PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Pythium”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 469 records · Page 26Linked to original sources

Three small RNAs jointly ensure secondary metabolism and biocontrol in Pseudomonas fluorescens CHA0.

In many Gram-negative bacteria, the GacS/GacA two-component system positively controls the expression of extracellular products or storage compounds. In the plant-beneficial rhizosphere bacterium Pseudomonas fluorescens CHA0, the GacS/GacA system is essential for the production of antibiotic compounds and hence for biological control of root-pathogenic fungi. The small (119-nt) RNA RsmX discovered in this study, together with RsmY and RsmZ, forms a triad of GacA-dependent small RNAs, which sequester the RNA-binding proteins RsmA and RsmE and thereby antagonize translational repression exerted by these proteins in strain CHA0. This small RNA triad was found to be both necessary and sufficient for posttranscriptional derepression of biocontrol factors and for protection of cucumber from Pythium ultimum. The same three small RNAs also positively regulated swarming motility and the synthesis of a quorum-sensing signal, which is unrelated to N-acyl-homoserine lactones, and which autoinduces the Gac/Rsm cascade. Expression of RsmX and RsmY increased in parallel throughout cell growth, whereas RsmZ was produced during the late growth phase. This differential expression is assumed to facilitate fine tuning of GacS/A-controlled cell population density-dependent regulation in P. fluorescens.

Bacterial Proteins↗

An endogenous peptide signal in Arabidopsis activates components of the innate immune response.

Innate immunity is initiated in animals and plants through the recognition of a variety of pathogen-associated molecules that in animals are called pathogen-associated molecular patterns and in plants are called elicitors. Some plant pathogen-derived elicitors have been identified as peptides, but peptide elicitors derived from the plant itself that activate defensive genes against pathogens have not been previously identified. Here, we report the isolation and characterization of a 23-aa peptide from Arabidopsis, called AtPep1, which activates transcription of the defensive gene defensin (PDF1.2) and activates the synthesis of H(2)O(2), both being components of the innate immune response. The peptide is derived from a 92-aa precursor encoded within a small gene that is inducible by wounding, methyl jasmonate, and ethylene. Constitutive expression of the AtPep1 precursor gene PROPEP1 in transgenic Arabidopsis plants causes a constitutive transcription of PDF1.2. When grown in soil, the transgenic plants exhibited an increased root development compared with WT plants and an enhanced resistance toward the root pathogen Pythium irregulare. Six paralogs of PROPEP1 are present in Arabidopsis, and orthologs have been identified in species of several agriculturally important plant families, where they are of interest for their possible use in crop improvement.

Acetates↗

Pulsed growth of fungal hyphal tips.

Somatic fungal hyphae are generally assumed to elongate at steady linear rates when grown under constant environmental conditions with ample nutrients. However, patterns of pulsed hyphal elongation were detected during apparent steady growth of hyphal tips in fungi from several major taxonomic groups (Oomycetes, Pythium aphanidermatum and Saprolegnia ferax; Zygomycetes, Gilbertella persicaria; Deuteromycetes, Trichoderma viride; Ascomycetes, Neurospora crassa and Fusarium culmorum; Basidiomycetes, Rhizoctonia solani). Growing hyphal tips were recorded with video-enhanced phase-contrast microscopy at high magnification, and digital images were measured at very short time intervals (1-5 s). In all fungi tested, the hyphal elongation rate was never perfectly steady but fluctuated continuously with alternating periods of fast and slow growth at more or less regular intervals. Pulsed growth was observed in fungi differing in cell diameter, overall growth rate, taxonomic position, and presence and pattern of Spitzenkörper organization, suggesting that this is a general phenomenon. Frequency and amplitude of the pulses varied among the test organisms. T. viride and N. crassa showed the most frequent pulses (average of 13-14 per min), and F. culmorum the least frequent (2.7 per min). Average pulse amplitude varied from 0.012 microns/s for F. culmorum to 0.068 microns/s for G. persicaria. In F. culmorum and T. viride, the fast phase of the growth pulses was correlated with the merger of satellite Spitzenkörper with the main Spitzenkörper. These findings are consistent with a causal relationship between fluctuations in the overall rate of secretory vesicle delivery/discharge at the hyphal apex and the fluctuations in hyphal elongation rate.

