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Indole-3-acetic acid production is rare among gut bacteria and reflects OFOR-driven amino acid oxidation in acetogens.

Indole-3-acetic acid (IAA) is a tryptophan-derived gut microbial metabolite with reported anti-inflammatory activities, but the organisms and anaerobic pathways that support robust production remain unclear. Screening 206 human gut bacterial isolates by LC-MS revealed that IAA production is rare: only five strains exceeded the limit of quantitation, and high-capacity production was confined to the acetogens Blautia hydrogenotrophica and Intestinibacter bartlettii. Across growth conditions, IAA was a minor product that rose alongside carbohydrate-sensitive, OFOR-linked catabolism of multiple amino acids, generating abundant branched-chain and aromatic organic acids. In gnotobiotic mice mono-colonized with I. bartlettii, these metabolites were produced in vivo but showed distinct host handling, with branched-chain fatty acids largely extracted between portal and peripheral plasma, whereas aromatic acids and their glycine conjugates appeared in plasma and urine. Genomic analyzes and heterologous enzyme assays identified expanded repertoires of 2-oxoacid:ferredoxin oxidoreductases (OFORs) with activities spanning pyruvate/oxaloacetate, branched-chain, and aromatic 2-oxoacids, including indolepyruvate conversion to indoleacetyl-CoA, a putative intermediate en route to IAA. Finally, position-specific 13C tracing showed that CO2 released during amino acid oxidation is reassimilated into acetate via reductive acetogenesis, indicating that gut acetogens can maintain redox balance without fermenting partner strains. Together, these findings show that high IAA output is restricted to select gut acetogens and linked to a broader OFOR-driven anaerobic metabolism that generates additional metabolites that are absorbed by the host.

Indoleacetic Acids

Excitation of indole-3-acetic acid (an auxin) in a linoleate-lipoxygenase system.

The weak luminescence that accompanies the linoleate-lipoxygenase reaction was greatly enhanced by the addition of indole analogues, and especially indole acetic acid. The main emitting species in the indole acetic acid-linoleate-lipoxygenase system was analysed spectrophotometrically in the visible region and ascribed to the transition of excited indole acetate in triplet state to its ground state. Such an excited indole acetate could be generated by transfer of energy from the excited CO2 and excited carbonyl (generated by the linoleate-lipoxygenase reaction) to indole acetate in the ground state, but not by cleavage of the dioxetane analog (positions 2 and 3 on the indole ring).

Deuterium

[Tryptophan-load in progressive scleroderma (author's transl)].

This presentation describes effects of oral tryptophan loading (5.0 g DL) on tryptophan metabolism in healthy subjects (n = 10) and persons with progressive scleroderma. N1-methylnicotinamide (N1MN), 3-hydroxyanthranilic acid (3 HAA), kynurine (KN), tryptamin (TA), xantheurenic acid (XA) were determinated. Alterations of tryptophan metabolism were evaluated by 24 h urinary excretions of the following metabolites: 5-hydroxy indolacetic acid (5 HAA) and indole-3-acetic acid (IAA). The pathological pathways were discussed, especially the way and influence of serotonine.

3-Hydroxyanthranilic Acid

Tryptophan-driven metabolomic shift in Acidobacteriaceae reveals phytohormones and antifungal metabolites.

UNLABELLED: Acidobacteriota is one of the most abundant phyla in soils and has recently attracted attention for its potential role in promoting phytosanitary benefits. The metabolomic capabilities of this phylum remain poorly characterized, with few experimentally confirmed metabolites described. To address these gaps, we combined untargeted metabolomic profiling with comparative genomic analyses to explore the functional potential of newly isolated Acidobacteriaceae strains. Genome mining across the Acidobacteriota phylum revealed the presence and taxon-specific enrichment of genes associated with plant-related traits, including phytohormone biosynthesis. In parallel, metabolomic analyses of OSMAC-derived extracts uncovered pronounced condition-dependent metabolic variation. Tryptophan supplementation was associated with marked metabolomic reprogramming, including changes in indole-derived metabolites, such as indole-3-acetic acid. Subsequent analyses linked these metabolic shifts to the suppression of phytopathogenic fungi and enabled the identification of malassezindoles and pityriacitrins as active compounds, confirmed by structure elucidation using NMR spectroscopy. Overall, these findings shed light on the previously unexplored metabolic potential of the Acidobacteriota phylum, emphasizing its ecological importance for phytosanitary applications. IMPORTANCE: Despite their ubiquity and genomic diversity, the functional metabolism of members of the Acidobacteriota has largely remained uncharacterized. This study links genomic predictions to experimentally verified metabolomic outputs of Acidobacteriaceae, demonstrating tryptophan-responsive metabolic shifts translating to phytohormones and metabolites suppressing fungal growth. Our work underscores the emerging role of Acidobacteriota as important contributors to soil ecosystem functioning and plant-microbe interactions.

