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Maintaining microbiome structure is critical for the health of both plants and animals. By re-screening a collection of Arabidopsis mutants affecting root immunity and hormone crosstalk, we identified a FERONIA ( FER ) receptor kinase mutant ( fer-8 ) with a rhizosphere microbiome enriched in Pseudomonas fluorescens without phylum-level dysbiosis. Using microbiome transplant experiments, we found that the fer-8 microbiome was beneficial. The effect of FER on rhizosphere pseudomonads was largely independent of its immune scaffold function, role in development and jasmonic acid autoimmunity. We found that the fer-8 mutant has reduced basal levels of reactive oxygen species (ROS) in roots and that mutants deficient in NADPH oxidase showed elevated rhizosphere pseudomonads. The addition of RALF23 peptides, a FER ligand, was sufficient to enrich P. fluorescens . This work shows that FER-mediated ROS production regulates levels of beneficial pseudomonads in the rhizosphere microbiome. A genetic screen identifies the versatile membrane receptor protein FERONIA as a key modulator of rhizosphere Pseudomonas and microbiome composition in Arabidopsis , through the control of basal levels of reactive oxygen species production.

β-Lactone natural products occur infrequently in nature but possess a variety of potent and valuable biological activities. They are commonly derived from β-hydroxy-α-amino acids, which are themselves valuable chiral building blocks for chemical synthesis and precursors to numerous important medicines. However, despite a number of excellent synthetic methods for their asymmetric synthesis, few effective enzymatic tools exist for their preparation. Here we report cloning of the biosynthetic gene cluster for the β-lactone antibiotic obafluorin and delineate its biosynthetic pathway. We identify a nonribosomal peptide synthetase with an unusual domain architecture and an L -threonine:4-nitrophenylacetaldehyde transaldolase responsible for (2 S ,3 R )-2-amino-3-hydroxy-4-(4-nitrophenyl)butanoate biosynthesis. Phylogenetic analysis sheds light on the evolutionary origin of this rare enzyme family and identifies further gene clusters encoding L -threonine transaldolases. We also present preliminary data suggesting that L -threonine transaldolases might be useful for the preparation of L - threo -β-hydroxy-α-amino acids. Obafluorin is a β-lactone antibiotic produced by Pseudomonas fluorescens . Here the authors present the biosynthetic gene cluster and biosynthetic pathway of obafluorin, which is characterized by a central transaldolase step catalysed by a rare L -threonine transaldolase.

Pyoverdines are siderophores synthesized by fluorescent Pseudomonas spp. Under iron-limiting conditions, these high-affinity ferric iron chelators are excreted by bacteria in the soil to acquire iron. Pyoverdines produced by beneficial Pseudomonas spp. ameliorate plant growth. Here, we investigate the physiological incidence and mode of action of pyoverdine from Pseudomonas fluorescens C7R12 on Arabidopsis (Arabidopsis thaliana) plants grown under iron-sufficient or iron-deficient conditions. Pyoverdine was provided to the medium in its iron-free structure (apo-pyoverdine), thus mimicking a situation in which it is produced by bacteria. Remarkably, apo-pyoverdine abolished the iron-deficiency phenotype and restored the growth of plants maintained in the iron-deprived medium. In contrast to a P. fluorescens C7R12 strain impaired in apo-pyoverdine production, the wild-type C7R12 reduced the accumulation of anthocyanins in plants grown in iron-deficient conditions. Under this condition, apo-pyoverdine modulated the expression of around 2,000 genes. Notably, apo-pyoverdine positively regulated the expression of genes related to development and iron acquisition/redistribution while it repressed the expression of defense-related genes. Accordingly, the growth-promoting effect of apo-pyoverdine in plants grown under iron-deficient conditions was impaired in iron-regulated transporter1 and ferric chelate reductase2 knockout mutants and was prioritized over immunity, as highlighted by an increased susceptibility to Botrytis cinerea This process was accompanied by an overexpression of the transcription factor HBI1, a key node for the cross talk between growth and immunity. This study reveals an unprecedented mode of action of pyoverdine in Arabidopsis and demonstrates that its incidence on physiological traits depends on the plant iron status.

