Exploring microbial diversity and interactions for asbestos modifying properties

Asbestos poses a substantial environmental health risk, and biological treatment offers a promising approach to mitigate its impact by altering its chemical composition. However, the dynamics of microbial co-inoculation in asbestos bioremediation remain poorly understood. This study investigates the effect of microbial single cultures and co-cultures on modifying crocidolite and chrysotile fibers, focusing on the extraction of iron and magnesium. Seventy bacterial and eighty-three fungal strains were isolated from five diverse sites, characterized phylogenetically using the 16S rRNA gene and ITS region, respectively, and assessed for siderophore and organic acid production. Most bacterial strains were identified as Pseudomonas, while Penicillium predominated among fungal strains. Ten bacterial and 25 fungal strains were found to produce both organic compounds. Four microbial co-cultures (one bacterium-bacterium, two fungus-bacterium, and one fungus-fungus) exhibiting synergistic effects in plate assays, alongside their respective single cultures, were incubated with crocidolite and chrysotile. ICP-OES analysis revealed that in crocidolite, the co-culture HRF19-HRB12 removed more iron than their single cultures, while Penicillium TPF36 showed the highest iron removal. The co-culture of two Pseudomonas strains (HRB12-RB5) exhibited the highest magnesium concentration in the supernatant. In chrysotile, the co-culture HRB12-RB5 removed more iron than their individual cultures, with Penicillium TFSF27 exhibiting the highest iron concentration in the solution. Penicillium TFSF27 and the co-culture TFSF27-TPF36 demonstrated the highest magnesium removal. SEM-XRMA analysis showed a significant reduction in iron and magnesium content, confirming elemental extraction from the fibers' structure. This study significantly broadens the range of microbial strains capable of modifying asbestos fibers and underscores the potential of microbial co-cultures in asbestos remediation.

Natural and Nature-Inspired Catechol Siderophores: A Promising Strategy for Rice Blast Management

The rice-blast fungus Pyricularia oryzae poses a significant threat to rice production worldwide. Ferroptosis, an iron-dependent form of regulated cell death, has recently been reported to be involved in P. oryzae pathogenicity during plant-fungal interactions. Ferroptosis regulates the developmental cell death of conidia necessary for appressorium maturation. In this study, we have established that a series of benzamides containing a chelating catechol moiety suppresses the formation/maturation of appressoria, which are essential for host infection by the rice blast fungus. Moreover, for the most active compounds we have shown that their activity can be at least partially reversed by adding exogenous Fe3+. These results highlight the close association between iron availability and appressorium maturation, opening new avenues for the development of targeted strategies for P. oryzae management.

Investigation of impact of siderophore and process variables on production of iron enriched Saccharomyces boulardii by Plackett-Burman design

The primary cause of anemia worldwide is due to poor diet and iron deficiency. Iron (Fe) enriched yeast can be the most effective way to manage anemia because of the capability for biotransformation of mineral to organic and bioavailable iron. To overcome the low richness of yeast, the use of siderophore as cellular iron carriers is a new approach. In this research, for the first time the potential of siderophore in increasing the Fe enrichment of Saccharomyces boulardii (S. boulardii), which is important because of its probiotic properties and resistance to different stresses, has been investigated to produce of potential iron supplements. For this purpose, siderophore was produced by Pseudomonas aeruginosa (P. aeruginosa). Siderophore impact, along with ten other independent process variables, has been studied on the efficiency of iron biotransformation by the Plackett-Burman design (PBD). The results showed that the highest biotransformation yield was 17.77 mg Fe/g dry cell weight (DCW) in the highest biomass weight of 9 g/l. Iron concentration is the most important variable, with contributions of 46% and 70.79% for biomass weight and biotransformation, respectively, followed by fermentation time, agitation speed, and KH2PO4 concentration. But increasing the level of siderophore and zinc led to a significant negative effect. siderophore inefficiency may be attributed to the absence of membrane receptors for pyoverdine (Pvd) and pyochelin (Pch) siderophores. Also, the steric hindrance of the cell wall mannan, the stickiness and sediment ability of the yeast, can create limitations in the absorption of elements. Such yeast can be used as a potential source of iron even for vegetarians and vegans in the form of medicinal and fortified food products to improve the treatment of anemia. It is recommended that further research be focused on increasing the iron enrichment of yeast by overcoming the structural barrier of the cell wall, investigating factors affecting membrane permeability and iron transport potential of other types of siderophores.

