Showing papers on "Mycelium published in 1999"
TL;DR: Various aspects of how the fatty acid signatures can be used for studies related to questions of biomass distribution and nutritional status of mycorrhizal fungi are discussed.
774 citations
TL;DR: Labeling patterns observed in lipids and carbohydrates after substrates were supplied to the mycorrhizal roots or the extraradical mycelium indicated that 13C-labeled glucose and fructose are effectively taken up by the fungus within the root and are metabolized to yield labeled carbohydrates and lipids.
Abstract: Both the plant and the fungus benefit nutritionally in the arbuscular mycorrhizal symbiosis: The host plant enjoys enhanced mineral uptake and the fungus receives fixed carbon. In this exchange the uptake, metabolism, and translocation of carbon by the fungal partner are poorly understood. We therefore analyzed the fate of isotopically labeled substrates in an arbuscular mycorrhiza (in vitro cultures of Ri T-DNA-transformed carrot [Daucus carota] roots colonized by Glomus intraradices) using nuclear magnetic resonance spectroscopy. Labeling patterns observed in lipids and carbohydrates after substrates were supplied to the mycorrhizal roots or the extraradical mycelium indicated that: (a) 13C-labeled glucose and fructose (but not mannitol or succinate) are effectively taken up by the fungus within the root and are metabolized to yield labeled carbohydrates and lipids; (b) the extraradical mycelium does not use exogenous sugars for catabolism, storage, or transfer to the host; (c) the fungus converts sugars taken up in the root compartment into lipids that are then translocated to the extraradical mycelium (there being little or no lipid synthesis in the external mycelium); and (d) hexose in fungal tissue undergoes substantially higher fluxes through an oxidative pentose phosphate pathway than does hexose in the host plant.
361 citations
TL;DR: This work demonstrates that hydrophobins not only have a function at the hyphal surface but also at the medium-air interface, which explains why fungi secrete large amounts of hydrophobin into their aqueous surroundings.
325 citations
TL;DR: It is confirmed that substances released by the AM fungus in the growth medium is the main factor explaining differential growth of the microorganisms tested and suggested that direct interactions exist between AM fungi and soil microorganisms, which might lead to changes in microbial equilibrium detrimental to pathogens.
Abstract: Arbuscular mycorrhizal (AM) fungi can reduce the incidence and importance of plant root diseases caused by pathogens. The mechanisms involved are not well characterized. We used an in vitro experimental system to test the hypothesis that the extraradical mycelium of AM fungi can interfere directly with microorganisms in the mycosphere and directly or indirectly reduce the population of plant pathogens. This system permitted the isolation of soluble substances released by the extraradical mycelium of Glomus intraradices. The AM fungus was grown on Daucus carota transformed roots in one compartment, while only the extraradical mycelium was allowed to grow in a second compartment. A freezing and centrifugation technique was developed for the extraction and concentration of substances present in the compartment containing only the AM fungal mycelium. Four soil-inhabiting microorganisms were selected, and conidial germination (fungi) or growth (bacteria) of these was studied in the presence and absence (control) of the extract. In comparison with the control, the results indicated that both the growth of Pseudomonas chlororaphis and the conidial germination of Trichoderma harzianum were stimulated in the presence of the AM fungal extract. In contrast, conidial germination of Fusarium oxysporum f. sp. chrysanthemi was reduced while the growth of Clavibacter michiganensis subsp. michiganensis was not affected. The measured effects in general were directly correlated with extract concentration. Differences in pH were noted between the extract containing substances released by the AM fungus and the non-AM control, but no significant influence of the pH on growth or conidial germination was noted, confirming that substances released by the AM fungus in the growth medium is the main factor explaining differential growth of the microorganisms tested. The results suggest that direct interactions exist between AM fungi and soil microorganisms, which might lead to changes in microbial equilibrium detrimental to pathogens.
313 citations
TL;DR: Dazomet application strongly suppressed colonisation of the linseed roots by AM fungi throughout the experiment, and analyses of bacteria-specific fatty acids indicated that the bacterial biomass in the soil was not affected by either dazomet or P application.
