Photoxenobactin E (1) is a natural product with an unusual thiocarboxylic acid terminus recently isolated from an entomopathogenic bacterium. The biosynthetic gene cluster associated with photoxenobactin E, and other reported derivatives, is very similar to that of piscibactin, the siderophore responsible for the iron uptake among bacteria of the Vibrionaceae family, including potential human pathogens. Here, the reisolation of 1 from the fish pathogen Vibrio anguillarum RV22 cultured under iron deprivation, its ability to chelate Ga(III), and the full NMR spectroscopic characterization of the Ga(III)-photoxenobactin E complex are presented. Our results show that Ga(III)-photoxenobactin E in solution exists in a thiol-thione tautomeric equilibrium, where Ga(III) is coordinated through the sulfur (thiol form) or oxygen (thione form) atoms of the thiocarboxylate group. This report represents the first NMR study of the chemical exchange between the thiol and thione forms associated with thiocarboxylate-Ga(III) coordination, including the kinetics of the interconversion process associated with this tautomeric exchange. These findings show significant implications for ligand design as they illustrate the potential of the thiocarboxylate group as a versatile donor for hard metal ions such as Ga(III).

The close relationship between infectious diseases and iron metabolism is well known, but a more detailed understanding based on current knowledge may provide new insights into the diagnosis and treatment of infectious diseases, considering the growing threat of antibiotic-resistant bacteria. This study investigated adult patients with bloodstream infections, temporal changes, and relationships between blood levels of iron and related markers, including hepcidin and lipocalin-2 (LCN2). We included 144 samples from 48 patients (mean age 72 years, 50% male), with 30 diagnosed with sepsis. During the acute phase of infection, blood levels of hepcidin and LCN2 increased rapidly, whereas iron levels decreased, with values in 95.8% of cases below the normal range (40-188 μg/dL). Later, hepcidin and LCN2 decreased significantly during the recovery phase, and the decreased iron concentrations were restored. In the case of persistent inflammation, iron remained decreased. Acute LCN2 levels were significantly higher in patients with sepsis (p < 0.01). Hypoferremia induced by increased hepcidin would reduce iron in the environment of extracellular pathogens, and the increased LCN2 would inhibit siderophores, resulting in the prevention of the pathogen\'s iron acquisition in each manner during the acute phase of bloodstream infection.

Intravenous gallium therapy is a non-antibiotic approach to limit Pseudomonas aeruginosa biofilm proliferation, by outcompeting iron for siderophore binding. Gallium therapy represents a viable therapeutic strategy for cystic fibrosis (CF) patients harbouring mucoid P. aeruginosa biofilm lung infections. Siderophore deficient P. aeruginosa isolates still demonstrate a hindered biofilm proliferation when exposed to gallium but it is currently unknown whether exogenous gallium has any disruptive influence on the exopolysaccharide (EPS), the major mucoid P. aeruginosa CF lung biofilm matrix component. To that end, Density-Functional Theory (DFT) was deployed to assess whether gallium (Ga3+) could be substituted into the mature mucoid EPS scaffold in preference of calcium (Ca2+)-the native EPS cross-linking ion. Removal of the stable, bound native calcium ions offers a large enthalpic barrier to the substitution and the mature EPS fails to accommodate exogenous gallium. This suggests that gallium, perhaps, is utilising a novel, possibly unknown, ferric uptake system to gain entry to siderophore deficient cells.

