Indole Compounds Research Articles

Endophytic bacteria associated with tissue culture and leaves of Plinia peruviana

Abstract: The objective of this work was to isolate endophytic bacteria from tissue culture and leaves of jaboticaba (Plinia peruviana) and to evaluate their potential as plant growth-promoting bacteria. The bacteria were isolated from nodal segments grown in vitro and from leaves from a tree under natural conditions, totaling 11 and 54 isolates, respectively. The isolates were characterized by colony morphology. The indolic compounds produced by the isolates, in the presence or absence of 100 mg L-1 tryptophan, were quantified. The greatest producers of these compounds were identified by sequencing the 16S rRNA gene and were inoculated on jaboticaba seeds, using Azospirillum brasilense (Ab-V6) as a positive control. The sensitivity of bacteria to eight antibiotics was also evaluated. All assessed bacteria produced indolic compounds, especially Bacillus sp., with a content of 27.41 μg mL-1. The germination rate of the seeds inoculated with Stenotrophomonas sp. was high - 97.34% compared with that of 74.67% of the negative control. Bacillus sp. and Stenotrophomonas sp. also sped up germination. Chloramphenicol limited the growth of 82% of the isolates, followed by amoxicillin, gentamicin, levofloxacin, and tetracycline, which limited 70%; erythromycin was only effective against 35%. The endophytic bacteria isolated from jaboticaba show characteristics of plant growth-promoting bacteria, and Bacillus sp. and Stenotrophomonas sp., obtained from tissue culture, are capable of enhancing jaboticaba seed germination.

Amino Acids in Intestinal Physiology and Health.

Dietary protein digestion is an efficient process resulting in the absorption of amino acids by epithelial cells, mainly in the jejunum. Some amino acids are extensively metabolized in enterocytes supporting their high energy demand and/or production of bioactive metabolites such as glutathione or nitric oxide. In contrast, other amino acids are mainly used as building blocks for the intense protein synthesis associated with the rapid epithelium renewal and mucin production. Several amino acids have been shown to support the intestinal barrier function and the intestinal endocrine function. In addition, amino acids are metabolized by the gut microbiota that use them for their own protein synthesis and in catabolic pathways releasing in the intestinal lumen numerous metabolites such as ammonia, hydrogen sulfide, branched-chain amino acids, polyamines, phenolic and indolic compounds. Some of them (e.g. hydrogen sulfide) disrupts epithelial energy metabolism and may participate in mucosal inflammation when present in excess, while others (e.g. indole derivatives) prevent gut barrier dysfunction or regulate enteroendocrine functions. Lastly, some recent data suggest that dietary amino acids might regulate the composition of the gut microbiota, but the relevance for the intestinal health remains to be determined. In summary, amino acid utilization by epithelial cells or by intestinal bacteria appears to play a pivotal regulator role for intestinal homeostasis. Thus, adequate dietary supply of amino acids represents a key determinant of gut health and functions.

Structures, mechanisms and applications of flavin-dependent halogenases.

Overall, this review highlights the structures, mechanisms and applications of flavin-dependent halogenases (FDHs) for future development of FDHs as potential biocatalysts. FDHs catalyze incorporation of halogen atoms into a broad range of substrates. The reactions involved in the production of various halogenated natural products which are important drugs. Typical substrates for FDHs include indole, pyrrole, phenolic and aliphatic compounds. In addition to organic substrates, all FDHs utilize reduced FAD (FADH-), oxygen and halides as co-substrates. Structural studies reveal that FDHs all have similar FAD binding sites. However, FDHs have variations between the different isotypes including different recognition residues for substrate binding and some unique loop structures and conformations. These different structural differences suggest that variations in reaction catalysis exist. However, limited knowledge of the reaction mechanisms of FDHs is currently available. Various biocatalytic applications of FDHs have been explored. Further investigation of the catalytic reactions of FDHs is essential for improving enzyme engineering work to enable FDHs catalysis of challenging reactions.

Towards understanding the electronic structure and ion fragmentation patterns of indole and related compounds

SynopsisElectronic structure and VUV-induced fragmentation of selected molecules of the indole family have been studied using valence photoemission spectroscopy (PES), core X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) and Photo-Electron Photo-Ion Coincidence (PEPICO).

