Restoration of the soil fertility under Cr(VI) and artificial drought condition by the utilization of plant growth-promoting Bacillus spp. SSAU2

The study explores the potential of an indigenous halo-tolerant microbe identified as Bacillus spp. SSAU-2 in enhancing soil fertility and promoting plant growth for sustainable agricultural practices under the influence of multiple abiotic stresses such as Cr(VI), high salinity, and artificial drought condition. The study investigated various factors influencing IAA synthesis by SSAU-2, such as pH (5 to 11), salinity (10 to 50 g/L), tryptophan concentration (0.5 to 1%), carbon (mannitol mand lactose), and nitrogen sources (peptone and tryptone). The highest IAA concentration was observed at pH 10 (1.695 mg/ml) and pH 11 (0.782 mg/ml). IAA synthesis was optimized at a salinity level of 30 g/l, with lower and higher salinity levels resulting in decreased IAA concentrations. Notably, the presence of mannitol and lactose significantly augmented IAA synthesis, while glucose and sucrose had inhibitory effects. Furthermore, peptone and tryptone played a pivotal role in enhancing IAA synthesis, while ammonium chloride exerted an inhibitory influence. SSAU-2 showed a diverse array of capabilities, including the synthesis of gibberellins, extracellular polymeric substances, siderophores, and hydrogen cyanide along with nitrogen fixation and ammonia production. The microbe could efficiently tolerate 45% PEG-6000 concentration and effectively produce IAA in 15% PEG concentration. It could also tolerate high concentration of Cr(VI) and synthesize IAA even in 50 ppm Cr(VI). The findings of this study provide valuable insights into harnessing the potential of indigenous microorganisms to promote plant growth, enhance soil fertility, and establish sustainable agricultural practices essential for restoring the health of ecosystems.

Roles of Pseudomonas aeruginosa siderophores in interaction with prokaryotic and eukaryotic organisms

Pseudomonas aeruginosa is an opportunistic pathogen that produces two types of siderophores, pyoverdine and pyochelin, that play pivotal roles in iron scavenging from the environment and host cells. P. aeruginosa siderophores can serve as virulence factors and perform various functions. Several bacterial and fungal species are likely to interact with P. aeruginosa due to its ubiquity in soil and water as well as its potential to cause infections in plants, animals, and humans. Siderophores produced by P. aeruginosa play critical roles in iron scavenging for prokaryotic species (bacteria) and eukaryotic hosts (fungi, animals, insects, invertebrates, and plants) as well. This review provides a comprehensive discussion of the role of P. aeruginosa siderophores in interaction with prokaryotes and eukaryotes as well as their underlying mechanisms of action. The evolutionary relationship between P. aeruginosa siderophore recognition receptors, such as FpvA, FpvB, and FptA, and those of other bacterial species has also been investigated.

Catechol-Siderophore Mimics Convey Nucleic Acid Therapeutics into Bacteria

Antibacterial resistance is a major threat for human health. There is a need for new antibacterials to stay ahead of constantly-evolving resistant bacteria. Nucleic acid therapeutics hold promise as powerful antibiotics, but issues with their delivery hamper their applicability. Here, we exploit the siderophore-mediated iron uptake pathway to efficiently transport antisense oligomers into bacteria. We appended a synthetic siderophore to antisense oligomers targeting the essential acpP gene in Escherichia coli. Siderophore-conjugated PNA and PMO antisense oligomers displayed potent antibacterial properties. Conjugates bearing a minimal siderophore consisting of a mono-catechol group showed equally effective. Targeting the lacZ transcript resulted in dose-dependent decreased β-galactosidase production, demonstrating selective protein downregulation. Applying this concept to Acinetobacter baumannii also showed concentration-dependent growth inhibition. Whole-genome sequencing of resistant mutants and competition experiments with the endogenous siderophore verified selective uptake through the siderophore-mediated iron uptake pathway. Lastly, no toxicity towards mammalian cells was found. Collectively, we demonstrate for the first time that large nucleic acid therapeutics can be efficiently transported into bacteria using synthetic siderophore mimics.

Purification and Characterization of Desferrioxamine B of Pseudomonas fluorescens and Its Application to Improve Oil Content, Nutrient Uptake, and Plant Growth in Peanuts

Microorganisms produce siderophores, which are low-molecular-weight iron chelators when iron availability is limited. The present analyzed the role of LNPF1 as multifarious PGPR for improving growth parameters and nutrient content in peanut and soil nutrients. Such multifarious PGPR strains can be used as effective bioinoculants for peanut farming. In this work, rhizosphere bacteria from Zea mays and Arachis hypogaea plants in the Salem area of Tamil Nadu, India, were isolated and tested for biochemical attributes and characteristics that stimulate plant growth, such as the production of hydrogen cyanide, ammonia (6 µg/mL), indole acetic acid (76.35 µg/mL), and solubilizing phosphate (520 µg/mL). The 16S rRNA gene sequences identified the isolate LNPF1 as Pseudomonas fluorescens with a similarity percentage of 99% with Pseudomonas sp. Isolate LNPF1 was evaluated for the production of siderophore. Siderophore-rich supernatant using a Sep Pack C18 column and Amberlite-400 Resin Column (λmax 264) produced 298 mg/L and 50 mg/L of siderophore, respectively. The characterization of purified siderophore by TLC, HPLC, FTIR, and 2D-NMR analysis identified the compound as desferrioxamine, a hydroxamate siderophore. A pot culture experiment determined the potential of LNPF1 to improve iron and oil content and photosynthetic pigments in Arachis hypogaea L. and improve soil nutrient content. Inoculation of A. hypogea seeds with LNPF1 improved plant growth parameters such as leaf length (60%), shoot length (22%), root length (54.68%), fresh weight (47.28%), dry weight (37%), and number of nuts (66.66) compared to the control (untreated seeds). This inoculation also improved leaf iron content (43.42), short iron content (38.38%), seed iron (46.72%), seed oil (31.68%), carotenoid (64.40%), and total chlorophyll content (98.%) compared to control (untreated seeds). Bacterized seeds showed a substantial increase in nodulation (61.65%) and weight of individual nodules (95.97) vis-à-vis control. The results of the present study indicated that P. fluorescens might be utilized as a potential bioinoculant to improve growth, iron content, oil content, number of nuts and nodules of Arachishypogaea L., and enrich soil nutrients.

Analysis of the vibrioferrin biosynthetic pathway of Vibrio parahaemolyticus

Siderophores are small-molecule iron chelators produced by many microorganisms that capture and uptake iron from the natural environment and host. Their biosynthesis in microorganisms is generally performed using non-ribosomal peptide synthetase (NRPS) or NRPS-independent siderophore (NIS) enzymes. Vibrio parahaemolyticus secretes its cognate siderophore vibrioferrin under iron-starvation conditions. Vibrioferrin is a dehydrated condensate composed of α-ketoglutarate, L-alanine, aminoethanol, and citrate, and pvsA (the gene encoding the ATP-grasp enzyme), pvsB (the gene encoding the NIS enzyme), pvsD (the gene encoding the NIS enzyme), and pvsE (the gene encoding decarboxylase) are engaged in its biosynthesis. Here, we elucidated the biosynthetic pathway of vibrioferrin through in vitro enzymatic reactions using recombinant PvsA, PvsB, PvsD, and PvsE proteins. We also found that PvsD condenses L-serine and citrate to generate O-citrylserine, and that PvsE decarboxylates O-citrylserine to form O-citrylaminoethanol. In addition, we showed that O-citrylaminoethanol is converted to alanyl-O-citrylaminoethanol by amidification with L-Ala by PvsA and that alanyl-O-citrylaminoethanol is then converted to vibrioferrin by amidification with α-ketoglutarate by PvsB.

Diversity and functional characteristics of culturable bacterial endosymbionts from cassava whitefly biotype Asia II-5, Bemisia tabaci

Whitefly Bemisia tabaci, a carrier of cassava mosaic disease (CMD), poses a significant threat to cassava crops. Investigating culturable bacteria and their impact on whiteflies is crucial due to their vital role in whitefly fitness and survival. The whitefly biotype associated with cassava and transmitting CMD in India has been identified as Asia II 5 through partial mitochondrial cytochrome oxidase I gene sequencing. In this study, bacteria associated with adult B. tabaci feeding on cassava were extracted using seven different media. Nutrient Agar (NA), Soyabean Casein Digest Medium (SCDM), Luria Bertani agar (LBA), and Reasoner's 2A agar (R2A) media resulted in 19, 6, 4, and 4 isolates, respectively, producing a total of 33 distinct bacterial isolates. Species identification through 16SrRNA gene sequencing revealed that all isolates belonged to the Bacillota and Pseudomonadota phyla, encompassing 11 genera: Bacillus, Cytobacillus, Exiguobacterium, Terribacillus, Brevibacillus, Enterococcus, Staphylococcus, Brucella, Novosphingobium, Lysobacter, and Pseudomonas. All bacterial isolates were tested for chitinase, protease, siderophore activity, and antibiotic sensitivity. Nine isolates exhibited chitinase activity, 28 showed protease activity, and 23 displayed siderophore activity. Most isolates were sensitive to antibiotics such as Vancomycin, Streptomycin, Erythromycin, Kanamycin, Doxycycline, Tetracycline, and Ciprofloxacin, while they demonstrated resistance to Bacitracin and Colistin. Understanding the culturable bacteria associated with cassava whitefly and their functional significance could contribute to developing effective cassava whitefly and CMD control in agriculture.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03949-0.

