Bacterial Siderophores Research Articles

Changes trend of physiological characteristics in maize as influenced by delaying irrigation and bacterial siderophore

Changes trend of physiological characteristics in maize as influenced by delaying irrigation and bacterial siderophore

Siderophore-mediated iron removal from chrysotile: Implications for asbestos toxicity reduction and bioremediation

Asbestos fibers are highly toxic (Group 1 carcinogen) due to their high aspect ratio, durability, and the presence of iron. In nature, plants, fungi, and microorganisms release exudates, which can alter the physical and chemical properties of soil minerals including asbestos minerals. We examined whether exudates from bacteria and fungi at environmentally relevant concentrations can alter chrysotile, the most widely used asbestos mineral, and lower its toxicity. We monitored the release of iron from chrysotile in the presence of organic acid ligands and iron-specific siderophores derived from bacteria and fungi and measured any change in fiber toxicity toward peritoneal macrophages harvested from mice. Both fungal and bacterial siderophores increased the removal of iron from asbestos fibers. In contrast, organic acid ligands at environmentally relevant concentrations neither released iron from fibers nor helped in siderophore-mediated iron removal. Removal of plant-available or exchangeable iron did not diminish iron dissolution by both types of siderophores, which indicates that siderophores can effectively remove structural iron from chrysotile fibers. Removal of iron by siderophore lowered the fiber toxicity; fungal siderophore appears to be more effective than bacterial siderophore in lowering the toxicity. These results indicate that prolonged exposure to siderophores, not organic acids, in the soil environment decreases asbestos fiber toxicity and possibly lowers the health risks. Thus, bioremediation should be explored as a viable strategy to manage asbestos-contaminated sites such as Brownfield sites, which are currently left untreated despite dangers to surrounding communities.

Intraspecific variability in Phaeocystis antarctica's response to iron and light stress.

Phaeocystis antarctica is an abundant phytoplankton species in the Southern Ocean, where growth is frequently limited by iron and light. Being able to grow under low iron conditions is essential to the species’ success, but there have been hints that this ability differs among clones. Here, we compare the growth, cell size and chlorophyll a concentrations of four P. antarctica clones cultured under different iron and light conditions. Iron was provided either as unchelated iron (Fe′) or bound to the bacterial siderophore desferrioxamine B, representing, respectively, the most and least bioavailable forms of iron which phytoplankton encounter in the marine environment. The growth rate data demonstrate that the clones vary in their ability to grow using organically bound iron, and that this ability is not related to their ability to grow at low inorganic iron concentrations. These results are consistent at low and high light. Physiologically, only three of the four clones shrink or decrease the concentration of chlorophyll a in response to iron limitation, and only one clone decreases colony formation. Together, our data show that P. antarctica clones 1) respond to the same degree of iron limitation using different acclimation strategies, and 2) vary in their ability to grow under the same external iron and light conditions. This physiological diversity is surprisingly large for isolates of a single phytoplankton species.

Ectopic Expression of Innate Immune Protein, Lipocalin-2, in Lactococcus lactis Protects Against Gut and Environmental Stressors.

Lipocalin-2 (Lcn2) is a multifunctional innate immune protein that exhibits antimicrobial activity by the sequestration of bacterial siderophores, regulates iron homeostasis, and augments cellular tolerance to oxidative stress. Studies in the murine model of colitis have demonstrated that Lcn2 deficiency exacerbates colitogenesis; however, the therapeutic potential of Lcn2 supplementation has yet to be elucidated. In light of its potential mucoprotective functions, we, herein, investigated whether expression of Lcn2 in the probiotic bacterium can be exploited to alleviate experimental colitis. Murine Lcn2 was cloned into the pT1NX plasmid and transformed into Lactococcus lactis to generate L. lactis-expressing Lcn2 (Lactis-Lcn2) or the empty plasmid (Lactis-Con). Lactis-Lcn2 was characterized by immunoblot and enzyme-linked immunosorbent assay and tested for its antimicrobial efficacy on Escherichia coli. The capacity of Lactis-Lcn2 and Lactis-Con to withstand adverse conditions was tested using in vitro viability assays. Dextran sodium sulfate colitis model was used to investigate the colonization ability and therapeutic potential of Lactis-Lcn2 and Lactis-Con. Lcn2 derived from Lactis-Lcn2 inhibited the growth of E. coli and reduced the bioactivity of enterobactin (E. coli-derived siderophore) in vitro. Lactis-Lcn2 displayed enhanced tolerance to adverse pH, high concentration of bile acids, and oxidative stress in vitro and survived better in the inflamed gut than Lactis-Con. Consistent with these features, Lactis-Lcn2 displayed better mucoprotection against intestinal inflammation than Lactis-Con when administered into mice with dextran sulfate sodium-induced acute colitis. Our findings suggest that Lcn2 expression can be exploited to enhance the survivability of probiotic bacteria during inflammation, which could further improve its efficacy to treat experimental colitis.