Acidobacteriota

Growth inhibition of Acinetobacter by 5-chloro-indole-3-acetic acid.

The Acinetobacter calcoaceticus-baumannii complex includes high-priority, multidrug-resistant pathogens for which novel antibiotics are urgently needed. Many bacterial strains from this complex harbor a so-called iac gene cluster that codes for the catabolism of indole-3-acetic acid (IAA). Here, we demonstrate that possession and expression of iac genes represent an Achilles' heel for Acinetobacter species, which can be exploited to suppress bacterial growth by treatment with IAA and its analog 5-chloro-IAA.IMPORTANCEAcinetobacter baumannii is a deadly bacterial pathogen and one of the leading causes of hospital-acquired infections worldwide. It is also known for its resistance to many antibiotics currently available. In this study, we show that Acinetobacter bacteria choke on a mixture of IAA and 5-chloro-IAA, offering a path to the discovery and development of a novel drug treatment.

Indoleacetic Acids

Ethylene signaling negatively regulates rapeseed resistance to Plasmodiophora brassicae.

Clubroot, caused by Plasmodiophora brassicae, poses a serious threat to the rapeseed (Brassica napus) industry. Due to B. napus being an allopolyploid with a complex genome and the current scarcity of available resistance gene resources, the molecular basis of rapeseed resistance to P. brassicae remains poorly understood. Here, we performed a functional characterization of BnEIN2 (ethylene-insensitive protein) to explore the role of ethylene signaling in rapeseed resistance to P. brassicae. The Bnein2 mutants generated through CRISPR/Cas9 technology exhibited enhanced resistance to P. brassicae, along with reduced 1-aminocyclopropane-1-carboxylic acid (ACC)/S-adenosyl-L-methionine (SAM) accumulation and ethylene insensitivity. Pharmacological assays demonstrated that inhibitors of ethylene biosynthesis or signaling improved the resistance of Bnein2 mutant plants to P. brassicae. Transcriptome analysis revealed that loss-of-function of BnEIN2 affected the expression of ethylene-, auxin-, and cytokinin-related genes. Moreover, the increased resistance of Bnein2 mutants to P. brassicae was accompanied by a reduction in auxin (indole-3-acetic acid, IAA) biosynthesis and degradation of cytokinin (trans-zeatin, TZ). Collectively, these findings establish the negative regulatory role of ethylene signaling in rapeseed resistance to P. brassicae. This study represents the first effort to elucidate rapeseed resistance to P. brassicae by directly obtaining rapeseed genetic material and offer novel insights into the hormonal regulatory network underlying disease resistance and valuable resources for breeding clubroot-resistant varieties.

BnEIN2

Genome-wide characterization of BraABCB transporters reveals their potential roles in hormone responses in Brassica rapa var. parachinensis.