Preclinical characterisation of gallium-68 labeled ferrichrome siderophore stereoisomers for PET imaging applications

BACKGROUND

Siderophores are small iron-binding molecules produced by microorganisms to facilitate iron acquisition from the environment. Radiolabelled siderophores offer a promising solution for infection imaging, as they can specifically target the pathophysiological mechanisms of pathogens. Gallium-68 can replace the iron in siderophores, enabling molecular imaging with positron emission tomography (PET). Stereospecific interactions play a crucial role in the recognition of receptors, transporters, and iron utilisation. Furthermore, these interactions have an impact on the host environment, affecting pharmacokinetics and biodistribution. This study examines the influence of siderophore stereoisomerism on imaging properties, with a focus on ferrirubin (FR) and ferrirhodin (FRH), two cis-trans isomeric siderophores of the ferrichrome type.

RESULTS

Tested siderophores were labelled with gallium-68 with high radiochemical purity. The resulting complexes differed in their in vitro characteristics. [68Ga]Ga-FRH showed less hydrophilic properties and higher protein binding values than [68Ga]Ga-FR. The stability studies confirmed the high radiochemical stability of both [68Ga]Ga-siderophores in all examined media. Both siderophores were found to be taken up by S. aureus, K. pneumoniae and P. aeruginosa with similar efficacy. The biodistribution tested in normal mice showed rapid renal clearance with low blood pool retention and fast clearance from examined organs for [68Ga]Ga-FR, whereas [68Ga]Ga-FRH showed moderate retention in blood, resulting in slower pharmacokinetics. PET/CT imaging of mice injected with [68Ga]Ga-FR and [68Ga]Ga-FRH confirmed findings from ex vivo biodistribution studies. In a mouse model of S. aureus myositis, both radiolabeled siderophores showed radiotracer accumulation at the site of infection.

CONCLUSIONS

The 68Ga-complexes of stereoisomers ferrirubin and ferrirhodin revealed different pharmacokinetic profiles. In vitro uptake was not affected by isomerism. Both compounds had uptake with the same bacterial culture with similar efficacy. PET/CT imaging showed that the [68Ga]Ga-complexes accumulate at the site of S. aureus infection, highlighting the potential of [68Ga]Ga-FR as a promising tool for infection imaging. In contrast, retention of the radioactivity in the blood was observed for [68Ga]Ga-FRH. In conclusion, the stereoisomerism of potential radiotracers should be considered, as even minor structural differences can influence their pharmacokinetics and, consequently, the results of PET imaging.

Evaluation of Bacillus isolates as a biological control agents against soilborne phytopathogenic fungi

Pesticides, used in agriculture to control plant diseases, pose risks to the environment and human health. To address this, there's a growing focus on biocontrol, using microorganisms instead of chemicals. In this study, we aimed to identify Bacillus isolates as potential biological control agents. We tested 1574 Bacillus isolates for antifungal effects against pathogens like Botrytis cinerea, Fusarium solani, and Rhizoctonia solani. Out of these, 77 isolates formed inhibition zones against all three pathogens. We then investigated their lytic enzyme activities (protease, chitinase, and chitosanase) and the production of antifungal metabolites (siderophore and hydrogen cyanide). Coagulase activity was also examined to estimate potential pathogenicity in humans and animals. After evaluating all mechanisms, 19 non-pathogenic Bacillus isolates with significant antifungal effects were chosen. Molecular identification revealed they belonged to B. subtilis (n = 19) strains. The 19 native Bacillus strains, demonstrating strong antifungal effects in vitro, have the potential to form the basis for biocontrol product development. This could address challenges in agricultural production, marking a crucial stride toward sustainable agriculture.

Buffer-free CAS assay using a diluted growth medium efficiently detects siderophore production and microbial growth

Siderophores are iron chelators and low-molecular-weight compounds secreted by various microorganisms under low-iron conditions. Many microorganisms produce siderophores in the natural environment as iron is an essential element for many of them. CAS assays are widely used to detect siderophores in cultures of various microorganisms; however, it is necessary to improve their sensitivity for the efficient application to fastidious microorganisms. We developed a simple, high-throughput CAS assay employing a buffer-free CAS reagent and diluted growth medium (10% dR2A) in a 96-well microplate. Using a diluted growth medium in agar plates suitable for iron-restricted conditions supported siderophore production by microorganisms from activated sludge. A buffer-free CAS reagent combined with a diluted growth medium revealed that these microorganisms tended to produce more siderophores or iron chelators than microorganisms under iron-rich conditions. Moreover, this buffer-free CAS assay easily and efficiently detected not only siderophore production but also the growth of fastidious microorganisms.

Citrobacter koseri inhibits the growth of Staphylococcus epidermidis by suppressing iron utilization

The human skin microbiome consists of many species of bacteria, including Staphylococcus aureus and S. epidermidis. Individuals with atopic dermatitis (AD) have an increased relative abundance of S. aureus, which exacerbates the inflammation of AD. Although S. epidermidis, a main component of healthy skin microbiota, inhibits the growth of S. aureus, the balance between S. epidermidis and S. aureus is disrupted in the skin of individuals with AD. In this study, we found that Citrobacter koseri isolated from patients with AD produces substances that inhibit the growth of S. epidermidis. Heat-treated culture supernatant (CS) of C. koseri inhibited the growth of S. epidermidis but not S. aureus. The genome of C. koseri has gene clusters related to siderophores and the heat-treated CS of C. koseri contained a high concentration of siderophores compared with the control medium. The inhibitory activity of C. koseri CS against the growth of S. epidermidis was decreased by the addition of iron, but not copper or zinc. Deferoxamine, an iron-chelating agent, also inhibited the growth of S. epidermidis, but not that of S. aureus. These findings suggest that C. koseri inhibits the growth of S. epidermidis by interfering with its iron utilization.

Trojan horselike T6SS effector TepC mediates both interference competition and exploitative competition

The type VI secretion system (T6SS) is a bacterial weapon capable of delivering antibacterial effectors to kill competing cells for interference competition, as well as secreting metal ion scavenging effectors to acquire essential micronutrients for exploitation competition. However, no T6SS effectors that can mediate both interference competition and exploitation competition have been reported. In this study, we identified a unique T6SS-1 effector in Yersinia pseudotuberculosis named TepC, which plays versatile roles in microbial communities. First, secreted TepC acts as a proteinaceous siderophore that binds to iron and mediates exploitative competition. Additionally, we discovered that TepC has DNase activity, which gives it both contact-dependent and contact-independent interference competition abilities. In conditions where iron is limited, the iron-loaded TepC is taken up by target cells expressing the outer membrane receptor TdsR. For kin cells encoding the cognate immunity protein TipC, TepC facilitates iron acquisition, and its toxic effects are neutralized. On the other hand, nonkin cells lacking TipC are enticed to uptake TepC and are killed by its DNase activity. Therefore, we have uncovered a T6SS effector, TepC, that functions like a "Trojan horse" by binding to iron ions to provide a valuable resource to kin cells, whereas punishing cheaters that do not produce public goods. This lure-to-kill mechanism, mediated by a bifunctional T6SS effector, may offer new insights into the molecular mechanisms that maintain stability in microbial communities.

Nobachelins, new siderophores from Nocardiopsisbaichengensis protecting Caenorhabditiselegans from Pseudomonasaeruginosa infection

The biosynthetic potential of actinobacteria to produce novel natural products is still regarded as immense. In this paper, we correlated a cryptic biosynthetic gene cluster to chemical molecules by genome mining and chemical analyses, leading to the discovery of a new group of catecholate-hydroxamate siderophores, nobachelins, from Nocardiopsisbaichengensis DSM 44845. Nobachelin biosynthesis genes are conserved in several bacteria from the family Nocardiopsidaceae. Structurally, nobachelins feature fatty-acylated hydroxy-ornithine and a rare chlorinated catecholate group. Intriguingly, nobachelins rescued Caenorhabditiselegans from Pseudomonasaeruginosa-mediated killing.

Cadmium-chelating ability of the siderophore DHBS secreted by Leclercia adecarboxylata FCH-CR2 and its action mechanism

As one of the most accumulative toxic heavy metals, cadmium (Cd) poses a major threat to human health. Bacterial siderophores, as small molecules with metal-absorbing ability, have great potential activity for Cd-reduction. In this study, the siderophore-producing bacterialstrain FCH-CR2 was isolated from a high-Cd contaminated soil using the CAS method. Leclercia adecarboxylata was identified through 16S rRNA sequence, homology analysis, colony morphology, physiological and biochemical tests. A siderophore, catechol type 2,3-dihydroxy-N-benzoyl-l-serine (DHBS) secreted by FCH-CR2, was purified using RP-HPLC and identified by LC-MS/MS. Intraperitoneal injection of DHBS significantly increased fecal Cd levels, and reduced Cd accumulation in organs. In density flooding theory (DFT) analysis, DHBS may bind to Cd via the hydroxyl site on the benzene ring. Besides, the isothermal titration calorimetry (ITC) assay revealed that the formation of Cd-DHBS is a spontaneous and endothermic reaction with ΔG = -21.4 kJ/mol and ΔH = 1.51 ± 0.142 kJ/mol.

