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81.
Sabine Kirner Philip E. Hammer D. Steven Hill Annett Altmann Ilona Fischer Laura J. Weislo Mike Lanahan Karl-Heinz van Pée James M. Ligon 《Journal of bacteriology》1998,180(7):1939-1943
Pyrrolnitrin is a secondary metabolite derived from tryptophan and has strong antifungal activity. Recently we described four genes, prnABCD, from Pseudomonas fluorescens that encode the biosynthesis of pyrrolnitrin. In the work presented here, we describe the function of each prn gene product. The four genes encode proteins identical in size and serology to proteins present in wild-type Pseudomonas fluorescens, but absent from a mutant from which the entire prn gene region had been deleted. The prnA gene product catalyzes the chlorination of l-tryptophan to form 7-chloro-l-tryptophan. The prnB gene product catalyzes a ring rearrangement and decarboxylation to convert 7-chloro-l-tryptophan to monodechloroaminopyrrolnitrin. The prnC gene product chlorinates monodechloroaminopyrrolnitrin at the 3 position to form aminopyrrolnitrin. The prnD gene product catalyzes the oxidation of the amino group of aminopyrrolnitrin to a nitro group to form pyrrolnitrin. The organization of the prn genes in the operon is identical to the order of the reactions in the biosynthetic pathway.The antibiotic pyrrolnitrin [3-chloro-4-(2′-nitro-3′-chlorophenyl)pyrrole] (PRN) is produced by many pseudomonads and has broad-spectrum antifungal activity (1, 5, 12–14, 17). PRN has been implicated as an important mechanism of biological control of fungal plant pathogens by several Pseudomonas strains (12–14), including P. fluorescens BL915, from which the prn genes were isolated (10).Tryptophan was identified as the precursor for PRN, based on the feeding of cultures with isotopically labeled and substituted tryptophan (2, 7, 8, 17, 25). Biosynthetic pathways were proposed as early as 1967 (7) and have been refined on the basis of tracer studies and the isolation of intermediates (Fig. (Fig.1)1) (2, 8, 17, 19, 23, 25). Recently, Hammer et al. (9) described the cloning and characterization of a 5.8-kb DNA region which encodes the PRN biosynthetic pathway. This DNA region confers the ability to produce PRN when expressed heterologously in Escherichia coli and contains four genes, prnABCD, each of which is required for PRN production. In the research described here, we used mutants in which each of the four genes was disrupted and strains which overexpress the individual genes to elucidate the function of each gene product in PRN biosynthesis. Open in a separate windowFIG. 1Biosynthetic pathways for PRN as proposed by van Pée et al. (23) (A) and by Chang et al. (2) (B). The reactions catalyzed by the PRN biosynthetic enzymes encoded by the prnABCD genes are indicated above the appropriate reaction arrows.
Open in a separate window
Open in a separate windowa+, PRN detected; −, PRN not detected. Hohaus et al. (11) presented additional evidence of the chlorinating activity of the prnA gene product, specifically, the chlorination of l-tryptophan to form 7-CLT by cell extracts from P. fluorescens strains which expressed the prnA gene, but which did not contain any of the other prn genes. To clarify which isomer was produced, Hohaus et al. (11) extracted 7-CLT from the bacteria and oxidized it to the corresponding indole-3-pyruvic acid with amino acid oxidases. Since the isolated 7-CLT was degraded by l-amino acid oxidase, but not by d-amino acid oxidase (11), it must be in the l configuration. The deduced amino acid sequence for prnA contains a consensus NAD binding site (9), and, indeed, NADH is a required cofactor for the prnA gene product.Cultures of BL915ΔORF2 produced 7-CLT, but 7-chloro-d-tryptophan (11) and other PRN biosynthetic intermediates were not detected (Fig. (Fig.3).3). BL915ΔORF2 produced PRN when supplied with exogenous MDA or APRN, but not when supplied with 7-CT (Table (Table2).2). When prnB was expressed in strain BL915ΔORF1–4, exogenously supplied 7-CT was converted to MDA (Fig. (Fig.4).4). These results indicate that the prnB gene product catalyzes the rearrangement of the indole ring to a phenylpyrrole and the decarboxylation of 7-CLT to convert 7-CLT to MDA. While it is somewhat surprising that a single enzyme carries out both the ring rearrangement and decarboxylation, Chang et al. (2) postulated a mechanism for such a reaction on a single enzyme some 16 years ago. The prnB gene product also catalyzed the production of APP (Fig. (Fig.4),4), presumably by using tryptophan as a substrate. Open in a separate windowFIG. 