Abstract: Linseed was grown in field plots included in a long-term P fertilisation experiment (0, 15 or 30 kg P ha −1 yr −1 for 20 yr). Two months before sowing, half of each plot was applied with dazomet to prevent the formation of arbuscular mycorrhiza (AM). The biomass of different groups of micro-organisms was estimated 28, 51 and 72 d after sowing based on amounts of certain fatty acids extracted from the soil. Dazomet application strongly suppressed colonisation of the linseed roots by AM fungi throughout the experiment. In plots with no dazomet application, root colonisation by the AM fungi increased from harvests 1 to 3 as judged both from microscopical estimates and from quantitative analysis of the AM fungal indicative fatty acid 16:1ω5. These methods also revealed that AM formation was reduced in P-fertilised plots. The phospholipid fatty acid (PLFA) 16:1ω5 decreased in dazomet-treated soil, and it was assumed that the PLFA 16:1ω5 remaining in treated soil originated from bacteria. The biomass of the extraradical AM mycelium could then be estimated by multiplying the difference in PLFA 16:1ω5 between dazomet treated and nontreated soils by a conversion factor. This calculation indicated that the biomass of the extraradical mycelium of AM fungi was about 10 times as high as the biomass of intraradical mycelium and that the extraradical mycelium constituted the largest fraction of the soil microbial biomass. Dazomet application also decreased the biomass of saprophytic fungi in the soil as indicated by the amount of PLFA 18:2ω6,9, while analyses of bacteria-specific fatty acids indicated that the bacterial biomass in the soil was not affected by either dazomet or P application.
309 citations
TL;DR: It is suggested that genetic exchange may occur through intermingling of nuclei during anastomosis formation and opens the way to studies of vegetative compatibility in natural populations of arbuscular mycorrhizal fungi.
Abstract: We observed anastomosis between hyphae originating from the same spore and from different spores of the same isolate of the arbuscular mycorrhizal fungi Glomus mosseae, Glomus caledonium, and Glomus intraradices. The percentage of contacts leading to anastomosis ranged from 35 to 69% in hyphae from the same germling and from 34 to 90% in hyphae from different germlings. The number of anastomoses ranged from 0.6 to 1.3 per cm (length) of hyphae in mycelia originating from the same spore. No anastomoses were observed between hyphae from the same or different germlings of Gigaspora rosea and Scutellospora castanea; no interspecific or intergeneric hyphal fusions were observed. We monitored anastomosis formation with time-lapse and video-enhanced light microscopy. We observed complete fusion of hyphal walls and the migration of a mass of particles in both directions within the hyphal bridges. In hyphal bridges of G. caledonium, light-opaque particles moved at the speed of 1.8 ± 0.06 μm/s. We observed nuclear migration between hyphae of the same germling and between hyphae belonging to different germlings of the same isolate of three Glomus species. Our work suggests that genetic exchange may occur through intermingling of nuclei during anastomosis formation and opens the way to studies of vegetative compatibility in natural populations of arbuscular mycorrhizal fungi.
222 citations
TL;DR: It seemed that growth of and phosphorus uptake by the external mycelium of G. intraradices were not affected by the antagonistic fungus T. harzianum, and the use of a compartmented growth system with root-free soil compartments suggests that nutrient competition is a likely means of interaction.
Abstract: Trichoderma harzianum is an effective biocontrol agent against several fungal soilborne plant pathogens. However, possible adverse effects of this fungus on arbuscular mycorrhizal fungi might be a drawback in its use in plant protection. The objective of the present work was to examine the interaction between Glomus intraradices and T. harzianum in soil. The use of a compartmented growth system with root-free soil compartments enabled us to study fungal interactions without the interfering effects of roots. Growth of the fungi was monitored by measuring hyphal length and population densities, while specific fatty acid signatures were used as indicators of living fungal biomass. Hyphal 33P transport and beta-glucuronidase (GUS) activity were used to monitor activity of G. intraradices and a GUS-transformed strain of T. harzianum, respectively. As growth and metabolism of T. harzianum are requirements for antagonism, the impact of wheat bran, added as an organic nutrient source for T. harzianum, was investigated. The presence of T. harzianum in root-free soil reduced root colonization by G. intraradices. The external hyphal length density of G. intraradices was reduced by the presence of T. harzianum in combination with wheat bran, but the living hyphal biomass, measured as the content of a membrane fatty acid, was not reduced. Hyphal 33P transport by G. intraradices also was not affected by T. harzianum. This suggests that T. harzianum exploited the dead mycelium but not the living biomass of G. intraradices. The presence of external mycelium of G. intraradices suppressed T. harzianum population development and GUS activity. Stimulation of the hyphal biomass of G. intraradices by organic amendment suggests that nutrient competition is a likely means of interaction. In conclusion, it seemed that growth of and phosphorus uptake by the external mycelium of G. intraradices were not affected by the antagonistic fungus T. harzianum; in contrast, T. harzianum was adversely affected by G. intraradices.