Radiation-Tolerant Fibrivirga spp. from Rhizosphere Soil: Genome Insights and Potential in Agriculture

The rhizosphere of plants contains a wide range of microorganisms that can be cultivated and used for the benefit of agricultural practices. From garden soil near the rhizosphere region, Strain ES10-3-2-2 was isolated, and the cells were Gram-negative, aerobic, non-spore-forming rods that were 0.3-0.8 µm in diameter and 1.5-2.5 µm in length. The neighbor-joining method on 16S rDNA similarity revealed that the strain exhibited the highest sequence similarities with "Fibrivirga algicola JA-25" (99.2%) and Fibrella forsythia HMF5405T (97.3%). To further explore its biotechnological potentialities, we sequenced the complete genome of this strain employing the PacBio RSII sequencing platform. The genome of Strain ES10-3-2-2 comprises a 6,408,035 bp circular chromosome with a 52.8% GC content, including 5038 protein-coding genes and 52 RNA genes. The sequencing also identified three plasmids measuring 212,574 bp, 175,683 bp, and 81,564 bp. Intriguingly, annotations derived from the NCBI-PGAP, eggnog, and KEGG databases indicated the presence of genes affiliated with radiation-resistance pathway genes and plant-growth promotor key/biofertilization-related genes regarding Fe acquisition, K and P assimilation, CO2 fixation, and Fe solubilization, with essential roles in agroecosystems, as well as genes related to siderophore regulation. Additionally, T1SS, T6SS, and T9SS secretion systems are present in this species, like plant-associated bacteria. The inoculation of Strain ES10-3-2-2 to Arabidopsis significantly increases the fresh shoot and root biomass, thereby maintaining the plant quality compared to uninoculated controls. This work represents a link between radiation tolerance and the plant-growth mechanism of Strain ES10-3-2-2 based on in vitro experiments and bioinformatic approaches. Overall, the radiation-tolerant bacteria might enable the development of microbiological preparations that are extremely effective at increasing plant biomass and soil fertility, both of which are crucial for sustainable agriculture.

Siderophores and metallophores: Metal complexation weapons to fight environmental pollution

Siderophores are small molecules of organic nature, released by bacteria to chelate iron from the surrounding environment and subsequently incorporate it into the cytoplasm. In addition to iron, these secondary metabolites can complex with a wide variety of metals, which is why they are commonly studied in the environment. Heavy metals can be very toxic when present in large amounts on the planet, affecting public health and all living organisms. The pollution caused by these toxic metals is increasing, and therefore it is urgent to find practical, sustainable, and economical solutions for remediation. One of the strategies is siderophore-assisted bioremediation, an innovative and advantageous alternative for various environmental applications. This research highlights the various uses of siderophores and metallophores in the environment, underscoring their significance to ecosystems. The study delves into the utilization of siderophores and metallophores in both marine and terrestrial settings (e.g. bioremediation, biocontrol of pathogens, and plant growth promotion), such as bioremediation, biocontrol of pathogens, and plant growth promotion, providing context for the different instances outlined in the existing literature and highlighting their relevance in each field. The study delves into the structures and types of siderophores focusing on their singular characteristics for each application and methodologies used. Focusing on recent developments over the last two decades, the opportunities and challenges associated with siderophores and metallophores applications in the environment were mapped to arm researchers in the fight against environmental pollution.

A Practical Toolkit for the Detection, Isolation, Quantification, and Characterization of Siderophores and Metallophores in Microorganisms

Siderophores are well-recognized low-molecular-weight compounds produced by numerous microorganisms to acquire iron from the surrounding environments. These secondary metabolites can form complexes with other metals besides iron, forming soluble metallophores; because of that, they are widely investigated in either the medicinal or environmental field. One of the bottlenecks of siderophore research is related to the identification of new siderophores from microbial sources. Herein we have compiled a comprehensive range of standard and updated methodologies that have been developed over the past few years to provide a comprehensive toolbox in this area to current researchers.

The potential of Hungarian bauxite residue isolates for biotechnological applications

Bauxite residue (red mud) is considered an extremely alkaline and salty environment for the biota. We present the first attempt to isolate, identify and characterise microbes from Hungarian bauxite residues. Four identified bacterial strains belonged to the Bacilli class, one each to the Actinomycetia, Gammaproteobacteria, and Betaproteobacteria classes, and two to the Alphaproteobacteria class. All three identified fungi strains belonged to the Ascomycota division. Most strains tolerated pH 8-10 and salt content at 5-7% NaCl concentration. Alkalihalobacillus pseudofirmus BRHUB7 and Robertmurraya beringensis BRHUB9 can be considered halophilic and alkalitolerant. Priestia aryabhattai BRHUB2, Penicillium chrysogenum BRHUF1 and Aspergillus sp. BRHUF2 are halo- and alkalitolerant strains. Most strains produced siderophores and extracellular polymeric substances, could mobilise phosphorous, and were cellulose degraders. These strains and their enzymes are possible candidates for biotechnological applications in processes requiring extreme conditions, e.g. bioleaching of critical raw materials and rehabilitation of alkaline waste deposits.

Thermophilic bacteria from Peruvian hot springs with high potential application in environmental biotechnology

Hot springs are extreme environments in which well-adapted microorganisms with biotechnological applications can thrive naturally. These thermal environments across Peruvian territory have, until now, remained poorly investigated. In this study, two hot springs, El Tragadero and Quilcate, located in Cajamarca (Peru) were selected in order to investigate the biotechnological potential of indigenous thermophilic bacteria. Enrichment and isolation processes were carried out using microbial mats, sediments, biofilms, and plastic polymers as samples. Screening for biosurfactants and siderophores production, as well as for polyethylene terephthalate (PET) hydrolysis was done using culture-dependent techniques. After molecular identification, Bacillus was found as the most abundant genus in both hot springs. Bacillus velezensis was found producing biosurfactants under high-level temperature. Anoxybacillus species (A. salavatliensis and A. gonensis) are here reported as siderophore-producing bacteria for the first time. Additionally, Brevibacillus and the less-known bacterium Tistrella mobilis were found demonstrating PET hydrolysis activity. Our study provides the first report of thermophilic bacteria isolated from Peruvian hot springs with biotechnological potential for the bioremediation of oil-, metal- and plastic-polluted environments.

