a role in promoting plant growth have never been characterized. In this study, untargeted metabolomics profiling of P. triticisoli BJ-18 indicated the existence of 101 known compounds, including N2-acetyl ornithine, which is the precursor of siderophores, plant growth regulators such as trehalose 6-phosphate, betaine and trigonelline, and other bioactive molecules such as oxymatrine, diosmetin, luotonin A, (-)-caryophyllene oxide and tetrahydrocurcumin. In addition, six compounds were also isolated from P. triticisoli BJ-18 using a combination of silica gel chromatography, sephadex LH-20, octadecyl silane (ODS), and high-performance liquid chromatography (HPLC). The compound structures were further analyzed by Nuclear Magnetic Resonance (NMR), Mass Spectrometry (MS), and Electronic Circular Dichroism (ECD). The six compounds included three classical siderophore fusarinines identified as deshydroxylferritriacetylfusigen, desferritriacetylfusigen, and triacetylfusigen, and three indolic acids identified as paenibacillic acid A, 3-indoleacetic acid (IAA), and 3-indolepropionic acid (IPA). Both deshydroxylferritriacetylfusigen and paenibacillic acid A have new structures. Fusarinines, which normally occur in fungi, were isolated from bacterium for the first time in this study. Both siderophores (compounds 1 and 2) showed antimicrobial activity against Escherichia coli, Staphylococcus aureus and Bacillus subtilis, but did not show obvious inhibitory activity against yeast Candida albicans, whereas triacetylfusigen (compound 3) showed no antibiosis activity against these test microorganisms. Paenibacillic acid A, IAA, and IPA were shown to promote the growth of plant shoots and roots, and paenibacillic acid A also showed antimicrobial activity against S. aureus. Our study demonstrates that siderophores and indolic acids may play an important role in plant growth promotion by P. triticisoli BJ-18.

Siderophore-Mediated Interactions Determine the Disease Suppressiveness of Microbial Consortia

Soil-borne pathogens cause high losses in crop yields globally. The development of environmentally friendly approaches is urgently needed, but is often constrained by complex interactions between root-associated microbes and pathogens. Here, we demonstrate that the interactions within microbial consortia mediated by iron-scavenging siderophores play an important role in reducing pathogen infection and enhancing plant health. This study provides a promising and novel research direction for dealing with a wide range of microbial infections through iron exploitation, which is important for the colonization and infection of both plant and human hosts by pathogens.

Interactions between plant pathogens and root-associated microbes play an important role in determining disease outcomes. While several studies have suggested that steering these interactions may improve plant health, such approaches have remained challenging in practice. Because of low iron availability in most soils, competition for iron via secreted siderophore molecules might influence microbial interaction outcomes. Here, we tested if bacterial interactions mediated by iron-scavenging siderophores can be used to predict the disease suppressiveness of microbial consortia against soilborne Ralstonia solanacearum, a bacterial pathogen in the tomato rhizosphere. Iron availability significantly affected the interactions within inoculated consortia and between the consortia and the pathogen. We observed contrasting effects of siderophores and other nonsiderophore metabolites on the pathogen growth, while the siderophore effects were relatively much stronger. Specifically, disease incidence was reduced in vivo when the inoculated consortia produced siderophores that the pathogen could not use for its own growth. Employing siderophore-mediated interactions to engineer functionally robust microbial inoculants shows promise in protecting plants from soilborne pathogens.

IMPORTANCE Soil-borne pathogens cause high losses in crop yields globally. The development of environmentally friendly approaches is urgently needed, but is often constrained by complex interactions between root-associated microbes and pathogens. Here, we demonstrate that the interactions within microbial consortia mediated by iron-scavenging siderophores play an important role in reducing pathogen infection and enhancing plant health. This study provides a promising and novel research direction for dealing with a wide range of microbial infections through iron exploitation, which is important for the colonization and infection of both plant and human hosts by pathogens.

Black phosphorus for fighting antibiotic-resistant bacteria: What is known and what is missing

Recently, two-dimensional black phosphorus (BP) nanomaterial has captured much attention due to its superb physiochemical and electronic properties and various promising biomedical applications. However, relatively few studies have explored its antimicrobial properties, particularly for targeting antibiotic-resistant pathogens. A comprehensive understanding of the bactericidal mechanisms of BP is essential for application of this material as an antimicrobial. This review discusses the physicochemical and electronic properties of BP that are relevant for antimicrobial applications, especially the unique characteristics that may play a role in overcoming drug resistance. The literature is discussed in the context of what is known and what information is missing. We also highlight the differences and advantages of BP over other two-dimensional nanomaterials (i.e., graphene oxide and molybdenum disulfide) for bactericidal activity. Finally, we analyze existing challenges and note topics that require future investigation to overcome current inadequacies, aiming to assist the safe development of BP-based nanotechnology for pathogen control.

Fe2+ Ions Alleviate the Symptom of Citrus Greening Disease

Citrus greening (CG) is among the most devastating citrus diseases worldwide. CG-infected trees exhibit interveinal chlorotic leaves due to iron (Fe) deficiency derived from CG; thus, Fe content is lower in infected leaves than in healthy leaves. In this study, we demonstrated that the foliar application of Fe2+ relieves the symptom of CG infection in citrus trees. We applied Fe2+ and citrate to the leaves of infected rough lemon plants. Following this treatment, a reduction in the number of yellow symptomatic leaves was observed, and their growth was restored. Using chlorophyll content as an index, we screened for effective Fe complexes and found that a high ratio of citrate to Fe2+ in the applied solution led to effects against CG in Shikuwasa trees. A high proportion of Fe2+ to total Fe was another key factor explaining the effectiveness of the solution in CG infection, indicating the importance of Fe2+ absorption into plant cells. We confirmed the proportion of Fe2+ to total Fe through the high correlation of reflectometry data via a triazine reaction and X-ray absorption fine structure analysis. These results demonstrate that the foliar application of a high-Fe2+ citrate solution can restore the growth of CG diseased trees.

Role of a 21-kDa iron-regulated protein IrpA in the uptake of ferri-exochelin by Mycobacterium smegmatis

AIMS

To characterize the 21-kDa iron-regulated cell wall protein in Mycobacterium smegmatis co-expressed with the siderophores mycobactin, exochelin and carboxymycobactin upon iron limitation.

METHODS AND RESULTS

Mycobacterium smegmatis, grown in the presence of 0·02 μg Fe ml^-1 (low iron) produced high levels of all the three siderophores, which were repressed in bacteria supplemented with 8 μg Fe ml^-1 (high iron). Exochelin, the major extracellular siderophore was the first to rise and was expressed at high levels during log phase of growth. Carboxymycobactin, a minor component in log phase iron-starved M. smegmatis continued to rise when cultured for longer periods, reaching levels greater than exochelin. Iron-starved bacteria expressed a 21-kDa iron-regulated protein (IrpA) that was identified as Clp protease subunit (MSMEG_3671) and characterized as a receptor for ferri-exochelin.