168 citations
TL;DR: The results indicate that chemical factors in this substrate had no direct inhibiting effect on the fungus and a biotic nature is suggested for the suppressiveness of the vermicompost.
Abstract: Vermicompost added to various container media significantly inhibited the infection of tomato plants by Fusarium oxysporum f. sp. lycopersici. The protective effect increased in proportion to the rate of application of vermicompost. Every type of container media amended with this substrate, used in the experiments, were suppressive to the pathogen. Vermicompost lost its activity after heating. Sterilized extracts of vermicompost added to potato dextrose agar stimulated the growth of F. oxysporum mycelium. The results indicate that chemical factors in this substrate had no direct inhibiting effect on the fungus. The total number of micro-organisms and populations of antagonistic bacteria and fungi were significantly higher in vermicompost than in the control peat substrate. A biotic nature is suggested for the suppressiveness of the vermicompost.
162 citations
TL;DR: Selected strains of three species of white rot fungi, Pleurotus ostreatus, Phanerochaete chrysosporium and Trametes versicolor, were grown in sterilized soil from straw inocula and their colonization rates and mycelium density values decreased in the above mentioned order.
Abstract: Selected strains of three species of white rot fungi, Pleurotus ostreatus, Phanerochaete chrysosporium and Trametes versicolor, were grown in sterilized soil from straw inocula The respective colonization rates and mycelium density values decreased in the above mentioned order Three- and four-ringed PAHs at 50 ppm inhibited growth of fungi in soil to some extent The activities of fungal MnP and laccase (units per g dry weight of straw or soil), extracted with 50 mM succinate-lactate buffer (pH 45), were 5 to 20-fold higher in straw compared to soil The enzyme activities per g dry soil in P ostreatus and T versicolor were similar, in contrast to P chrysosporium, where they were extremely low Compared to the aerated controls, P ostreatus strains reduced the levels of anthracene, pyrene and phenanthrene by 81–87%, 84–93% and 41–64% within 2 months, respectively During degradation of anthracene, all P ostreatus strains accumulated anthraquinone PAH removal rates in P chrysosporium and T versicolor soil cultures were much lower
161 citations
TL;DR: In this article, nutritional interactions involving transfer of elements from one mycelium to the other have been monitored dynamically using radioactive tracers and a non-destructive electronic autoradiography system.
Abstract: SUMMARY Interactions between saprotrophic and ectomycorrhizal fungi have been largely ignored, although their mycelia often share the same microsites The mycelial systems show general similarity to each other and, although the enzymatic potential of the saprotrophic fungi is generally considered to be higher, the importance of organic nutrient sources to ectomycorrhizal fungi is now widely accepted In the experiments described here, nutritional interactions involving transfer of elements from one mycelium to the other have been monitored dynamically using radioactive tracers and a non-destructive electronic autoradiography system Microcosms were used in which mycelial systems of the ectomycorrhizal fungi Suillus variegatus and Paxillus involutus, extending from Pinus sylvestris host plants, were confronted with mycelia of the saprotroph Hypholomafasciculare extending from wood blocks The fungi showed a clear morphological confrontation response The mycorrhizal mycelium often formed dense patches over the Hypholoma mycelia Up to 25 % of the 32p present in the Hypholoma mycelium was captured by the mycorrhizal fungi and translocated to the plant host within 30 d The transfer of 32p to the saprotroph from labelled mycorrhizal mycelium was one to two orders of magnitude lower The significance of this transfer as a 'short cut' in nutrient cycling is discussed
151 citations
TL;DR: It is hypothesized that actively absorbed carbohydrates from the root are translocated to the peripheral hyphae along a concentration gradient of sugars and polyols by means of active translocation and diffusion in cell elements and by acropetal water transport in the cord vessels.
Abstract: The mycelium of Suillus bovinus slowly absorbed [U-14C]glucose and other tracers from droplets placed on the cords, translocated them to the peripheral hyphae and exuded them into fluid drops on the hyphal tips. The exudate was characterized by 1H NMR spectroscopy and by sugar and amino acid analysis. The exuded compounds were mainly carbohydrates and peptides. Acetic acid and oxalic acid were also present in the exudate along with a number of unidentified compounds. Released ions (K, Na, Cl, P, Mg and Ca) were identified by X-ray microanalysis. The mycelium was shown to reabsorb up to 65% of the exuded 14C compounds in 2 days. Glucose, mannitol, glutamic acid (pH 3.2), and Rb+ (as well as other mineral ions) were all readily absorbed by the mycelium, while oxalic acid at pH 4.2 and glutamic acid at pH 6.5 were not. Exudation of fluid droplets on the surface of the hydrophobic mycorrhizal fungus S. bovinus may represent an ecophysiologically important function of the extramatrical hyphae, which provides an interface for interaction with the immediate hyphal environment and its other microorganisms where the peripheral hyphae exchange their photosynthetically derived products for nutrients to be used later by the pine host. We hypothesize that actively absorbed carbohydrates from the root are translocated to the peripheral hyphae along a concentration gradient of sugars and polyols by means of active translocation and diffusion in cell elements and by acropetal water transport in the cord vessels.