Self-assembly of new O- and S-heterocycle-based protective layers for copper in acid solution.

In order to explore the effects of the structures of organic molecules on their performance and develop high-efficiency self-assembly monolayers (SAMs), two heterocycle-based indole compounds, namely FYBI and TYBI, have been synthesized by a simple route. Herein, we show that FYBI and TYBI can effectively self-assemble on a copper surface and form strong anti-corrosive monolayers to protect copper in acid medium. The compositions, morphologies, and thicknesses of the SAMs have been investigated by XPS, FTIR, SEM and ellipsometry analyses. The optimal self-assembly conditions and inhibition performance of the SAMs with O- or S-heterocycles have been studied by electrochemical tests. According to the results, TYBI displays more powerful inhibition performance than FYBI. Furthermore, the high-resolution XPS and quantum calculation results reveal that the S-heterocycle indole (TYBI) can readily donate electrons to the empty d orbital of Cu and form more robust, hydrophobic, and anti-corrosive SAMs than the O-heterocycle indole (FYBI). The inhibited corrosion is achieved by inhibiting the generation of Cu2+. This systematic study on the performance of various heterocycle-based organic compounds gives a fresh perspective for forming SAMs with certain characteristics, such as anti-corrosion ability or super-hydrophobicity.

Isolation and selection of endophytic spore-forming bacteria with plant growth promoting properties isolated from Ilex paraguariensis St. Hil. (yerba mate).

Yerba mate (Ilex paraguariensis St. Hil.) is a species native to the subtropical regions of South America. Despite being an important crop for the region, there are few studies on the use of microorganisms to improve the growth of seedlings in the nursery stage. The objective of this study was to isolate spore-forming endophytic bacteria with plant growth promoting properties associated with yerba mate seedlings and determine their phytobeneficial effect under controlled laboratory conditions. Isolates were selected based on their sporulation capacity and evaluated for in vitro plant growth promoting properties (nitrogen fixation, phosphate solubilization, production of siderophores and synthesis of indolic compounds). Yerba mate seedlings were inoculated with the most promising isolates, which were identified via analyses of the sequence of their 16S rDNA gene as Bacillus circulans (12RS3) and Bacillus altitudinis (19RS3, T5S-T4). After 120 days plants showed higher root dry weight when inoculated with isolate 19RS3 and higher shoot dry weight with 19RS3 and T5S-T4. In conclusion, further studies to determine the ability of these isolates to adapt to the climatic conditions and to survive amidst the native soil microflora in yerba mate cultivated native soils, will be crucial for developing such strains as biofertilizer.

Iridium‐Catalyzed Cycloisomerization of Alkynoic Acids: Synthesis of Unsaturated Lactones

AbstractThe iridium‐catalyzed cycloisomerization of various alkynoic acids was successfully developed, and a series of five‐, six‐, and especially seven‐membered unsaturated lactones were constructed with moderate yields and excellent regioselectivities (up to 68% yield, >99:1 rr). In addition, the indole compound can be easily prepared with 75% yield through this efficient synthetic methodology. Moreover, a plausible mechanism for this Ir‐catalyzed cycloisomerization of alkynoic acids was proposed.magnified image

Achromobacter sp. FB-14 harboring ACC deaminase activity augmented rice growth by upregulating the expression of stress-responsive CIPK genes under salinity stress.

Soil salinity is one of the major plant growth and yield-limiting constraints in arid and semi-arid regions of the world. In addition to the oxidative damage, increasing salt stress is associated with elevated cellular ethylene levels due to the synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) in large amounts. The objective of the current study was to elucidate the inoculation effect of an ACC deaminase (ACCD)-producing phytobeneficial strain Achromobacter sp. FB-14 on rice plants to alleviate the salinity effects by upregulation of the stress-responsive CIPK genes. The strain FB-14 was isolated by using nutrient agar medium at 855mM NaCl concentration and it was taxonomically identified as Achromobacter sp. with more than 99% 16S rRNA gene sequence similarity with many Achromobacter species. The strain FB-14 demonstrated substantial in vitro potential for ACCD activity, synthesis of indole compounds, and phosphate solubilization up to 100mM NaCl concentration in the culture medium. The gene corresponding to ACCD activity (acdS) was amplified and sequenced in order to confirm the inherent enzyme activity of the strain at a molecular level. The rifampicin-resistant derivative of strain FB-14 was recovered from the rice rhizosphere on antibiotic medium up to 21days of sowing. Moreover, the strain FB-14 was inoculated on rice plants under salinity and it not only enhanced the growth of rice plants in terms of root and shoot length, and fresh and dry weight, but also upregulated the expression of stress-responsive CIPK genes (OsCIPK03, OsCIPK12, and OsCIPK15) according to the results of qRT-PCR analysis. To the best of our knowledge, this is the first report deciphering the role of plant-beneficial Achromobacter strain relieving the rice plants from salt stress by promoting the growth and enhancing the expression of stress-responsive CIPK genes.