4In vivo conversion of PRN biosynthetic intermediates by the products of single prn genes. Individual genes were expressed on plasmids in the host strain BL915ΔORF1–4, and biosynthetic intermediates were added to the culture medium as indicated. Culture extracts were separated by TLC on silica plates with toluene as the mobile phase. Metabolites were visualized with van Urk’s reagent. Arrows indicate the positions of APP (dark green), MDA (olive green), APRN (reddish brown), and PRN (purple).MDA accumulated in cultures of BL915ΔORF3, but APP, APRN, and PRN were not detected (Fig. (Fig.3).3). BL915ΔORF3 was able to produce PRN when supplied with APRN in the culture medium, but not when supplied with 7-CT or MDA (Table (Table2).2). Strain BL915ΔORF1–4 expressing prnC converted exogenously supplied MDA to APRN (Fig. (Fig.4).4). These data indicate that the prnC gene product catalyzes the chlorination of MDA to form APRN. Cell extracts of the P. fluorescens strain which overexpresses the prnC gene (but does not contain the other prn genes) can also catalyze the chlorination of MDA to form APRN (11).The prnC gene is homologous to the chl gene from Streptomyces aureofaciens, which encodes a chlorinating enzyme for tetracycline biosynthesis (3, 9). Like prnA, the prnC deduced amino acid sequence contains a consensus NAD binding region (9), and NADH is required for the chlorination of MDA (11). While both prnA and prnC encode halogenating enzymes, they show no homology to previously cloned haloperoxidases (9) or to each other. Furthermore, in contrast to haloperoxidases (16), the two NADH-dependent halogenating enzymes in the PRN biosynthesis pathway are substrate specific (i.e., the tryptophan halogenase does not catalyze the chlorination of MDA and vice versa) (11).APRN accumulated in cultures of BL915ΔORF4 (Fig. (Fig.3),3), and this mutant was not able to produce PRN when supplied with any of the known PRN biosynthetic intermediates. Strain BL915ΔORF1–4 expressing prnD converted exogenously supplied APRN to PRN (Fig. (Fig.4).4). These results indicate that the prnD gene product catalyzes the oxidation of the amino group of APRN to a nitro group forming PRN. In vitro experiments by Kirner and van Pée (15) had suggested that this reaction is catalyzed by a chloroperoxidase; however, gene disruption experiments demonstrated that chloroperoxidases are not involved in PRN biosynthesis in vivo (16). Instead, this oxidation is more likely to be catalyzed by a class IA oxygenase (20), as suggested by the homology of prnD with these enzymes (9).We have shown that each prn gene encodes a protein found in the wild-type BL915 strain and have demonstrated in vivo that these four gene products carry out four biochemical steps which convert l-tryptophan to PRN. None of the conversions were observed in strain BL915ΔORF1–4, from which the entire 5.8-kb prn gene region has been deleted (Fig. (Fig.4).4). The arrangement of the genes in the operon is identical to the sequence of reactions in the biosynthetic pathway proposed by van Pée et al. (23) (Fig. (Fig.11).Chang et al. (2) proposed an alternate biosynthetic scheme (Fig. (Fig.1B)1B) and reported the conversion of exogenously supplied APP to PRN in vivo. Similarly, Zhou et al. (25) reported the conversion of APP to APRN in a cell-free system. These workers concluded that APP is an intermediate in PRN biosynthesis and that ring rearrangement precedes