Thirty-six BraABCB genes were identified in Brassica rapa var. parachinensis; expression and interaction analyses suggest BraABCB27 and BraABCB28 as hormone-responsive candidates associated with BRI1-related proteins. ABCB transporters are ATP-dependent membrane proteins that mediate the transport of diverse substrates, including phytohormones, and play important roles in plant development and environmental adaptation. Previous studies in Arabidopsis have shown that several ABCB proteins participate in phytohormone transport, including auxin and brassinosteroid transport, whereas the functions of their homologs in Brassica rapa var. parachinensis remain poorly understood. In this study, 36 BraABCB genes were identified and classified into four phylogenetic groups. Conserved domain analysis showed that BraABCB proteins contain typical nucleotide-binding domains and transmembrane domains. Chromosomal distribution, collinearity, and Ka/Ks analyses suggested that the BraABCB family is evolutionarily conserved and mainly subject to purifying constraints. Promoter analysis and RT-qPCR assays of selected Group IV BraABCB genes revealed diverse expression patterns and responses to drought, high temperature, brassinolide, and indole-3-acetic acid treatments. Subcellular localization assays showed that selected Group IV BraABCB proteins exhibited predominant plasma membrane localization. Notably, BraABCB27 and BraABCB28, two close AtABCB1/AtABCB19-related homologs, showed detectable physical associations with BRI1-related proteins in BiFC and split-ubiquitin yeast two-hybrid assays. Together, these results provide a genome-wide characterization of the BraABCB gene family and identify BraABCB27 and BraABCB28 as candidate genes for future studies of their possible associations with BR-related membrane processes and hormone-regulated growth responses in B. rapa var. parachinensis.

Plant Growth Regulators

Genome sequence data of the chitinase-producing bacterium Paenibacillus mucilaginosus YWY-5.1.

Paenibacillus mucilaginosus is a beneficial bacterium widely applied as a biofertilizer in agriculture. To date, genomic information on this species remains limited; however, no genome assemblies from Vietnam have been reported. This work presented the draft genome of P. mucilaginosus YWY-5.1, a promising strain with strong chitin-degrading capability and agricultural potential, isolated from Yok Don National Park, Vietnam, using Illumina technology. Results showed that the assembled genome comprised 48 contigs with 4,076,146 bp and 73.8% GC-content. Genome annotation identified 3,611 protein-coding genes, 2 rRNA genes, and 53 tRNA genes. A total of 150 carbohydrate-active enzyme-related genes were predicted from the genome; among them, seven putative chitinolytic genes were identified, including 4 genes related to family 18 chitinase, 2 genes to family 20 β-N-acetylglucosaminidase, and one gene to auxiliary activity family 10. In addition, at least 32 genes related to plant growth-promoting functions were identified, including those associated with indole-3-acetic acid production, phosphate and potassium solubilization, siderophore biosynthesis, iron uptake, ACC metabolism, and nitrate transport and reduction. Furthermore, genome mining identified 4 biosynthetic gene clusters probably involved in secondary metabolite production, of which 3 displayed no similarity to previously reported clusters, indicating potential for novel bioactive compounds. These genomic data improved our understanding of the biodegradation capacity and agricultural potential of P. mucilaginosus YWY-5.1 isolated from Vietnam, and provided a valuable genomic resource for future functional and biotechnological investigations toward crop production and related fields.

Chitinases

Bioremediation potential of lead and cadmium tolerant bacteria isolated from industrial (tannery) effluents.

Heavy metal pollution from tannery industries presents significant environmental and public health concerns due to the toxicity and persistence of metals such as Pb2+ and Cd2+. This study aimed to isolate and characterize indigenous Pb2+ and Cd2+-tolerant bacteria from tannery effluents and contaminated soils of highly polluted areas in Dhaka for potential bioremediation applications. A total of 72 Pb2+-tolerant and 52 Cd2+-tolerant bacterial isolates were obtained using metal-supplemented LB agar. The minimum inhibitory concentrations (MICs) recorded were 4000 ppm for Pb2+ and 250 ppm for Cd2+. Quantitative analysis demonstrated removal efficiencies of 93.91% for Pb2+ and 89.66% for Cd2+. All isolates exhibited plant growth-promoting traits, including phosphate solubilization, ammonia production, indole-3-acetic acid (IAA) production, and cellulase activity. Most isolates were antibiotic-sensitive, though some showed multidrug resistance, emphasizing the need for biosafety evaluation. The most promising isolates were partially identified as Enterobacter spp. and K. pneumoniae. Protein expression profiling by SDS-PAGE revealed metal-responsive proteins ranging from 25 to 75 kDa under selective Pb2+ and Cd2+ stress. Genomic and proteomic analyses further indicated the involvement of efflux pump-associated genes in metal resistance, where cusR was identified as a common resistance gene among the dominant strains. Overall, these findings suggest that the indigenous K. pneumoniae possesses strong potential for Pb2+ and Cd2+ removal, along with plant growth-promoting capabilities, making them promising candidate for bioremediation and phytoremediation strategies.