Characterization of bacterial endophytes from the roots of native and cultivated Brazil nut trees (Bertholletia excelsa)

ABSTRACT Brazil nut is a very important nontimber forest product in the Amazon region. Propagation of this tree still represents a challenge due to slow and uneven seed germination. In this context, plant growth-promoting bacteria can facilitate the process of propagation. The aims of this study were to isolate and characterize endophytic bacteria from the roots of Brazil nut trees in native terra firme forest and cultivation areas in northern Brazil, and to identify mechanisms by which bacteria act in plant growth promotion. Overall, 90 bacterial isolates were obtained from the roots of Brazil nut trees in monoculture, agroforestry and native forest areas by using different semisolid media. The isolates were characterized by sequencing the 16S rRNA gene. Plant growth-promoting characteristics were evaluated by the presence of the nifH gene, aluminum phosphate solubilization and the production of indole compounds. The isolates were affiliated with 18 genera belonging to 5 different classes (α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, Bacilli and Actinobacteria). The genus Bacillus was predominant in the forest and monoculture areas. Fourteen isolates presented the nifH gene. Most of the bacteria were able to solubilize aluminum phosphate and synthetize indole compounds. The results indicated high diversity of endophytic bacteria present among the roots of Brazil nut trees, mainly in the agroforestry area, which could be related to soil attributes. Among the 90 isolates, the 22 that presented the best results regarding plant growth promotion traits were good candidates for testing in seedling production of Brazil nut trees.

Substituent effects on antioxidant activity of monosubstituted indole‐3‐carbinols: A DFT study

AbstractIndole‐3‐carbinol (I3C) is an indole compound with proven health benefits and thus potential preventive medicine and therapeutic applications. Here the origins of the substituent effects on the antioxidant activity of monosubstituted indole‐3‐carbinols (I3Cs) were studied in silico by calculating their thermochemical properties using the (RO)B3LYP/6‐311++G(2df,2p)//B3LYP/6‐311G(d,p) model chemistry. It was found that the electron withdrawing groups such as CF3, CN, COOH, COOMe can increase the bond dissociation energy (BDE) values of N‐H bonds and decrease the BDE(C8‐H) values, while the presence of the Br, Cl, F, Me, NMe2, NH2, NHMe, OH, OMe, Ph groups seems to decline the BDE(X‐H)s (X = N, C). It is worth noticing that a sequential electron transfer mechanism is responsible for these I3Cs with the strong electron donating groups including NMe2, NHMe and NH2, while a hydrogen atom transfer mechanism is likely favored for the remaining monosubstituted I3Cs. The kinetic study according to the HAT mechanism showed that the CH3OO• radical scavenging of 2‐NMe2‐I3C derivative has the highest rate constant (k = 1.93×1010 M‐1s‐1) and it is higher than that of typical antioxidants i.e. Trolox or ascorbic acid. Thus, the results appear to suggest that the N‐Br‐I3C and 2‐NMe2‐I3C compounds are potential antioxidants.