chlorination (Fig. (Fig.1B).1B). In the present study, APP accumulated only in strains which overexpressed the prnB gene. Furthermore, APP was not detected in cultures of BL915ΔORF1, which contains functional prnBCD genes expressed from the native promoter, as would be expected if the ring rearrangement (catalyzed by the prnB gene product) occurs before the first chlorination step (catalyzed by the prnA gene product). Like Hamill et al. (8) and van Pée et al. (23), we demonstrated that exogenously supplied 7-CT is converted to PRN. These results, together with the finding that the gene product of prnA catalyzes the NADH-dependent chlorination of l-tryptophan to 7-CLT (11), support the biosynthetic pathway proposed by van Pée et al. (23) (Fig. (Fig.1A)1A) and suggest that APP is a side product or dead-end metabolite. Purification and kinetic characterization of the prnA and prnB gene products, including investigations of substrate specificity and regioselectivity, will further clarify the roles of 7-CLT and APP in the PRN biosynthetic pathway.If APP is indeed a dead-end metabolite, it would be advantageous to tightly regulate the amount of prnB gene product present in cells, thus minimizing the diversion of substrate into APP. The prnB gene begins with GTG (9), which is a two- to threefold-less-efficient initiation codon than ATG (18); however, the prnB open reading frame is apparently translationally coupled to the prnA open reading frame (9). Coupling increases translational efficiency and is thought to be a mechanism to ensure coordinate expression of the coupled genes (18). In PRN biosynthesis, translational coupling of prnA and prnB may be a mechanism to regulate the level of prnB gene product present in cells and minimize the diversion of tryptophan to APP. 相似文献
Bacterial strains and plasmids.
The bacterial strains and plasmids used in this study are described in Table Table1.1. Pseudomonas strains were cultured in Luria-Bertani medium at 28°C. Antibiotics, when used, were added at the following concentrations: tetracycline, 30 μg/ml; and kanamycin, 50 μg/ml. The expression vector pPEH14 consists of the Ptac promoter and rrnB ribosomal terminator from pKK223-3 (Pharmacia, Uppsala, Sweden) cloned into the BglII site of the broad-host-range plasmid pRK290 (4). Ptac is a strong constitutive promoter in Pseudomonas (unpublished data). The PRN biosynthetic genes are the coding regions described by Hammer et al. (9). Each coding region was cloned from the translation initiation codon to the stop codon by PCR with restriction sites added to the ends to facilitate cloning. For prnB, the native GTG initiation codon was changed to ATG. The clones were sequenced after PCR.TABLE 1
Bacterial strains and plasmids used in this study| P. fluorescens strain or plasmid | Characteristics | Source or reference |
|---|---|---|
| Strains | ||
| BL915 | Wild type | 10 |
| BL915ΔORF1 | Deletion in prnA of BL915, Prn−, Kmr | 9 |
| BL915ΔORF2 | Deletion in prnB of BL915, Prn−, Kmr | 9 |
| BL915ΔORF3 | Deletion in prnC of BL915, Prn−, Kmr | 9 |
| BL915ΔORF4 | Deletion in prnD of BL915, Prn−, Kmr | 9 |
| BL915ΔORF1–4 | Deletion in prnABCD of BL915, Prn−, Kmr | 9 |
| Plasmids | ||
| pPEH14(prnA) | pRK290 carrying Ptac functionally fused to the 1.6-kb prnA coding region | This study |
| pPEH14(prnB) | pRK290 carrying Ptac functionally fused to the 1.1-kb prnB coding region | This study |
| pPEH14(prnC) | pRK290 carrying Ptac functionally fused to the 1.7-kb prnC coding region | This study |
| pPEH14(prnD) | pRK290 carrying Ptac functionally fused to the 1.1-kb prnD coding region | This study |
Chemical standards.
7-Cl-d,l-tryptophan (7-CT) was synthesized as described by van Pée et al. (24). Monodechloroaminopyrrolnitrin (MDA) was extracted from cultures of P. aureofaciens and verified as described by van Pée et al. (23). Aminopyrrolnitrin (APRN) was prepared from PRN by reduction with sodium dithionite (22). PRN was synthesized according to the method of Gosteli (6).Western analysis.