This study investigates the biosynthesis of iron oxide nanoparticles (Fe 2 O 3 NPs) using the cell-free supernatant of Pseudomonas fluorescens . The synthesized Fe 2 O 3 NPs were characterized through UV–VIS, XRD, FTIR, FESEM, EDX, TEM, BET, and VSM analyses. The XRD results confirmed that Fe 2 O 3 NPs were successfully synthesized and EDX analysis indicated that iron accounted for 89.5% of the sample composition. Imaging via SEM and TEM revealed average diameters of 20.43 ± 5.38 nm and 24.32 ± 5.03 nm, respectively. The antimicrobial effects of Fe 2 O 3 NPs were assessed against four bacterial strains and four fungal species. Inhibition zones of 8.35 ± 0.103 mm and 8.31 ± 0.128 mm were observed for Pseudomonas syringae and Staphylococcus aureus at a concentration of 400 μg mL −1 of Fe 2 O 3 NPs. Antifungal efficacy showed growth rate reductions of 90.4% for Aspergillus niger , 71.1% for Monilinia fructigena , 68.8% for Botrytis cinerea , and 84.2% for Penicillium expansum , compared to controls. The nanoparticles demonstrated photocatalytic degradation efficiencies of 89.93%, 84.81%, and 79.71% for methyl violet, methyl orange, and methylene blue, respectively. Also Fe 2 O 3 NPs exhibited significant DPPH free radical scavenger activity with an IC 50 value of 8.45 ± 0.59 μg mL −1 . The study’s findings underscored the significant potential of Fe 2 O 3 NPs in addressing environmental pollution and combating pathogenic microorganisms.

We provide here a comparative genome analysis of ten strains within the Pseudomonas fluorescens group including seven new genomic sequences. These strains exhibit a diverse spectrum of traits involved in biological control and other multitrophic interactions with plants, microbes, and insects. Multilocus sequence analysis placed the strains in three sub-clades, which was reinforced by high levels of synteny, size of core genomes, and relatedness of orthologous genes between strains within a sub-clade. The heterogeneity of the P. fluorescens group was reflected in the large size of its pan-genome, which makes up approximately 54% of the pan-genome of the genus as a whole, and a core genome representing only 45-52% of the genome of any individual strain. We discovered genes for traits that were not known previously in the strains, including genes for the biosynthesis of the siderophores achromobactin and pseudomonine and the antibiotic 2-hexyl-5-propyl-alkylresorcinol; novel bacteriocins; type II, III, and VI secretion systems; and insect toxins. Certain gene clusters, such as those for two type III secretion systems, are present only in specific sub-clades, suggesting vertical inheritance. Almost all of the genes associated with multitrophic interactions map to genomic regions present in only a subset of the strains or unique to a specific strain. To explore the evolutionary origin of these genes, we mapped their distributions relative to the locations of mobile genetic elements and repetitive extragenic palindromic (REP) elements in each genome. The mobile genetic elements and many strain-specific genes fall into regions devoid of REP elements (i.e., REP deserts) and regions displaying atypical tri-nucleotide composition, possibly indicating relatively recent acquisition of these loci. Collectively, the results of this study highlight the enormous heterogeneity of the P. fluorescens group and the importance of the variable genome in tailoring individual strains to their specific lifestyles and functional repertoire.

In vitro reconstitution of five enzymes elucidates the biosynthetic pathway of obafluorin (Obi) and reveals that ObiF uses an unusual thioesterase domain to cyclize the product to a strained β-lactone during release from the NRPS assembly line. Nonribosomal peptide synthetases (NRPSs) are multidomain modular biosynthetic assembly lines that polymerize amino acids into a myriad of biologically active nonribosomal peptides (NRPs). NRPS thioesterase (TE) domains employ diverse release strategies for off-loading thioester-tethered polymeric peptides from termination modules typically via hydrolysis, aminolysis, or cyclization to provide mature antibiotics as carboxylic acids/esters, amides, and lactams/lactones, respectively. Here we report the enzyme-catalyzed formation of a highly strained β-lactone ring during TE-mediated cyclization of a β-hydroxythioester to release the antibiotic obafluorin (Obi) from an NRPS assembly line. The Obi NRPS (ObiF) contains a type I TE domain with a rare catalytic cysteine residue that plays a direct role in β-lactone ring formation. We present a detailed genetic and biochemical characterization of the entire Obi biosynthetic gene cluster in plant-associated Pseudomonas fluorescens ATCC 39502 that establishes a general strategy for β-lactone biogenesis.

Endophytic bacteria hold tremendous potential for use as biocontrol agents. Our study aimed to investigate the biocontrol activity of Pseudomonas fluorescens BRZ63, a new endophyte of oilseed rape (Brassica napus L.) against Rhizoctonia solani W70, Colletotrichum dematium K, Sclerotinia sclerotiorum K2291, and Fusarium avenaceum. In addition, features crucial for biocontrol, plant growth promotion, and colonization were assessed and linked with the genome sequences. The in vitro tests showed that BRZ63 significantly inhibited the mycelium growth of all tested pathogens and stimulated germination and growth of oilseed rape seedlings treated with fungal pathogens. The BRZ63 strain can benefit plants by producing biosurfactants, siderophores, indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and ammonia as well as phosphate solubilization. The abilities of exopolysaccharide production, autoaggregation, and biofilm formation additionally underline its potential to plant colonization and hence biocontrol. The effective colonization properties of the BRZ63 strain were confirmed by microscopy observations of EGFP-expressing cells colonizing the root surface and epidermal cells of Arabidopsis thaliana Col-0. Genome mining identified many genes related to the biocontrol process, such as transporters, siderophores, and other secondary metabolites. All analyses revealed that the BRZ63 strain is an excellent endophytic candidate for biocontrol of various plant pathogens and plant growth promotion.