Antibiogram

Long-day photoperiod promotes growth of pea (Pisum sativum L.) via auxin biosynthesis and polar transport.

Photoperiodic sensitivity is an essential factor that may affect agricultural practices under current climate scenarios. This study used pea (Pisum sativum) to examine effects of varying photoperiods on growth and photosynthetic parameters and then reveal the mechanistic basis of this process by linking them with tissue-specific distribution of auxin and regulation of related genes. This was achieved by transcriptome sequencing, genome-wide gene family identification, and expression pattern analysis. Best results in terms of growth and yield were obtained with a 20 h/4 h light/dark photoperiod and these plants had the highest content of endogenous indole-3-acetic acid (IAA) in both the shoot apex and the root. Genes consistently upregulated with prolonged light exposure were significantly enriched in pathways related to light signal transduction, photosynthetic carbon metabolism, and phytohormone signal transduction. Through genome-wide identification, we characterized the TAA/TAR and YUCCA families (key gene families involved in auxin biosynthesis) as well as the PIN family (responsible for auxin polar transport) in pea. Extending the light duration positively affected expression of several genes related to auxin biosynthesis and transport, among them members of the Elongated Hypocotyl (HY) and Phytochrome-Interacting Factor (PIF) families being key light-induced transcription factors, PsTAR2, the principal gene regulating auxin biosynthesis, as well as PsPIN4, PsPIN5, PsPIN11, and PsPIN13 which mediate polar auxin transport. By elucidating mechanisms underlying the coordinated regulation of pea growth by light and auxin, this work provides a significant reference for photoperiod research on long-day crops for both protected- and field-based horticulture.

Auxin

The van urk-Salkowski reagent--a sensitive and specific chromogenic reagent for silica gel thin-layer chromatographic detection and identification of indole derivatives.

The chromogenic reagent described has been tested with seventy-nine indole derivatives and found to be very sensitive and indole-specific. The lower limit of detection on silica gel thin-layer plates was between 25 and 50 ng for most indoles. Phenols and hydroxy-, and amino-benzoic acids, hydroxy-, and methoxy-cinnamic acids did not yield chromophores with the exception of p-amino-benzoic acid and p-hydroxy-cinnamic acid which gave yellow and pink chromophores at concentrations greater than 1 and 2 mug. Although many of the C-3 substituted indoles such as indole-3-acetic acid and tryptamine had colors in the reddish-violet-blue color region, most exhibited sufficient color differentiation to allow their identification by thin-layer chromatography. The procedure was simple and required only 10 min from the time of spraying the thin-layer plate until full color development was reached. The colors had a wide spectral range from yellow of the indole-3-glyoxylamide chromophore to blue of the melatonin chromophore, and were extremely stable.

Benzaldehydes

The auxin gatekeepers: Evolution and diversification of the YUCCA family.

The critically important YUCCA (YUC) gene family is highly conserved and specific to the plant kingdom, primarily responsible for the final and rate-limiting step for indole-3-acetic acid (IAA) biosynthesis. IAA is an essential phytohormone, involved in virtually all aspects of plant growth and development. In addition, IAA is involved in fine-tuning plant responses to biotic and abiotic interactions and stresses. While the YUC gene family has significantly expanded throughout the plant kingdom, a detailed analysis of the evolutionary patterns driving this diversification has not been performed. Here, we present a comprehensive phylogenetic analysis of the YUC family, combining YUCs from species representing key evolutionary plant lineages. The evolutionary history of YUCs is complex and suggests multiple recruitment events via horizontal gene transfer from bacteria. We identify and hierarchically classify the YUC family into an early diverging grade, five distinct classes and 41 subclasses. Angiosperm YUC diversity and expansion are explained in the context of protein sequence conservation, as well as spatial and gene expression patterns. The presented YUC gene landscape offers new perspectives on the distribution and evolutionary trends of this crucial family, which facilitates further YUC characterization within plant development and response to environmental change.

Indoleacetic Acids

Integrated phenotype, endogenous hormones and transcriptome analysis revealed the mechanism of response of Phoebe bournei seedlings to shade signals.