To produce antigen, each prn gene was subcloned into a pET3 vector and transformed into E. coli BL21(De3) (Novagen, Inc., Madison, Wis.). Inclusion bodies were purified from induced cultures with protocols from Novagen. Inclusion body protein (100 μg) was run on a preparative Laemmli polyacrylamide electrophoresis gel, blotted to nitrocellulose filters, and stained with Ponceau S. The major band was excised, solubilized in dimethyl sulfoxide, and used by Duncroft, Inc. (Lovettsville, Va.), to immunize goats and produce antiserum against each PRN protein.Cultures of P. fluorescens BL915 were grown for 48 h in Luria-Bertani medium with the appropriate antibiotics. The cells were pelleted and resuspended in a small volume of Tris-EDTA. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western analysis were performed as described by Sambrook et al. (21). The primary antiserum (goat anti-PRN protein) was diluted 1/1,000, and the secondary antibody (rabbit anti-goat immunoglobulin G conjugated to peroxidase; Pierce, Rockford, Ill.) was diluted 1/3,000. Bands were visualized with an enhanced chemiluminescence kit (Amersham, Arlington Heights, Ill.). This Western analysis demonstrated that each antibody recognized a single protein band from wild-type BL915, and these bands were not present in BL915ΔORF1–4 (Fig. (Fig.2).2). The molecular weights of the recognized proteins were consistent with the sizes predicted from the gene sequences. Each prn gene was expressed on a plasmid in BL915ΔORF1–4. In each case, the protein product of the cloned gene reacted only with the expected antibody and was identical in size to the band detected by that antibody in wild-type BL915 (Fig. (Fig.2).2). Open in a separate windowFIG. 2Western blot analysis of the protein products of prn genes cloned from P. fluorescens BL915. Individual genes were expressed on plasmids in the host strain BL915ΔORF1–4. BL915 wild-type and BL915ΔORF1–4 controls are included on each blot. Blots A, B, C, and D were probed with antibodies raised against the products of prnA, prnB, prnC, and prnD, respectively. Arrows indicate the positions of the 60- and 42-kDa molecular mass markers.Intermediate analysis and feeding experiments.
To determine which biosynthetic intermediates were produced by the prn gene deletion mutants, 2-day-old cultures were extracted with an equal volume of ethyl acetate. The organic phase was dried under vacuum, and the residue was dissolved in a small volume of methanol. Thin-layer chromatography (TLC) was performed on silica-coated plates with toluene or hexane-ethyl acetate (2:1) as the mobile phase. PRN, APRN, MDA, and aminophenylpyrrole (APP) were visualized with van Urk’s reagent as described previously (22).To further clarify which biosynthetic step was blocked in each deletion mutant, intermediate feeding experiments were conducted. Cultures (10 ml) were incubated at 28°C for 48 h. Biosynthetic intermediates were dissolved in a small volume of methanol and added to 4 ml of culture at the following final concentrations: 7-CT, 2.5 μg/ml; MDA, 25 μg/ml; APRN, 12.5 μg/ml. The cultures were incubated for an additional 4 h at 28°C and then extracted with ethyl acetate and analyzed by TLC and liquid chromatography-mass spectrometry as described above.MDA, APRN, and PRN were not detected in cultures of BL915ΔORF1 (Fig. (Fig.3),3), indicating that this mutant is blocked at an early step in PRN biosynthesis. BL915ΔORF1 was able to produce PRN when 7-CT, MDA, or APRN was supplied exogenously (Table (Table2).2). When prnA was expressed in the absence of other prn genes (i.e., in BL915ΔORF1–4), 7-chloro-l-tryptophan (7-CLT) accumulated. The identity of 7-CLT was verified by comparison of results of high-performance liquid chromatography and mass spectra with chemically synthesized 7-CT. These results indicate that the prnA gene product catalyzes the chlorination of l-tryptophan. Open in a separate windowFIG. 3Accumulation of PRN biosynthetic intermediates in P. fluorescens BL915 and prn gene deletion mutants derived from it. Extracts from 2-day-old cultures were separated by TLC on silica plates with hexane-ethyl acetate (2:1 [vol/vol]) as the mobile phase. Metabolites were visualized with van Urk’s reagent. Arrows indicate the positions of MDA (olive green), APRN (reddish brown), and PRN (purple).TABLE 2
Production of PRN by deletion mutants when supplied with biosynthetic intermediates in the growth medium| Strain | Result with intermediate added to culturesa
| ||
|---|---|---|---|
| 7-CT | MDA | APRN | |
| BL915ΔORF1 | + | + | + |
| BL915ΔORF2 | − | + | + |
| BL915ΔORF3 | − | − | + |
| BL915ΔORF4 | − | − | − |
82.