Design and Modulation of Selectivity toward Vanadium(V) and Uranium(VI) Ions: Coordination Properties and Affinity of Hydroxylamino-Triazine Siderophores

Based on the strong binding and high selectivity properties of 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H2bihyat) for [UVIO2]2+, novel binucleating ligands (BLs) N,N',N″,N‴-((1,4-phenylenebis(oxy))bis(1,3,5-triazine-6,2,4-triyl))tetrakis(N-methylhydroxylamine) (H4qtn), N1,N4-bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)benzene-1,4-diamine (H4pdl), and N1,N2-bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)ethane-1,2-diamine (H4enl) were synthesized. Binuclear complexes formed by coordination of hard metal ions with H4qtn are thermodynamically more stable than their mononuclear analogues with H2bihyat due to the increase in entropy accompanying the formation of more chelate rings. Reaction of either H4qtn or H4pdl or H4enl with [UVIO2]2+ and [VVO2]+ resulted in the isolation of the binuclear complexes [(UVIO2)2(μ-qtn)(H2O)4] (1), [(VVO2)2(μ-qtn)][PPh4]2[PPh4] (2), [(UVIO2)2(μ-pdl)(H2O)2(MeOH)2] (3), [(VVO2)2(μ-pdl)][PPh4]2 (4), [(UVIO2)2(μ-enl)(H2O)4] (5), and [(VVO2)2(μ-enl)][PPh4]2 (6). The binuclear complexes 1-6 were characterized by single-crystal X-ray diffraction analysis in solid state and by NMR and ESI-MS in solution. The comparison of the coordination ability of the BLs with either pyridine-2,6-dicarboxylic acid (H2dipic) or H2bihyat or CO32- toward [UVIO2]2+ and [VVO2]+ was investigated by NMR and UV-vis spectroscopies and DFT theoretical calculations, revealing a superior performance of BLs. The selectivity of the BLs for [UVIO2]2+ over [VVO2]+ is decreased compared to that of H2bihyat but increases considerably at pH > 9 values. Formation of the mixed-metal binuclear species [UVIO2(μ-O)VVO2] influences the selectivity and dynamics of the reaction of H4qtn for [UVIO2]2+ and [VVO2]+ in aqueous solution. The results of this study provide crucial information for the ligand design and the development of stronger and more selective systems.

Engineering Siderophore Biosynthesis and Regulation Pathways to Increase Diversity and Availability

Siderophores are small metal chelators synthesized by numerous organisms to access iron. These secondary metabolites are ubiquitously present on Earth, and because their production represents the main strategy to assimilate iron, they play an important role in both positive and negative interactions between organisms. In addition, siderophores are used in biotechnology for diverse applications in medicine, agriculture and the environment. The generation of non-natural siderophore analogs provides a new opportunity to create new-to-nature chelating biomolecules that can offer new properties to expand applications. This review summarizes the main strategies of combinatorial biosynthesis that have been used to generate siderophore analogs. We first provide a brief overview of siderophore biosynthesis, followed by a description of the strategies, namely, precursor-directed biosynthesis, the design of synthetic or heterologous pathways and enzyme engineering, used in siderophore biosynthetic pathways to create diversity. In addition, this review highlights the engineering strategies that have been used to improve the production of siderophores by cells to facilitate their downstream utilization.

Huitlacoche (Ustilago maydis), an Iconic Mexican Fungal Resource: Biocultural Importance, Nutritional Content, Bioactive Compounds, and Potential Biotechnological Applications

Worldwide, the fungus known as huitlacoche (Ustilago maydis (DC.) Corda) is a phytopathogen of maize plants that causes important economic losses in different countries. Conversely, it is an iconic edible fungus of Mexican culture and cuisine, and it has high commercial value in the domestic market, though recently there has been a growing interest in the international market. Huitlacoche is an excellent source of nutritional compounds such as protein, dietary fiber, fatty acids, minerals, and vitamins. It is also an important source of bioactive compounds with health-enhancing properties. Furthermore, scientific evidence shows that extracts or compounds isolated from huitlacoche have antioxidant, antimicrobial, anti-inflammatory, antimutagenic, antiplatelet, and dopaminergic properties. Additionally, the technological uses of huitlacoche include stabilizing and capping agents for inorganic nanoparticle synthesis, removing heavy metals from aqueous media, having biocontrol properties for wine production, and containing biosurfactant compounds and enzymes with potential industrial applications. Furthermore, huitlacoche has been used as a functional ingredient to develop foods with potential health-promoting benefits. The present review focuses on the biocultural importance, nutritional content, and phytochemical profile of huitlacoche and its related biological properties as a strategy to contribute to global food security through food diversification; moreover, the biotechnological uses of huitlacoche are also discussed with the aim of contributing to the use, propagation, and conservation of this valuable but overlooked fungal resource.