Direct comparison of Arabidopsis gene expression reveals different responses to melatonin versus auxin

BackgroundMelatonin (N-acetyl-5-methoxytryptamine) in plants, regulates shoot and root growth and alleviates environmental stresses. Melatonin and the phyto-hormone auxin are tryptophan-derived compounds. However, it largely remains controversial as to whether melatonin and auxin act through similar or overlapping signalling and regulatory pathways.ResultsHere, we have used a promoter-activation study to demonstrate that, unlike auxin (1-naphthalene acetic acid, NAA), melatonin neither induces Direct repeat 5 DR5 expression in Arabidopsis thaliana roots under normal growth conditions nor suppresses the induction of Alternative oxidase 1a AOX1a in leaves upon Antimycin A treatment, both of which are the hallmarks of auxin action. Additionally, comparative global transcriptome analysis conducted on Arabidopsis treated with melatonin or NAA revealed differences in the number and types of differentially expressed genes. Auxin (4.5 μM) altered the expression of a diverse and large number of genes whereas melatonin at 5 μM had no significant effect but melatonin at 100 μM had a modest effect on transcriptome compared to solvent-treated control. Interestingly, the prominent category of genes differentially expressed upon exposure to melatonin trended towards biotic stress defence pathways while downregulation of key genes related to photosynthesis was observed.ConclusionTogether these findings indicate that though they are both indolic compounds, melatonin and auxin act through different pathways to alter gene expression in Arabidopsis thaliana. Furthermore, it appears that effects of melatonin enable Arabidopsis thaliana to prioritize biotic stress defence signalling rather than growth. These findings clear the current confusion in the literature regarding the relationship of melatonin and auxin and also have greater implications of utilizing melatonin for improved plant protection.

Medicago truncatula root developmental changes by growth-promoting microbes isolated from Fabaceae, growing on organic farms, involve cell cycle changes and WOX5 gene expression.

Both root nodules and the rhizosphere of Fabaceae plants grown on organic farms are a rich source of bacteria, mainly from the families Enterobacteriaceae and Pseudomonadaceae. The enhanced root system growth in M. truncatula after inoculation with selected bacteria includes an increase of nuclei in the cell cycle S phase and a reduction in phase G2 as well as an enhanced expression of the WOX5 gene. Synthetic fertilizers and pesticides are commonly used to improve plant quality and health. However, it is necessary to look for other efficient and also environmentally safe methods. One such method involves the use of bacteria known as plant growth-promoting bacteria (PGPB). Seventy-two bacterial isolates from the rhizospheric soil and root nodule samples of legumes, including bean, alfalfa, lupine and barrel medic, grown on an organic farm in Western Pomerania (Poland) were screened for their growth-promoting capacities and 38 selected isolates were identified based on 16S rRNA gene sequencing. The analysis showed the isolates to represent 17 strains assigned to 6 families: Enterobacteriaceae, Pseudomonadaceae, Xanthomonadaceae, Rhizobiaceae, Bacillaceae and Alcaligenaceae. Pot experiments showed that 13 strains, capable of producing indole compounds from tryptophan in vitro, could significantly enhance the root and shoot weight of 10-week-old Medicago truncatula seedlings. Compared to non-inoculated seedlings, the root system of inoculated ones was more branched; in addition, the root length, surface area and, especially, the root volume were higher. The 24-h root inoculation with the three selected strains increased the nuclei population in the G1 and S phases, decreased it in the G2 phase and enhanced the WUSCHEL-related Homeobox5 (WOX5) gene expression in root tips and lateral zones. The "arrest" of nuclei in the S phase and the enhancement of the WOX5 gene expression were observed to gradually disappear once the bacterial suspension was rinsed off the seedling roots and the roots were transferred to water for further growth. This study shows that the nodules and rhizosphere of legumes grown on organic farms are a rich source of different PGPB species and provides new data on the ability of these bacteria to interfere with cell cycle and gene expression during the root development.

Biosynthesis and purification of indole-3-acetic acid by halotolerant rhizobacteria isolated from Little Runn of Kachchh