Synthesis and antibacterial activities of baulamycin A inspired derivatives

SbnE is an essential enzyme for staphyloferrin B biosynthesis in Staphylococcus aureus. An earlier study showed that natural product baulamycin A has in vitro inhibitory activity against SbnE and antibacterial potency. A SAR study with analogues of baulamycin A was conducted to identify potent inhibitors of SbnE and/or effective antibiotics against MRSA. The results show that selected analogues, including 11, 18, 21, 24a, 24c, 24m and 24n, exhibit single-digit micromolar inhibitory potencies against SbnE (IC50s = 1.81-8.94 μM) and 11, 24m, 24n possess significant activities against both SbnE (IC50s = 4.12-6.12 μM) and bacteria (MICs = 4-32 μg/mL). Biological investigations revealed that these substances possess potent cell wall disruptive activities and that they inhibit siderophore production in MRSA. Among the selected analogues, 7 has excellent antibiotic activities both gram-positive and -negative bacteria (0.5-4 μg/mL). Moreover, these analogues significantly impede biofilm formation in a concentration-dependent manner. Taken together, the results of the investigation provide valuable insight into the nature of novel baulamycin A analogues that have potential efficacy against MRSA owing to their membrane damaging activity and/or inhibitory efficacy against siderophore production.

Selenite bioreduction with concomitant green synthesis of selenium nanoparticles by a selenite resistant EPS and siderophore producing terrestrial bacterium

Environmental bacterial isolates play a very important role in bioremediation of metals and toxic metalloids. A bacterial strain with high selenite (SeO32-) tolerance and reducing capability was isolated from electronic waste dump site in Banaras Hindu University, Varanasi, India. Based on 16 S rRNA sequencing and BLAST search, this bacterial isolate was identified as Bacillus paramycoides and designated as strain MF-14. It tolerated Sodium selenite up to 110 mM when grown aerobically in LB broth and reduced selenite into elemental selenium (Se0) significantly within 24 h with concomitant biosynthesis of selenium nanoparticles as clearly revealed by brick red precipitate and specific surface plasmon resonance peak at 210 nm using UV-Visible spectrophotometer. Scanning electron microscopy (SEM) analysis of this bacterial strain exposed to 1mM and 5 mM selenite also demonstrated morphological alterations as cell enlargement due to accumulation and bioprecipitation of elemental selenium (Se0). The FTIR analysis clearly demonstrated that functional groups present on the surface of biogenic selenium nanoparticles (SeNPs) play a significant role in the stabilization and capping of SeNPs. Furthermore, these SeNPs were characterized using spectroscopic analysis involving Dynamic light scattering, zeta potential, XPS, FTIR, XRD and Raman spectroscopy which clearly revealed particle size 10-700 nm, amorphous nature, stability as well as it's oxidation state. The biochemical studies have demonstrated that membrane bound reductase enzyme may be responsible for significant reduction of selenite into elemental selenium. Therefore, we may employ Bacillus paramycoides strain MF-14 successfully for bioremediation of selenite contaminated environmental sites with concomitant green synthesis of SeNPs.

Biofortification revisited: Addressing the role of beneficial soil microbes for enhancing trace elements concentration in staple crops

Trace element deficiency is a pervasive issue contributing to malnutrition on a global scale. The primary cause of this hidden hunger is related to low dietary intake of essential trace elements, which is highly prevalent in numerous regions across the world. To address deficiency diseases in humans, fortification of staple crops with vital trace elements has emerged as a viable solution. Current methods for fortifying crops encompass chemical amendments, genetic breeding, and transgenic approaches, yet these approaches possess certain limitations, constraining their agricultural application. In contrast, fortifying staple crops through the utilization of soil-beneficial microbes has emerged as a promising and economically feasible approach to enhance trace element content in crops. A specific subset of these beneficial soil microbes, referred to as plant growth-promoting microbes, have demonstrated their ability to influence the interactions between plants, soil, and minerals. These microbes facilitate the transport of essential soil minerals, such as zinc, iron, and selenium, into plants, offering the potential for the development of tailored bioinoculants that can enhance the nutritional quality of cereals, pulses, and vegetable crops. Nevertheless, further research efforts are necessary to comprehensively understand the molecular mechanisms underlying the uptake, transport, and augmentation of trace element concentrations in staple crops. By delving deeper into these mechanisms, customized bioinoculants of soil-beneficial microbes can be developed to serve as highly effective strategies in combating trace element deficiency and promoting global nutritional well-being.

RGS4 impacts carbohydrate and siderophore metabolism in Trichoderma reesei

BACKGROUND

Adaptation to complex, rapidly changing environments is crucial for evolutionary success of fungi. The heterotrimeric G-protein pathway belongs to the most important signaling cascades applied for this task. In Trichoderma reesei, enzyme production, growth and secondary metabolism are among the physiological traits influenced by the G-protein pathway in a light dependent manner.

RESULTS

Here, we investigated the function of the SNX/H-type regulator of G-protein signaling (RGS) protein RGS4 of T. reesei. We show that RGS4 is involved in regulation of cellulase production, growth, asexual development and oxidative stress response in darkness as well as in osmotic stress response in the presence of sodium chloride, particularly in light. Transcriptome analysis revealed regulation of several ribosomal genes, six genes mutated in RutC30 as well as several genes encoding transcription factors and transporters. Importantly, RGS4 positively regulates the siderophore cluster responsible for fusarinine C biosynthesis in light. The respective deletion mutant shows altered growth on nutrient sources related to siderophore production such as ornithine or proline in a BIOLOG phenotype microarray assay. Additionally, growth on storage carbohydrates as well as several intermediates of the D-galactose and D-arabinose catabolic pathway is decreased, predominantly in light.

CONCLUSIONS

We conclude that RGS4 mainly operates in light and targets plant cell wall degradation, siderophore production and storage compound metabolism in T. reesei.

Isolation of cadmium-resistance and siderophore-producing endophytic bacteria and their potential use for soil cadmium remediation

Endophyte-assisted phytoremediation is an emerging technique for soil heavy metals (HMs) remediation and has become a research focus in the world because of the benefits of endophytes on plant growth and uptake of HMs. In this study, multifunctional endophytic bacteria strains were isolated and screened, and the feasibility of these strains for soil cadmium (Cd) remediation was investigated by soil incubation experiments and pot experiments. All endophytic bacteria were isolated from the roots of woody plants grown on Cd-contaminated soil. Seven endophytic bacteria strains had capacities to tolerate Cd toxicity and produce siderophores, and sequence analysis of the 16S rRNA gene classified these strains as belonging to the genera Burkholderia, Pseudomonas, Pantoea, and Herbaspirillum. All strains were able to produce hydroxamate siderophores (32.40%-91.49%) and had three or more plant growth promoting properties such as phosphorus solubilization, nitrogen fixation, indole acetic acid and 1-aminocyclopropane-1-carboxylate deaminase production. They were all strongly resistant to Cd2+ toxicity, with the minimum inhibitory concentration in LB medium ranging from 1.5 mM to 9.0 mM. Except for strain Burkholderia contaminans JLS17, other strains showed decreasing removal rates within continuously elevated Cd2+ concentration of 10-100 mg L-1. Compared with the uninoculated treatment, the inoculation of strains B.contaminans JLS17, Pseudomonas lurida JLS32, and Pantoea endophytica JLS50 effectively increased the concentration of acid-soluble Cd and decreased the concentration of reducible, oxidizable, and residual Cd in the soils of different Cd contamination levels. In pot experiments, inoculation of strains JLS17 and YTG72 significantly (p < 0.05) promoted the growth of above-ground parts and root system of slash pine (Pinus elliottii) under Cd stress. This study provides a valuable biological resource for endophyte-assisted phytoremediation and a theoretical basis for the application of endophytic bacteria for remediation of Cd-contaminated soil.

Improved engineering of Pseudomonas aeruginosa to study the adaptation of pyoverdine production under intra- or inter- specific bacterial competition

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.

The prospective role of cefiderocol in the management of carbapenem-resistant Acinetobacter baumannii infections: review of the evidence

Carbapenem-resistant Acinetobacter baumannii (CRAB) has been classified by the World Health Organization as being in the critical category of pathogens requiring urgent new antibiotic treatment options. Cefiderocol, the first approved siderophore cephalosporin, was designed for the treatment of CR Gram-negative pathogens, particularly the non-fermenting species A. baumannii and Pseudomonas aeruginosa. Cefiderocol is mostly stable against hydrolysis by serine- and metallo-beta-lactamases, which are leading causes of carbapenem resistance. This review collates the available evidence on the in vitro activity, pharmacokinetics/pharmacodynamics, and efficacy and safety of cefiderocol, and outlines its current role in the management of CRAB infections. In vitro surveillance data show susceptibility rates of >90% for cefiderocol against CRAB isolates as well as in vitro synergism with a variety of antibiotics that are recommended in guidelines. The clinical efficacy of cefiderocol monotherapy against CRAB infections has been demonstrated in the descriptive, open-label CREDIBLE-CR and the non-inferiority, double-blind APEKS-NP randomised clinical trials and in real-world cases in patients with underlying health problems. To date, the frequency of on-therapy development of resistance to cefiderocol in A. baumannii appears to be low, but monitoring is highly recommended. Within current treatment guidelines for moderate-to-severe CRAB infections, cefiderocol is recommended for infections in which other antibiotics failed and in combination with other active antibiotics. In vivo preclinical data support the combination of sulbactam or avibactam with cefiderocol to enhance efficacy and to suppress emergence of resistance to cefiderocol. The benefit of combination therapy in clinical setting is yet to be determined in prospective studies.