CONCLUSIONS

Ferri-exochelin is the preferred siderophore in M. smegmatis and this ferri-exochelin: IrpA machinery is absent in Mycobacterium tuberculosis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Exochelin machinery is functional in M. smegmatis and the carboxymycobactin-mycobactin machinery is the sole iron uptake system in M. tuberculosis. The absence of the ferri-exochelin: IrpA system in the pathogen signifies the importance of the carboxymycobactin-mycobactin system machinery in M. tuberculosis.

miR-148 targets CiGadd45ba and CiGadd45bb to modulate the inflammatory response to bacterial infection in grass carp

In grass carp (Ctenopharyngodon idella), septicemia is a systemic inflammatory response to bacterial infection. Once infected bacteria, a hyper-inflammatory state that could lead to septic shock and death. There is increasing evidence that microRNAs are involved in the regulation of the inflammatory response. Ctenopharyngodon idella growth arrest and DNA damage-inducible 45 ba and bb (CiGadd45ba and CiGadd45bb) are two subtypes of Gadd45b. In the present study, miR-148 was confirmed to be involved in the inflammatory response after infection with Aeromonas hydrophila. Dual-luciferase reporter assays and miRNA expression profiling confirmed that miR-148 targeted both CiGadd45ba and CiGadd45bb. Transfection with miR148 mimics and inhibitors altered the expression levels of proinflammatory genes, suggesting that miRNAs regulate the immune response in grass carp. Our results provide a theoretical basis for studying the molecular mechanism underlying the regulation of inflammation by miR-148 in grass carp.

Predicting substrate exchange in marine diatom-heterocystous cyanobacteria symbioses

In the open ocean, some phytoplankton establish symbiosis with cyanobacteria. Some partnerships involve diatoms as hosts and heterocystous cyanobacteria as symbionts. Heterocysts are specialized cells for nitrogen fixation, and a function of the symbiotic cyanobacteria is to provide the host with nitrogen. However, both partners are photosynthetic and capable of carbon fixation, and the possible metabolites exchanged and mechanisms of transfer are poorly understood. The symbiont cellular location varies from internal to partial to fully external, and this is reflected in the symbiont genome size and content. In order to identify the membrane transporters potentially involved in metabolite exchange, we compare the draft genomes of three differently located symbionts with known transporters mainly from model free-living heterocystous cyanobacteria. The types and numbers of transporters are directly related to the symbiont cellular location: restricted in the endosymbionts and wider in the external symbiont. Three proposed models of metabolite exchange are suggested which take into account the type of transporters in the symbionts and the influence of their cellular location on the available nutrient pools. These models provide a basis for several hypotheses that given the importance of these symbioses in global N and C budgets, warrant future testing.

A Plasmid-Encoded FetMP-Fls Iron Uptake System Confers Selective Advantages to Salmonella enterica Serovar Typhimurium in Growth under Iron-Restricted Conditions and for Infection of Mammalian Host Cells

The resistance plasmid pUO-StVR2, derived from virulence plasmid pSLT, is widespread in clinical isolates of Salmonella enterica serovar Typhimurium recovered in Spain and other European countries. pUO-StVR2 carries several genes encoding a FetMP-Fls system, which could be involved in iron uptake. We therefore analyzed S. Typhimurium LSP 146/02, a clinical strain selected as representative of the isolates carrying the plasmid, and an otherwise isogenic mutant lacking four genes (fetMP-flsDA) of the fetMP-fls region. Growth curves and determination of the intracellular iron content under iron-restricted conditions demonstrated that deletion of these genes impairs iron acquisition. Thus, under these conditions, the mutant grew significantly worse than the wild-type strain, its iron content was significantly lower, and it was outcompeted by the wild-type strain in competition assays. Importantly, the strain lacking the fetMP-flsDA genes was less invasive in cultured epithelial HeLa cells and replicated poorly upon infection of RAW264.7 macrophages. The genes were introduced into S. Typhimurium ATCC 14028, which lacks the FetMP-Fls system, and this resulted in increased growth under iron limitation as well as an increased ability to multiply inside macrophages. These findings indicate that the FetMP-Fls iron acquisition system exceeds the benefits conferred by the other high-affinity iron uptake systems carried by ATCC 14028 and LSP 146/02. We proposed that effective iron acquisition by this system in conjunction with antimicrobial resistance encoded from the same plasmid have greatly contributed to the epidemic success of S. Typhimurium isolates harboring pUO-StVR2.

Post-Translational Protein Deimination Signatures in Serum and Serum-Extracellular Vesicles of Bos taurus Reveal Immune, Anti-Pathogenic, Anti-Viral, Metabolic and Cancer-Related Pathways for Deimination

The bovine immune system is known for its unusual traits relating to immunoglobulin and antiviral responses. Peptidylarginine deiminases (PADs) are phylogenetically conserved enzymes that cause post-translational deimination, contributing to protein moonlighting in health and disease. PADs also regulate extracellular vesicle (EV) release, forming a critical part of cellular communication. As PAD-mediated mechanisms in bovine immunology and physiology remain to be investigated, this study profiled deimination signatures in serum and serum-EVs in Bos taurus. Bos EVs were poly-dispersed in a 70-500 nm size range and showed differences in deiminated protein cargo, compared with whole sera. Key immune, metabolic and gene regulatory proteins were identified to be post-translationally deiminated with some overlapping hits in sera and EVs (e.g., immunoglobulins), while some were unique to either serum or serum-EVs (e.g., histones). Protein-protein interaction network analysis of deiminated proteins revealed KEGG pathways common for serum and serum-EVs, including complement and coagulation cascades, viral infection (enveloped viruses), viral myocarditis, bacterial and parasitic infections, autoimmune disease, immunodeficiency intestinal IgA production, B-cell receptor signalling, natural killer cell mediated cytotoxicity, platelet activation and hematopoiesis, alongside metabolic pathways including ferroptosis, vitamin digestion and absorption, cholesterol metabolism and mineral absorption. KEGG pathways specific to EVs related to HIF-1 signalling, oestrogen signalling and biosynthesis of amino acids. KEGG pathways specific for serum only, related to Epstein-Barr virus infection, transcription mis-regulation in cancer, bladder cancer, Rap1 signalling pathway, calcium signalling pathway and ECM-receptor interaction. This indicates differences in physiological and pathological pathways for deiminated proteins in serum-EVs, compared with serum. Our findings may shed light on pathways underlying a number of pathological and anti-pathogenic (viral, bacterial, parasitic) pathways, with putative translatable value to human pathologies, zoonotic diseases and development of therapies for infections, including anti-viral therapies.