Abstract Abiotic stresses are increasing globally at an alarming rate. On the contrary, demand for food is ever increasing with the rise in population and salts stress has been the major one reported to affect photosynthetic machinery and thereby reduce growth and yield. Halo-tolerant plant growth promoting rhizobacteria that have ability to work under salt stress and promote plant growth along-with enhanced synthesis of secondary metabolites including phytohormones (Indole Acetic Acid (IAA) and volatile compounds is being widely studied. The present work describes isolation, characterization and identification of IAA, producing halotolerant PGPR from Cumin cyminum rhizosphere cultivated in saline areas of Kachchhh, Gujarat, India. Initially, the IAA secreting ability was assessed for 20 bacterial isolates and three potential isolates that had ability to synthesize IAA under saline conditions (2% w/v NaCl) were selected for further studies. The cultures were identified as Bacillus subtilis, Rheinheimera sp. and Rhizobium sp. by partial sequencing of 16S rRNA gene, the nucleotide sequences has been submitted to NCBI, GenBank. The IAA producing ability under salt stress was assessed for all three cultures and was observed to be 250 ± 0.1 μg/ml, 220 ± 0.1 μg/ml and 200 ± 0.1 μg/ml for Rheinheimera sp. Rhizobium sp. and Bacillus subtilis respectively. The total estimation of IAA biosynthesis by Rheinheimera sp. was done by TLC and HPLC of extracted IAA and reference indolic compounds. This is the first time that Rheinheimera sp. is the being selected for IAA production and development of Halo-tolerant PGPR for field based studies and applications.

Diversity of sugarcane root-associated endophytic Bacillus and their activities in enhancing plant growth.

Plant tissues are the reservoirs of beneficial and harmful microbes that regulates plant growth. In the present study, we investigated the diversity, function and colonization of sugarcane roots associated with Bacillus spp. A total of 20 Bacillus strains were isolated and identified by 16S rRNA gene sequencing, and their genetic diversity was examined by BOX, ERIC, REP, (GTG)5 PCR techniques. Among all Bacillus isolates, 65% showed indole acetic acid-like compounds production, 50% solubilized phosphorus and 25% of the isolates were able to secrete siderophore. Moreover, all 20 Bacillus isolates showed antifungal activity against eight fungal pathogens and 11 of them (55%) antagonized tomato grey mold. Based on the plant growth-promoting traits and antifungal potential, isolate Y8 was selected for root and plant tissue colonization assays and a greenhouse-level sugarcane growth promotion study. Fluorescence microscopy results confirmed that isolate Y8 has a strong ability to colonize in the sugarcane root and leaves, and the root surface association of Y8 was confirmed by scanning electron microscopy. Furthermore, greenhouse experimental results demonstrated that Y8 has a significant effect on enhancing sugarcane biomass and root length. Endophytic Bacillus strains have growth-promoting properties and anti-fungal ability that can enhance plant fitness in an eco-friendly manner. Endophytic Bacillus strains would be a potential alternative to chemical fertilizer as well as a biocontrol agent in the future.

Silver nanoparticles affect phenolic and phytoalexin composition of Arabidopsis thaliana.

Silver nanoparticles are widely used in industry, medicine, biotechnology and agriculture. As a consequence, these nanoparticles are reaching the environment as waste products, which might have a negative impact on the environment, especially on plants. This includes the elicitation of various biochemical processes in plants. In this article, we report on the changes in secondary metabolic profile of Arabidopsis thaliana seedlings subjected to silver nanoparticle treatment in vitro. Briefly, various sizes (10nm, 40nm and 100nm in diameter) and concentrations (0.5-5.0ppm) of silver nanoparticles were tested. Ultraperformance liquid chromatography coupled with ultraviolet and fluorescence detectors as well as hyphenated to a high-resolution mass spectrometer (UPLC-PDA-FLR, UPLC-HESI-HRMS) and HPLC - ion trap mass spectrometer (HPLC-ESI-MS/MS), were applied to identify and quantify secondary metabolites. To understand whether silver ions could induce changes in the secondary metabolite profile, seedlings treated with silver nitrate in concentrations equivalent to these of nanoparticles were also analysed. The results showed significant differences in the accumulation of phenolic and indole compounds between treatments. Silver nanoparticles and silver ions induced the biosynthesis of camalexin, hydroxycamalexin O-hexoside and hydroxycamalexin malonyl-hexoside. These compounds are important phytoalexins for Brassicaceae family (especially for Camelinae clad) and are also synthetized in response to biotic and abiotic stresses. Statistically significant changes have been also observed for five phenolic compounds and 5'Glucosyl-dihydroneoascorbigen in different treatment conditions.