Activity Cycles↗

Spoilage of vegetable crops by bacteria and fungi and related health hazards.

After harvest, vegetables are often spoiled by a wide variety of microorganisms including many bacterial and fungal species. The most common bacterial agents are Erwinia carotovora, Pseudomonas spp., Corynebacterium, Xanthomonas campestris, and lactic acid bacteria with E. carotovora being the most common, attacking virtually every vegetable type. Fungi commonly causing spoilage of fresh vegetables are Botrytis cinerea, various species of the genera Alternaria, Aspergillus, Cladosporium, Colletotrichum, Phomopsis, Fusarium, Penicillium, Phoma, Phytophthora, Pythium and Rhizopus spp., Botrytis cinerea, Ceratocystis fimbriata, Rhizoctonia solani, Sclerotinia sclerotiorum, and some mildews. A few of these organisms show a substrate preference whereas others such as Botrytis cinerea, Colletotrichum, Alternaria, Cladosporium, Phytophthora, and Rhizopus spp., affect a wide variety of vegetables causing devastating losses. Many of these agents enter the plant tissue through mechanical or chilling injuries, or after the skin barrier has been broken down by other organisms. Besides causing huge economic losses, some fungal species could produce toxic metabolites in the affected sites, constituting a potential health hazard for humans. Additionally, vegetables have often served as vehicles for pathogenic bacteria, viruses, and parasites and were implicated in many food borne illness outbreaks. In order to slow down vegetable spoilage and minimize the associated adverse health effects, great caution should be taken to follow strict hygiene, good agricultural practices (GAPs) and good manufacturing practices (GMPs) during cultivation, harvest, storage, transport, and marketing.

Bacteria↗

Influence of environmental factors on composition of volatile constituents and biological activity of Helichrysum italicum (Roth) Don (Asteraceae).

The biovariability of Helichrysum italicum (Roth) Don grown wild in Calabria and Sardinia (Italy) was reported. This species has been characterized through the detection, isolation and quantitative evaluation of chemical markers (alpha-terpinolene, trans-cariophyllene and neryl acetate) by GC and GC-MS. Antioxidant activity of the methanolic H. italicum extracts using DPPH and beta-carotene bleaching test showed that the Calabrian samples were more active than those from Sardinia. The antibacterial activity of all extracts evidenced the best performance on the Gram positive bacteria particularly on Micrococcus luteus. Moreover, antifungal activity of all extracts was also tested evidencing important results particularly on the phytopathogene fungus Pythium ultimum. In general, as regards the antifungal activity, the extracts from Sardinia were more active than those from Calabria. The phytochemical analysis and the biological activity data suggested a possible use of these plant matrices in alimentary, cosmetic and pharmaceutical fields.

Anti-Bacterial Agents↗

Five Serbian reservoirs contain different fungal propagules.

This paper presents results of a mycological survey conducted in five large reservoirs in Serbia (Sjenica, Barje, Garasi, Meduvrsje and Ovcar-Kablar) that have different hydrobiological and production characteristics. The sampling was conducted in March, June, August and October 2002. Quantitative analysis of fungal communities showed that the average number of colony-forming units in these reservoirs was 1966-5682/L of water. The highest number of CFUs was found in the alpha-mesosaprobic (Class III) Ovcar-Kablar Reservoir and the lowest was in the oligosaprobic (Class I) Sjenica Reservoir. CFUs were higher in samples taken near lake bottoms and in littoral zones rich with macrovegetation than in the middle depths. In these reservoirs 48 species were identified from 720 isolates. The dominant genera were Penicillium, Aspergillus, Cladosporium, Fusarium, Rhizopus, Mucor, Phoma and Verticillium. The autochthonous aquatic fungal community comprised these species: Achlya americana, A. diffusa, A. racemosa, Dictyuchus sterile, Isoachlya toruloides, Leptomitus lacteus, Pythium ultimum, Saprolegnia ferax, S. hypogyna and S. monica. My results indicate that aquatic fungi on the whole are better represented in lakes with a higher trophic status.