Human host-defense peptide LL-37 targets stealth siderophores

A growing number of evidence shows that human-associated microbiota is an important contributor in health and disease. However, much of the complexity of host-microbiota interaction remains to be elucidated both at cellular and molecular levels. Siderophores are chemically diverse, ferric-specific chelators synthesized and secreted by microbes to secure their iron acquisition. The host defense peptide LL-37 is ubiquitously produced at epithelial surfaces modulating microbial communities and suppressing pathogenic strains. The present work demonstrates that LL-37 binds tightly siderocalin-resistant stealth siderophores which are important contributors to the virulence of several pathogens. As indicated by circular dichroism spectroscopic experiments, addition of aerobactin and rhizoferrin increases the membrane active α-helical conformation of the partially folded peptide. The cationic nature of LL-37 (+6 net charge at pH 7.4) and the multiple carboxylate groups present in siderophores refer to the dominant contribution of electrostatic interactions in the stabilization of peptide-chelator adducts. It is proposed that aside siderocalin proteins, LL-37 may be a complementary, less specific component of the siderophore scavenging repertoire of the innate immune system.

LPS Modulates the Expression of Iron-Related Immune Genes in Two Antarctic Notothenoids

The non-specific immunity can induce iron deprivation as a defense mechanism against potential bacterial pathogens, but little information is available as to its role in Antarctic fish. In this study the response of iron metabolism related genes was evaluated in liver and head kidney of the Antarctic notothenoids Notothenia coriiceps and Notothenia rossii 7 days after lipopolysaccharide (LPS) injection. Average plasma Fe²⁺ concentration was unaffected by treatment in any of the species. The gene expression response to LPS varied between tissues and species, being stronger in N. coriiceps and more prominent in the head kidney than liver. The reaction to LPS was marked by increased individual variability in most genes analyzed, even when the change in expression was not statistically significant, suggesting different individual sensitivity and coping responses in these wild fish. We found that iron related genes had an attenuated and homogenous response to LPS but there was no detectable relationship between plasma Fe²⁺ and gene expression. However, overall in both tissues and species LPS exposure set a multilevel response that concur to promote intracellular accumulation of iron, an indication that Antarctic Notothenoids use innate nutritional immunity as a resistance mechanism against pathogens.

Bacterial siderophores in community and host interactions

Iron is an essential trace element for most organisms. A common way for bacteria to acquire this nutrient is through the secretion of siderophores, which are secondary metabolites that scavenge iron from environmental stocks and deliver it to cells via specific receptors. While there has been tremendous interest in understanding the molecular basis of siderophore synthesis, uptake and regulation, questions about the ecological and evolutionary consequences of siderophore secretion have only recently received increasing attention. In this Review, we outline how eco-evolutionary questions can complement the mechanistic perspective and help to obtain a more integrated view of siderophores. In particular, we explain how secreted diffusible siderophores can affect other community members, leading to cooperative, exploitative and competitive interactions between individuals. These social interactions in turn can spur co-evolutionary arms races between strains and species, lead to ecological dependencies between them and potentially contribute to the formation of stable communities. In brief, this Review shows that siderophores are much more than just iron carriers: they are important mediators of interactions between members of microbial assemblies and the eukaryotic hosts they inhabit.

miR-23a-3p and miR-23a-5p target CiGadd45ab to modulate inflammatory response and apoptosis in grass carp

Ctenopharyngodon idella growth arrest and DNA damage-inducible 45 ab (CiGadd45ab) is a subtype of the Gadd45a gene of the Gadd45 family in grass carp. There is increasing evidence that microRNAs (miRNAs) are involved in the regulation of inflammatory and apoptotic responses. However, little is known about the regulatory effects of miRNAs on CiGadd45ab expression. In the present study, CiGadd45ab was identified as a target gene of miR-23a-3p and miR-23a-5p, based on miRNA expression profiling and a dual-luciferase reporter assay. In addition, miR-23a-3p and miR-23a-5p were both confirmed to be involved in the inflammatory response following infection with Aeromonas hydrophila by targeting CiGadd45ab. Transfection with miR-23a-3p and miR-23a-5p mimics and inhibitor altered proinflammatory gene expression and apoptosis rate, thereby suggesting that miRNAs regulate immune response and anti-apoptosis by targeting CiGadd45ab in grass carp. Our results provide a theoretical basis for exploring the molecular mechanisms by which miR-23a-3p and miR-23a-5p target CiGadd45ab to regulate inflammation and apoptosis against bacterial infection in grass carp.

Vibrio parahaemolyticus FcrX, a Fur-controlled regulator that inhibits repression by Fur

Iron is an essential nutrient for most organisms, but its limited availability and inherent toxicity necessitate the strict regulation of iron homeostasis. In bacteria, iron starvation affects a broad range of phenotypes including virulence, motility and biofilm formation. For Vibrio parahaemolyticus, a marine bacterium and pathogen, iron limitation is a signal modulating swarmer cell differentiation. In this work, we show the iron regulation of swarming works through the ferric uptake regulator protein Fur. We identified a new Fur-controlled regulator that is upregulated upon iron starvation. FcrX is a 144-amino acid protein containing a domain of unknown function (DUF2753) with three tetratricopeptide repeats. We found that overexpressing fcrX⁺ was sufficient to induce swarming, luminescence and iron uptake gene expression in multiple Vibrio species; furthermore, ectopic expression increased the transcription of a Fur-controlled gene in Escherichia coli. FcrX production increased intracellular iron. Thus, the overexpression of fcrX⁺ phenocopied a fur mutant and may prove a generally useful tool to ectopically derepress the Fur regulon. Both V. parahaemolyticus and E. coli Fur interacted with FcrX, and this interaction was altered by iron availability. These data support a model in which this new regulator of iron homeostasis limits the repressive action of Fur.

Forging New Antibiotic Combinations under Iron-Limiting Conditions

Pseudomonas aeruginosa is a multidrug-resistant nosocomial pathogen. We showed previously that thiostrepton (TS), a Gram-positive thiopeptide antibiotic, is imported via pyoverdine receptors and synergizes with iron chelator deferasirox (DSX) to inhibit the growth of P. aeruginosa and Acinetobacter baumannii clinical isolates. A small number of P. aeruginosa and A. baumannii isolates were resistant to the combination, prompting us to search for other compounds that could synergize with TS against those strains. From literature surveys, we selected 14 compounds reported to have iron-chelating activity, plus one iron analogue, and tested them for synergy with TS. Doxycycline (DOXY), ciclopirox olamine (CO), tropolone (TRO), clioquinol (CLI), and gallium nitrate (GN) synergized with TS. Individual compounds were bacteriostatic, but the combinations were bactericidal. Our spectrophotometric data and chrome azurol S agar assay confirmed that the chelators potentiate TS activity through iron sequestration rather than through their innate antimicrobial activities. A triple combination of TS plus DSX plus DOXY had the most potent activity against P. aeruginosa and A. baumannii isolates. One P. aeruginosa clinical isolate was resistant to the triple combination but susceptible to a triple combination containing higher concentrations of CLI, CO, or DOXY. All A. baumannii isolates were susceptible to the triple combinations. Our data reveal a diverse set of compounds with dual activity as antibacterial agents and TS adjuvants, allowing combinations to be tailored for resistant clinical isolates.