Book•
01 Aug 1999
TL;DR: Fungi and Man: Interacting with the authors' Lifestyle is discussed, from Trophophase to Idiophase, and more.
Abstract: Introduction. Part 1. The Fungal Lifestyle. 2. The Mycelium. 3. The Substrate. 4. Nutrients. Part 2. 5. Water: Living with Desiccation. 6. Oxygen and Lack of it. 7. Using Light. 8. Withstanding Extremes of Temperature. 9. Competitive: Living with Neighbours. Part 3. 10. From Trophophase to Idiophase. 11. Nuclear Relationships. 12. Spores: Dispersive Propagules. 13. Spore Germination: Starting a New Colon. 14. Fungi and Man: Interacting with our Lifestyle.
TL;DR: In 1996 and 1997, 325 isolates of Botrytis cinerea were collected from 35 commercial greenhouses growing ornamental crops in South Carolina to determine the incidence of resistance to benzimidazole and dicarboximide fungicides.
Abstract: In 1996 and 1997, 325 isolates of Botrytis cinerea were collected from 35 commercial greenhouses growing ornamental crops in South Carolina to determine the incidence of resistance to benzimidazole and dicarboximide fungicides. Conidium germination was assessed on a defined agar medium amended with either thiophanate-methyl (a benzimidazole) or vinclozolin (a di-carboximide). A total of 53 representative isolates were evaluated further for conidium germination and mycelium growth on fungicide-amended medium and for infection of geranium seedlings treated with thiophanate-methyl or vinclozolin at label rates. Isolates were considered sensitive to thiophanate-methyl or vinclozolin when the effective concentration of the fungicide active ingredient resulting in 50% inhibition of germination (EC50-germ) was ≤5 μg/ml or when the effective concentration of fungicide active ingredient resulting in 50% inhibition of mycelium growth (EC50-growth) was ≤1 μg/ml. Of all isolates, 81% (262/325) were resistant...
TL;DR: Anti‐tumor active polysaccharide against Sarcoma 180 was isolated by DEAE‐Sepharose CL‐6B and Sepharose 4B column chromatography from the hot‐water soluble fraction of the mycelium of liquid‐cultured Agaricus blazei mill and the analyses of 13C‐NMR and GC‐MS suggested that it was preliminarily glucomannan with a main chain of D‐mannopyranosyl residues.
Abstract: SUMMARY: Anti-tumor active polysaccharide against Sarcoma 180 was isolated by DEAESepharose CL-6B and Sepharose 4B column chromatography from the hot-water soluble fraction of the mycelium of liquid-cultured Agaricus blazei mill. This polysaccharide did not react with antibodies of anti-tumor polysaccharides such as lentinan, gliforan, and FIII-2-b which is one of anti-tumor polysaccharides from Agaricus blazei. Moreover, the analyses of 13C-NMR and GC-MS suggested that this polysaccharide was preliminarily glucomannan with a main chain of [g-l,2-1inked D-mannopyranosyl residues and 13-D-glucopyranosyl-3-O13-D-glucopyranosyl residues as a side chain. This polysaccharide was completely different from the anti-tumor polysaccharide from fruiting body ofAgaricus blazei, ~-1,6-glucan.
TL;DR: It was shown that increased fungal growth due to yeast was mainly in vegetative hyphae and less in storage structures, indicating a possible interactive component with arbuscular mycorrhizal hyphal growth and phosphorus uptake.