A conserved mitochondrial surveillance pathway is required for defense against Pseudomonas aeruginosa.

All living organisms exist in a precarious state of homeostasis that requires constant maintenance. A wide variety of stresses, including hypoxia, heat, and infection by pathogens perpetually threaten to imbalance this state. Organisms use a battery of defenses to mitigate damage and restore normal function. Previously, we described a Caenorhabditis elegans-Pseudomonas aeruginosa assay (Liquid Killing) in which toxicity to the host is dependent upon the secreted bacterial siderophore pyoverdine. Although pyoverdine is also indispensable for virulence in mammals, its cytological effects are unclear. We used genetics, transcriptomics, and a variety of pathogen and chemical exposure assays to study the interactions between P. aeruginosa and C. elegans. Although P. aeruginosa can kill C. elegans through at least 5 different mechanisms, the defense responses activated by Liquid Killing are specific and selective and have little in common with innate defense mechanisms against intestinal colonization. Intriguingly, the defense response utilizes the phylogenetically-conserved ESRE (Ethanol and Stress Response Element) network, which we and others have previously shown to mitigate damage from a variety of abiotic stresses. This is the first report of this networks involvement in innate immunity, and indicates that host innate immune responses overlap with responses to abiotic stresses. The upregulation of the ESRE network in C. elegans is mediated in part by a family of bZIP proteins (including ZIP-2, ZIP-4, CEBP-1, and CEBP-2) that have overlapping and unique functions. Our data convincingly show that, following exposure to P. aeruginosa, the ESRE defense network is activated by mitochondrial damage, and that mitochondrial damage also leads to ESRE activation in mammals. This establishes a role for ESRE in a phylogenetically-conserved mitochondrial surveillance system important for stress response and innate immunity.

The rhizoferrin biosynthetic gene in the fungal pathogen Rhizopus delemar is a novel member of the NIS gene family

Iron is essential for growth and in low iron environments such as serum many bacteria and fungi secrete ferric iron-chelating molecules called siderophores. All fungi produce hydroxamate siderophores with the exception of Mucorales fungi, which secrete rhizoferrin, a polycarboxylate siderophore. Here we investigated the biosynthesis of rhizoferrin by the opportunistic human pathogen, Rhizopus delemar. We searched the genome of R. delemar 99–880 for a homologue of the bacterial NRPS-independent siderophore (NIS) protein, SfnaD, that is involved in biosynthesis of staphyloferrin A in Staphylococcus aureus. A protein was identified in R. delemar with 22% identity and 37% similarity with SfnaD, containing an N-terminal IucA/IucC family domain, and a C-terminal conserved ferric iron reductase FhuF-like transporter domain. Expression of the putative fungal rhizoferrin synthetase (rfs) gene was repressed by iron. The rfs gene was cloned and expressed in E.coli and siderophore biosynthesis from citrate and diaminobutane was confirmed using high resolution LC–MS. Substrate specificity was investigated showing that Rfs produced AMP when oxaloacetic acid, tricarballylic acid, ornithine, hydroxylamine, diaminopentane and diaminopropane were employed as substrates. Based on the production of AMP and the presence of a mono-substituted rhizoferrin, we suggest that Rfs is a member of the superfamily of adenylating enzymes. We used site-directed mutagenesis to mutate selected conserved residues predicted to be in the Rfs active site. These studies revealed that H484 is essential for Rfs activity and L544 may play a role in amine recognition by the enzyme. This study on Rfs is the first characterization of a fungal NIS enzyme. Future work will determine if rhizoferrin biosynthesis is required for virulence in Mucorales fungi.