Structural Requirements for Ga3+ Coordination in Synthetic Analogues of the Siderophore Piscibactin Deduced by Chemical Synthesis and Density Functional Theory Calculations

Stereoselective total synthesis of several analogues of piscibactin (Pcb), the siderophore produced by different pathogenic Gram-negative bacteria, was performed. The acid-sensitive α-methylthiazoline moiety was replaced by a more stable thiazole ring, differing in the configuration of the OH group at the C-13 position. The ability of these Pcb analogues to form complexes with Ga³⁺ as a mimic of Fe³⁺ showed that the configuration of the hydroxyl group at C-13 as 13S is crucial for the chelation of Ga³⁺ to preserve the metal coordination, while the presence of a thiazole ring instead of the α-methylthiazoline moiety does not affect such coordination. A complete ¹H and ¹³C NMR chemical shift assignment of the diastereoisomer mixtures around C9/C10 was done for diagnostic stereochemical disposition. Additionally, density functional theory calculations were performed not only for confirming the stereochemistry of the Ga³⁺ complex among the six possible diastereoisomers but also for deducing the ability of these to form octahedral coordination spheres with gallium. Finally, the lack of antimicrobial activity of Pcb and Pcb thiazole analogue Ga³⁺ complexes against Vibrio anguillarum agrees with one of the roles of siderophores in protecting pathogens from metal ion toxicity. The efficient metal coordination shown by this scaffold suggests its possible use as a starting point for the design of new chelating agents or vectors for the development of new antibacterials that exploit the "Trojan horse" strategy using the microbial iron uptake mechanisms. The results obtained will be of great help in the development of biotechnological applications for these types of compounds.

Research progress on iron uptake pathways and mechanisms of foodborne microorganisms and their application in the food sector

Iron is one of the essential nutrients for almost all microorganisms. Under iron-limited conditions, bacteria can secrete siderophores to the outside world to absorb iron for survival. This process requires the coordinated action of energy-transducing proteins, transporters, and receptors. The spoilage factors of some spoilage bacteria and the pathogenic mechanism of pathogenic bacteria are also closely related to siderophores. Meanwhile, some siderophores have also gradually evolved toward beneficial aspects. First, a variety of siderophores are classified into three aspects. In addition, representative iron uptake systems of Gram-negative and Gram-positive bacteria are described in detail to understand the common and specific pathways of iron uptake by various bacteria. In particular, the causes of siderophore-induced bacterial pathogenicity and the methods and mechanisms of inhibiting bacterial iron absorption under the involvement of siderophores are presented. Then, the application of siderophores in the food sector is mainly discussed, such as improving the food quality of dairy products and meat, inhibiting the attack of pathogenic bacteria on food, improving the plant growth environment, and promoting plant growth. Finally, this review highlights the unresolved fate of siderophores in the iron uptake system and emphasizes further development of siderophore-based substitutes for traditional drugs, new antibiotic-resistance drugs, and vaccines in the food and health sectors.

A Four-Step Platform to Optimize Growth Conditions for High-Yield Production of Siderophores in Cyanobacteria

In response to Iron deprivation and in specific environmental conditions, the cyanobacteria Anabaena flos aquae produce siderophores, iron-chelating molecules that in virtue of their interesting environmental and clinical applications, are recently gaining the interest of the pharmaceutical industry. Yields of siderophore recovery from in vitro producing cyanobacterial cultures are, unfortunately, very low and reach most of the times only analytical quantities. We here propose a four-step experimental pipeline for a rapid and inexpensive identification and optimization of growth parameters influencing, at the transcriptional level, siderophore production in Anabaena flos aquae. The four-steps pipeline consists of: (1) identification of the promoter region of the operon of interest in the genome of Anabaena flos aquae; (2) cloning of the promoter in a recombinant DNA vector, upstream the cDNA coding for the Green Fluorescent Protein (GFP) followed by its stable transformation in Escherichia Coli; (3) identification of the environmental parameters affecting expression of the gene in Escherichia coli and their application to the cultivation of the Anabaena strain; (4) identification of siderophores by the combined use of high-resolution tandem mass spectrometry and molecular networking. This multidisciplinary, sustainable, and green pipeline is amenable to automation and is virtually applicable to any cyanobacteria, or more in general, to any microorganisms.

Emerging Target-Directed Approaches for the Treatment and Diagnosis of Microbial Infections

With the rising levels of drug resistance, developing efficient antimicrobial therapies has become a priority. A promising strategy is the conjugation of antibiotics with relevant moieties that can potentiate their activity by target-directing. The conjugation of siderophores with antibiotics allows them to act as Trojan horses by hijacking the microorganisms' highly developed iron transport systems and using them to carry the antibiotic into the cell. Through the analysis of relevant examples of the past decade, this Perspective aims to reveal the potential of siderophore-antibiotic Trojan horses for the treatment of infections and the role of siderophores in diagnostic techniques. Other conjugated molecules will be the subject of discussion, namely those involving vitamin B12, carbohydrates, and amino acids, as well as conjugated compounds targeting protein degradation and β-lactamase activated prodrugs.