Mycobacterium marinum produces distinct mycobactin and carboxymycobactin siderophores to promote growth in broth and phagocytes

Mycobacterium marinum is a model organism for pathogenic Mycobacterium species, including Mycobacterium tuberculosis, the causative agent of tuberculosis. These pathogens enter phagocytes and replicate within the Mycobacterium-containing vacuole, possibly followed by vacuole exit and growth in the host cell cytosol. Mycobacteria release siderophores called mycobactins to scavenge iron, an essential yet poorly soluble and available micronutrient. To investigate the role of M. marinum mycobactins, we purified by organic solvent extraction and identified by mass spectrometry the lipid-bound mycobactin (MBT) and the water-soluble variant carboxymycobactin (cMBT). Moreover, we generated by specialised phage transduction a defined M. marinum ΔmbtB deletion mutant predicted to be defective for mycobactin production. The M. marinum ΔmbtB mutant strain showed a severe growth defect in broth and phagocytes, which was partially complemented by supplying the mbtB gene on a plasmid. Furthermore, purified Fe-MBT or Fe-cMBT improved the growth of wild type as well as ΔmbtB mutant bacteria on minimal plates, but only Fe-cMBT promoted the growth of wild-type M. marinum during phagocyte infection. Finally, the intracellular growth of M. marinum ΔmbtB in Acanthamoeba castellanii amoebae was restored by coinfection with wild-type bacteria. Our study identifies and characterises the M. marinum MBT and cMBT siderophores and reveals the requirement of mycobactins for extra- and intracellular growth of the pathogen.

Genomic diversity in flavobacterial pathogens of aquatic origin

Flavobacterium species are considered important fish pathogens in wild and cultured fish throughout the world. They can cause acute, subacute, and chronic infections, which are mainly characterized by gill damage, skin lesions, and deep necrotic ulcerations. Primarily, three Flavobacterium species, F. branchiophilum, F. columnare, and F. psychrophilum, have been reported to cause substantial losses to freshwater fish. In this study, we evaluated genomes of 86 Flavobacterium species isolated from aquatic hosts (mainly fish) to identify their unique and shared genome features. Our results showed that F. columnare genomes cluster into four different genetic groups. In silico secretion system analysis identified that all genomes carry type I (T1SS) and type IX (T9SS) secretion systems, but the number of type I secretion system genes shows diversity between species. F. branchiophilum, F. araucananum, F. chilense, F. spartansii, and F. tructae genomes have full type VI secretion system (T6SS). F. columnare, F. hydatis, and F. plurextorum carry partial T6SS with some of the T6SS genes missing. F. columnare, F. araucananum, F. chilense, F. spartansii, F. araucananum, F. tructae, Flavobacterium sp., F. crassostreae, F. succinicans, F. hydatis, and F. plurextorum carry most of the type IV secretion system genes (T4SS). F. columnare genetic groups 1 and 2, Flavobacterium sp., and F. crassostreae encode the least number of antibiotic resistance elements. F. hydatis, F. chilense, and F. plurextorum encode the greatest number of antibiotic resistance genes. Additionally, F. spartansii, F. araucananum, and chilense encode the greatest number of virulence genes while Flavobacterium sp. and F. crassostreae encode the least number of virulence genes. In conclusion, comparative genomics of Flavobacterium species of aquatic origin will help our understanding of Flavobacterium pathogenesis.

Insights into irr and rirA gene regulation on the virulence of Brucella melitensis M5-90

Iron is a fundamental element required by most organisms, including Brucella. Several researchers have suggested that the iron response regulator (irr) and rhizobial iron regulator (rirA) genes regulate iron acquisition by Brucella abortus, influencing heme synthesis by and virulence of this pathogen. However, little is known about another Brucella species, Brucella melitensis. In this research, we successfully constructed two mutants: M5-90Δirr and M5-90ΔrirA. The adhesion, invasion, and intracellular survivability of these two mutants were evaluated in RAW264.7 cells infected with 1 × 10⁶ CFU of M5-90Δirr, M5-90ΔrirA, or M5-90. We also tested the sensitivity of cells to hydrogen peroxide and their ability to grow. In addition, the virulence of these two mutants was evaluated in BALB/c mice. The results showed that the ability of these two mutants to invade and adhere inside the murine macrophages RAW264.7 was attenuated but their ability to replicate intracellularly was strengthened, enhancing the resistance to hydrogen peroxide. The M5-90Δirr mutant showed stronger growth ability than the parental strain under iron-limiting conditions. No differences were observed in the number of bacteria in spleen between M5-90 and M5-90Δirr at 7 or 15 days postinfection. However, the number of M5-90ΔrirA in spleen reduced significantly at 15 days postinfection. The splenic index of the M5-90Δirr group is evidently lower than that of M5-90. This is the first report that irr and rirA genes of B. melitensis are associated not only with virulence but also with growth ability. Together, our data suggest that M5-90Δirr is a promising Brucella vaccine candidate.

Blood protein polymorphisms and the gut bacteria: impact of probiotic Lactobacillus acidophilus Narine on Salmonella carriage in sheep

Related to previous reports on correlations between an animal's genotype, its commensal microbiota, and the ability to resist infections, the aim of the current study was to investigate the associations between sheep genotype and 5-methylcytosine (5-mC) DNA methylation patterns, sheep genotype and cell surface hydrophobicity of sheep gut commensal bacteria. In addition, the effect of the probiotic Lactobacillus acidophilus strain INMIA 9602 Er 317/402 (probiotic formulation Narine) on Salmonella carriage in sheep at Armenian farms was also investigated. Allelotypes and genotypes of different pathogen-sensitive sheep breeds from Armenian farms were studied based on genetic markers of blood transferrin, albumin, and ceruloplasmin. Additionally, the differences between the breeds of Mazekh, Balbas, and Mazekh/Balbas hybrids were reported. The relationship between host sheep blood transferrin and albumin polymorphisms and cell surface hydrophobicity/5-mC DNA methylation patterns from the predominant gut commensal bacteria was shown. The Narine probiotic eliminates Salmonella from the sheep gut microbiota. At the same time, no significant changes in the percentage of 5-mC DNA methylation of predominant gut bacteria after probiotic administration were observed. The evaluation of bacterial cell surface hydrophobicity, the most significant factor affecting bacterial adhesion, as well as 5-mC DNA methylation, might be used for specific sheep husbandry/breeding programs. This study suggests that the commercial probiotic Narine could potentially be used to reduce Salmonella carriage in sheep.