3-Hydroxy-pyridin-4(1H)-ones as siderophores mediated delivery of isobavachalcone enhances antibacterial activity against pathogenic Pseudomonas aeruginosa

The natural prenylated chalcone isobavachalcone (IBC) shows good antibacterial activity against Gram-positive bacteria but is ineffective against Gram-negative bacteria, most likely due to the outer membrane barrier of Gram-negative bacteria. The Trojan horse strategy has been shown to be an effective strategy to overcome the reduction in the permeability of the outer membrane of Gram-negative bacteria. In this study, eight different 3-hydroxy-pyridin-4(1H)-one-isobavachalcone conjugates were designed and synthesized based on the siderophore Trojan horse strategy. The conjugates exhibited 8- to 32-fold lower minimum inhibitory concentrations (MICs) and 32- to 177-fold lower half-inhibitory concentrations (IC₅₀s) against Pseudomonas aeruginosa PAO1 as well as clinical multidrug-resistant (MDR) strains compared to the parent IBC under iron limitation. Further studies showed that the antibacterial activity of the conjugates was regulated by the bacterial iron uptake pathway under different iron concentration conditions. Studies on the antibacterial mechanism of conjugate 1b showed that it exerts antibacterial activity by disrupting cytoplasmic membrane integrity and inhibiting cell metabolism. Finally, conjugate 1b showed a lower cytotoxic effects on Vero cells than IBC and a positive therapeutic effect in the treatment of bacterial infections caused by Gram-negative bacteria PAO1. Overall, this work demonstrates that IBC can be delivered to Gram-negative bacteria when combined with 3-hydroxy-pyridin-4(1H)-ones as siderophores and provides a scientific basis for the development of effective antibacterial agents against Gram-negative bacteria.

Ferritinophagy-mediated iron competition in RUTIs: Tug-of-war between UPEC and host

Uropathogenic Escherichia coli (UPEC) is the main pathogen of recurrent urinary tract infections (RUTIs). Urinary tract infection is a complicated interaction between UPEC and the host. During infection, UPEC can evade the host's immune response and retain in bladder epithelial cells, which requires adequate nutritional support. Iron is the first necessary trace element in life and a key nutritional factor, making it an important part of the competition between UPEC and the host. On the one hand, UPEC grabs iron to satisfy its reproduction, on the other hand, the host relies on iron to build nutritional immunity defenses against UPEC. Ferritinophagy is a selective autophagy of ferritin mediated by nuclear receptor coactivator 4, which is not only a way for the host to regulate iron metabolism to maintain iron homeostasis, but also a key point of competition between the host and UPEC. Although recent studies have confirmed the role of ferritinophagy in the progression of many diseases, the mechanism of potential interactions between ferritinophagy in UPEC and the host is poorly understood. In this paper, we reviewed the potential mechanisms of ferritinophagy-mediated iron competition in the UPEC-host interactions. This competitive relationship, like a tug-of-war, is a confrontation between the capability of UPEC to capture iron and the host's nutritional immunity defense, which could be the trigger for RUTIs. Therefore, understanding ferritinophagy-mediated iron competition may provide new strategies for exploring effective antibiotic alternative therapies to prevent and treat RUTIs.

Identification and characterization of siderophilic biocontrol strain SL-44 combined with whole genome

Using rhizobacteria as biological fertilizer is gradually expanding in agriculture as excellent substitutes for chemical fertilizers. Bacillus subtilis SL-44 is a plant growth-promoting rhizobacteria screened from the severely salinized cotton rhizosphere soil in Xinjiang. Study showed that indole-3-acetic acid, organic acid production, nitrogen fixation, and other beneficial secondary metabolite secretion can be synthesized by stain SL-44. At the same time, fencyclin, lipopeptide, chitinase, and other antifungal substances were also detected from the secretion of Bacillus subtilis SL-44, which can effectively control plant diseases. Siderophore separated from SL-44 was verified by HPLC, and results showed it was likely bacillibactin. This study also verified that SL-44 has high antifungal activity against Rhizoctonia solani through in vitro antifungal experiments. The B. subtilis SL-44 whole genome was sequenced and annotated to further explore the biotechnological potential of SL-44. And a large number of genes involved in the synthesis of anti-oxidative stress, antibiotic, and toxins were found. Genome-wide analysis provides clear evidence to support the great potential of B. subtilis SL-44 strain to produce multiple bioantagonistic natural products and growth-promoting metabolites, which may facilitate further research into effective therapies for harmful diseases.

Pyoverdine Analysis - From High-resolution MS/MS Fragmentation to Ion Mobility Measurements

Microorganisms produce iron chelators called siderophores that are a rich source for drug discovery or plant protective agents. Pyoverdines are a class of siderophores from fluorescent Pseudomonas members and consist of different peptide chains specific to each bacterial species. The structural elucidation and characterization of pyoverdines require comprehensive analytical methods as bacterial extracts are complex mixtures. Here, we present a high-throughput UHPLC-MS/MS pipeline and the application of ion mobility spectrometry to facilitate research in the field of medicine and agriculture.

High affinity iron uptake by pyoverdine in Pseudomonas aeruginosa involves multiple regulators besides Fur, PvdS, and FpvI

Pseudomonas aeruginosa is a Gram-negative bacterium which can cause serious infections among immune-depressed people including cystic fibrosis patients where it can colonize the lungs causing chronic infections. Iron is essential for P. aeruginosa and can be provided via three sources under aerobic conditions: its own siderophores pyochelin (PCH) and pyoverdine (PVD), xenosiderophores, or heme, respectively. Pyoverdine is the high affinity siderophore and its synthesis and uptake involve more than 30 genes organized in different operons. Its synthesis and uptake are triggered by iron scarcity via the Fur regulator and involves two extra cytoplasmic sigma factors (ECF), PvdS for the biosynthesis of PVD and FpvI for the uptake via the TonB-dependent FpvA outer membrane transporter and other periplasmic and inner membrane proteins. It appeared recently that the regulation of PVD biosynthesis and uptake involves other regulators, including other ECF factors, and LysR regulators. This is the case especially for the genes coding for periplasmic and inner membrane proteins involved in the reduction of Fe3+ to Fe2+ and the transport of ferrous iron to the cytoplasm that appears to represent a crucial step in the uptake process.

Cytoplasmic Delivery of an Antibiotic, Trimethoprim, with a Simple Bidentate Catechol Analog as a Siderophore Mimetic

Concerns about antibiotic-resistant Gram-negative pathogens are escalating, and accordingly siderophore-based intracellular antibiotic delivery is attracting more attention as an effective means to overcome these infections. Despite the successful clinical translation of this strategy, the delivery potential of siderophores has been limited to periplasm targeting, and this has appreciably restricted the repertoire of applicable antibiotics. To overcome this shortcoming of the current technology, this study focused on investigating the capability of simple bidentate catechol analogs to function as vehicles for cytoplasmic antibiotic delivery. Specifically, by employing trimethoprim, an inhibitor of dihydrofolate reductase located in the cytoplasm, as a model antibiotic, a chemical library of chelator-antibiotic conjugates featuring four different catechol analogs was prepared. Then, their various pharmacological properties and antimicrobial activities were evaluated. Analysis of these characterization data led to the identification of the active conjugates exhibiting notable iron- and trimethoprim-dependent potency against Escherichia coli. Further characterization of these hit molecules using E. coli mutant strains revealed that 2,3-dihydroxybenzoate could effectively deliver several corresponding conjugates to the cytoplasm by exploiting the siderophore uptake machineries present across the outer and inner membranes, originally designated for the native siderophore of E. coli, enterobactin. Considering the synthetic simplicity, such a catechol analog could have appreciable usage in potentiating cytoplasm-active antibiotics against recalcitrant Gram-negative pathogens.

Genomics assisted characterization of plant growth-promoting and metabolite producing psychrotolerant Himalayan Chryseobacterium cucumeris PCH239

Here, we report the first complete genome of a psychrotolerant and yellow-pigmented rhizobacteria Chryseobacterium cucumeris PCH239. It was obtained from the rhizospheric soil of the Himalayan plant Bergenia ciliata. The genome consists of a single contig (5.098 Mb), 36.3% G + C content, and 4899 genes. The cold adaptation, stress response, and DNA repair genes promote survivability in a high-altitude environment. PCH239 grows in temperature (10-37 °C), pH (6.0-8.0), and NaCl (2.0%). The genome derived plant growth-promoting activities of siderophore production (siderophore units 53 ± 0.6), phosphate metabolism (PSI 5.0 ± 0.8), protease, indole acetic acid production (17.3 ± 0.5 µg/ml), and ammonia (2.89 ± 0.4 µmoles) were experimentally validated. Interestingly, PCH239 treatment of Arabidopsis seeds significantly enhances germination, primary, and hairy root growth. In contrast, Vigna radiata and Cicer arietinum seeds had healthy radicle and plumule elongation, suggesting varied plant growth-promotion effects. Our findings suggested the potential of PCH239 as a bio-fertilizer and biocontrol agent in the challenging conditions of cold and hilly regions.