Bacterial Siderophores: Classification, Biosynthesis, Perspectives of Use in Agriculture

Siderophores are synthesized and secreted by many bacteria, yeasts, fungi, and plants for Fe (III) chelation. A variety of plant-growth-promoting bacteria (PGPB) colonize the rhizosphere and contribute to iron assimilation by plants. These microorganisms possess mechanisms to produce Fe ions under iron-deficient conditions. Under appropriate conditions, they synthesize and release siderophores, thereby increasing and regulating iron bioavailability. This review focuses on various bacterial strains that positively affect plant growth and development through synthesizing siderophores. Here we discuss the diverse chemical nature of siderophores produced by plant root bacteria; the life cycle of siderophores, from their biosynthesis to the Fe-siderophore complex degradation; three mechanisms of siderophore biosynthesis in bacteria; the methods for analyzing siderophores and the siderophore-producing activity of bacteria and the methods for screening the siderophore-producing activity of bacterial colonies. Further analysis of biochemical, molecular-biological, and physiological features of siderophore synthesis by bacteria and their use by plants will allow one to create effective microbiological preparations for improving soil fertility and increasing plant biomass, which is highly relevant for sustainable agriculture.

Genetic Engineering of Talaromyces marneffei to Enhance Siderophore Production and Preliminary Testing for Medical Application Potential

Siderophores are compounds with low molecular weight with a high affinity and specificity for ferric iron, which is produced by bacteria and fungi. Fungal siderophores have been characterized and their feasibility for clinical applications has been investigated. Fungi may be limited in slow growth and low siderophore production; however, they have advantages of high diversity and affinity. Hence, the purpose of this study was to generate a genetically modified strain in Talaromyces marneffei that enhanced siderophore production and to identify the characteristics of siderophore to guide its medical application. SreA is a transcription factor that negatively controls iron acquisition mechanisms. Therefore, we deleted the sreA gene to enhance the siderophore production and found that the null mutant of sreA (ΔsreA) produced a high amount of extracellular siderophores. The produced siderophore was characterized using HPLC-MS, HPLC-DAD, FTIR, and 1H- and 13C-NMR techniques and identified as a coprogen B. The compound showed a powerful iron-binding activity and could reduce labile iron pool levels in iron-loaded hepatocellular carcinoma (Huh7) cells. In addition, the coprogen B showed no toxicity to the Huh7 cells, demonstrating its potential to serve as an ideal iron chelator. Moreover, it inhibits the growth of Candida albicans and Escherichia coli in a dose-dependent manner. Thus, we have generated the siderophore-enhancing strain of T. marneffei, and the coprogen B isolated from this strain could be useful in the development of a new iron-chelating agent or other medical applications.

Assessing the genomic composition, putative ecological relevance and biotechnological potential of plasmids from sponge bacterial symbionts

Plasmid-mediated transfer of genes can have direct consequences in several biological processes within sponge microbial communities. However, very few studies have attempted genomic and functional characterization of plasmids from marine host-associated microbial communities in general and those of sponges in particular. In the present study, we used an endogenous plasmid isolation method to obtain plasmids from bacterial symbionts of the marine sponges Stylissa carteri and Paratetilla sp. and investigated the genomic composition, putative ecological relevance and biotechnological potential of these plasmids. In total, we isolated and characterized three complete plasmids, three plasmid prophages and one incomplete plasmid. Our results highlight the importance of plasmids to transfer relevant genetic traits putatively involved in microbial symbiont adaptation and host-microbe and microbe-microbe interactions. For example, putative genes involved in bacterial response to chemical stress, competition, metabolic versatility and mediation of bacterial colonization and pathogenicity were detected. Genes coding for enzymes and toxins of biotechnological potential were also detected. Most plasmid prophage coding sequences were, however, hypothetical proteins with unknown functions. Overall, this study highlights the ecological relevance of plasmids in the marine sponge microbiome and provides evidence that plasmids of sponge bacterial symbionts may represent an untapped resource of genes of biotechnological interest.

Production and Potential Genetic Pathways of Three Different Siderophore Types in Streptomyces tricolor Strain HM10

Siderophores are iron-chelating low-molecular-weight compounds that bind iron (Fe3+) with a high affinity for transport into the cell. The newly isolated strain Streptomyces tricolor HM10 secretes a pattern of secondary metabolites. Siderophore molecules are the representatives of such secondary metabolites. S. tricolor HM10 produces catechol, hydroxamate, and carboxylate types of siderophores. Under 20 μM FeCl3 conditions, S. tricolor HM10 produced up to 6.00 µg/mL of catechol siderophore equivalent of 2,3-DHBA (2,3-dihydroxybenzoic acid) after 4 days from incubation. In silico analysis of the S. tricolor HM10 genome revealed three proposed pathways for siderophore biosynthesis. The first pathway, consisting of five genes, predicted the production of catechol-type siderophore similar to petrobactin from Bacillus anthracis str. Ames. The second proposed pathway, consisting of eight genes, is expected to produce a hydroxamate-type siderophore similar to desferrioxamine B/E from Streptomyces sp. ID38640, S. griseus NBRC 13350, and/or S. coelicolor A3(2). The third pathway exhibited a pattern identical to the carboxylate xanthoferrin siderophore from Xanthomonas oryzae. Thus, Streptomyces strain HM10 could produce three different types of siderophore, which could be an incentive to use it as a new source for siderophore production in plant growth-promoting, environmental bioremediation, and drug delivery strategy.