Effects of microRNA-731 on inflammation and apoptosis by targeting CiGadd45aa in grass carp

Ctenopharyngodon idellagrowth arrest and DNA damage-inducible 45aa (CiGadd45aa) is a member of the Gadd45 family of immune-related proteins in grass carp. There is increasing evidence that microRNAs (miRNAs) are involved in the regulation of inflammatory responses and apoptosis. However, little is known about the regulatory effects of miRNAs on CiGadd45aa expression in grass carp. In the present study, CiGadd45aa was identified as a target gene of miR-731 based on miRNA expression profiling and dual-luciferase reporter assay. Our study revealed that miR-731 targets CiGadd45aa and regulates the expression of proinflammatory factors, thereby regulating immune response in grass carp. In addition, CiGadd45aa and miR-731 were both found induced apoptosis. Hence, our findings provide a theoretical basis for exploring the molecular mechanism by which miR-731 regulates inflammation and apoptosis in grass carp.

Molecular characterisation of multi-drug resistant Escherichia coli of bovine origin

Antimicrobial resistance reported in bacteria of animal origin is considered a major challenge to veterinary public health. In this study, the genotypic and phenotypic characterisation of twelve Escherichia coli isolates of bovine origin is reported. Twelve bacterial isolates of animal origin were selected from a previous study based on their multidrug resistant (MDR) profile. Efflux pump activity was measured using ethidium bromide (EtBr) and the biofilm forming ability of the individual strains was assessed using a number of phenotypic assays. All isolates were resistant to tetracyclines and a number of isolates expressed resistance to fluoroquinolones which was also confirmed in silico by the presence of these resistance markers. Amino acid substitutions in the quinolone resistance-determining regions were identified in all isolates and the presence of several siderophores were also noted. Whole genomesequence (WGS) data showed different STs that were not associated with epidemic STs or virulent clonal complexes. Seven isolates formed biofilms in minimal media with some isolates showing better adaptation at 25 °C while others at 37 °C. The capacity to efflux EtBr was found to be high in 4 isolates and impaired in 4 others. The pathogenicity of three selected isolates was assessed in zebrafish embryo infection models, revealing isolates CFS0355 and CFS0356 as highly pathogenic. These results highlight the application of NGS technologies combined with phenotypic assays in providing a better understanding of E. coli of bovine origin and their adaptation to this niche environment.

Iron homeostasis disorder in piglet intestine

Intestinal iron homeostasis is like the Zhong-Yong in traditional Chinese culture, which is a dynamic balance between Yin and Yang.

A novel mechanism of inhibition by phenylthiourea on PvdP, a tyrosinase synthesizing pyoverdine of Pseudomonas aeruginosa

The biosynthesis of pyoverdine, the major siderophore of Pseudomonas aeruginosa, is a well-organized process involving a discrete number of enzyme-catalyzed steps. The final step of this process involves the PvdP tyrosinase, which converts ferribactin into pyoverdine. Thus, inhibition of the PvdP tyrosinase activity provides an attractive strategy to interfere with siderophore synthesis to manage P. aeruginosa infections. Here, we report phenylthiourea as a non-competitive inhibitor of PvdP for which we solved a crystal structure in complex with PvdP. The crystal structure indicates that phenylthiourea binds to an allosteric binding site and thereby interferes with its tyrosinase activity. We further provide proofs that PvdP tyrosinase inhibition by phenylthiourea requires the C-terminal lid region. This provides opportunities to develop inhibitors that target the allosteric site, which seems to be confined to fluorescent pseudomonads, and not the tyrosinase active site. Furthermore, increases the chances to identify PvdP inhibitors that selectively interfere with siderophore synthesis.

Transcriptional analysis of RstA/RstB in avian pathogenic Escherichia coli identifies its role in the regulation of hdeD-mediated virulence and survival in chicken macrophages

Avian pathogenic Escherichia coli (APEC) causes avian colibacillosis in poultry, which is characterized by systemic infections such as septicemia, air sacculitis, and pericarditis. APEC uses two-component regulatory systems (TCSs) to handle the stressful environments present in infected hosts. While many TCSs in E. coli have been well characterized, the RstA/RstB system in APEC has not been thoroughly investigated. The involvement of the RstA regulator in APEC pathogenesis was demonstrated during previous studies investigating its role in APEC persistence in chicken macrophages and respiratory infections. However, the mechanism underlying this phenomenon has not been clarified. Transcriptional analysis of the effect of rstAB deletion was therefore performed to improve the understanding of the RstA/RstB regulatory mechanism, and particularly its role in virulence. The transcriptomes of the rstAB mutant and the wild-type strain E058 were compared during their growth in the bloodstreams of challenged chickens. Overall, 198 differentially expressed (DE) genes were identified, and these indicated that RstA/RstB mainly regulates systems involved in nitrogen metabolism, iron acquisition, and acid resistance. Phenotypic assays indicated that the rstAB mutant responded more to an acidic pH than the wild-type strain did, possibly because of the repression of the acid-resistance operons hdeABD and gadABE by the deletion of rstAB. Based on the reported RstA box motif TACATNTNGTTACA, we identified four possible RstA target genes (hdeD, fadE, narG, and metE) among the DE genes. An electrophoretic mobility shift assay confirmed that RstA binds directly to the promoter of hdeD, and β-galactosidase assays showed that hdeD expression was reduced by rstAB deletion, indicating that RstA directly regulates hdeD expression. The hdeD mutation resulted in virulence attenuation in both cultured chicken macrophages and experimentally infected chickens. In conclusion, our data suggest that RstA affects APEC E058 virulence partly by directly regulating the acidic resistance gene hdeD.

The influence of linkages between 1-hydroxy-2(1H)-pyridinone coordinating groups and a tris(2-aminoethyl)amine core in a novel series of synthetic hexadentate iron(III) chelators on antimicrobial activity

Resistance of pathogens to antimicrobials is a major current healthcare concern. In a series of linked studies, we have investigated synthetic iron chelators based on hydroxy-pyridinone ligands as novel bacteriostatic agents. Herein we describe our synthesis of several useful building blocks based on the 1-hydroxy-2(1H)-pyridinone moiety, including a novel formyl derivative, which were combined with a tris(2-aminoethyl)amine core to obtain a series of new high-affinity hexadentate Fe(III) chelators. The design principle examined by this series is the size and flexibility of the linker between the core and the metal ligands. Measurement of the pKa and stability constants (Fe³⁺ and Cu²⁺) of representative coordinating groups was performed to help rationalise the biological activity of the chelators. The novel chelators were tested on a panel of representative microorganisms with some effectively inhibiting microbial growth. We demonstrate that the nature and position of the linker between the hydroxypyridinone and the tris(2-aminoethyl)amine core has considerable impact upon microbial growth inhibition and that both amide or amine linkages can give efficacious chelators.

Antimicrobial secondary metabolites from agriculturally important bacteria as next-generation pesticides

The whole organisms can be packaged as biopesticides, but secondary metabolites secreted by microorganisms can also have a wide range of biological activities that either protect the plant against pests and pathogens or act as plant growth promotors which can be beneficial for the agricultural crops. In this review, we have compiled information about the most important secondary metabolites of three important bacterial genera currently used in agriculture pest and disease management.