Abstract: The influence of three organic compounds and bakers' dry yeast on growth of external mycelium and phosphorus uptake of the arbuscular mycorrhizal fungus Glomus intraradices Schenck & Smith (BEG 87) was examined. Two experiments were carried out in compartmentalized growth systems with root-free sand or soil compartments. The sand and soil in the root-free compartments were left untreated or uniformly mixed with one of the following substrates (0.5 mg g−1 soil): bakers' dry yeast, bovine serum albumin, starch or cellulose. Effects of the organic substrates on biomass and hyphal length density of the arbuscular mycorrhizal fungus were examined by using specific fatty acid signatures in combination with direct microscopy. Micro-organisms other than the arbuscular mycorrhizal fungus were measured by fatty acid signatures, and radioactive 33P labelling of the root-free soil was used to determine arbuscular mycorrhizal hyphal phosphorus uptake. In general, hyphal growth of G. intraradices was enhanced by yeast and bovine serum albumin, whereas the carbon sources, starch and cellulose, depressed fungal growth. By analysing the fatty acid 16[ratio ]1ω5 from phospholipids (indicating mycelium) and neutral lipids (indicating storage structures) it was shown that increased fungal growth due to yeast was mainly in vegetative hyphae and less in storage structures. Arbuscular mycorrhizal hyphal phosphorus uptake was decreased by cellulose, but unaffected by the other substrates compared with the control. This means that both growth and phosphorus transport by the arbuscular mycorrhizal fungus were decreased under cellulose treatment. However, the composition of the microbial community varied under different substrate conditions indicating a possible interactive component with arbuscular mycorrhizal hyphal growth and phosphorus uptake.
TL;DR: It is reported that the hyphae of Streptomyces antibioticus die through an orderly process of internal cell dismantling that permits the doomed Hyphae to be eliminated with minimum disruption of the colony architecture.
Abstract: During the life cycle of the streptomycetes, large numbers of hyphae die; the surviving ones undergo cellular differentiation and appear as chains of spores in the mature colony. Here we report that the hyphae of Streptomyces antibioticus die through an orderly process of internal cell dismantling that permits the doomed hyphae to be eliminated with minimum disruption of the colony architecture. Morphological and biochemical approaches revealed progressive disorganization of the nucleoid substructure, followed by degradation of DNA and cytoplasmic constituents with transient maintenance of plasma membrane integrity. Then the hyphae collapsed and appeared empty of cellular contents but retained an apparently intact cell wall. In addition, hyphal death occurred at specific regions and times during colony development. Analysis of DNA degradation carried out by gel electrophoresis and studies on the presence of dying hyphae within the mycelium carried out by electron microscopy revealed two rounds of hyphal death: in the substrate mycelium during emergence of the aerial hyphae, and in the aerial mycelium during formation of the spores. This suggests that hyphal death in S. antibioticus is somehow included in the developmental program of the organism.
TL;DR: Sparse root development in the soils of the N-deficient, control plants indicated that WSA formation was primarily influenced by AM hyphae, and AM fungi and roots interacted as the factors that affect soil aggregation, regardless of N nutrition.
Abstract: The effect of the form of N nutrition on soil stability is an important consideration for the management of sustainable agricultural systems. We grew soybean [Glycine max (L.) Merr.] plants in pot cultures in unsterilized soil, and treated them by (1) inoculating them with Bradyrhizobium japonicum, fertilizing with (2) nitrate or (3) ammonia, or (4) by providing only minimum N amendment for the controls. The soils were sampled at 3-week intervals to determine changes in water-stable soil aggregates (WSA), soil pH, the development of roots, arbuscular mycorrhizal (AM) soil and root colonization, and selected functional groups of soil bacteria. The soil fauna was assayed at the end of the experiment (9 weeks). WSA was correlated positively with root and AM soil mycelium development, but negatively with total bacterial counts. Soil arthropod (Collembola) numbers were negatively correlated with AM hyphal length. Soils of nodulated and ammonia-fertilized plants had the highest levels of WSA and the lowest pH at week 9. Sparse root development in the soils of the N-deficient, control plants indicated that WSA formation was primarily influenced by AM hyphae. The ratio of bacterial counts in the water-stable versus water-unstable soil fractions increased for the first 6 weeks and then declined, while counts of anaerobic bacteria increased with increasing WSA. The numbers of soil invertebrates (nematodes) and protozoans did not correlate with bacterial counts or AM soil-hyphal lengths. Soil pH did not affect mycorrhiza development, but actinomycete counts declined with decreasing soil pH. AM fungi and roots interacted as the factors that affect soil aggregation, regardless of N nutrition.
TL;DR: It is concluded that the external mycelia of ectomycorrhizal fungi strongly influence the Pi -uptake capacity of the pine seedlings, and that some mycobionts are well equipped to compete with other soil microorganisms for Pi present at low concentrations in soil solution.