Colony Count, Microbial↗

Maize terpene synthase 8 (ZmTPS8) produces a blend of sesquiterpenes and contributes to defense against pests and pathogens.

Maize (Zea mays) produces terpenoid-based chemical defenses through a large family of terpene synthases, but the contributions of individual enzymes to specific compounds and stress resistance remain difficult to predict. Maize terpene synthase 8 (ZmTPS8) produces multiple sesquiterpenes in heterologous systems, but its in planta function remains unknown. We integrated a metabolite genome-wide association study (mGWAS), CRISPR/Cas9 generated tps8 loss-of-function mutants, metabolite profiling, and biotic stress assays to define ZmTPS8's role in terpene synthesis and biotic stress responses. The mGWAS identified ZmTPS8 as the primary locus associated with herbivore-induced emission of the sesquiterpene volatile germacrene D. Consistently, ZmTPS8 expression was induced by foliar and root herbivory, and tps8 mutants exhibited reduced emission of germacrene D, α-copaene, and δ-cadinene during Spodoptera frugiperda feeding. Loss of ZmTPS8 increased S. frugiperda larval growth but did not affect the belowground herbivore Diabrotica virgifera virgifera. ZmTPS8 also contributed to resistance against sugarcane mosaic virus, and the fungal pathogen Fusarium verticillioides, affecting terpenoid profiles, global metabolism, and fungal toxin production, but had no impact on Cochliobolus heterostrophus or Pythium spp. susceptibility. Together, these results demonstrate that ZmTPS8 contributes to maize defense in a threat-dependent manner, shaping volatile emissions and defense outcomes.

Zea mays↗

Stress-responsive alpha-dioxygenase expression in tomato roots.

Alpha-dioxygenase (alpha-DOX) enzymes catalyse the oxygenation of fatty acids to yield a newly identified group of oxylipins that play a role in protecting tissues from oxidative damage and cell death. In tomato (Lycopersicon esculentum Mill.) alpha-DOX was identified as salt-regulated by differential display of mRNA, and is represented by a small gene family comprising at least three members: LEalpha-DOX1, -2, and -3 of which only LEalpha-DOX1 was salt-responsive. The enhancement of LEalpha-DOX1 expression in roots by salt, wounding and challenge with Pythium aphanidermatum (Edson) Fitzp. suggests that alpha-DOX-generated oxylipins may mediate the response of roots to these environmental stresses. In roots, LEalpha-DOX1 was abscisic acid (ABA)-responsive. However, in the ABA-deficient mutant flacca salt-responsive expression was equivalent to that in the wild type. Similarly, in roots exposed to fluridone (FLU) salt up-regulated expression; however, in this case salt-responsive LEalpha-DOX1 expression was greater than that in roots that were not exposed to FLU. A possible explanation for this is provided by the role of ABA in suppressing ethylene accumulation in osmotically stressed roots. The ethylene-generating agent ethephon and precursor 1-aminocyclopropane-1-carboxylic acid markedly elevated LEalpha-DOX1 expression, and this enhanced expression was suppressed by ABA. LEalpha-DOX1 expression in salt-stressed roots was not markedly affected by AVG indicating that ABA may be responsible for enhanced alpha-DOX expression in salt-treated roots.

Abscisic Acid↗

Ancient origin of elicitin gene clusters in Phytophthora genomes.

The genus Phytophthora belongs to the oomycetes in the eukaryotic stramenopile lineage and is comprised of over 65 species that are all destructive plant pathogens on a wide range of dicotyledons. Phytophthora produces elicitins (ELIs), a group of extracellular elicitor proteins that cause a hypersensitive response in tobacco. Database mining revealed several new classes of elicitin-like (ELL) sequences with diverse elicitin domains in Phytophthora infestans, Phytophthora sojae, Phytophthora brassicae, and Phytophthora ramorum. ELIs and ELLs were shown to be unique to Phytophthora and Pythium species. They are ubiquitous among Phytophthora species and belong to one of the most highly conserved and complex protein families in the Phytophthora genus. Phylogeny construction with elicitin domains derived from 156 ELIs and ELLs showed that most of the diversified family members existed prior to divergence of Phytophthora species from a common ancestor. Analysis to discriminate diversifying and purifying selection showed that all 17 ELI and ELL clades are under purifying selection. Within highly similar ELI groups there was no evidence for positively selected amino acids suggesting that purifying selection contributes to the continued existence of this diverse protein family. Characteristic cysteine spacing patterns were found for each phylogenetic clade. Except for the canonical clade ELI-1, ELIs and ELLs possess C-terminal domains of variable length, many of which have a high threonine, serine, or proline content suggesting an association with the cell wall. In addition, some ELIs and ELLs have a predicted glycosylphosphatidylinositol site suggesting anchoring of the C-terminal domain to the cell membrane. The eli and ell genes belonging to different clades are clustered in the genomes. Overall, eli and ell genes are expressed at different levels and in different life cycle stages but those sharing the same phylogenetic clade appear to have similar expression patterns.