Susannetom Dieck Lydia Sanmartí-Vila Kristina Langnaese Karin Richter Stefan Kindler Antje Soyke Heike Wex Karl-Heinz Smalla Udo K?mpf Jürgen-Theodor Fr?nzer Markus Stumm Craig C. Garner Eckart D. Gundelfinger 《The Journal of cell biology》1998,142(2):499-509
The molecular architecture of the cytomatrix of presynaptic nerve terminals is poorly understood. Here we show that Bassoon, a novel protein of >400,000 M
r, is a new component of the presynaptic cytoskeleton. The murine bassoon gene maps to chromosome 9F. A comparison with the corresponding rat cDNA identified 10 exons within its protein-coding region. The Bassoon protein is predicted to contain two double-zinc fingers, several coiled-coil domains, and a stretch of polyglutamines (24 and 11 residues in rat and mouse, respectively). In some human proteins, e.g., Huntingtin, abnormal amplification of such poly-glutamine regions causes late-onset neurodegeneration. Bassoon is highly enriched in synaptic protein preparations. In cultured hippocampal neurons, Bassoon colocalizes with the synaptic vesicle protein synaptophysin and Piccolo, a presynaptic cytomatrix component. At the ultrastructural level, Bassoon is detected in axon terminals of hippocampal neurons where it is highly concentrated in the vicinity of the active zone. Immunogold labeling of synaptosomes revealed that Bassoon is associated with material interspersed between clear synaptic vesicles, and biochemical studies suggest a tight association with cytoskeletal structures. These data indicate that Bassoon is a strong candidate to be involved in cytomatrix organization at the site of neurotransmitter release. 相似文献
83.
Marion Stoffels Rudolf Amann Wolfgang Ludwig Dariusch Hekmat Karl-Heinz Schleifer 《Applied and environmental microbiology》1998,64(3):930-939
This study was performed with a laboratory-scale fixed-bed bioreactor degrading a mixture of aromatic compounds (Solvesso100). The starter culture for the bioreactor was prepared in a fermentor with a wastewater sample of a car painting facility as the inoculum and Solvesso100 as the sole carbon source. The bacterial community dynamics in the fermentor and the bioreactor were examined by a conventional isolation procedure and in situ hybridization with fluorescently labeled rRNA-targeted oligonucleotides. Two significant shifts in the bacterial community structure could be demonstrated. The original inoculum from the wastewater of the car factory was rich in proteobacteria of the alpha and beta subclasses, while the final fermentor enrichment was dominated by bacteria closely related to Pseudomonas putida or Pseudomonas mendocina, which both belong to the gamma subclass of the class Proteobacteria. A second significant shift was observed when the fermentor culture was transferred as inoculum to the trickle-bed bioreactor. The community structure in the bioreactor gradually returned to a higher complexity, with the dominance of beta and alpha subclass proteobacteria, whereas the gamma subclass proteobacteria sharply declined. Obviously, the preceded pollutant adaptant did not lead to a significant enrichment of bacteria that finally dominated in the trickle-bed bioreactor. In the course of experiments, three new 16S as well as 23S rRNA-targeted probes for beta subclass proteobacteria were designed, probe SUBU1237 for the genera Burkholderia and Sutterella, probe ALBO34a for the genera Alcaligenes and Bordetella, and probe Bcv13b for Burkholderia cepacia and Burkholderia vietnamiensis. Bacteria hybridizing with the probe Bcv13b represented the main Solvesso100-degrading population in the reactor.Many branches of industry produce waste gases which contain odorous organic and inorganic components. Apart from the conventional thermal and physicochemical techniques for removal of pollutants from exhaust air, biological waste gas treatment is becoming more and more important. This kind of treatment is advantageous in cases in which the recovery of the components (e.g., absorption in liquids and adsorption in solids) or the utilization of a thermal process (thermal or catalytic combustion) is not economical. Today