Abstract: SUMMARY Short-term phosphate uptake rates were measured on intact ectomycorrhizal and non-mycorrhizal Pinits sylvestris seedlings using a new, non-destructive method. Uptake was quantified in semihydroponics from the depletion of Pi in a nutrient solution percolating through plant containers. Plants were grown for 1 or 2 months after inoculation at a low relative nutrient addition rate of 3 % d-1 and under P limitation. Four ectomycorrhizal fungi were studied: Paxillus involutus, Suillus lhteus, Suillus bovinuls and Thelephora terrestris. The Pi-uptake capacity of mycorrhizal plants increased sharply in the month after inoculation. The increase was dependent on the development of the mycobionts. A positive correlation was found between the Pi-uptake rates of the seedlings and the active fungal biomass in the substrate as measured by the ergosterol assay. The highest Pi-uptake rates were found in seedlings associated with fungi producing abundant external mycelia. At an external Pi concentration of 10 jM, mycorrhizal seedlings reached uptake rates that were 2.5 (T. terrestris) to 8.7 (P. involutus) times higher than those of non-mycorrhizal plants. The increased uptake rates did not result in an increased transfer of nutrients to the plant tissues. Nutrient depletion was ultimately similar between mycorrhizal and non-mycorrhizal plants in the semihydroponic system. Net P, absorption followed Michaelis-Menten kinetics: uptake rates declined with decreasing Pi concentrations in the nutrient solution. This reduction was most pronounced in nonmycorrhizal seedlings and plants colonized by T. terrestris. The results confirm that there is considerable heterogeneity in affinity for P, uptake among the different mycobionts. It is concluded that the external mycelia of ectomycorrhizal fungi strongly influence the Pi-uptake capacity of the pine seedlings, and that some mycobionts are well equipped to compete with other soil microorganisms for P, present at low concentrations in soil solution.
TL;DR: Differences in the mechanisms of phosphate metabolism in the mycelium of AMF from different genera on a tropical host might be determined by the life-cycle strategies of these fungi, in particular the formation of auxiliary cells in Gigaspora.
Abstract: A glasshouse experiment was done to assess the development and phosphate metabolism of mycorrhizas formed by species of arbuscular mycorrhizal fungi (AMF) from two different genera, Gigaspora and Glomus on Desmodium ovalifolium plants at three concentrations of a phosphate source. The addition of phosphate (0-100 mg P kg(-1))had no effect on the alkaline phosphatase activity, stained histochemically, in the intra-radical mycelium of Gigaspora rosea (BEG111), but decreased that of Glomus manihotis (BEG112) over a 10-wk period. The alkaline phosphatase activity of the extra-radical mycelium was unaffected by increasing phosphate addition (0-100 mg P kg(-1)) in both species of AMF ol er a IO-wk period. The extra-radical mycelium of Gi. rosea (BEG111) accumulated polyphosphate, determined by staining with 4',6-diamidino-2-phenylindole, whereas polyphosphate was not detected in the extra-radical mycelium of G. manihotis (BEG112). This work indicates differences in the mechanisms of phosphate metabolism in the mycelium of AMF from different genera on a tropical host. This might be determined by the life-cycle strategies of these fungi, in particular the formation of auxiliary cells in Gigaspora. The possibility of a negative-feedback mechanism between alkaline phosphatase and polyphosphate in the extra-radical mycelium of Gi. rosea (BEG111) and the role of polyphosphate in the symbiosis are discussed.
TL;DR: In this article, the development of 12 litter and seven phylloplane fungal species was examined from spore germination to colony sporulation across a series of environmentally relevant UV-B doses.
TL;DR: The results show that the fungus is able to change its gene expression in response to stimuli other than the plant, and the molecular mechanisms underlying the pre-symbiotic stages and the cell-to-cell communication between AM fungi and other soil microorganisms are unknown.
Abstract: Arbuscular mycorrhizal (AM) fungi form the most widespread symbiosis of the plant kingdom. More than 80% of vascular plants are susceptible to colonization by the zygomycetous fungi from the order Glomales, and profit significantly by the nutrient exchange between plant and fungus. However, knowledge of the biology of these fungi still remains elusive because of their obligate biotrophism and, up to now, unculturability. The molecular mechanisms underlying the presymbiotic stages and the cell-to-cell communication between AM fungi and other soil microorganisms are, particularly, unknown. Here, we study these aspects by means of a molecular approach to monitor changes in the gene expression of the fungus Glomus mosseae (BEG12) in response to the rhizobacterium Bacillus subtilis NR1. The bacterium was found to induce specific increases in mycelial growth as well as changes in expression of GmFOX2, a highly conserved gene encoding a multifunctional protein of the peroxisomal β-oxidation. We determined the ge...