Study of Cadmium Metal Resistance in Stenotrophomonas maltophilia

Metal-resistant bacteria are recommended for metal removal applications due to their rapid multiplication and growth rates. To ensure safety replenishment in contaminated areas frequently hampered by heavy metal toxicity, it is crucial to comprehend their coping mechanisms under heavy metal stress. This study primarily examines the role of EPS (exopolysaccharide) in Stenotrophomonas maltophilia, a Gram-negative, aerobic, and rod-shaped bacteria, in response to Cd, as well as the binding behavior and biosorption mechanism between EPS and Cd, using SEM and FTIR. The studies showed that Stenotrophomonas maltophilia, can resist up to 150 μM of Cd due to the binding of Cd to EPS. SEM analysis showed significant morphological changes and FTIR was to identify main structural groups like carboxyl and hydroxyl which confirms the presence of EPS. The study will also describe the mechanism of cross-reactivity between exopolysaccharide and siderophore production in metal-tolerant Stenotrophomonas maltophilia. This study proved that siderophore-mediated metal detoxification and effective absorption have been linked to metal chelation.

Pseudomonas citri sp. nov., a potential novel plant growth promoting bacterium isolated from rhizosphere soil of citrus

A novel potential plant growth promoting bacterium, designated OPS13-3^T, was isolated from rhizosphere soil of citrus in Aotou Town of Guangzhou, Guangdong Province, PR China. It showed high ability to dissolve insoluble inorganic phosphate and organic phosphorus and to produce 3-indoleacetic acid (IAA) and siderophore. Cells of the novel strain were Gram-stain-negative, rod-shaped, aerobic and motile with polar flagellum. It shared the highest 16S rRNA gene similarity with Pseudomonas mucoides CCUG 74874^T (98.7%) and P. bijieensis LMG 31948^T (98.7%). Phylogenetic analyses based the 16S rRNA gene and genome sequences revealed that strain OPS13-3^T belonged to the genus Pseudomonas, and was most closely related to P. mediterranea ICMP 14184^T and P. corrugate ICMP 5819^T. The average nucleotide identity (ANI) and DNA-DNA hybridization (dDDH) values between the novel strain and closely relatives with high 16S rRNA gene similarities were 80.8‒87.5% and 24.7‒34.6%, respectively, which were much below the threshold values for species delimitation. The major fatty acids included C_16:0, C_10:0 3-OH and summed feature 3 (C_16:1ω7c and/or C_16:1ω6c). It took ubiquinone 9 as the predominant respiratory quinone and the polar lipids contained phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), three unidentified phospholipids, an unidentified aminophospholipid and an unidentified lipid. Based on the phylogenetic, phenotypic and chemotaxonomic analyses and genome comparison, strain OPS13-3^T should be considered as a novel species of the genus Pseudomonas, for which the name Pseudomonas citri sp. nov. is proposed (type strain OPS13-3^T = GDMCC 1.3118^T = JCM 35385^T).

Azospirillum-Bacillus associations: synergistic effects on in vitro PGP traits and growth of pearl millet at early seedling stage under limited moisture conditions

The association of plant beneficial Azospirillum and Bacillus spp. strains expressing different sets of PGP traits may have complementary or supplementary effects on host plants. In the present investigation, A. formosense and Bacillus spp. strains showing diverse PGP traits (IAA production, nitrogenase activity, phosphate, zinc and potassium solubilization, siderophores, antagonism against phytopathogens, osmotic stress tolerance, etc.) were assessed for compatibility by cross-streaking and co-culturing. Under co-culture (Azospirillum + Bacillus), a significant increase in the expression of PGP traits, nitrogenase activity (up to 89%), phosphate solubilization (upto 236%), siderophore production (upto 20%) was observed as compared to individual Azospirillum culture, indicating synergistic effect of co-culture. IAA production was higher in Azospirillum sp. strains as compared to Bacillus spp. strains, when cultured individually; however, when co-cultured, the IAA levels were in the mid-range indicating the contributory effects of compatible strains. The effect of individual Azospirillum and Bacillus strains and their co-inoculation was also assessed on the growth of pearl millet at early stages under moisture-deficit stress imposed using PEG6000 (0, 10, and 20%). Co-inoculation enhanced seed germination (up to 10, 3, and 6% increase under 0, 10, and 20% PEG, respectively, over individual Azospirillum treatment), root traits (increased root hair density and lateral branches), and seedling vigor indices (up to 22, 32, 43% increase in seed vigor index I and 8, 14, and 10% increase in seed vigor index II under 0, 10, 20% PEG, respectively, over individual Azospirillum treatment) under normal as well as moisture-deficit conditions suggesting the role of Bacillus spp. strains in better adaptation of the plants to stress and higher yield potential. The synergistic effect of co-cultured Azospirillum and Bacillus strains on PGP traits indicated metabolic interplay between the two strains which needs to be further understood. The positive effect of co-inoculation on plant growth under moisture-deficit stress indicated the promise of Azospirillum and Bacillus as a synergistic bioformulation for combating nutrient and drought stress in pearl millet, particularly in nutrient-poor dryland agricultural systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03503-4.

LCN2-Fungal siderophore-iron binding and uptake leads to oxidative stress and cell death in hepatocellular carcinoma cell line HepG2

Microorganisms produce non-ribosomal peptides called siderophores for the purpose of iron acquisition. Mammalian immune system is well-known for producing small secretory proteins called lipocalins upon bacterial infection. These proteins sequester siderophores produced by invading bacterial pathogens rendering them unable to acquire iron from the host. However, this is not their sole function. In addition to transferrin and lactoferrin, lipocalins are also known to transport siderophore-bound iron to the host cells. While binding of bacterial siderophores with human lipocalin is well studied, binding of the fungal counterpart is still not confirmed and fully understood. Apart from pathogen-affected cells, developing cancerous cells also show varying expression level of different proteins including those involved in iron transport. The possibility of exogenous fungal siderophore-mediated iron transport via lipocalin and its receptor in mammalian cells has not yet been explored much. In present investigation we have checked differential expression of human lipocalin, LCN2 in hepatocellular carcinoma cell lines HepG2 as well as its normal counterpart WRL-68 and computationally determined the feasibility of LCN2 binding with fungal siderophore. Further in case of a stable complex being formed, whether this complex has the ability to transport iron through its specific receptor was assessed. Also, we have tried to explore possible mechanism of fungal-siderophore mediated oxidative stress leading to significant cell death in cancerous cells. This study will thus be useful towards finding a new way of treating hepatocellular carcinoma via inducing siderophore-mediated cell death in cancerous cells.Communicated by Ramaswamy H. Sarma.

Nonribosomal peptide synthetase gene clusters and characteristics of predicted NRPS-dependent siderophore synthetases in Armillaria and other species in the Physalacriaceae

Fungal secondary metabolites are often pathogenicity or virulence factors synthesized by genes contained in secondary metabolite gene clusters (SMGCs). Nonribosomal polypeptide synthetase (NRPS) clusters are SMGCs which produce peptides such as siderophores, the high affinity ferric iron chelating compounds required for iron uptake under aerobic conditions. Armillaria spp. are mostly facultative necrotrophs of woody plants. NRPS-dependent siderophore synthetase (NDSS) clusters of Armillaria spp. and selected Physalacriaceae were investigated using a comparative genomics approach. Siderophore biosynthesis by strains of selected Armillaria spp. was evaluated using CAS and split-CAS assays. At least one NRPS cluster and other clusters were detected in the genomes studied. No correlation was observed between the number and types of SMGCs and reported pathogenicity of the species studied. The genomes contained one NDSS cluster each. All NDSSs were multi-modular with the domain architecture (ATC)₃(TC)₂. NDSS clusters of the Armillaria spp. showed a high degree of microsynteny. In the genomes of Desarmillaria spp. and Guyanagaster necrorhizus, NDSS clusters were more syntenic with NDSS clusters of Armillaria spp. than to those of the other Physalacriaceae species studied. Three A-domain orthologous groups were identified in the NDSSs, and atypical Stachelhaus codes were predicted for the A3 orthologous group. In vitro biosynthesis of mainly hydroxamate and some catecholate siderophores was observed. Hence, Armillaria spp. generally contain one highly conserved, NDSS cluster although some interspecific variations in the products of these clusters is expected. Results from this study lays the groundwork for future studies to elucidate the molecular biology of fungal phyto-pathogenicity.

Pseudomonas aeruginosa virulence attenuation by inhibiting siderophore functions

Pseudmonas aeruginosa is a Gram-negative bacterium known to be ubiquitous and recognized as one of the leading causes of infections such as respiratory, urinary tract, burns, cystic fibrosis, and in immunocompromised individuals. Failure of antimicrobial therapy has been documented to be attributable due to the development of various resistance mechanisms, with a proclivity to develop additional resistance mechanisms rapidly. P. aeruginosa virulence attenuation is an alternate technique for disrupting pathogenesis without impacting growth. The iron-scavenging siderophores (pyoverdine and pyochelin) generated by P. aeruginosa have various properties like scavenging iron, biofilm formation, quorum sensing, increasing virulence, and toxicity to the host. As a result, developing an antivirulence strategy, specifically inhibiting the P. aeruginosa siderophore, has been a promising therapeutic option to limit their infection. Several natural, synthetic compounds and nanoparticles have been identified as potent inhibitors of siderophore production/biosynthesis, function, and transport system. The current review discussed pyoverdine and pyochelin's synthesis and transport system in P. aeruginosa. Furthermore, it is also focused on the role of several natural and synthetic compounds in reducing P. aeruginosa virulence by inhibiting siderophore synthesis, function, and transport. The underlying mechanism involved in inhibiting the siderophore by natural and synthetic compounds has also been explained. KEY POINTS: • Pseudomonas aeruginosa is an opportunistic pathogen linked to chronic respiratory, urinary tract, and burns infections, as well as cystic fibrosis and immunocompromised patients. • P. aeruginosa produces two virulent siderophores forms: pyoverdine and pyochelin, which help it to survive in iron-deficient environments. • The inhibition of siderophore production, transport, and activity using natural and synthesized drugs has been described as a potential strategy for controlling P. aeruginosa infection.