Algal Proteins↗

Nucleotide sequences of 5S ribosomal RNA from four oomycete and chytrid water molds.

The nucleotide sequences of the 5S rRNAs of the oomycete water molds Saprolegnia ferax and Pythium hydnosporum and of the chytrid water molds Blastocladiella simplex and Phlyctochytrium irregulare were determined by chemical and enzymatic partial degradation of 3' and 5' end-labelled molecules, followed by gel sequence analysis. The two oomycete sequences differed in 24 positions and the two chytrid sequences differed in 27 positions. These pairs differed in a mean of 44 positions. The chytrid sequences clearly most resemble the sequence from the zygomycete Phycomyces, while the oomycete sequences appear to be allied with those from protozoa and slime molds.

Base Sequence↗

Two novel MvaT-like global regulators control exoproduct formation and biocontrol activity in root-associated Pseudomonas fluorescens CHA0.

Pseudomonas fluorescens CHA0 protects various crop plants against root diseases caused by pathogenic fungi. Among a range of exoproducts excreted by strain CHA0, the antifungal compounds 2,4-diacetylphloroglucinol (DAPG) and pyoluteorin (PLT) are particularly relevant to the strain's biocontrol potential. Here, we report on the characterization of MvaT and MvaV as novel regulators of biocontrol activity in strain CHA0. We establish the two proteins as further members of an emerging family of MvaT-like regulators in pseudomonads that are structurally and functionally related to the DNA-binding protein H-NS. In mvaT and mvaV in frame-deletion mutants of strain CHA0, PLT production was enhanced about four- and 1.5-fold, respectively, whereas DAPG production remained at wild-type levels. Remarkably, PLT production was increased up to 20-fold in an mvaT mvaV double mutant. DAPG biosynthesis was almost completely repressed in this mutant. The effects on antibiotic production could be confirmed by following expression of gfp-based reporter fusions to the corresponding biosynthetic genes. MvaT and MvaV also influenced levels of other exoproducts, motility, and physicochemical cell-surface properties to various extents. Compared with the wild type, mvaT and mvaV mutants had an about 20% reduced capacity (in terms of plant fresh weight) to protect cucumber from a root rot caused by Pythium ultimum. Biocontrol activity was nearly completely abolished in the double mutant Our findings indicate that MvaT and MvaV act together as further global regulatory elements in the complex network controlling expression of biocontrol traits in plant-beneficial pseudomonads.

Amino Acid Sequence↗

Mapping the elicitor and necrotic sites of Phytophthora elicitins with synthetic peptides and reporter genes controlled by tobacco defense gene promoters.

Elicitins are 10-kDa proteins secreted by Phytophthora and Pythium fungi that elicit a hypersensitive-like necrotic reaction, leading to resistance against fungal and bacterial plant pathogens. Induction of necrosis and resistance were previously shown to be borne by different sites of the molecule. Furthermore, sequence comparison indicated several potential residues necessary for necrosis. The role of one of these residues was previously evidenced with site-directed mutagenesis. In order to locate other necrosis-determining sites and reveal the defense-eliciting sites, we synthesized a series of synthetic peptides. Tests were performed on two types of transgenic tobacco plants, both transformed with a construction containing the beta-glucuronidase reporter gene, in one case controlled by the promoter of the multiple stimulus response gene str 246C and in the other by the promoter of the pathogenesis-related gene PR1a. We report that only certain peptides were found to be active. Whereas PR1a induction was consistently correlated with induction of necrosis, four peptides were observed to induce only str 246C expression without necrosis, which led to differentiate the defense-eliciting sites from the necrotic sites. From the structure-function relationship thus obtained, two different defense pathways were inferred to be independently induced by elicitins.