Engineering siderophore production in Pseudomonas to improve asbestos weathering

Iron plays a key role in microbial metabolism and bacteria have developed multiple siderophore-driven mechanisms due to its poor bioavailability for organisms in the environment. Iron-bearing minerals generally serve as a nutrient source to sustain bacterial growth after bioweathering. Siderophores are high-affinity ferric iron chelators, of which the biosynthesis is tightly regulated by the presence of iron. Pyoverdine-producing Pseudomonas have shown their ability to extract iron and magnesium from asbestos waste as nutrients. However, such bioweathering is rapidly limited due to repression of the pyoverdine pathway and the low bacterial requirement for iron. We developed a metabolically engineered strain of Pseudomonas aeruginosa for which pyoverdine production was no longer repressed by iron as a proof of concept. We compared siderophore-promoted dissolution of flocking asbestos waste by this optimized strain to that by the wild-type strain. Interestingly, pyoverdine production by the optimized strain was seven times higher in the presence of asbestos waste and the dissolution of magnesium and iron from the chrysotile fibres contained in flocking asbestos waste was significantly enhanced. This innovative mineral weathering process contributes to remove toxic iron from the asbestos fibres and may contribute to the development of an eco-friendly method to manage asbestos waste.

Plant-Microbe Interaction in Sustainable Agriculture: The Factors That May Influence the Efficacy of PGPM Application

The indiscriminate use of chemical fertilizers and pesticides has caused considerable environmental damage over the years. However, the growing demand for food in the coming years and decades requires the use of increasingly productive and efficient agriculture. Several studies carried out in recent years have shown how the application of plant growth-promoting microbes (PGPMs) can be a valid substitute for chemical industry products and represent a valid eco-friendly alternative. However, because of the complexity of interactions created with the numerous biotic and abiotic factors (i.e., environment, soil, interactions between microorganisms, etc.), the different formulates often show variable effects. In this review, we analyze the main factors that influence the effectiveness of PGPM applications and some of the applications that make them a useful tool for agroecological transition.

Paenibacillus arenosi sp. nov., a siderophore-producing bacterium isolated from coastal sediment

In this study, strain CAU 1523^T, a novel Gram-positive-positive bacterium isolated from marine sediment collected from the coast of Busan, Republic of Korea, was characterized using a polyphasic taxonomic approach. This strain showed growth at a temperature range of 20-37 °C (optimum, 30 °C), a pH range of 6.5-9.5 (optimum, 7.5), and in the presence of 0-3% (w/v) NaCl (optimum, 1%). Phylogenetic analysis based on 16S rRNA gene sequencing and 92 concatenated core genes indicated that CAU 1523^T belonged to the genus Paenibacillus, sharing the highest sequence similarity with P. assamensis JCM 13186^T (98.0%). CAU 1523^T was differentiated from other Paenibacillus species by average nucleotide identity, average amino acid identity, and digital DNA-DNA hybridization values, using cut-off values of 95-96%, 90%, and 70%, respectively, for closely related strains. The genome of CAU 1523^T possessed various biosynthetic gene clusters, one of which encoded a putative siderophore-interacting protein. Siderophore production by the isolate was confirmed using the qualitative chrome azurol sulfonate (CAS) agar assay. Based on its phylogenetic and physiological characteristics, strain CAU 1523^T represents a novel, siderophore-producing species within the genus Paenibacillus, for which the name Paenibacillus arenosi sp. nov. is proposed, with the type strain CAU 1523^T (= KCTC 43108^T = MCCC 1K04063^T).

Trends of High-Impact Studies in Pharmacology and Pharmacy: A Cross-Sectional Study

Objective: To investigate the trends of high-impact studies in pharmacology and pharmacy research and to provide evidence for future research in the field of pharmacology and pharmacy.

Methods: A cross-sectional study was performed to understand the current status of high-impact studies (top 1%) in pharmacology and pharmacy research via InCites tool based on Web of Science Core Collection. VOSViewer software was used to visualize the results. The outcomes included development trends, countries, subject areas, research institutes, collaborative networks, and subject terms.

Results: We found 4,273 high-impact (top 1%) studies between 2011 and 2020 in the field of pharmacology and pharmacy. The number of studies increased from 366 in 2011 to 510 in 2020. These studies were mainly distributed in the following Web of Science subject categories: pharmacology and pharmacy (n = 4,188); neurosciences (n = 397); chemistry, multidisciplinary (n = 359); chemistry, medicinal (n = 314); microbiology (n = 301); biotechnology and applied microbiology (n = 280). These studies were cited in 646,855 studies from more than 100 Web of Science subject categories, and studies in pharmacology pharmacy accounted for the largest share of these citations. The top three countries that contributed the highest number of studies were the United States, United Kingdom, and China. The top three institutions that contributed the highest number of studies in the United States were the University of California System, the National Institutes of Health (NIH), and Harvard University. The top research collaborative circle was from universities in the United States. The top international collaborative circle was from universities from the United States, United Kingdom, Australia, and China. The subject-term analysis indicated that cancer was still the top disease, NF-κB was the top signaling pathway, and drug-delivery and nanoparticles were the top methods.