Ectopic expression of innate immune protein Lipocalin-2 in probiotic Lactococcus lactis protects against environmental and gut inflammatory stressors

Abstract Overexpression of lipocalin-2 (Lcn2), an acute phase protein, has been demonstrated to enhance cellular resistance to oxidative stress in various mammalian cell lines, in addition to mediating anti-bacterial effects by sequestering bacterial siderophores (iron chelators). To investigate whether Lcn2 could be exploited to augment the stability and efficacy of probiotic bacteria, we have engineered the recombinant Lactococcus lactis (MG1363) that expresses the murine Lcn2 (LactisLcn2) and the empty plasmid (LactisCon). The expression of Lcn2 did not impair the growth of LactisLcn2, especially since L. lactis do not require iron for its growth. In contrast, the L. Lactis-derived Lcn2 was effective in mitigating the bioactivity of enterobactin (E. coli-derived siderophore) and inhibited the growth of E. coli in vitro. The sequestration of iron in LactisLcn2 could, in part, explain its ability to inhibit the iron-dependent growth of E. coli. Moreover, the Lcn2 expression also augments the capacity of LactisLcn2 to withstand various environmental stressors in vitro, including extreme pH, toxicity of bile salts, H2O2-, and myeloperoxidase-mediated bacterial killing. When administered into mice with DSS-induced acute colitis, LactisLcn2 was observed to survive better in the inflamed gut and provide superior mucoprotection against intestinal inflammation when compared with LactisCon. Overall, our findings suggest that Lcn2 expression can be exploited to augment the iron-scavenging capability and survivability of probiotic bacteria against adverse conditions, which could further enhance their efficacy to treat inflammatory bowel diseases.

Enterobactin, a metallophore, mitigates the immune responses of macrophages

Abstract Iron is required to facilitate the redox activity of heme proteins expressed in both immune and non-immune cells. In this study, we investigated whether the chelation of iron by enterobactin (Ent; a prototypical bacterial siderophore) can affect the immune and nitrosative responses of RAW 264.7 and bone marrow-derived macrophages. We observed that Ent dose-dependently inhibited the LPS-induced secretion of cytokines (i.e., serum amyloid A, IL-6, lipocalin 2) and nitrite in the macrophages. The LPS-induced expression of inducible nitric oxide synthase (iNOS; a heme protein) was also inhibited by Ent at both the mRNA and protein levels. To demonstrate the physiological relevance of these findings, we next investigated whether Ent could protect the intracellular pathogen Salmonella enterica serovars typhimurium in the gentamycin protection assay. Ent reduced the nitrite levels in Salmonella-infected macrophages, but upregulated the expression of iNOS (mRNA, protein) and Arginase-1 (mRNA). More importantly, Ent-treated macrophages were impaired in mediating the killing of Salmonella. Ent-sufficient Salmonella also survived better compared with their isogenic Ent-deficient strains, whereas the addition of exogenous Ent substantially improved the survival of both strains. The inhibitory effects of Ent, however, were abrogated when saturated with iron (1:1 ratio), thus indicating that Ent is required to be in its iron-free form to mediate efficient inhibition on the macrophages. Taken together, our findings advance the concept that Ent not only facilitate bacterial iron uptake, but also serve to safeguard bacteria against macrophage immune responses.

Siderophores in clinical isolates of Klebsiella pneumoniae promote ciprofloxacin resistance by inhibiting the oxidative stress

To explore the relevance of and understand the potential mechanisms behind the production of siderophores by clinical isolates of K. pneumoniae and ciprofloxacin (CIP) resistance, we divided the K. pneumoniae isolates into two groups based on bacterial siderophores production: high siderophore-yielding group (39 strains) and low siderophore-yielding group (38 strains). The rate of CIP resistance in K. pneumoniae (27/39 = 69.23%) from the high siderophore-yielding group was significantly higher than that (16/38 = 42.11%) in the low siderophore-yielding group (p < 0.05). Furthermore, we noted that bacterial siderophores production was positively correlating with CIP resistance as indicated by the minimum inhibitory concentration (MIC; p < 0.05). However, siderophore-related antibiotic resistance had no relationship with DNA gyrase GyrA mutation (p > 0.05). Siderophore-related antibiotic resistance was accompanied by efflux pump functions, but was not directly relevant to it. Furthermore, we found that the oxidative stress response was significantly lower in high siderophore-yielding strains compared to those isolates which had a low siderophores yield (12.17 vs. 30.91 of average fluorescence value; p < 0.01). There was a consistent inverse correlation between the production of bacterial siderophores and oxidative stress response (p < 0.05). Although CIP induced oxidative stress in both high and low siderophore-yielding strains (p < 0.01), oxidative stress in high siderophore-yielding strains was significantly lower than in low siderophore-yielding strains (p < 0.01). Our data suggest that siderophores of K. pneumoniae clinical isolates promote CIP resistance through inhibition of the bacterial oxidative stress response, indicating that reduction of bacterial oxidative stress could provide a new avenue for control of bacterial drug resistance.