Deep adsorptive desulfurization over ion-exchanged zeolites: Individual and simultaneous effect of aromatic and nitrogen compounds

The presence of aromatics and nitrogen compounds in petroleum fuel has a strong inhibiting impact on deep adsorptive desulfurization (ADS). This work aimed to clarify the individual and simultaneous effect of these compounds on ADS of the most refractory sulfur-containing polyaromatic compounds (dibenzothiophene and 4,6-dimethyldibenzothiophene) over Na–Y, Ni–Y, La–Y, Ce–Y and Ni–Ce–Y zeolites in a fixed bed system at ambient conditions. Polyaromatics (naphthalene) and nitrogen (quinoline and indole) compounds caused a marked decrease in the sulfur adsorption capacity, while the nitrogen compounds decreased the sulfur adsorption capacity more than naphthalene. The negative electrostatic potential of compounds might play an important role in the adsorptive selectivity on the pre-reduced Ni–Y zeolite. The results show that the adsorption sites of aromatics and nitrogen compounds on the adsorbents are the same as for the sulfur compounds. This competitive adsorption was very strong especially for the metal that enhanced π-complexation interaction. The reduced Ni2+ introduced into Na–Y zeolite increased resistance to aromatics and nitrogen compounds on ADS. For the spent adsorbent, the regeneration efficiency, in terms of the desorption amount, depended on the similarity of the polarity of the solvent (hexane and toluene) and adsorbate, where a high temperature and low flow rate of solvent favored the extraction of adsorbates leading to an increased regeneration efficiency. This study provides an insight into the interactions among these three kinds of components and adsorbents, which is useful for further development of the ADS process.

Synthesis, Antiviral Activity, and Induction of Plant Resistance of Indole Analogues Bearing Dithioacetal Moiety.

A series of compounds with potential activity to induce plant resistance was synthesized from indole and thiol compounds and methodically evaluated for antiviral activity. The results indicated that some of the synthesized compounds had high antipotato virus Y (PVY), anticucumber mosaic virus, and antitobacco mosaic virus activities. Notably, compound D21 exhibited the best activity against PVY among these compounds in vivo, and the 50% effective concentrations (EC50) of protection activity is 122 μg/mL, which was distinctively better than the corresponding values for ribavirin (653 μg/mL), Ningnanmycin (464 μg/mL), and Xiangcaoliusuobingmi (279 μg/mL). Interestingly, we found that the protection activity of D21 was associated with improvement of chlorophyll content and defense-related enzyme activities. Moreover, D21 could trigger the malate dehydrogenase (MDH) signaling pathway, as further confirmed by the MDH activity evaluation. Hence, D21 can protect plants against viral activity and has potential as a novel activator for plant resistance induction.

Indole-3-Acetic Acid in Burkholderia pyrrocinia JK-SH007: Enzymatic Identification of the Indole-3-Acetamide Synthesis Pathway.

Burkholderia pyrrocinia JK-SH007 is a plant growth-promoting bacteria (PGPB), that can promote the growth of poplar and other trees, and, production of the plant hormone indole-3-acetic acid (IAA) is one of the reasons for this effect. Therefore, the aims of this study were to evaluate the effect of the external environment on the synthesis of IAA by B. pyrrocinia JK-SH007 and to perform a functional analysis of its IAA synthesis pathway. In this study, IAA and its synthetic intermediates indole-3-acetamide (IAM), indole-3-pyruvic acid (IPyA), tryptamine (TAM), and indole-3-acetonitrile (IAN) were detected in B. pyrrocinia JK-SH007 fermentation broth by high-performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS), and these indolic compounds were also found in the cell-free extraction of B. pyrrocinia JK-SH007, but the genomic analysis of B. pyrrocinia JK-SH007 indicated that IAA biosynthesis was mainly through the IAM and TAM pathways. The effects of L-tryptophan (L-Trp), temperature and pH on the synthesis of IAA were investigated, and the results showed that L-Trp exerted a significant effect on IAA synthesis and that 37°C and pH 7 were the optimal conditions IAA production by B. pyrrocinia JK-SH007. In addition, the protein expression of tryptophan 2-monooxygenase and indoleacetamide hydrolase, which are the key enzymes of the indole acetamide-mediated IAA synthesis pathway, was analyzed, and their activity was verified by substrate feeding experiments. The results revealed the existence of an IAA synthesis pathway mediated by IAM and indicated that this pathway plays a role in B. pyrrocinia JK-SH007. This study lays the foundation for further exploration of the specific pathway and mechanism of IAA synthesis in B. pyrrocinia JK-SH007.