Involvement of exogenous arsenic-reducing bacteria in root surface biofilm formation promoted phytoextraction of arsenic

Root surface biofilm (RSB) is the last window for pollutants entering plant roots and thus plays a critical role in the phytoextraction of pollutants. Exogenous arsenic-reducing bacteria (EARB) have been adopted to enhance the phytoextraction of arsenic (As). However, whether EARB would be involved in RSB formation together with indigenous bacteria and the role of EARB involvement in As phytoextraction are still unknown. Herein, two EARB strains and two phytoextractors (wheat and maize) were selected to investigate the involvement of EARB in RSB formation and its role in As phytoextraction. Results showed that EARB successfully participated in RSB formation together with indigenous bacteria, attributing to their strong chemotaxis and biofilm formation abilities induced by root exudates. The involvement of EARB in RSB formation significantly enhanced As accumulation in plant roots, since more arsenite (As(III)) caused by arsenate (As(V)) reduction in RSB was absorbed by roots. Its underlying mechanism was further elucidated. EARB involvement increased phylum Proteobacteria to produce more siderophores in RSB. Siderophores then improved photosynthesis by increasing catalase and peroxidase activities and decreasing the malondialdehyde of plants. These actions further raised the shoot fresh weight to enhance As accumulation in plant roots. Moreover, mesophyll cell in wheat has a stronger As(V) reduction ability than that in maize, resulting in opposite distribution patterns of As(III) and As(V) in wheat and maize shoots. This study provides a new understanding of phytoextraction enhanced by exogenous bacteria and fills the gap in the role of EARB in As phytoextraction from the perspective of the RSB microregion.

Bioinoculant mediated regulation of signalling cascades in various stress responses in plants

Bio-inoculation involves the association of plant with some beneficial microorganisms, and among these microbiotas, those bacteria which can promote plant growth and development are known as Plant Growth Promoting Rhizobacteria (PGPR). It can help a plant directly or indirectly, which includes root development, biological nitrogen (N₂) fixation, stress tolerance, cell division and elongation, solubilization of Zinc, Phosphate, Potassium, soil health improvement and many more. PGPR have gained attention as it can be used as biofertilizers and helpful in bioremediation techniques, which in turn can reduce the chemical dependency in agriculture. PGPR mediated plant growth and stress management is developed by the virtue of the interaction of plant and microbial signalling pathways. On the other hand, environmental stresses are something to which a plant is always exposed irrespective of other factors. The present review is all about the better understanding of the convergence strategies of these signalling molecules and the ambiguities of signalling activities occurring in the host due to the interaction with PGPR under environmental stressed conditions.

Phylogenomics and gene selection in Aspergillus welwitschiae: Possible implications in the pathogenicity in Agave sisalana

Aspergillus welwitschiae causes bole rot disease in sisal (Agave sisalana and related species) which affects the production of natural fibers in Brazil, the main worldwide producer of sisal fibers. This fungus is a saprotroph with a broad host range. Previous research established A. welwitschiae as the only causative agent of bole rot in the field, but little is known about the evolution of this species and its strains. In this work, we performed a comparative genomics analysis of 40 Aspergillus strains. We show the conflicting molecular identity of this species, with one sisal-infecting strain sharing its last common ancestor with Aspergillus niger, having diverged only 833 thousand years ago. Furthermore, our analysis of positive selection reveals sites under selection in genes coding for siderophore transporters, Sodium‑calcium exchangers, and Phosphatidylethanolamine-binding proteins (PEBPs). Herein, we discuss the possible impacts of these gene functions on the pathogenicity in sisal.

Strategies and progresses for enhancing targeted antibiotic delivery

Antibiotic resistance is a global health issue and a potential risk for society. Antibiotics administered through conventional formulations are devoid of targeting effect and often spread to various undesired body sites, leading to sub-lethal concentrations at the site of action and thus resulting in emergence of resistance, as well as side effects. Moreover, we have a very slim antibiotic pipeline. Drug-delivery systems have been designed to control the rate, time, and site of drug release, and innovative approaches for antibiotic delivery provide a glint of hope for addressing these issues. This review elaborates different delivery strategies and approaches employed to overcome the limitations of conventional antibiotic therapy. These include antibiotic conjugates, prodrugs, and nanocarriers for local and targeted antibiotic release. In addition, a wide range of stimuli-responsive nanocarriers and biological carriers for targeted antibiotic delivery are discussed. The potential advantages and limitations of targeted antibiotic delivery strategies are described along with possible solutions to avoid these limitations. A number of antibiotics successfully delivered through these approaches with attained outcomes and potentials are reviewed.

The effect of siderophore virulence genes entB and ybtS on the virulence of Carbapenem-resistant Klebsiella pneumoniae

OBJECTIVE

With the detection rate increasing each year, highly resistant and virulent CRKP has been a serious challenge to clinical treatment because of the high morbidity and mortality. Considering the virulence of CRKP is closely related to over-expression of siderophore, the high detection rate of entB and ybtS genes in highly virulent CRKP may be an important reason for the high virulence phenotype of CRKP. Therefore, in this study, single/double knockout and complemented strains of siderophore virulence genes entB and ybtS were constructed to clarify the effect of siderophore virulence genes on the virulence of CRKP.

METHODS

1.The wire drawing experiment, mucus phenotype screening experiment, and PCR amplification were used to screen the target strain WT. the entB gene deletion strain △entB and the complementation strain C-△entB, ybtS gene deletion strain ΔybtS and complementation strain C-ΔybtS, entB and ybtS double gene deletion strain ΔentB + ybtS and complementation strain C-ΔentB + ybtS,were constructed by CrispR-Cas9 gene editing technology. PCR method was used to test whether the knockout and complementation were successful. 2. The colony morphology and mucus phenotype of the experimental strains were observed and the siderophore ability of the experimental strains was tested. Then the growth curves, biofilm-forming ability, and anti-serum killing ability of the strains were determined. 3. In order to understand the virulence of the experimental strain, the mouse intraperitoneal infection model was established to draw the survival curves and determine LD50 of experiment strains. Then to clarify the colonization ability of the experimental strains in the lung and liver of mice, the pathological biopsies were used to observe histopathological changes and ELISA method was used to determine the inflammatory factors IL-1β, LI-3 and TNF-α.

RESULTS

1 CRKP-27 was screened as the target strain WT, which is characterized by positive wire drawing test, strong mucus, strong virulence and carrying both entB and ybtS genes. The single/double knockout and complemented strains of siderophore virulence genes entB and ybtS were successfully constructed. 2 Siderophore virulence genes entB and ybtS had no significant effect on the colony morphology, mucus phenotype (drawing test) and biofilm formation ability of CRKP strains. The CRKP strains with entB and ybtS genes could significantly increase siderophore production. Although both the entB and ybtS genes could impair the growth rate of the CRKP strain, the role of ybtS gene was relatively slow. entB and ybtS genes enhanced the antiserum killing ability of CRKP strains. 3 The presence of entB and ybtS genes reduced the survival rate of mice infected with CRKP strains. Histopathological changes and inflammatory factor levels in the lungs and livers of infected mice were enhanced by the presence of entB and ybtS genes. Mice infected with the same strain had higher histopathological changes and levels of inflammatory factors in the lungs than in the livers.

CONCLUSIONS

1.The siderophore virulence genes entB and ybtS have no significant effect on the colony morphology, mucus phenotype and biofilm formation ability of CRKP strains.2.The siderophore virulence genes entB and ybtS can significantly enhance the virulence of the CRKP strain, but weaken its growth ability.

Induction of Iron Stress in Hepatocellular Carcinoma Cell Lines by Siderophore of Aspergillus nidulans Towards Promising Anticancer Effect

Hepatocellular carcinoma is among the leading causes of cancer-related deaths worldwide and needs efficient and feasible approach of treatment. Present study focuses on exploring the anticancer activity of a secondary metabolite called siderophore of Aspergillus nidulans against hepatocellular carcinoma cell line HepG2. These small peptides are produced by microorganisms including fungi for scavenging iron from its surroundings. Fungi including Aspergillus spp. are known to produce siderophores under iron-limited conditions. Siderophores have high affinity towards iron and are classified into various types. In the present study, siderophore isolated and purified from fungal cultures was confirmed to be of hydroxamate type by chrome azurol sulfonate and Atkin's assay. HPLC analysis confirmed purity while LC-ESI-MS revealed that the siderophore is triacetyl fusigen. Cancerous cells, HepG2, grown under siderophore treatment showed inhibition in growth and proliferation in a dose- and time-dependent manner. Reduction in viability and metabolic activity was evident upon treatment as seen in trypan blue, MTT and WST assay. Fluorescent staining using PI and DAPI confirmed the same while DCFDA staining revealed increased reactive oxygen species production which might have led to cell death and deterioration. Such increase in ROS has been correlated with iron accumulation by assessing intracellular iron level through ICP-MS. To assess the effect of siderophore treatment on normal cells, WRL-68, same assays were carried out but the effect was mostly non-significant up to 48 h. Thus, present work suggests that an optimum dose of siderophore purified from A. nidulans culture might prove a useful anticancer agent.