Effect of microbial siderophores on mammalian non-malignant and malignant cell lines

BackgroundIron is a vital nutrient for all cells, and malignant cells have a higher requirement for the metal due to their rapid multiplication. Bacterial siderophores can be used to reduce free ferric ion concentration from the cellular environment.MethodsIn the present study, we have evaluated effect of three siderophores – exochelin-MS, mycobactin S and deferoxamine B on the proliferation of mammalian cell lines using MTT assay.ResultsThese siderophores caused a significant decrease in the viability of malignant cells, without significantly affecting non-malignant cells.ConclusionsBased on these results, we suggest that iron-chelation therapy could be explored as an adjunctive therapeutic option against cancer along with other therapies.

Bacterial siderophores promote plant growth: Screening of catechol and hydroxamate siderophores

ABSTRACTThe aim of the study was to determine the quality and quantity of siderophores produced by bacteria isolated from plants' roots. The second aim was to determine the effect of siderophores on plants growth (Festuca rubra L. and Brassica napus L.). The study was carried out using bacteria isolated from roots of: Arabidopsis thaliana L., F. rubra, and Agrostis capillaris L., growing on the heavy metals contaminated area. The chrome azurol sulfonate (CAS) test, Arnow's test for catechol siderophores, and Csaksy's test for hydroxamate siderophores were performed. Among the bacteria, 42 isolates (39%) had a positive result in the CAS. Endophytic bacteria were mostly producing the catechol siderophores. It was found that F. rubra is the plant which is linked with the highest number of siderophores producing bacteria. The highest concentration of siderophores was noted for ectorhizospheric bacteria associated with A. thaliana, hyperaccumulating plant. It was found that hydroxamate siderophores are mainly produced by ectorhizosphere and rhizoplane bacteria. The siderophores producing bacteria reduced the toxicity of metals and improved the phytoremediation. Siderophores treatment increased the growth of plants in the biological assay, growing on two different soils: one highly contaminated with heavy metals and the second strongly alkaline soil.

Mitochondria-penetrating peptides conjugated to desferrioxamine as chelators for mitochondrial labile iron.

Desferrioxamine (DFO) is a bacterial siderophore with a high affinity for iron, but low cell penetration. As part of our ongoing project focused on DFO-conjugates, we synthesized, purified, characterized and studied new mtDFOs (DFO conjugated to the Mitochondria Penetrating Peptides TAT49-57, 1A, SS02 and SS20) using a succinic linker. These new conjugates retained their strong iron binding ability and antioxidant capacity. They were relatively non toxic to A2780 cells (IC50 40–100 μM) and had good mitochondrial localization (Rr +0.45 –+0.68) as observed when labeled with carboxy-tetramethylrhodamine (TAMRA) In general, mtDFO caused only modest levels of mitochondrial DNA (mtDNA) damage. DFO-SS02 retained the antioxidant ability of the parent peptide, shown by the inhibition of mitochondrial superoxide formation. None of the compounds displayed cell cycle arrest or enhanced apoptosis. Taken together, these results indicate that mtDFO could be promising compounds for amelioration of the disease symptoms of iron overload in mitochondria.

Unambiguous identification and discovery of bacterial siderophores by direct injection 21 Tesla Fourier transform ion cyclotron resonance mass spectrometry

Under iron-limiting conditions, bacteria produce low molecular mass Fe(iii) binding molecules known as siderophores to sequester the Fe(iii), along with other elements, increasing their bioavailability. Siderophores are thought to influence iron cycling and biogeochemistry in both marine and terrestrial ecosystems and hence the need for rapid, confident characterization of these compounds has increased. In this study, the type of siderophores produced by two marine bacterial species, Synechococcus sp. PCC 7002 and Vibrio cyclitrophicus 1F53, were characterized by use of a newly developed 21 T Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FTICR MS) with direct injection electrospray ionization. This technique allowed for the rapid detection of synechobactins from Synechococcus sp. PCC 7002 as well as amphibactins from Vibrio cyclitrophicus 1F53 based on high mass accuracy and resolution allowing for observation of specific Fe isotopes and isotopic fine structure enabling highly confident identification of these siderophores. When combined with molecular network analysis two new amphibactins were discovered and verified by tandem MS. These results show that high-field FTICR MS is a powerful technique that will greatly improve the ability to rapidly identify and discover metal binding species in the environment.