Ferric Uptake Regulator (FurA) is Required for Acidovorax citrulli Virulence on Watermelon

Acidovorax citrulli is the causal agent of bacterial fruit blotch, a serious threat to commercial watermelon and melon crop production worldwide. Ferric uptake regulator (Fur) is a global transcription factor that affects a number of virulence-related functions in phytopathogenic bacteria; however, the role of furA has not been determined for A. citrulli. Hence, we constructed an furA deletion mutant and a corresponding complement in the background of A. citrulli strain xlj12 to investigate the role of the gene in siderophore production, concentration of intracellular Fe²⁺, bacterial sensitivity to hydrogen peroxide, biofilm formation, swimming motility, hypersensitive response induction, and virulence on melon seedlings. The A. citrulli furA deletion mutant displayed increased siderophore production, intracellular Fe²⁺ concentration, and increased sensitivity to hydrogen peroxide. In contrast, biofilm formation, swimming motility, and virulence on melon seedlings were significantly reduced in the furA mutant. As expected, complementation of the furA deletion mutant restored all phenotypes to wild-type levels. In accordance with the phenotypic results, the expression levels of bfrA and bfrB that encode bacterioferritin, sodB that encodes iron/manganese superoxide dismutase, fliS that encodes a flagellar protein, hrcN that encodes the type III secretion system (T3SS) ATPase, and hrcC that encodes the T3SS outer membrane ring protein were significantly downregulated in the A. citrulli furA deletion mutant. In addition, the expression of feo-related genes and feoA and feoB was significantly upregulated in the furA mutant. Overall, these results indicated that, in A. citrulli, FurA contributes to the regulation of the iron balance system, and affects a variety of virulence-related traits.

GAPDH, rhbC, and vapA gene expression in Rhodococcus equi cultured under different iron concentrations

The ability of Rhodococcus equi to survive in macrophages and cause pneumonia in foals depends on vapA and rhbC genes, which produce the virulence-associated protein A (VapA) and the rhequichelin siderophore, respectively. Virulent R. equi acquires Fe from transferrin by unknown mechanisms. Our objectives were to determine the role of GAPDH in Fe homeostasis, to further characterize GAPDH, rhbC, and vapA expression under iron homeostasis, and to document the occurrence of rhbC gene in R. equi isolates. Therefore, vapA + R. equi was cultured under excessive, physiologic, and restricted iron concentrations, and quantitative culture and gene expression were performed. The relative expression of GAPDH, rhbC, and vapA after 48 h of culture were analyzed by qPCR. To determine the rhbC occurrence, total DNA was extracted from R. equi isolated from foals with clinical rhodococcosis (n = 22), healthy horses (feces, n = 16; nasal swab, n = 9), soil (n = 6), and 2 ATCC reference strains. Conventional PCR was performed to identify genus/species, vapA, and rhbC genes. Iron restriction proportionally decreased R. equi growth rates, and induced high expression of both GAPDH and vapA. The putative role of GAPDH in R. equi iron homeostasis should be further investigated. rhbC was significantly up-regulated under both Fe excess and critical starvation. The rhbC gene was identified in all clinical isolates and soil, but it was absent in 2 isolates from healthy horses, suggesting that rhequichelin is not required for R. equi nasal and intestinal colonization.

The Role of Iron Regulation in Immunometabolism and Immune-Related Disease

Immunometabolism explores how the intracellular metabolic pathways in immune cells can regulate their function under different micro-environmental and (patho-)-physiological conditions (Pearce, 2010; Buck et al., 2015; O'Neill and Pearce, 2016). In the last decade great advances have been made in studying and manipulating metabolic programs in immune cells. Immunometabolism has primarily focused on glycolysis, the TCA cycle and oxidative phosphorylation (OXPHOS) as well as free fatty acid synthesis and oxidation. These pathways are important for providing the energy needs of cell growth, membrane rigidity, cytokine production and proliferation. In this review, we will however, highlight the specific role of iron metabolism at the cellular and organismal level, as well as how the bioavailability of this metal orchestrates complex metabolic programs in immune cell homeostasis and inflammation. We will also discuss how dysregulation of iron metabolism contributes to alterations in the immune system and how these novel insights into iron regulation can be targeted to metabolically manipulate immune cell function under pathophysiological conditions, providing new therapeutic opportunities for autoimmunity and cancer.

The structure of the bacterial iron-catecholate transporter Fiu suggests that it imports substrates via a two-step mechanism

The ferric iron uptake (Fiu) transporter from Escherichia coli functions in the transport of iron–catecholate complexes across the bacterial outer membrane, providing the bacterium with iron, which is essential for growth. Recently it has become clear that Fiu also represents a liability for E. coli because its activity allows import of antimicrobial compounds that mimic catecholate. This inadvertent import suggests the potential utility of antimicrobial catechol siderophore mimetics in managing bacterial infections. However, to fully exploit these compounds, a detailed understanding of the mechanism of transport through Fiu and related transporters is required. To address this question, we determined the crystal structure of Fiu at 2.1–2.9 Å and analyzed its function in E. coli. Through analysis of the Fiuo crystal structure, in combination with in silico docking and mutagenesis, we provide insight into how Fiu and related transporters bind catecholate in a surface-exposed cavity. Moreover, through determination of the structure of Fiu in multiple crystal states, we revealed the presence of a large, selectively gated cavity in the interior of this transporter. This chamber is large enough to accommodate the Fiu substrate and may allow import of substrates via a two-step mechanism. This would avoid channel formation through the transporter and inadvertent import of toxic molecules. As Fiu and its homologs are the targets of substrate-mimicking antibiotics, these results may assist in the development of these compounds.

Isolation, Screening, and Characterization of Plant-Growth-Promoting Bacteria from Durum Wheat Rhizosphere to Improve N and P Nutrient Use Efficiency

The main goal of this paper was to select promising microorganisms which could potentially act as plant-growth-promoting bacteria (PGPB) for durum wheat of Foggia County. At this scope, a new statistical framework, based on multivariate analyses and the evaluation of the statistical distribution of each trait, was used. Four hundred and seventy-four isolates were isolated from the rhizosphere of durum wheat in Foggia County and preliminarily screened as a function of four target indices (ammonium production, siderophores production, P-solubilization, and nitrification). After this step, the number of strains was reduced and the remaining isolates were tested through a quantitative approach, to assess the production of IAA (indole acetic acid), P-mineralization, and nitrification. In this second step, the cut-off was based on the whole population trend by evaluating for each trait the medians and quartiles. As a result, 16 promising isolates were selected and identified by 16S rDNA sequencing (Bacillus, Pseudomonas, Stenotrophomonas, and Lysinibacillus). The last step of this research was a preliminary validation in a growth chamber on eight strains. As screening and simple indices, two quantitative measures were chosen. The main result was the selection of at least three isolates (6P, 20P, and 25A) for a future field validation. They increased biomass and height by respectively 50% and 25%.