TL;DR: Five different hydrophobin-encoding cDNA clones from Cladosporium fulvum were isolated from cDNA libraries, made from nutrient-depleted mycelium, and showed clear differences in expression patterns at various stages of development, and in liquid media lacking either carbon or nitrogen.
Abstract: Five different hydrophobin-encoding cDNA clones from Cladosporium fulvum were isolated from cDNA libraries, made from nutrient-depleted mycelium. One cDNA clone was identical to the previously isolated hydrophobin HCf-1. The other clones were named HCf-2, -3, -4 and -5. HCf-1, -2, -3 and -4 show a high degree of identity, and are predicted to encode class I hydrophobins. HCf-5 encodes a class II hydrophobin. The expression patterns of these hydrophobins at various stages of development, and in liquid media lacking either carbon or nitrogen, or both, showed clear differences. All hydrophobins were more strongly expressed during sporulation than before, with HCf-4 and -5 showing the highest increase. Expression of HCf genes in infected plants was also higher at 16 days than at 10 days after infection. The expression of HCf-5 in sporulating mycelium was much lower in planta than in vitro. All HCf genes were upregulated under conditions of nutrient deprivation. HCf-1, -2, -3 and -4 showed highest levels of transcription in medium lacking both carbon and nitrogen. Expression of HCf-5 was highest in medium lacking nitrogen but containing carbon. HCf-1 was generally the most abundant hydrophobin. The introduction of multiple copies of HCf-1, which caused cosuppression of the endogenous HCf-1 gene, was shown to affect the expression of HCf-2, -3 and -4 also. Expression of HCf-4 was suppressed, but expression of HCf-2 and -3 was upregulated. Expression of HCf-5 was not changed.
TL;DR: In this paper, a versatile peroxidase able to oxidize Mn2+ as well as phenolic and nonphenolic aromatic compounds is produced in peptone-containing liquid cultures of Pleurotus eryngii encoded by the gene mnpl. The regulation of its transcript levels was investigated by Northern blotting of total RNA.
Abstract: A versatile peroxidase able to oxidize Mn2+ as well as phenolic and nonphenolic aromatic compounds is produced in peptone-containing liquid cultures of Pleurotus eryngii encoded by the gene mnpl. The regulation of its transcript levels was investigated by Northern blotting of total RNA. High-peroxidase transcripts and activity were found in cultures grown in glucose-peptone medium, whereas only basal levels were detected in glucose-ammonium medium. The addition of more than 25 μM Mn2+ to the former medium did not result in detectable peroxidase transcripts or activity. Potential regulators were also added to isolated mycelium. In this way, it was shown that high transcript levels (in peroxidase-expressing mycelium) were maintained on peptone, whereas expression was not induced in short-term incubation experiments. Similar results were obtained with Mn2+ ions. Strong induction of mnpl expression was caused by exogenous H2O2 or by continuous H2O2 generation during redox cycling of menadione. By the use of the latter system in the presence of Fe3+, which catalyzes the reduction of H2O2 to hydroxyl radical, it was shown for the first time that the presence of this strong oxidant causes a rapid increase of the transcripts of a ligninolytic peroxidase. In conclusion, peptone and Mn2+ affect the levels of transcripts of this versatile peroxidase in culture, and reduced oxygen species induce short-term expression in isolated mycelium, probably via a stress response mechanism.
TL;DR: Inoculation of potato plants with AM fungus increased the weight of the biggest tuber and the total weight of tubers per pot and thus the inoculation has potential use for post-vitro transplanted plants for microtuber production.
TL;DR: It is shown here that extraradical structures of AM fungi can survive the winter in the soil at their site of synthesis, even after the elimination of any potential contribution from the part of the mycorrhizae inside the roots.
TL;DR: Rhizopus oryzae, a zygomycete, was found to decolorize, dechlorinate, and detoxify bleach plant effluent at lower cosubstrate concentrations than the basidiomycetes previously investigated.