Algal Proteins↗

Induced expression of sarcotoxin IA enhanced host resistance against both bacterial and fungal pathogens in transgenic tobacco.

We demonstrate here that induced expression of sarcotoxin IA, a bactericidal peptide from Sarcophaga peregrina, enhanced the resistance of transgenic tobacco plants to both bacterial and fungal pathogens. The peptide was produced with a modified PR1a promoter, which is further activated by salicylic acid treatment and necrotic lesion formation by pathogen infection. Host resistance to infection of bacteria Erwinia carotovora subsp. carotovora and Pseudomonas syringae pv. tabaci was shown to be dependent on the amounts of sarcotoxin IA expressed. Since we found antifungal activity of the peptide in vitro, transgenic seedlings were also inoculated with fungal pathogens Rhizoctonia solani and Pythium aphanidermatum. Transgenic plants expressing higher levels of sarcotoxin were able to withstand fungal infection and remained healthy even after 4 weeks, while control plants were dead by fungal infection after 2 weeks.

Anti-Bacterial Agents↗

Deleterious impact of a virulent bacteriophage on survival and biocontrol activity of Pseudomonas fluorescens strain CHAO in natural soil.

Many biotic and abiotic factors affect the persistence and activity of beneficial pseudomonads introduced into soil to suppress plant diseases. One such factor may be the presence of virulent bacteriophages that decimate the population of the introduced bacteria, thereby reducing their beneficial effect. We have isolated a lytic bacteriophage (phi)GP100) that specifically infects the biocontrol bacterium Pseudomonas fluorescens CHA0 and some closely related Pseudomonas strains. phiGP100 was found to be a double-stranded-DNA phage with an icosahedral head, a stubby tail, and a genome size of approximately 50 kb. Replication of phiGP100 was negatively affected at temperatures higher than 25 degrees C. phiGP100 had a negative impact on the population size and the biocontrol activity of P. fluorescens strain CHA0-Rif (a rifampicin-resistant variant of CHA0) in natural soil microcosms. In the presence of phiGP100, the population size of strain CHA0-Rif in soil and on cucumber roots was reduced more than 100-fold. As a consequence, the bacterium's capacity to protect cucumber against a root disease caused by the pathogenic oomycete Pythium ultimum was entirely abolished. In contrast, the phage affected neither root colonization and nor the disease suppressive effect of a phiDGP100-resistant variant of strain CHA0-Rif. To our knowledge, this study is the first to illustrate the potential of phages to impair biocontrol performance of beneficial bacteria released into the natural soil environment.

Bacteriophages↗

Infections in E-beta thalassemia.

Infection is a major complication and the leading cause of death in thalassemia, especially E-beta thalassemia. The spectrum of infections in E-beta thalassemia include mild and severe infections, therapy-related infections such as Yersinia enterocolitica infection associated with desferrioxamine (DFO) therapy, and transfusion-transmitted disease, as well as unique infections such as with pythiosis. Prospective studies in Thailand indicate that patients with E-beta thalassemia had more frequent episodes of both mild and severe infections. The former included upper respiratory tract infection, acute gastroenteritis, cutaneous abscess, and gingivitis. Severe infections occurred more commonly in patients with splenectomy and included septicemia, pneumonia, biliary tract infection, salmonellosis, and urinary tract infection. Responsible organisms were Escherichia coli (26%), Klebsiella pneumoniae (23%), Salmonella (15%), and Streptococcus pneumoniae (13%). Other organisms included Pseudomonas, Staphylococci, Burkholderia pseudomallei (melioidosis), and Aeromonas. Patients undergoing DFO therapy are at risk for Y. enterocolitica infection which may be localized to mesenteric nodes and tonsils or occur as a generalized form such as septicemia. Recently, we have seen a unique infection so-called vascular pythiosis. Patients usually presented with clinical features of vascular occlusion of lower limbs from ascending arteritis and thrombosis. The causative organism, Pythium insidiosum, is fungus-like, in the kingdom Stramenopila, and in the class Oomycetes. The mortality rate is high and the only effective treatment has been early amputation or possibly immunotherapy. The predisposing factors of infections in thalassemia include splenectomy, iron overload, anemia, and granulocyte dysfunctions. General management of infections in thalassemia consist of prevention, i.e., immunization with pneumococcal and hepatitis vaccines, oral penicillins especially in patients with splenectomy, removal of predisposing factors such as gallstones, iron overload, and appropriate antibiotics.