Outer membrane protein OmpU is related to iron balance in Vibrio alginolyticus

Outer membrane protein U (OmpU) is a major porin from Vibrio alginolyticus and has been considered a vaccine candidate against infection by V. alginolyticus. After pre-incubated with polyclonal antibody against rOmpU, V. alginolyticus showed a 78% decrease in extracellular iron level, suggesting that interruption of OmpU could increase intracellular iron level. The mRNA expression of ompU under iron-limited conditions was determined using real-time reverse transcriptase PCR. The mRNA level of ompU was downregulated to 0.27-, 0.036- and 0.019-fold after the addition of the iron chelator 2,2'-bipyridyl for 10, 30 and 60 min, respectively. In addition, the promoter of ompU contained a ferric uptake regulator (Fur) binding site, which revealed the potential regulation of ompU by Fur and iron. Fur from V. alginolyticus was purified and used for electrophoretic mobility shift assay. The result showed that in the absence of Fe²⁺, purified recombinant Fur could specifically bind to the promoter DNA of ompU, while in the presence of Fe²⁺, the binding of Fur and the promoter DNA was suppressed. Our study preliminarily explored the function of OmpU in iron balance in V. alginolyticus, and these findings were helpful in understanding iron metabolism in V. alginolyticus.

Structural Insights into Substrate Recognition and Activity Regulation of the Key Decarboxylase SbnH in Staphyloferrin B Biosynthesis

Staphyloferrin B is a hydroxycarboxylate siderophore that is crucial for the invasion and virulence of Staphylococcus aureus in mammalian hosts where free iron ions are scarce. The assembly of staphyloferrin B involves four enzymatic steps, in which SbnH, a pyridoxal 5'-phosphate (PLP)-dependent decarboxylase, catalyzes the second step. Here, we report the X-ray crystal structures of S. aureus SbnH (SaSbnH) in complex with PLP, citrate, and the decarboxylation product citryl-diaminoethane (citryl-Dae). The overall structure of SaSbnH resembles those of the previously reported PLP-dependent amino acid decarboxylases, but the active site of SaSbnH showed unique structural features. Structural and mutagenesis analysis revealed that the citryl moiety of the substrate citryl-l-2,3-diaminopropionic acid (citryl-l-Dap) inserts into a narrow groove at the dimer interface of SaSbnH and forms hydrogen bonding interactions with both subunits. In the active site, a conserved lysine residue forms an aldimine linkage with the cofactor PLP, and a phenylalanine residue is essential for accommodating the l-configuration Dap of the substrate. Interestingly, the freestanding citrate molecule was found to bind to SaSbnH in a conformation inverse to that of the citryl group of citryl-Dae and efficiently inhibit SaSbnH. As an intermediate in the tricarboxylic acid (TCA) cycle, citrate is highly abundant in bacterial cells until iron depletion; thus, its inhibition of SaSbnH may serve as an iron-dependent regulatory mechanism in staphyloferrin B biosynthesis.

Investigating the influence of iron on Campylobacter jejuni transcriptome in response to acid stress

The capacity of C. jejuni to survive acid and capture iron is a requirement for C. jejuni to colonize host and cause infection. Herein, we aimed to characterize the influence of iron on Campylobacter acid response. The capacity of C. jejuni to survive acid stress was greatly enhanced in presence of iron. Moreover, the acid stimulon of C. jejuni under iron-enriched condition was investigated using the microarray approach. A total of 211 genes were differentially expressed in C. jejuni. Differentially expressed genes were included in 21 functional groups that control Campylobacter physiology. C. jejuni induced expression of many genes that were previously shown to be important for Campylobacter acid survival such as flagella biogenesis genes and genes involved in cell envelope biogenesis. The microarray results were validated using RT-qPCR where there was a great similarity in data obtained by both techniques. Finally, comparative analysis with previous studies showed that acid exposure induced expression of many genes in C. jejuni that were not detected in other studies such as genes encoding for the heat shock proteins GroEL and GroES. Current data could help us understand the mechanism of C. jejuni acid survival and consequently overcome infection by this enteric pathogen.

Pseudomonas aeruginosa possesses three distinct systems for sensing and using the host molecule haem

Pathogens have developed several strategies to obtain iron during infection, including the use of iron-containing molecules from the host. Haem accounts for the vast majority of the iron pool in vertebrates and thus represents an important source of iron for pathogens. Using a proteomic approach, we have identified in this work a previously uncharacterized system, which we name Hxu, that together with the known Has and Phu systems, is used by the human pathogen Pseudomonas aeruginosa to respond to haem. We show that the Has and Hxu systems are functional signal transduction pathways of the cell-surface signalling class and report the mechanism triggering the activation of these signalling systems. Both signalling cascades involve an outer membrane receptor (HasR and HxuA respectively) that upon sensing haem in the extracellular medium produces the activation of an σ^ECF factor in the cytosol. HxuA has a major role in signalling and a minor role in haem acquisition in conditions in which the HasR and PhuR receptors or other sources of iron are present. Remarkably, P. aeruginosa compensates the lack of the HasR receptor by increasing the production of HxuA, which underscores the importance of haem signalling for this pathogen.

Fe3+ enhanced degradation of oxytetracycline in water by pseudomonas

The application and fate of antibiotics are closely related to human health and the ecological balance, which has gradually aroused the widespread global concerns. Long-term antibiotic residues can easily induce antibiotic resistance and antibiotic resistance genes (ARGs) in the environment. Although many studies have investigated the metabolic pathways of biosynthesis or degradation of oxytetracycline (OTC) and its influencing factors under laboratory or controlled conditions, the understanding of OTC degradation pathways and influencing factors in the environment is still poor. In the present study, the role of Pseudomonas (T4) in OTC biodegradation were investigated with different carbon sources, metal ions, substrate concentrations, temperatures, and pH values, as well as the temporal changes in the relative abundance of OTC ARGs. It was found that OTC could be degraded by T4 as a sole carbon source. Comparison with Cu²⁺, the addition of Fe³⁺ could significantly promote the growth of T4, and then increased the OTC degradation percentage to 65.3%. The initial concentration of OTC, temperature, and pH had significant impacts on OTC degradation. At the initial OTC concentration of 50 mg L^-1, the percentage degradation of OTC by T4 could reach 81.0% at the presence of Fe³⁺, and at 40 °C and pH = 7. Common tetracycline ARGs were not found during the OTC degradation by T4 in the present study. The eight main putative OTC degradation byproducts were identified by ultra-high definition accurate-mass quadrupole time-of-flight tandem mass spectrometry (QTOF/MS). Six different reaction types and seven possible degradation pathways were proposed, including enol-ketone conversion, hydroxylation, dehydration, deamination, demethylation and decarbonylation. Under optimal conditions, the OTC degradation percentages by T4 could reach to 88.2%, 91.6% and 92.0% in pond water, fish wastewater and industrial wastewater, respectively. These results demonstrate the high effectiveness of T4 at the presence of Fe³⁺ for the enhanced biodegradation of OTC in water environment, without resulting in the occurrence of ARGs. This has important implications for the removal of OTC from aquatic environments by the technology proposed from this study.