Understory tree seedlings are subjected to prolonged shading stress imposed by the canopy foliage, which significantly impedes their growth. A hallmark of shaded environments is a reduced red to far-red light ratio (R: FR). This study elucidates the physiological and molecular responses of the endangered tree species Phoebe bournei to shading signals. Seedlings were exposed to white light (control) and simulated shading environments with R: FR ratios of 1.5, 0.8, and 0.2. The findings reveal that an increase in the proportion of far-red light significantly enhances seedling height, root-collar diameter, internode length, petiole length, leaf surface area, and leaf biomass. Differentially expressed genes (DEGs) in each treatment group predominantly enrich pathways associated with hormone signaling, stress responses, and photosynthesis. Validation experiments demonstrate that shading promotes the activity of Rubisco and RCA enzymes, total chlorophyll (Chl) accumulation, and elevated levels of hormones including indole-3-acetic acid (IAA), gibberellic acid (GA3), salicylic acid (SA)/methyl salicylate (MeSA), cytokinins (CK), abscisic acid (ABA), and jasmonic acid (JA). Weighted Gene Co-expression Network Analysis (WGCNA) identifies seven hub genes linked to photosynthesis and plant hormone regulation: MYB, KSC, SUAR, CESA POD, CESA, and SAUR. Collectively, shading signals induce P. bournei seedlings to elongate their stems and petioles, enhance photosynthetic enzyme activity, and accumulate specific hormones, with pertinent genes actively participating in light signal transduction. This research sheds light on the shading response mechanism of P. bournei, providing a robust theoretical framework for the breeding of shade-tolerant trees and the conservation of endangered species.

Transcriptome

Host genetic regulation of xylem-resident Pseudomonas enhances cucumber growth.

BACKGROUND: Although endophytic microorganisms play a critical role in plant growth and stress resilience, the genetic basis underlying host selection of beneficial microbiota-particularly within the xylem-remains poorly understood. Cucumber (Cucumis sativus), as a crop model with a well-developed system for studying vascular biology, offers a valuable system to investigate the host genetic determinants of xylem microbiome assembly. RESULTS: By conducting population-level microbiome profiling across 109 cucumber accessions, we identified a conserved xylem microbiota dominated by Proteobacteria. Within this community, 20 core amplicon sequence variants (ASVs) were consistently present in xylem sap. Genome-wide association mapping identified a host genetic locus, CsXPR1, which encodes a tetratricopeptide repeat protein that regulates the abundance of the dominant xylem-colonized Pseudomonas ASV_4. Colonization patterns of ASV_4 varied across host genotypes and were correlated with CsXPR1 expression levels, suggesting a precision genetic regulation of bacterial entry into vascular tissues. Pseudomonas fulva strain 220, with 97% 16S rRNA gene identity with ASV_4, could colonize in cucumber xylem by inoculation of either roots or leaves. Genome analysis and plate assays revealed the biosynthesis of indole-3-acetic acid (IAA), solubilization of phosphate, and a range of plant beneficial traits in strain 220. Inoculation with strain 220 significantly enhanced growth in cucumber, but only in CsXPR1 haplotype that exhibited high gene expression and higher recruitment capacity of the strain. These benefits included notable increases in plant height (38%), stem diameter (36%), leaf area (61%), fresh and dry weight (51% and 85%, respectively), and a 4.57-fold increase in 4-methyleneglutamine content within the xylem sap. CONCLUSION: Our findings reveal a complete "gene-to-function" pathway where the host gene CsXPR1 mediates a genotype-dependent growth promotion. It achieves this by regulating the xylem colonization of a beneficial bacterium, Pseudomonas fulva, which in turn enhances plant growth by enriching the xylem sap with the key metabolite 4-methyleneglutamine. Video Abstract.

Cucumis sativus

Whole-genome sequencing and characterization of Pseudomonas stutzeri P1 endophyte isolated from potato unveils plant growth-promoting and other traits.