Solubilization of Pb-bearing apatite Pb5(PO4)3Cl by bacteria isolated from polluted environment

The main purpose of this study was to test if microorganisms isolated from heavily polluted environments can enhance dissolution of Pb-apatite (pyromorphite) resulting in remobilization of lead. Three bacterial strains belonging to the genus Pseudomonas isolated from underground mines in SW Poland were used in batch experiments of pyromorphite solubilization carried out in phosphate reach and phosphate poor media. Bacteria growth and evolution of Pb and phosphate concentrations as well as pH were determined. Additionally the concentration of bacterial siderophores in leaching solution was assayed. All bacterial strains were able to grow in both media in the presence of pyromorphite. The number of bacterial cells was from one to two orders of magnitude higher in the phosphate rich media. In the phosphate poor media the only source of P was the dissolving lead apatite. Bacteria enhanced the solubility of pyromorphite resulting in elevated Pb concentrations, up to 853 μg L−1 in phosphate-rich medium and 6112 μg L−1 in phosphate-poor medium, compared to less than 100 μg L−1 in an abiotic control sample. Production of siderophores was characteristic for each culture and was much lower (10–1000 fold) in the phosphate-poor medium. This study demonstrates for the first time that indigenous bacteria can directly and indirectly promote the mobilization of lead from pyromorphite. This phenomenon should be considered in long term risk assessment of Pb contaminated soils after reclamation processes because bacteria can play a significant role in the efficiency of clean-up efforts and overall geochemical cycling of Pb.

Modulation of urinary siderophores by the diet, gut microbiota and inflammation in mice

Mammalian siderophores are believed to play a critical role in maintaining iron homeostasis. However, the properties and functions of mammalian siderophores have not been fully clarified. In this study, we have employed Chrome Azurol S (CAS) assay which is a well-established method for bacterial siderophores study, to detect and quantify mammalian siderophores in urine samples. Our study demonstrates that siderophores in urine can be altered by diet, gut microbiota and inflammation. C57BL/6 mice, fed on plant-based chow diets which contain numerous phytochemicals, have more siderophores in the urine compared to those fed on purified diets. Urinary siderophores were up-regulated in iron overload conditions, but not altered by other tested nutrients status. Further, germ-free mice displayed 50% reduced urinary siderophores, in comparison to conventional mice, indicating microbiota biotransformation is critical in generating or stimulating host metabolism to create more siderophores. Altered urinary siderophores levels during inflammation suggest that host health conditions influence systemic siderophores level. This is the first report to measure urinary siderophores as a whole, describing how siderophores levels are modulated under different physiological conditions. We believe that our study opens up a new field in mammalian siderophores research and the technique we used in a novel manner has the potential to be applied to clinical purpose.

Siderophore vaccine conjugates protect against uropathogenic Escherichia coli urinary tract infection

Uropathogenic Escherichia coli (UPEC) is the primary cause of uncomplicated urinary tract infections (UTIs). Whereas most infections are isolated cases, 1 in 40 women experience recurrent UTIs. The rise in antibiotic resistance has complicated the management of chronic UTIs and necessitates new preventative strategies. Currently, no UTI vaccines are approved for use in the United States, and the development of a highly effective vaccine remains elusive. Here, we have pursued a strategy for eliciting protective immunity by vaccinating with small molecules required for pathogenesis, rather than proteins or peptides. Small iron-chelating molecules called siderophores were selected as antigens to vaccinate against UTI for this vaccine strategy. These pathogen-associated stealth siderophores evade host immune defenses and enhance bacterial virulence. Previous animal studies revealed that vaccination with siderophore receptor proteins protects against UTI. The poor solubility of these integral outer-membrane proteins in aqueous solutions limits their practical utility. Because their cognate siderophores are water soluble, we hypothesized that these bacterial-derived small molecules are prime vaccine candidates. To test this hypothesis, we immunized mice with siderophores conjugated to an immunogenic carrier protein. The siderophore-protein conjugates elicited an adaptive immune response that targeted bacterial stealth siderophores and protected against UTI. Our study has identified additional antigens suitable for a multicomponent UTI vaccine and highlights the potential use of bacterial-derived small molecules as antigens in vaccine therapies.