Chemo-Mechanical Coupling in the Transport Cycle of a Heme ABC Transporter

The heme importer from pathogenic bacteria is a member of the ATP-binding cassette (ABC) transporter family, which uses the energy of ATP-binding and hydrolysis for extensive conformational changes. Previous studies have indicated that conformational changes after heme translocation are triggered by ATP-binding to nucleotide binding domains (NBDs) and then, in turn, induce conformational transitions of the transmembrane domains (TMDs). In this study, we applied a template-based iterative all-atom molecular dynamics (MD) simulation to predict the ATP-bound outward-facing conformation of the Burkholderia cenocepacia heme importer BhuUV-T. The resulting model showed a stable conformation of the TMD with the cytoplasmic gate in the closed state and the periplasmic gate in the open state. Furthermore, targeted MD simulation predicted the intermediate structure of an occluded form (Occ) with bound ATP, in which both ends of the heme translocation channel are closed. The MD simulation of the predicted Occ revealed that Ser147 on the ABC signature motifs (LSGG[Q/E]) of NBDs occasionally flips and loses the active conformation required for ATP-hydrolysis. The flipping motion was found to be coupled to the inter-NBD distance. Our results highlight the functional significance of the signature motif of ABC transporters in regulation of ATPase and chemo-mechanical coupling mechanism.

Iron and fecundity among Tsimane' women of Bolivia

Background and objectives

Iron is critical for women's reproduction, and iron-deficiency anemia is a global health problem for mothers. While public health programs have aimed to correct iron deficiency in reproductive-aged women with supplementation, a small group of studies have shown that too much iron also has negative effects on birth outcomes. We hypothesize that women's iron levels evolved within a narrow optimum, and predict that hemoglobin (Hb) levels would be associated with women's fecundity.

Methodology

We used the publicly available, longitudinal Tsimane' Amazonian Panel Study to test the association between -Hb levels and hazard of having a next birth (a measure of fecundity) among 116 parous, reproductive-aged Tsimane' women of Bolivia. A Cox proportional hazards model was used to model Hb level and other predictors against the event of next birth across the observation period, which began at each woman's previous birth.

Results

The higher the Hb level, the lower the hazard of a woman giving birth within the study observation period (hazard ratio=0.82, P = 0.03). However, there was no evidence that low Hb reduced women's fecundity.

Conclusions and implications

These results demonstrate that high Hb influences women's fecundity. These results supports the growing body of literature showing that iron metabolism is critical for understanding the evolution of women's reproduction. More work is needed to determine the evolved optimal range of iron levels for reproductive-aged women.

Lay summary

Lower chance of pregnancy among Tsimane' women with high Hb levels, suggesting evolved optimal Hb levels in women.

Targeting Mobilization of Ferrous Iron in Pseudomonas aeruginosa Infection with an Iron(II)-Caged LpxC Inhibitor

Iron is essential to all life, and competition for this vital nutrient is central to host-pathogen interactions during infection. The opportunistic Gram-negative pathogen Pseudomonas aeruginosa utilizes a diverse array of iron-acquisition strategies, including those enabling import of extracellular ferrous iron. We hypothesize that soluble and redox-active ferrous iron can be employed to activate caged antibiotics at sites of infection in vivo. Here we describe new chemistry that expands the application of our laboratory's Fe²⁺-activated-prodrug chemistry to cage hydroxamic acids, a class of drugs that present manifold development challenges. We synthesize the caged form of a known LpxC inhibitor and show that it is efficacious in an acute P. aeruginosa mouse-lung infection model, despite showing little activity in cell-culture experiments. Overall, our results are consistent with the Fe²⁺-promoted uncaging of an antibacterial payload at sites of infection in an animal and lend support to recent reports indicating that extracellular pools of ferrous iron can be utilized by bacterial pathogens like P. aeruginosa during infection.

Functions and regulation of lipocalin-2 in gut-origin sepsis: a narrative review

Lipocalin-2 (Lcn2), an innate immune protein, has come to be recognized for its roles in iron homeostasis, infection, and inflammation. In this narrative review, we provide a comprehensive description based on currently available evidence of the clinical implications of Lcn2 and its therapeutic potency in gut-origin sepsis. Lcn2 appears to mitigate gut barrier injury via maintaining homeostasis of the microbiota and exerting antioxidant strategy, as well as by deactivating macrophages and inducing immune cell apoptosis to terminate systemic hyper-inflammation. We propose that development of a therapeutic strategy targeting lipocalin-2 could be highly promising in the management of gut-origin sepsis.

Hijacking the Heme Acquisition System of Pseudomonas aeruginosa for the Delivery of Phthalocyanine as an Antimicrobial

To survive in the iron-devoid environment of their host, pathogenic bacteria have devised multifarious cunning tactics such as evolving intricate heme transport systems to pirate extracellular heme. Yet, the potential of heme transport systems as antimicrobial targets has not been explored. Herein we developed a strategy to deliver antimicrobials by exploiting the extracellular heme acquisition system protein A (HasA) of Pseudomonas aeruginosa. We demonstrated that, analogous to heme uptake, HasA can specifically traffic an antimicrobial, gallium phthalocyanine (GaPc), into the intracellular space of P. aeruginosa via the interaction of HasA with its outer membrane receptor HasR. HasA enables water-insoluble GaPc to be mistakenly acquired by P. aeruginosa, permitting its sterilization (>99.99%) by irradiation with near-infrared (NIR) light, irrespective of antibiotic resistance. Our findings substantiate that bacterial heme uptake via protein-protein recognition is an attractive target for antimicrobials, enabling specific and effective sterilization.

The human iron-proteome

Organisms from all kingdoms of life use iron-proteins in a multitude of functional processes. We applied a bioinformatics approach to investigate the human portfolio of iron-proteins. We separated iron-proteins based on the chemical nature of their metal-containing cofactors: individual iron ions, heme cofactors and iron-sulfur clusters. We found that about 2% of human genes encode an iron-protein. Of these, 35% are proteins binding individual iron ions, 48% are heme-binding proteins and 17% are iron-sulfur proteins. More than half of the human iron-proteins have a catalytic function. Indeed, we predict that 6.5% of all human enzymes are iron-dependent. This percentage is quite different for the various enzyme classes. Human oxidoreductases feature the largest fraction of iron-dependent family members (about 37%). The distribution of iron proteins in the various cellular compartments is uneven. In particular, the mitochondrion and the endoplasmic reticulum are enriched in iron-proteins with respect to the average content of the cell. Finally, we observed that genes encoding iron-proteins are more frequently associated to pathologies than the all other human genes on average. The present research provides an extensive overview of iron usage by the human proteome, and highlights several specific features of the physiological role of iron ions in human cells.