On the origin of amphi-enterobactin fragments produced by Vibrio campbellii species

Amphi-enterobactin is an amphiphilic siderophore isolated from a variety of microbial Vibrio species. Like enterobactin, amphi-enterobactin is a triscatecholate siderophore; however, it is framed on an expanded tetralactone core comprised of four l-Ser residues, of which one l-Ser is appended by a fatty acid and the remaining l-Ser residues are appended by 2,3-dihydroxybenzoate (DHB). Fragments of amphi-enterobactin composed of 2-Ser-1-DHB-FA and 3-Ser-2-DHB-FA have been identified in the supernatant of Vibrio campbellii species. The origin of these fragments has not been determined, although two distinct isomers could exist for 2-Ser-1-DHB-FA and three distinct isomers could exist for 3-Ser-2-DHB-FA. The fragments of amphi-enterobactin could originate from hydrolysis of the amphi-enterobactin macrolactone, or from premature release due to an inefficient biosynthetic pathway. Unique masses in the tandem MS analysis establish that certain fragments isolated from the culture supernatant must originate from hydrolysis of the amphi-enterobactin macrolactone, while others cannot be distinguished from premature release during biosynthesis or hydrolysis of amphi-enterobactin.

In vitro antibacterial activity of cefiderocol against recent multidrug-resistant carbapenem-nonsusceptible Enterobacterales isolates

Cefiderocol, a siderophore-containing cephalosporin with broad-spectrum antimicrobial activity against many β-lactam-resistant Gram-negative bacteria, was tested by broth microdilution against 104 carbapenem-non-susceptible Enterobacterales clinical isolates from 2011 to 2018. Carbapenemase identification was determined using PCR followed by targeted gene sequencing or whole genome sequencing (WGS). All isolates were multidrug-resistant, 89.4% (93/104) and produced a serine (KPC or SME) carbapenemase, with as many as four β-lactamases present. A VIM-1 or NDM-1 metallo-β-lactamase was confirmed in 6.7% of the isolates (N = 5 and 2, respectively). All isolates were susceptible to cefiderocol, unlike the comparator agents. Susceptibility for comparators ranged from 24.0% for meropenem to 91.3%, 92.3% and 96.1% for imipenem-relebactam, ceftazidime-avibactam and meropenem-vaborbactam, respectively; 48.1%, 75.2% and 79.8% of the isolates were susceptible to omadacycline, colistin and eravacycline, respectively. Two isolates with cefiderocol MICs of 2 mg/L had mutations or deletions of the iron transport genes fhuA/E or fepA, as determined by WGS.

Diversity and antimicrobial potential of the culturable rhizobacteria from medicinal plant Baccharis trimera Less D.C

Plant microbiota is usually enriched with bacteria producers of secondary metabolites and represents a valuable source of novel species and compounds. Here, we analyzed the diversity of culturable root-associated bacteria of the medicinal native plant Baccharis trimera (Carqueja) and screened promising isolates for their antimicrobial properties. The rhizobacteria were isolated from the endosphere and rhizosphere of B. trimera from Ponta Grossa and Ortigueira localities and identified by sequencing and restriction analysis of the 16S rDNA. The most promising isolates were screened for antifungal activities and the production of siderophores and biosurfactants. B. trimera presented a diverse community of rhizobacteria, constituted of 26 families and 41 genera, with a predominance of Streptomyces and Bacillus genera, followed by Paenibacillus, Staphylococcus, Methylobacterium, Rhizobium, Tardiphaga, Paraburkholderia, Burkholderia, and Pseudomonas. The more abundant genera were represented by different species, showing a high diversity of the microbiota associated to B. trimera. Some of these isolates potentially represent novel species and deserve further examination. The communities were influenced by both the edaphic properties of the sampling locations and the plant niches. Approximately one-third of the rhizobacteria exhibited antifungal activity against Sclerotinia sclerotiorum and Colletotrichum gloeosporioides, and a high proportion of isolates produced siderophores (25%) and biosurfactants (42%). The most promising isolates were members of the Streptomyces genus. The survey of B. trimera returned a diverse community of culturable rhizobacteria and identified potential candidates for the development of plant growth-promoting and protection products, reinforcing the need for more comprehensive investigations of the microbiota of Brazilian native plants and habitats.

Effect of Pseudomonas putida-producing pyoverdine on copper uptake by Helianthus annuus cultivated on vineyard soils

Bioaugmentation-assisted phytoextraction was used to reduce the Cu load in vineyard soils. While performance is usually the endpoint of such studies, here we identified some mechanisms underlying Cu soil to plant transfer, particularly the role of siderophores in the extraction of Cu from the soil-bearing phases and its phytoavailability. Carbonated vs. non‑carbonated vineyard soils were cultivated with sunflower in rhizoboxes bioaugmented with Pseudomonas putida. gfp-Tagged P. putida was monitored in the soil and pyoverdine (Pvd), Cu, Fe, Mn, and Zn were measured in the soil solution. Trace elements (TE) were analysed in the roots and shoots. Plant growth and nutritional status were also measured. With bioaugmentation, the concentration of total Cu (vs. Cu²⁺) in the soil solution increased (decreased) by a factor of 1.6 to 2.6 (7 to 13) depending on the soil. The almost 1:1 relationship between the excess of Fe + Cu mobilized from the solid phase and the amount of Pvd in the soil solution in bioaugmented treatments suggests that Pvd mobilized Fe and Cu mainly by ligand-controlled dissolution via a 1:1 metal-Pvd complex. Bioaugmentation increased the Cu concentration by 17% in the shoots and by 93% in the roots, and by 30% to 60% the sunflower shoot biomass leading to an increase in the amount of Cu phytoextracted by up to 87%. The amount of Fe, Mn, Zn, and P also increased in the roots and shoots. Contrary to what was expected, carbonated soil did not increase the mobilization of TE. Our results showed that bioaugmentation increased phytoextraction, and its performance can be further improved by promoting the dissociation of Pvd-Cu complex in the solution at the soil-root interface.

Isolation and identification of multi-trait plant growth-promoting rhizobacteria from coastal sand dune plant species of Pohang beach

Rhizobacteria are root-associated bacteria that influence plant growth by various direct and indirect mechanisms. In quest of efficient plant growth-promoting rhizobacteria (PGPR) with multiple plant growth-promoting traits, a total of 52 rhizobacterial isolates were isolated from the rhizospheric soil collected at Pohang beach, Republic of Korea. The bacterial isolates were evaluated in vitro for their plant growth-promoting traits like production of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, indole-3-acetic acid (IAA), siderophore, and phosphate solubilization activities. More than 28% of the isolates revealed all of the multi-trait plant growth-promoting activities, whereas 11.54% exhibited robust results for producing IAA, ACC deaminase, siderophore, and phosphate solubilization activities. Similarly, 36% isolates were capable for the production of IAA, siderophore, and ACC deaminase, while 32% revealed phosphate solubilization and siderophore production. The isolates with prominent multi-trait plant growth-promoting activities were identified based on 16S rRNA gene sequences and matched to Pseudomonas koreensis-(S4T10), Pseudomonas fluorescens-(S3B1), Serratia fonticola-(S1T1), Sphingobacterium multivorum-(S1B1), Brevundimonas vesicularis-(S1T13), and Arthrobacter sp.-(S2T9) with 99-100% similarity. Our results confirm that further evaluation of these PGPR (exhibiting multi-traits for plant growth promotion) is required on crop plants to reveal their pragmatic role under normal and abiotic stress conditions and add into the consortium of biofertilizers for sustainable agriculture.

A comprehensive method to elucidate pyoverdines produced by fluorescent Pseudomonas spp. by UHPLC-HR-MS/MS

Microbial secondary metabolites represent a rich source for drug discovery, plant protective agents, and biotechnologically relevant compounds. Among them are siderophores, iron-chelating molecules, that show a great influence on bacterial community assembly and the potential to control pathogen invasions. One of such a siderophore is pyoverdine that is produced by fluorescent Pseudomonas members and consists of different peptide chains specific to each bacterial species. The identification and structural elucidation of such suites of siderophores remain widely underexplored as general high-throughput analytical protocols are missing. Therefore, a dedicated method was established allowing a rapid localization and structural elucidation of pyoverdines. Liquid bacterial culture samples were purified by an easy small-scale solid-phase extraction (SPE). Ultra-high-performance liquid chromatography high-resolution tandem mass spectrometry (UHPLC-HR-MS/MS) separated highly polar pyoverdines and their derivatives. All ion fragmentation (AIF) generated mass spectra containing the characteristic fragments of the biological precursor of pyoverdine, ferribactin. This led to the revelation of the mass of secreted pyoverdines. Targeted MS/MS experiments at multiple collision energies accomplished the full structure elucidation of the pyoverdine peptide chain. A mass calculator and a fragmentation predictor facilitated greatly the interpretation of MS/MS spectra by providing accurate masses for a straightforward comparison of measured and theoretical values. The method was successfully validated using four well-known pyoverdines with various peptide chains. Finally, the applicability was proven by the analysis of 13 unknown pyoverdines secreted by sampled bacterial cultures. Among these, 4 novel pyoverdine peptide chains were discovered and are herein reported for the first time.