three different process variations for biological waste gas treatment are used: biofilters, bioscrubbers, and trickle-bed bioreactors. In biofilters and trickle-bed reactors, the pollutant-degrading microorganisms are immobilized on a carrier material, whereas in bioscrubbers the microorganisms are dispersed in the liquid phase. Biofilters and bioscrubbers are preferred in industry, while biofilters are common in compost production and sewage plants (10).Biological waste gas treatment has a long tradition. Already in 1953, a soil system was employed for the treatment of odorous sewer exhaust gases in Long Beach, Calif. (25), and although up to now a lot of efforts have been funneled into process engineering (14, 17, 18, 24), current knowledge of the involved microorganisms is still very limited. Diversity of the microbial communities in the bioreactors for the exhaust gas purification have mostly been analyzed by culture-dependent methods (9, 12, 28, 31). However, there is a large discrepancy between the total (direct) microscopic cell counts and viable plate counts in many ecosystems and every cultivation medium selects for certain microorganisms. Therefore, cultivation-based studies of bacterial populations may give wrong impressions of the actual community structure in an ecosystem (35). A possible means of avoiding qualitative and quantitative errors in the analysis of microbial community structure in complex ecosystems is the use of fluorescently labeled, rRNA-targeted oligonucleotides (5) for the in situ identification and enumeration of bacteria. This method has already been used successfully in complex microbial communities, such as multispecies biofilms (6, 22, 26), trickling filters (27), and activated sludge (37).The current study was performed with a laboratory-scale trickle-bed bioreactor degrading a mixture of aromatic compounds (Solvesso100). The starter culture for the inoculation of the bioreactor was an enrichment prepared in a fermentor which was itself started with a wastewater sample from a car painting factory as the inoculum and Solvesso100 as the sole carbon source. The goal of our study was to use for the first time fluorescent in situ hybridization (FISH) to investigate the microbial community structure and dynamics in the fermentor and the bioreactor during start-up. One of the open questions was whether the fermentor enrichment, which is done in suspension, indeed selects for those bacteria that later are immobilized in the bioreactor. In the course of this study, new 16S as well as 23S rRNA-targeted probes for phylogenetic groups within the beta subclass of the class Proteobacteria have been developed and applied in order to obtain a higher taxonomic resolution of the molecular techniques. The molecular data were compared to those obtained by traditional cultivation-dependent techniques. 相似文献
84.
Ludwig Wolfgang Amann Rudolf Martinez-Romero Esperanza Schönhuber Wilhelm Bauer Stephan Neef Alexander Schleifer Karl-Heinz 《Plant and Soil》1998,204(1):1-19
Ribosomal ribonucleic acids are excellent marker molecules for the elucidation of bacterial phylogeny; they also provide useful target sites for identification and detection with nucleic acid probes. Based on the currently available 16S rRNA sequence data, bacteria of the rhizobial phenotype (plant nodulation, nitrogen fixation) are members of three moderately related phylogenetic sub-groups of the -subclass of the Proteobacteria: i.e. the rhizobia group, the bradyrhizobia group, and the azorhizobia group. All rhizobia, azo-, brady-, meso- and sinorhizobia are closely related to and in some cases phylogenetically intermixed with, non-symbiotic and/or non-nitrogen-fixing bacteria. Especially in the case of Bradyrhizobium japonicum strains, the 16S rRNA sequence data indicate substantial heterogeneity. Specific probe design and evaluation are discussed. A multiprobe concept for resolving specificity problems with group specific probes is presented. In situ identification with group specific probes of rhizobia in cultures as well as rhizobia and cyanobacteria within plant material is shown. 相似文献
85.