Endophytic bacteria play an important role in plant growth promotion and stress tolerance, offering sustainable alternatives to chemical inputs in agriculture. In this study, an endophytic bacterial strain P1 was isolated and identified as Pseudomonas stutzeri, a plant-associated bacterium exhibiting multiple plant growth-promoting traits (PGPTs). Biochemical (qualitative and quantitative) and in vitro analyses demonstrated nitrogen fixation, phosphate solubilization, ammonia production, indole-3-acetic acid (IAA) production, biofilm formation, and tolerance to abiotic stresses, including salinity and drought. Furthermore, the P1 strain displayed strong biocontrol activity against the fungal pathogen Fusarium oxysporum f. sp. cumini, indicating its potential to mitigate biotic stress. Whole-genome sequencing generated a high-quality complete genome of 4,758,235 bp. Functional annotation showed enrichment of metabolic pathways associated with plant-microbe interactions and environmental adaptation. Further analyses using KEGG and PGPT-pred data confirmed the presence of genes associated with direct and indirect PGPT, such as nitrogen fixation, phosphate solubilization, biofilm formation, and stress tolerance. The genome also contained genes related to CAZymes, adhesion, and motility, highlighting a strong plant association, whereas the genome lacked major virulence factors and antimicrobial traits, supporting the non-pathogenic nature of the P1 strain. Overall, these findings demonstrate the potential of P1 as a promising bioinoculant candidate for sustainable agriculture in the potato sector.

PGPT-associated genes

Whole-Genome Analysis and Growth-Promoting Mechanism of Klebsiella pneumoniae YMK25 from Maize Rhizobacteria.

Plant growth-promoting rhizobacteria (PGPR) are microorganisms that enhance plant growth through various mechanisms. In the context of global agriculture, which faces fertilizer dependency and environmental pollution, developing eco-friendly microbial fertilizers has become crucial for enhancing agricultural sustainability. To identify highly effective PGPR, we isolated 102 bacterial strains from maize rhizosphere soil using the dilution plating method. The strains were screened for growth-promoting abilities using functional media, resulting in the selection of strain YMK25 for its exceptional capabilities in nitrogen fixation, solubilization of inorganic and organic phosphorus, indole-3-acetic acid (IAA) production, and siderophore production. Strain YMK25 produced IAA at a concentration of 80.49 ± 0.68 μg/mL and exhibited a relative siderophore expression level of 43.68%. Morphological analysis, 16S rDNA gene sequence analysis, and whole-genome sequencing confirmed that strain YMK25 is Klebsiella pneumoniae. Whole-genome analysis revealed a total genome length of 5,115,280 bp, a GC content of 57.61%, and it contained 4746 coding genes. Gene annotation results indicated genes involved in siderophore synthesis, phosphatase activity, and other plant growth-promoting functions, which align with the verified characteristics of strain YMK25. Furthermore, this strain exhibited significant metabolic capabilities. The pot experiment demonstrated that strain YMK25 promotes maize plant growth and assists in nutrient fixation in these plants. In conclusion, strain YMK25 is a high-quality PGPR with substantial potential for application in agricultural production, presenting promise for widespread use in sustainable agriculture.

Klebsiella pneumoniae

Endophytic fungi isolated from coffee plants promote Arabidopsis thaliana growth and suppress soil-borne fungal pathogens.

Endophytic beneficial microorganisms are widely used in agriculture for promoting plant growth and enhancing plant defense mechanisms. This study aimed to characterize endophytic fungi isolated from the roots of coffee plants cultivated in organic agroforestry systems and evaluate their potential as biocontrol agents against fungal pathogens, as well as their ability to promote plant growth. Biocontrol activity was assessed using in vitro dual-culture assays on potato dextrose agar, measuring the inhibition of pathogen growth. Plant growth promotion was evaluated by co-cultivating Arabidopsis thaliana seedlings with fungal isolates on Murashige and Skoog medium. Isolates were further subjected to both qualitative and quantitative biochemical characterization. A total of 18 endophytic fungal strains were identified and classified in five genera: Colletotrichum, Fusarium, Simplicillium, Lasiodiplodia and Trichoderma. Among these, ten Trichoderma isolates demonstrated strong antagonistic activity against selected fungal pathogens and significantly enhanced the growth of Arabidopsis seedlings in vitro. These beneficial effects were associated with the production of siderophores and indole-3-acetic acid, as well as the apparent nitrogen availability -- likely mediated through interactions with nitrogen-fixing bacteria.

Arabidopsis