Functional characterization of cultivable gut bacterial communities associated with rugose spiralling whitefly, Aleurodicus rugioperculatus Martin

Gut symbiotic bacteria provide protection and nutrition to the host insect. A high reproductive rate and dispersal ability of the rugose spiralling whitefly help this polyphagous species to develop and thrive on many horticultural crops. In this study, we isolated the cultivable gut bacteria associated with rugose spiralling whitefly and demonstrated their role in the host insect. We also studied the influence of antibiotics on the rugose spiralling whitefly oviposition. A total of 70 gut bacteria were isolated from the second nymphal stage of rugose spiralling whitefly reared on coconut, banana, and sapota using seven growth media. From the 70 isolates, chitinase, siderophore (51), protease (44), and Glutathione-S-Transferase producers (16) were recorded. The activities of chitinase, siderophore, protease, and Glutathione-S-Transferase in the gut bacterial isolates of rugose spiralling whitefly ranged from 0.07 to 3.96 µmol^-1 min^-1 mL^-1, 10.01 to 76.93%, 2.10 to 83.40%, and 5.21 to 24.48 nmol^-1 min^-1 mL^-1 μg^-1 protein, respectively. The16S rRNA gene sequence analysis revealed that bacterial genera associated with the gut of rugose spiralling whitefly included Bacillus, Exiguobacterium, Acinetobacter, Lysinibacillus, Arthrobacter, and Pseudomonas. Based on the susceptibility of the gut bacteria to antibiotics, 11antibiotic treatments were administered to the host plant leaves infested with the nymphal stages. The antibiotics were evaluated for their effect on rugose spiralling whitefly oviposition. Among the antibiotic treatments, carbenicillin (100 µg mL^-1) + ciprofloxacin (5 µg mL^-1) significantly reduced the oviposition (13 eggs spiral^-1) and egg hatchability (61.54%) of rugose spiralling whitefly. Disruption of chitinase, siderophore, protease, and detoxification enzyme producers and elimination of these symbionts through antibiotics altered the host insect physiology and indirectly affected whitefly oviposition. In conclusion, gut bacteria-based management strategies might be used as insecticides for the effective control of whiteflies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03081-3.

Genomic insights into the biosynthesis and physiology of the cyanobacterial neurotoxin 2,4-diaminobutanoic acid (2,4-DAB)

Cyanobacteria are an ancient clade of photosynthetic prokaryotes, whose worldwide occurrence, especially in water, presents health hazards to humans and animals due to the production of a range of toxins (cyanotoxins). These include the sometimes co-occurring, non-encoded diaminoacid neurotoxins 2,4-diaminobutanoic acid (2,4-DAB) and its structural analogue β-N-methylaminoalanine (BMAA). Knowledge of the biosynthetic pathway for 2,4-DAB, and its role in cyanobacteria, is lacking. The aspartate 4-phosphate pathway is a known route of 2,4-DAB biosynthesis in other bacteria and in some plant species. Another pathway to 2,4-DAB has been described in Lathyrus species. Here, we use bioinformatics analyses to investigate hypotheses concerning 2,4-DAB biosynthesis in cyanobacteria. We assessed the presence or absence of each enzyme in candidate biosynthesis routes, the aspartate 4-phosphate pathway and a pathway to 2,4-DAB derived from S-adenosyl-L-methionine (SAM), in 130 cyanobacterial genomes using sequence alignment, profile hidden Markov models, substrate specificity/active site identification and the reconstruction of gene phylogenies. In the aspartate 4-phosphate pathway, for the 18 species encoding diaminobutanoate-2-oxo-glutarate transaminase, the co-localisation of genes encoding the transaminase with the downstream decarboxylase or ectoine synthase - often within hybrid non-ribosomal peptide synthetase (NRPS)-polyketide synthases (PKS) clusters, NRPS-independent siderophore (NIS) clusters and incomplete ectoine clusters - is compatible with the hypothesis that some cyanobacteria use the aspartate 4-phosphate pathway for 2,4-DAB production. Through this route, in cyanobacteria, 2,4-DAB may be functionally associated with environmental iron-scavenging, via the production of siderophores of the schizokinen/synechobactin type and of some polyamines. In the pathway to 2,4-DAB derived from SAM, eight cyanobacterial species encode homologs of SAM-dependent 3-amino-3-carboxypropyl transferases. Other enzymes in this pathway have not yet been purified or sequenced. Ultimately, the biosynthesis of 2,4-DAB appears to be either restricted to some cyanobacterial species, or there may be multiple and additional routes, and roles, for the synthesis of this neurotoxin.

Salicylate coordination in metal-protochelin complexes

Molybdenum (Mo) is an essential trace element for bacteria that is utilized in myriad metalloenzymes that directly couple to the biogeochemical cycling of nitrogen, sulfur, and carbon. In particular, Mo is found in the most common nitrogenase enzyme, and the scarcity and low bioavailability of Mo in soil may be a critical factor that contributes to the limitation of nitrogen fixation in forests and agroenvironments. To overcome this scarcity, microbes produce exudates that specifically chelate scarce metals, promoting their solubilization and uptake. Here, we have determined the structure and stability constants of Mo bound by protochelin, a siderophore produced by bacteria under Mo-depleted conditions. Spectrophotometric titration spectra indicated a coordination shift from a catecholate to salicylate binding mode for Mo^VI-protochelin (Mo-Proto) complexes at pH < 5. pKa values obtained from analysis of titrations were 4.8 ± 0.3 for Mo^VIO₂H₃Proto^- and 3.3 ± 0.1 for Mo^VIO₂H₄Proto. The occurrence of negatively charged Mo-Proto complexes at pH 6 was also confirmed by mass spectrometry. K-edge Extended X-ray absorption fine structure spectroscopy confirmed the change in Mo coordination at low pH, and structural fitting provides insights into the physical architecture of complexes at neutral and acidic pH. These findings suggest that Mo can be chelated by protochelin across a wide environmental pH range, with a coordination shift occurring at pH < 5. This chelation and associated coordination shift may impact biological availability and mineral surface retention of Mo under acidic conditions.

Generation and characterisation of a semi-synthetic siderophore-immunogen conjugate and a derivative recombinant triacetylfusarinine C-specific monoclonal antibody with fungal diagnostic application

Invasive pulmonary aspergillosis (IPA) is a severe life-threatening condition. Diagnosis of fungal disease in general, and especially that caused by Aspergillus fumigatus is problematic. A. fumigatus secretes siderophores to acquire iron during infection, which are also essential for virulence. We describe the chemoacetylation of ferrated fusarinine C to diacetylated fusarinine C (DAFC), followed by protein conjugation, which facilitated triacetylfusarinine C (TAFC)-specific monoclonal antibody production with specific recognition of the ferrated form of TAFC. A single monoclonal antibody sequence was ultimately elucidated by a combinatorial strategy involving protein LC-MS/MS, cDNA sequencing and RNAseq. The resultant murine IgG2_a monoclonal antibody was secreted in, and purified from, mammalian cell culture (5 mg) and demonstrated to be highly specific for TAFC detection by competitive ELISA (detection limit: 15 nM) and in a lateral flow test system (detection limit: 3 ng), using gold nanoparticle conjugated- DAFC-bovine serum albumin for competition. Overall, this work reveals for the first time a recombinant TAFC-specific monoclonal antibody with diagnostic potential for IPA diagnosis in traditional and emerging patient groups (e.g., COVID-19) and presents a useful strategy for murine Ig sequence determination, and expression in HEK293 cells, to overcome unexpected limitations associated with aberrant or deficient murine monoclonal antibody production.

The Mexican giant maize of Jala landrace harbour plant-growth-promoting rhizospheric and endophytic bacteria

The giant landrace of maize Jala is a native crop cultured in Nayarit and Jalisco States in the occident of México. In this study, after screening 374 rhizospheric and endophytic bacteria isolated from rhizospheric soil, root, and seed tissues of maize Jala, a total of 16 bacterial strains were selected for their plant-growth-promoting potential and identified by 16S rRNA phylogenetic analysis. The isolates exhibited different combinations of phenotypic traits, including solubilisation of phosphate from hydroxyapatite, production of a broad spectrum of siderophores such as cobalt, iron, molybdenum, vanadium, or zinc (Co²⁺, Fe³⁺, Mo^2 +, V⁵⁺, Zn²⁺), and nitrogen fixation capabilities, which were detected in both rhizospheric and endophytic strains. Additional traits such as production of 1-aminocyclopropane-1-carboxylate deaminase and a high-rate production of Indoleacetic Acid were exclusively detected on endophytic isolates. Among the selected strains, the rhizospheric Burkholderia sp., and Klebsiella variicola, and the endophytic Pseudomonas protegens significantly improved the growth of maize plants in greenhouse assays and controlled the infection against Fusarium sp. 50 on fresh maize cobs. These results present the first deep approach on handling autochthonous microorganisms from native maize with a potential biotechnological application in sustainable agriculture as biofertilizers or biopesticides.