86.
Stefan Zielonka Martin Empting Julius Grzeschik Doreen K?nning Caroline J Barelle Harald Kolmar 《MABS-AUSTIN》2015,7(1):15-25
In addition to antibodies with the classical composition of heavy and light chains, the adaptive immune repertoire of sharks also includes a heavy-chain only isotype, where antigen binding is mediated exclusively by a small and highly stable domain, referred to as vNAR. In recent years, due to their high affinity and specificity combined with their small size, high physicochemical stability and low-cost of production, vNAR fragments have evolved as promising target-binding scaffolds that can be tailor-made for applications in medicine and biotechnology. This review highlights the structural features of vNAR molecules, addresses aspects of their generation using immunization or in vitro high throughput screening methods and provides examples of therapeutic, diagnostic and other biotechnological applications. 相似文献
87.
88.
Sabine Illsinger Karl-Heinz Schmidt Thomas Lücke Bernhardt Vaske Bettina Bohnhorst Anibh Martin Das 《Amino acids》2010,38(3):959-972
Plasma and urine amino acids were determined by ion-exchange chromatography in 80 healthy preterm infants divided into three
groups: (1) 23 0/7–28 0/7, (2) 28 1/7–32 0/7 and (3) 32 1/7–35 0/7 weeks of gestation. Samples were collected from days 5
to 57 of life, when infants were exclusively orally fed. Infants with evidence of underlying diseases were excluded. Concentrations
of most plasma amino acids increased with gestational and maturational age; urinary excretion followed an opposite course.
Few amino acids depended on postnatal age. Plasma amino acids did not correlate inversely to their counterparts in urine indicating
that plasma amino acids do not simply reflect kidney function. Some amino acids in blood and urine were linked to nutrient
intake and body weight. Our data clearly indicate the heterogeneity of the preterm cohort; therefore, gestational age-matched
reference values have to be used for diagnostic purposes in preterm infants. 相似文献
89.
90.
Beate Achatz Karl-Heinz Kogel Philipp Franken Frank Waller 《Plant signaling & behavior》2010,5(12):1685-1687
Root colonization by the basidiomycete fungus Piriformospora indica induces host plant tolerance against abiotic and biotic stress, and enhances growth and yield. As P. indica has a broad host range, it has been established as a model system to study beneficial plant-microbe interactions. Moreover, its properties led to the assumption that P. indica shows potential for application in crop plant production. Therefore, possible mechanisms of P. indica improving host plant yield were tested in outdoor experiments: Induction of higher grain yield in barley was independent of elevated pathogen levels and independent of different phosphate fertilization levels. In contrast to the arbuscular mycorrhiza fungus Glomus mosseae total phosphate contents of host plant roots and shoots were not significantly affected by P. indica. Analysis of plant development and yield parameters indicated that positive effects of P. indica on grain yield are due to accelerated growth of barley plants early in development.Key words: mycorrhiza, barley development, Piriformospora indica, phosphate uptake, grain yield, pathogen resistanceThe wide majority of plant roots in natural ecosystems is associated with fungi, which very often play an important role for the host plants'' fitness.1 The widespread arbuscular mycorrhizal (AM) symbiosis formed by fungi of the phylum Glomeromycota is mainly characterized by providing phosphate to their host plant in exchange for carbohydrates.2,3 Fungi of the order Sebacinales also form beneficial interactions with plant roots and Piriformospora indica is the best-studied example of this group.4 This endophyte was originally identified in the rhizosphere of shrubs in the Indian Thar desert,5 but it turned out that the fungus colonizes roots of a very broad range of mono- and dicotyledonous plants,6 including major crop plants.7–9 Like other mutualistic endophytes, P. indica colonizes roots in an asymptomatic manner10 and promotes growth in several tested plant species.6,11,12 The root endophyte, moreover, enhances yield in barley and tomato and increases in both plants resistance against biotic stresses,7,9 suggesting that application in agri- and horticulture could be successful. 相似文献