Conclusion: The high-impact studies in pharmacology and pharmacy research have grown over time. The United States, the United Kingdom, and China are the top countries that contributed the high-impact studies. Cancer is still the greatest challenge in the field of disease treatment. It calls for more international collaboration in pharmacology and pharmacy research, which will help discover novel drugs.

Preparation of S-iron-enriched yeast using siderophores and its effect on iron deficiency anemia in rats

Efforts to obtain organic trace elements have been made, including yeast enrichment and transformation, but the application of yeast for this purpose is restricted by poor tolerance and low enrichment. Siderophores play an important role in iron transport. Thus, the role of siderophores in iron transport under high-iron conditions and the application of siderophores in the enrichment of elements was explored. The results showed that some siderophores from iron-tolerant strains promoted yeast growth and increased its intracellular iron content. Among them, siderophore TZT-12 (from LK1110) was the best for promoting yeast growth and iron conversion. The siderophore-iron-enriched yeast (S-iron-enriched yeast) effectively restored the iron concentration, and an iron concentration of 59.40 mg/g was obtained by adding TZT-12. Iron deficiency anemia in rats was significantly mitigated with S-iron-enriched yeast compared with ferrous sulfate. These findings provide a new perspective on the preparation of organic trace elements for supplementation or food fortification.

Siderophores: Importance in bacterial pathogenesis and applications in medicine and industry

Iron is an essential element for all microorganisms. Siderophores are low-weight, high-affinity iron chelating molecules produced in response to iron deficiency by Gram-positive and Gram-negative bacteria which also known as essential virulence factors of bacteria. Several studies have indicated that defective production and/or function of these molecules as well as iron acquisition systems in pathogens are associated with a reduction in pathogenicity of bacteria. Because of their potential role in various biological pathways, siderophores have been received special attention as secondary metabolites. Siderophores can detect iron levels in a variety of environments with a biosensor function. In medicine, siderophores are used to deliver antibiotics (Trojan horse strategy) to resistant bacteria and to treat diseases such as cancer and malaria. In this review, we discuss the iron acquisition pathways in Gram-positive and -negative bacteria, importance of siderophore production in pathogenesis of bacteria, classification of siderophores, and main applications of siderophores in medicine and industry.

Production, Purification, and Characterization of Bacillibactin Siderophore of Bacillus subtilis and Its Application for Improvement in Plant Growth and Oil Content in Sesame

Siderophores are low molecular weight secondary metabolites produced by microorganisms under low iron stress as a specific iron chelator. In the present study, a rhizospheric bacterium was isolated from the rhizosphere of sesame plants from Salem district, Tamil Nadu, India and later identified as Bacillus subtilis LSBS2. It exhibited multiple plant-growth-promoting (PGP) traits such as hydrogen cyanide (HCN), ammonia, and indole acetic acid (IAA), and solubilized phosphate. The chrome azurol sulphonate (CAS) agar plate assay was used to screen the siderophore production of LSBS2 and quantitatively the isolate produced 296 mg/L of siderophores in succinic acid medium. Further characterization of the siderophore revealed that the isolate produced catecholate siderophore bacillibactin. A pot culture experiment was used to explore the effect of LSBS2 and its siderophore in promoting iron absorption and plant growth of Sesamum indicum L. Data from the present study revealed that the multifarious Bacillus sp. LSBS2 could be exploited as a potential bioinoculant for growth and yield improvement in S. indicum.

Macrocyclic polyketides with siderophore mode of action from marine heterotrophic Shewanella algae: Prospective anti-infective leads attenuate drug-resistant pathogens

AIMS

Biotechnological and chemical characterization of previously undescribed homologous siderophore-type macrocyclic polyketides from heterotrophic Shewanella algae Microbial Type Culture Collection (MTCC) 12715 affiliated with Rhodophycean macroalga Hypnea valentiae of marine origin, with significant anti-infective potential against drug-resistant pathogens.

METHODS AND RESULTS

The heterotrophic bacterial strain in symbiotic association with intertidal macroalga H. valentiae was isolated to homogeneity in a culture-dependent method and screened for bioactivities by spot-over-lawn assay. The bacterial organic extract was purified and characterized by extensive chromatographic and spectroscopic methods, respectively, and was assessed for antibacterial activities with disc diffusion and microtube dilution methods. The macrocyclic polyketide compounds exhibited wide-spectrum of anti-infective potential against clinically significant vancomycin-resistant Enterococcus faecalis (VREfs), methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and Klebsiella pneumonia with minimum inhibitory concentration of about 1-3 µg ml^-1 , insomuch as the antibiotics chloramphenicol and ampicillin were active at ≥6·25 µg ml^-1 . The studied compounds unveiled Fe³⁺ chelating activity, which designated that their prospective anti-infective activities against the pathogens could be due to their siderophore mechanism of action. In support of that, the bacterium exhibited siderophore production on bioassay involving the cast upon culture agar plate, and the presence of siderophore biosynthetic gene (≈1000 bp) (MF 981936) further corroborated the inference. In silico molecular modelling with penicillin-binding protein (PBP2a) coded by mecA genes of MRSA (docking score -11·68 to -12·69 kcal mol^-1 ) verified their in vitro antibacterial activities. Putative biosynthetic pathway of macrocyclic polyketides through stepwise decarboxylative condensation initiated by malonate-acyl carrier protein further validated their structural and molecular attributes.