Pseudomonas aeruginosa (PA) is a common cause of chronic infections, particularly feared by cystic fibrosis patients. PA colonizes the lung where it adapts to the local environment, and/or to treatments by drugs. This genotypic and phenotypic adaptation, in turns, influences its interaction with its environment, like bacteria from the microbiota. As an example, to access iron, PA produces and secretes two siderophores, pyoverdine and pyochelin that are iron chelators scavenging iron from the environment and bringing it back into the bacterial cells. Siderophores production depends on the level of iron starvation, on the presence of other bacteria, etc. this latter component being less well investigated. Even if studies on bacterial interactions, and their evolution, have been increasing since several years, we are still facing a lack of tools, for example, to specifically follow the growth of PA isolates in such competitive environments. We thus improved a cloning method to gain time in the cloning steps, to lower the polar effects, and to accurately follow the interactions of any PA isolate with other bacteria. For that, a fluorescent reporter gene was inserted between two genes, the glutamine-fructose-6-phosphate transaminase (glmS) and PA5548. This reporter was efficiently produced either from an inducible or a house-keeping promoter, and its expression did not lead to polar effects. We used this strain to study intra and inter-specific bacterial competitions for iron between different lung pathogens. We thus grew wild-type PA together either with an isogenic PA ΔpvdS variant, that does not produce the most efficient siderophore pyoverdine, or with Klebsiella pneumoniae or Acinetobacter baumanii, two other lung pathogens. We finally monitored the effect of the loss of pvdS on the competition between PA and the other bacterial species. These studies enabled us to differentiate intra from inter specific competitions, both arising in the lung environment, and pinpoint the importance of the bacterial specie for the adaptation of pyoverdine production.

Lysobacter is a genus of bacteria emerging as new biocontrol agents in agriculture. Although iron acquisition is essential for the bacteria, no siderophore has been identified from any Lysobacter. Here, we report the identification of the first siderophore, N1,N8-bis(2,3-dihydroxybenzoyl)spermidine (lysochelin), and its biosynthetic gene cluster from Lysobacter enzymogenes. Intriguingly, the deletion of the spermidine biosynthetic gene encoding arginine decarboxylase or SAM decarboxylase eliminated lysochelin and the antifungals, HSAF and its analogues, which are key to the disease control activity and to the survival of Lysobacter under oxidative stresses caused by excess iron. The production of lysochelin and the antifungals is greatly affected by iron concentration. Together, the results revealed a previously unrecognized system, in which L. enzymogenes produces a group of small molecules, lysochelin, spermidine, and HSAF and its analogues, that are affected by iron concentration and critical to the growth and survival of the biocontrol agent.

Cotton leaf worm (Spodoptera littoralis) is a pest that produces important losses in horticultural and ornamental crops in greenhouse, being classified as quarantine pest A2 by EPPO. One of the strategies proposed to control agricultural pests in a health and environmentally friendly way is biological control with entomopathogenic fungi. The genus of filamentous fungi Trichoderma includes different species with direct (infection, antibiosis, anti-feeding, etc.) and indirect (systemic activation of plant defenses) insecticidal capacity, however, the species T. hamatum has never been described previously as entomopathogenic. In this work, the entomopathogenic capacity of T. hamatum on S. littoralis L3 larvae was analyzed by applying spores and fungal filtrates (topically and orally). Infection by spores was compared with the commercial entomopathogenic fungus Beauveria bassiana, obtaining similar results with respect to the production of larval mortality. Oral application of spores reported high mortality and fungal colonization of larvae, however, T. hamatum did not show chitinase activity when grown in the presence of S. littoralis tissues. Therefore, infection of S. littoralis larvae by T. hamatum is through natural openings such as mouth, anus or spiracles. With respect to the application of filtrates, only those obtained from the liquid culture of T. hamatum in contact with S. littoralis tissues reported a significant reduction in larval growth. Metabolomic analysis of the filtrates determined that the filtrate with insecticidal capacity presented the siderophore rhizoferrin in large quantities, which could be responsible for this activity. However, the production of this siderophore had never been previously described in Trichoderma and its insecticidal capacity was unknown. In conclusion, T. hamatum presents entomopathogenic capacity against S. littoralis larvae through the application of spores and filtrates, and both ways could be the basis for the development of efficient bioinsecticides against the pest.