A Biomimetic, One-Step Transformation of Simple Indolic Compounds to Malassezia-Related Alkaloids with High AhR Potency and Efficacy.

Malassezia furfur isolates from diseased skin preferentially biosynthesize compounds which are among the most active known aryl-hydrocarbon receptor (AhR) inducers, such as indirubin, tryptanthrin, indolo[3,2-b]carbazole, and 6-formylindolo[3,2-b]carbazole. In our effort to study their production from Malassezia spp., we investigated the role of indole-3-carbaldehyde (I3A), the most abundant metabolite of Malassezia when grown on tryptophan agar, as a possible starting material for the biosynthesis of the alkaloids. Treatment of I3A with H2O2 and use of catalysts like diphenyldiselenide resulted in the simultaneous one-step transformation of I3A to indirubin and tryptanthrin in good yields. The same reaction was first applied on simple indole and then on substituted indoles and indole-3-carbaldehydes, leading to a series of mono- and bisubstituted indirubins and tryptanthrins bearing halogens, alkyl, or carbomethoxy groups. Afterward, they were evaluated for their AhR agonist activity in recombinant human and mouse hepatoma cell lines containing a stably transfected AhR-response luciferase reporter gene. Among them, 3,9-dibromotryptanthrin was found to be equipotent to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as an AhR agonist, and 3-bromotryptanthrin was 10-times more potent than TCDD in the human HG2L7.5c1 cell line. In contrast, 3,9-dibromotryptanthrin and 3-bromotryptanthrin were ∼4000 and >10,000 times less potent than TCDD in the mouse H1L7.5c3 cell line, respectively, demonstrating that they are species-specific AhR agonists. Involvement of the AhR in the action of 3-bromotryptanthrin was confirmed by the ability of the AhR antagonists CH223191 and SR1 to inhibit 3-bromotryptanthrin-dependent reporter gene induction in human HG2L7.5c1 cells. In conclusion, I3A can be the starting material used by Malassezia for the production of both indirubin and tryptanthrin through an oxidation mechanism, and modification of these compounds can produce some highly potent, efficacious and species-selective AhR agonists.

Plant growth-promoting potential of bacteria associated to pioneer plants from an active volcanic site of Chiapas (Mexico)

The use of microbial inoculants is an effective biotechnological alternative to increase crop productivity. In this work we studied the diversity of the Plant Growth Promoting Bacteria (PGPB) associated with pioneer plants that grow at the surroundings of the crater-lake of El Chichón volcano. Cheilanthes aemula (Pteridaceae) and Andropogon glomeratus (Poaceae) plants were dominant in this area. A total of 80 endophytes and 128 strains from the rhizosphere were isolated using selective culture media, and then characterized phenotypically. Isolates were tested for growth in high salt concentrations, at different pH and in moderate concentrations of heavy metals. The genetic diversity and identity of the strains were revealed by BOX_PCR and by sequencing of 16S rRNA gene. A. glomeratus isolates were classified within the genera Brevibacillus, Sinomonas, Sphingobium, Chryseobacterium, Pantoea, Ralstonia, Burkholderia, Serratia, Bacillus, Sphingomonas and Methylobacterium using 16S rDNA gene sequence analysis. C. aemula isolates were grouped into the genera Dyella, Burkholderia, Microbacterium, Enterobacter, Exiguobacterium, Pandoraea, Methylobacterium, Kocuria and Agrobacterium. The rhizospheric and endophytic strains were distinguished by their ability to produce different extracellular enzymes. The extremophile isolates had the ability to produce indole compounds (IAA), solubilize phosphate, synthesize siderophores, ACC deaminase and nitrogenase and showed a positive effect on the growth of Phaseolus vulgaris and upon the total content of nitrogen and phosphorus of plants. The diversity of bacteria associated to the pioneer plants had multifunctional qualities as PGPB that may contribute to their adaptation and proliferation at this active volcano and be used efficiently as biofertilizers to promote plant growth in organic farming systems