Bacterial Infections↗

Oocydin A, a chlorinated macrocyclic lactone with potent anti-oomycete activity from Serratia marcescens.

A unique chlorinated macrocyclic lactone, termed oocydin A, was isolated from a strain of Serratia marcescens growing as an epiphyte on Rhyncholacis pedicillata, an aquatic plant native to the Carrao river of the Venezuelan-Guyanan region of South America. The lactone has a molecular mass of 470 Da, and contains one atom of chlorine, a carboxyl group and a tetrahydrofuran ring internal to a larger macrocyclic ring. MICs of approximately 0.03 microg ml(-1) were noted for oocydin A against such phytopathogenic oomycetes as Pythium ultimum, Phytophthora parasitica, Phytophthora cinnamomi and Phytophthora citrophora. With regard to the true fungi, oocydin A had either minimal or no effect against certain Fungi Imperfecti (including several pathogens of humans), two ascomycetes and a basidiomycete. Oocydin A may have potential as an antimycotic in agricultural applications and especially for crop protection.

Antifungal Agents↗

Elicitor-Induced Changes in Ca2+ Influx, K+ Efflux, and 4-Hydroxybenzoic Acid Synthesis in Protoplasts of Daucus carota L.

Suspension-cultured carrot cells (Daucus carota) and their protoplasts respond to a fungal elicitor prepared from the culture medium of Pythium aphanidermatum by accumulating 4-hydroxybenzoic acid (4-HBA). Protoplasts release the compound into the culture medium. Using 45CaCl2 as a tracer, we were able to demonstrate that the secretion of 4-HBA is preceded by a rapid increase in the Ca2+ influx and a concomitant K+ efflux. If the increased Ca2+ influx was prevented by ethyleneglycol-bis([beta]-aminoethylether)-N,N[prime]-tetraacetic acid, 4-HBA synthesis was inhibited by 70%. These results are discussed with regard to signal transduction from the plasma membrane to the nucleus of carrot protoplasts.

Journal Article↗

Uncoupled defense gene expression and antimicrobial alkaloid accumulation in elicited opium poppy cell cultures.

Treatment of opium poppy (Papaver somniferum L.) cell cultures with autoclaved mycelial homogenates of Botrytis sp. resulted in the accumulation of sanguinarine. Elicitor treatment also caused a rapid and transient induction in the activity of tyrosine/dopa decarboxylase (TYDC, EC 4.1.1.25), which catalyzes the conversion of L-tyrosine and L-dopa to tyramine and dopamine, respectively, the first steps in sanguinarine biosynthesis. TYDC genes were differentially expressed in response to elicitor treatment. TYDC1-like mRNA levels were induced rapidly but declined to near baseline levels within 5 h. In contrast, TYDC2-like transcript levels increased more slowly but were sustained for an extended period. Induction of TYDC mRNAs preceded that of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) mRNAs. An elicitor preparation from Pythium aphanidermatum was less effective in the induction of TYDC mRNA levels and alkaloid accumulation; however, both elicitors equally induced accumulation of PAL transcripts. In contrast, treatment with methyl jasmonate resulted in an induction of TYDC but not PAL mRNAs. The calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide and the protein kinase inhibitor staurosporine partially blocked the fungal elicitor-induced accumulation of sanguinarine. However, only staurosporine and okadaic acid, an inhibitor of protein phosphatases 1 and 2A, blocked the induction of TYDC1-like transcript levels, but they did not block the induction of TYDC2-like or PAL transcript levels. These data suggest that activation mechanisms for PAL, TYDC, and some later sanguinarine biosynthetic enzymes are uncoupled.

Acetates↗