CONCLUSIONS

The studied siderophore-type macrocyclic polyketides from S. algae MTCC 12715 with significant anti-infective potential could be considered as promising candidates for pharmaceutical and biotechnological applications, especially against emerging multidrug-resistant pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study exhibited the heterotrophic bacteria in association with intertidal macroalga as propitious biological resources to biosynthesize novel antibacterial agents.

Biotechnology of Rhodococcus for the production of valuable compounds

Bacteria belonging to Rhodococcus genus represent ideal candidates for microbial biotechnology applications because of their metabolic versatility, ability to degrade a wide range of organic compounds, and resistance to various stress conditions, such as metal toxicity, desiccation, and high concentration of organic solvents. Rhodococcus spp. strains have also peculiar biosynthetic activities that contribute to their strong persistence in harsh and contaminated environments and provide them a competitive advantage over other microorganisms. This review is focused on the metabolic features of Rhodococcus genus and their potential use in biotechnology strategies for the production of compounds with environmental, industrial, and medical relevance such as biosurfactants, bioflocculants, carotenoids, triacylglycerols, polyhydroxyalkanoate, siderophores, antimicrobials, and metal-based nanostructures. These biosynthetic capacities can also be exploited to obtain high value-added products from low-cost substrates (industrial wastes and contaminants), offering the possibility to efficiently recover valuable resources and providing possible waste disposal solutions. Rhodococcus spp. strains have also recently been pointed out as a source of novel bioactive molecules highlighting the need to extend the knowledge on biosynthetic capacities of members of this genus and their potential utilization in the framework of bioeconomy. KEY POINTS: • Rhodococcus possesses promising biosynthetic and bioconversion capacities. • Rhodococcus bioconversion capacities can provide waste disposal solutions. • Rhodococcus bioproducts have environmental, industrial, and medical relevance. Graphical abstract.

Draft genomes and initial characteriaztion of siderophore producing pseudomonads isolated from mine dump and mine drainage

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High and stable siderophore production.

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Identification of siderophore biosynthesis gene clusters.

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Beech wood hydrolysate as alternative carbon source.

Siderophores are of high interest for biotechnological, pharmaceutical, agricultural and industrial applications. Although they are synthesized by various organisms, the yield is usually low which hindrances their suitability for broad range uses. Thus, it is necessary to identify novel producers and to increase the understanding of the biosynthesis pathways. Herein we report the isolation of two novel Pseudomonas strains and the identification of the gene clusters for the biosynthesis of pseudomonine as well as pyochelin and pyoverdine.

Metabolites Produced by Alkaliphiles with Potential Biotechnological Applications

Alkaliphiles are a diverse group of relatively less known microorganisms living in alkaline environments. To thrive in alkaline environments, alkaliphiles require special adaptations. This adaptation may have evolved metabolites which can be useful for biotechnological processes or other applications. In fact, certain metabolites are found unique to alkaliphiles or are effectively produced by alkaliphiles. This probably aroused the interest in metabolites of alkaliphiles. During recent years, many alkaliphilic microbes have been isolated, especially in countries having alkaline environments, like soda lakes. Even if the number of such isolated alkaliphiles is large, their metabolites have not yet been extensively analyzed and exploited. This is expected to come in the years ahead. So far, the focus of interests in metabolites from alkaliphiles falls into categories such as organic acids, ingredients for foodstuffs and cosmetics, antibiotics, and substances which modify properties of other materials used in industry. This chapter deals with biotechnologically important metabolites of alkaliphiles including compatible solutes, biosurfactants, siderophores, carotenoids, exopolysaccharides, and antimicrobial agents. It also covers the promising potential of alkaliphiles as sources of bioplastic raw materials. Moreover, an overview of the patent literature related to alkaliphiles is highlighted. Graphical Abstract.

Siderophores: From natural roles to potential applications

Siderophores are secondary metabolites produced by different organisms in order to scavenge iron from their surrounding environment making this essential element available to the cell. Presenting high affinity for ferric iron, siderophores are secreted out to form soluble ferric complexes that can be taken up by the organisms. Siderophores present complex chemistry that allows them to form the strongest iron-chelating complexes. Interest in this field is always up to date and new siderophores are found with new roles and applications. For example, siderophores participate to the mobilization of iron and other elements and are involved in virulence processes. Recently, a strong relation between siderophores and oxidative stress tolerance has been also highlighted. Their application in medicine has been widely studied as well as in agriculture. However, new fields are paying attention to the use of siderophores as green-iron chelators. In particular, siderophores have been proposed for the preservation of cultural heritage.