A biotransformation pair consisting of vinblastine: vincristine present in the Catharanthus roseus plant is of immense pharmacological significance. In this study, we successfully transformed vinblastine into vincristine outside the plant using Pseudomonas aeruginosa 8485 and Pseudomonas fluorescens 2421 and evaluated the antiangiogenic potential of thus produced vincristine through the CAM assay. The toxicity assay showed that both Pseudomonas spp. can tolerate varying concentrations (25–100 µl of 1 mg/ml) of vinblastine. The biotransformation was performed in a liquid nutrient broth medium containing vinblastine (25–100 µl), and Pseudomonas spp. inoculums (50–150 µl) by incubating at 30 °C and 37 °C, respectively for 8 days. The process was optimized for substrate and culture concentrations, pH, temperature, and rotation speed (rpm) for the highest conversion. Analysis using LC–MS/MS confirmed the presence of vincristine as a product of the vinblastine biotransformation by two Pseudomonas spp . P. fluorescens 2421 showed a faster conversion rate with 95% of vinblastine transformed within 24 h than P. aeruginosa 8485, which demonstrated a conversion rate of 92% on the 8 th day. From LC–MS/MS analysis, the optimal conditions for the reaction were determined as vinblastine (25 µl), microbial inoculums (150 µl or 200 × 10 6 and 210 × 10 6  CFU/ml), pH 7.4, rotation speed of 180 rpm, and temperatures of 30 °C and 37 °C with incubation time of 8 days. The vincristine produced exhibited potent antiangiogenic activity in the CAM assay reducing the thickness and branching of blood vessels in a dose-dependent manner. The study concludes that both Pseudomonas spp. showed promise for vincristine production from vinblastine, without compromising its antiangiogenic properties.

This study investigates the effects of lead stress on tomato plants and explores the potential role of plant growth-promoting rhizobacteria (PGPR) to alleviate this stress. The experiment was conducted in pots, introducing varying lead levels (0, 100, 200, 300, 400, and 500 mg kg⁻¹) using lead nitrate. For rhizobacterial inoculation, pre-characterized LTPGP strains S5 Pseudomonas fluorescens A506 and S10 Pseudomonas fluorescens LMG 2189 were used. Data were recorded on growth parameters (shoot and root length, fresh and dry weight), physiological attributes (chlorophyll content, proline content, electrolyte leakage, and lead accumulation), and antioxidant activities (catalase, peroxidase, superoxide dismutase) in tomato plants. Results revealed that lead contamination significantly impaired plant growth, reducing shoot and root lengths by approximately 49.78–57.62%, and negatively impacted physiological attributes and antioxidant enzyme activities. However, inoculation with PGPR strains S5 and S10 led to notable improvements in growth parameters, enhanced physiological traits, and better antioxidant activities, effectively mitigating lead stress. These findings highlights the potential of PGPR to improve tomato plant resilience to lead contamination.

Background Pseudomonas fluorescens is a Gram-negative bacterium with a remarkable metabolic and physiological versatility that enables it to adapt and colonize diverse ecological niches, including the human small intestine. While serotonin is primarily found in high concentrations in gut tissue, its levels in the lumen can be elevated in conditions such as celiac disease, where P. fluorescens is also found in increased abundance. The potential effects of serotonin on P. fluorescens in such contexts remain unclear. Results We demonstrate that P. fluorescens metabolizes serotonin primarily into 5-hydroxyindole-3-acetic acid (5-HIAA) and, to a lesser extent, into 5-hydroxytryptophol and N-acetylserotonin. Gene expression analysis revealed significant changes in oxidative stress-related pathways over time, and proteomic analysis confirmed the shifts seen particularly in amino acid catabolic pathways. Serotonin metabolism also enhanced bacterial resistance to oxidative stress, suggesting a protective role. Conclusions The findings reveal a novel mechanism by which serotonin modulates the metabolism and stress responses of P. fluorescens . This study provides insight into how P. fluorescens adapts to serotonin-rich environments, such as in celiac disease, and may inform future research on microbial interactions with host-derived metabolites in disease contexts.