Antibacterial resistance is a healthcare burden. Among Gram-negative bacteria, Pseudomonas aeruginosa belongs to the first list of antibiotic-resistant \"priority pathogens\" described by the World Health Organization. Formerly Pseudomonas pseudomallei, Burkholderia pseudomallei, responsible for melioidosis, is considered as a potential bioterrorist weapon by the Centers of Diseases Control and Prevention. We are interested in the development of new ways to combat these bacteria, targeted due to their high level of resistance to antibiotics via a lack of membrane permeability or efflux. Using iron transport systems is a promising strategy to bypass the bacteria cell membrane and restore the activity of conventional antibiotics such as ciprofloxacin. Specific outer membrane receptors are necessary to most microbes as they allow iron uptake, essential for their survival through siderophore-dependent mechanisms. These systems may allow the introduction of antibacterial agents, chemically coupled to a natural or synthetic siderophore molecule to form siderophore-antibiotic conjugates. In this work, we describe the synthesis of six new siderophore analog-ciprofloxacin conjugates including cleavable linker or not. The siderophore analogs correspond to a mono-catechol or a hydroxypyridinone moiety recognized by both Pseudomonas and Burkholderia species. Physico-chemical studies showed that (i) conjugates were unable to interact or cross the membrane by passive diffusion and (ii) conjugates with cleavable linker are stable in physiologic environment. Biological evaluations have highlighted a promising compound 2d, bearing an hydroxypyridinone moiety with a cleavable linker, active on a large panel of strains of Pseudomonas aeruginosa, Burkholderia pseudomallei and Burkholderia thailandensis without toxicity observed in vitro.

Although urinary tract infections (UTIs) affect many people, they are usually a disease observed in women. UTIs happen when exogenous and endogenous bacteria enter the urinary tract and colonize there. Cystitis and pyelonephritis occur when bacteria infect the bladder and the kidneys, respectively. UTIs become much serious if the bacteria causing the infection are antibiotic resistant. Since the pathogenic microorganisms have been adopted to current antibiotics via genetic variations, UTIs have become an even more severe health problem. Therefore, there is a great need for the discovery of novel antibiotics. Genome mining of nonpathogenic and pathogenic Escherichia coli strains for investigating secondary metabolites were conducted by the antiSMASH analysis. When the resulting secondary metabolites were examined, it was found that some of the siderophores are effective in UTIs. In conclusion, since the siderophore production in E. coli is directly related to UTIs, these molecules can be a good target for development of future pharmaceutical approaches and compounds. Siderophores can also be used in industrial studies due to their higher chelating affinity for iron.

Investigations of phytoplankton responses to iron stress in seawater are complicated by the fact that iron concentrations do not necessarily reflect bioavailability. Most studies to date have been based on single species or field samples and are problematic to interpret. Here, we report results from an experimental cocultivation model system that enabled us to evaluate interspecific competition as a function of iron content and form, and to study the effect of nutritional conditions on the proteomic profiles of individual species. Our study revealed that the dinoflagellate Amphidinium carterae was able to utilize iron from a hydroxamate siderophore, a strategy that could provide an ecological advantage in environments where siderophores present an important source of iron. Additionally, proteomic analysis allowed us to identify a potential candidate protein involved in iron acquisition from hydroxamate siderophores, a strategy that is largely unknown in eukaryotic phytoplankton.

Trichoderma hamatum FBL 587 isolated from DDT-contaminated agricultural soils stands out as a remarkable strain with DDT-resistance and the ability to enhance DDT degradation process in soil. Here, whole genome sequencing and RNA-Seq studies for T. hamatum FBL 587 under exposure to DDT were performed. In the 38.9 Mb-genome of T. hamatum FBL 587, 10,944 protein-coding genes were predicted and annotated, including those of relevance to mycoremediation such as production of secondary metabolites and siderophores. The genome-scale transcriptional responses of T. hamatum FBL 587 to DDT exposure showed 1706 upregulated genes, some of which were putatively involved in the cellular translocation and degradation of DDT. With regards to DDT removal capacity, it was found upregulation of metabolizing enzymes such as P450s, and potentially of downstream DDT-transforming enzymes such as epoxide hydrolases, FAD-dependent monooxygenases, glycosyl- and glutathione-transferases. Based on transcriptional responses, the DDT degradation pathway could include transmembrane transporters of DDT, antioxidant enzymes for oxidative stress due to DDT exposure, as well as lipases and biosurfactants for the enhanced solubility of DDT. Our study provides the first genomic and transcriptomic data on T. hamatum FBL 587 under exposure to DDT, which are a base for a better understanding of mycoremediation strategies for DDT-polluted sites.