Protozoa stimulate the plant beneficial activity of rhizospheric pseudomonads

AimsThe functioning of plant-associated bacteria is strongly influenced by their interaction with other organisms. For instance, bacteria upregulate the production of secondary metabolites in presence of protozoa and we hypothesised that this interaction may contribute to plant health.MethodsHere, we tested if the effect of beneficial pseudomonads on wheat growth and health is modified by co-inoculation with the bacterivorous amoeba Acanthamoeba castellanii. We assessed effects of this co-inoculation in absence and presence of the root pathogen Pythium ultimum.ResultsIn absence of amoebae, bacterial isolates had few beneficial effects and some isolates exacerbated growth inhibition by the pathogen (despite their reported beneficial effects in vitro). Effects on plant growth in absence and presence of the pathogen were negatively correlated. Co-inoculation with amoebae suppressed this relationship, leading to plant growth promotion in absence and reduction of deleterious effects in presence of the pathogen. The positive effect of amoebae in absence of the pathogen could be related to bacterial siderophore production in vitro.ConclusionsOur results illustrate the discrepancy between in vitro and in vivo effects of plant beneficial bacteria. Incorporation of other rhizospheric trophic components such as protists may be a key factor to influence the plant-beneficial potential of bacteria in vivo.

Predictive characterization of hypothetical proteins in Staphylococcus aureus NCTC 8325.

Staphylococcus aureus is one of the most common hospital acquired infections. It colonizes immunocompromised patients and with the number of antibiotic resistant strains increasing, medicine needs new treatment options. Understanding more about the proteins this organism uses would further this goal. Hypothetical proteins are sequences thought to encode a functional protein but for which little to no evidence of that function exists. About half of the genomic proteins in reference strain S. aureus NCTC 8325 are hypothetical. Since annotation of these proteins can lead to new therapeutic targets, a high demand to characterize hypothetical proteins is present. This work examines 35 hypothetical proteins from the chromosome of S. aureus NCTC 8325. Examination includes physiochemical characterization; sequence homology; structural homology; domain recognition; structure modeling; active site depiction; predicted protein-protein interactions; protein-chemical interactions; protein localization; protein stability; and protein solubility. The examination revealed some hypothetical proteins related to virulent domains and protein-protein interactions including superoxide dismutase, O-antigen, bacterial ferric iron reductase and siderophore synthesis. Yet other hypothetical proteins appear to be metabolic or transport proteins including ABC transporters, major facilitator superfamily, S-adenosylmethionine decarboxylase, and GTPases. Progress evaluating some hypothetical proteins, particularly the smaller ones, was incomplete due to limited homology and structural information in public repositories. These data characterizing hypothetical proteins will contribute to the scientific understanding of S. aureus by identifying potential drug targets and aiding in future drug discovery.

Transposon-mediated random gene disruption with moderate halophilic bacteria and its application for halophilic bacterial siderophore analysis.

Analytical conditions using chromo azurol S was validated for quantification of siderophore in aqueous samples, followed by the characterization of siderophore derived from newly isolated moderately halophilic bacteria. Conditions with good linearity between the absorbance and the siderophore concentration were obtained at a siderophore concentration less than 20 µM, in the wavelength range between 630 and 660 nm with developing time for at least 2 h. Of the halophilic bacteria isolated from Tunisian soil, Halomonas sp., namely strain 21a was selected as siderophore producing halophiles. The strain produced siderophore significantly in the absence of iron in minimal medium. Siderophore-deficient mutant, namely IIa10, of the strain 21a was obtained from gene disruptant library constructed using transposon complex by electroporation. Genomic sequence analysis of the mutant IIa10 revealed that the transposon-inserted gene was TonB-dependent receptor.

Fungal Innate Immunity Induced by Bacterial Microbe-Associated Molecular Patterns (MAMPs).

Plants and animals detect bacterial presence through Microbe-Associated Molecular Patterns (MAMPs) which induce an innate immune response. The field of fungal–bacterial interaction at the molecular level is still in its infancy and little is known about MAMPs and their detection by fungi. Exposing Fusarium graminearum to bacterial MAMPs led to increased fungal membrane hyperpolarization, a putative defense response, and a range of transcriptional responses. The fungus reacted with a different transcript profile to each of the three tested MAMPs, although a core set of genes related to energy generation, transport, amino acid production, secondary metabolism, and especially iron uptake were detected for all three. Half of the genes related to iron uptake were predicted MirA type transporters that potentially take up bacterial siderophores. These quick responses can be viewed as a preparation for further interactions with beneficial or pathogenic bacteria, and constitute a fungal innate immune response with similarities to those of plants and animals.