Abstract: Rhizopus oryzae, a zygomycete, was found to decolorize, dechlorinate, and detoxify bleach plant effluent at lower cosubstrate concentrations than the basidiomycetes previously investigated. With glucose at 1 g/liter, this fungus removed 92 to 95% of the color, 50% of the chemical oxygen demand, 72% of the adsorbable organic halide, and 37% of the extractable organic halide in 24 h at temperatures of 25 to 45°C and a pH of 3 to 5. Even without added cosubstrate the fungus removed up to 78% of the color. Monomeric chlorinated aromatic compounds were removed almost completely, and toxicity to zebra fish was eliminated. The fungal mycelium could be immobilized in polyurethane foam and used repeatedly to treat batches of effluent. The residue after treatment was not further improved by exposure to fresh R. oryzae mycelium.
TL;DR: The results indicate that co-inoculating a helper bacterium together with an ectomycorrhizal fungus can be an efficient way of optimizing controlled mycorrhization techniques for the production of high-quality Douglas-fir planting stocks.
Abstract: We inoculated disinfected soil at two Douglas-fir bareroot forest nurseries with three doses (8×105, 8×107 and 8×109 cfu m−2) of the rifampin-resistant mycorrhiza helper bacterium Pseudomonas fluorescens strain BBc6R8 and the ectomycorrhizal fungus Laccaria bicolor strain S238N. In one of the two nurseries, two doses of fungal inoculum (50 and 100 mg m−2 dry weight (DW) mycelium entrapped in alginate beads at the constant dose of 1 l m−2) were tested. For all bacterial treatments the density of P. fluorescens BBc6R8 in the soil, determined by dilution plating, dropped below the detection limit (10−2 cfu g−1 DW soil) 2 weeks after inoculation. Fifteen weeks after inoculation, the introduced bacterium could be detected by enrichment only in the treatments inoculated with the highest bacterial dose. Two years after inoculation, P. fluorescens BBc6R8 could not be detected in the soil of any of the bacterial treatments. Five months after inoculation and sowing, bacterial inoculation significantly increased the percentage of mycorrhizal short roots on plants inoculated with either low or high amounts of L. bicolor, in one of the two nurseries. The lowest bacterial dose increased mycorrhizal colonization from 45 to 70% in plants inoculated with the low amount of fungal inoculum, and from 64 to 77% in plants inoculated with the high amount of fungal inoculum. The lowest bacterial dose increased mycorrhizal colonization more than the highest bacterial dose. The same L. bicolor mycorrhizal index (70%) was obtained with 50 mg m−2 DW mycelium plus the bacterium than with twice this fungal dose and no bacterium (64%). Two years after inoculation, the height of the mycorrhizal Douglas-firs in the other nursery was significantly increased by the lowest bacterial dose (from 40.7 to 42.6 cm). These results indicate that co-inoculating a helper bacterium together with an ectomycorrhizal fungus can be an efficient way of optimizing controlled mycorrhization techniques for the production of high-quality Douglas-fir planting stocks. They also confirm that BBc6R8 acts at a low population density (less than 102 cfu g−1 soil); this contrasts with most PGPR effects discussed in the literature, where the minimal inoculation dose of 105 cfu g−1 soil is required to obtain the beneficial effect.
TL;DR: Severe plant N deficiency reduced the percentage root length colonised, hyphal length, total N uptake by hyphae and dry weight of mycorrhizal plants, and a sufficient N supply to the roots was important for the development of an extensive mycelium.
Abstract: The contribution of hyphae of Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) to the acquisition of mineral nitrogen by Triticum aestivum L. cv. Hano (wheat) was tested under conditions of low P and high N (+N−P) or low N (−N−P). Mycorrhizal colonisation increased the shoot dry weight and plant tissue concentrations of P and cations. However, N tissue concentrations of mycorrhizal plants were not increased, although nitrate reductase activities were significantly higher (in vivo activity) in +N−P mycorrhizal compared to non-mycorrhizal roots. Severe plant N deficiency reduced the percentage root length colonised (but not the percentage viable colonisation), hyphal length, total N uptake by hyphae and dry weight of mycorrhizal plants. Although mycorrhizal colonisation did not affect the overall plant N status, hyphae transported 1% (−N−P) and 7% (+N−P) of the N-labelled NH4NO3 to mycorrhizal plants over 48 h. The higher rate of hyphal N uptake was apparently related to the more extensive hyphal growth at the higher level of plant N supply. However, the hyphal N supply was not sufficiently high to sustain adequate N nutrition of the plants supplied with very low amounts of N to the roots. Conversely, a sufficient N supply to the roots was important for the development of an extensive mycelium.
TL;DR: Interestingly, in a situation of bioprotection, only low levels of the activities normally associated with the infection by A. euteiches were detected, suggesting that the synthesis of these proteins is directly linked to the growth or virulence of the pathogen.
Abstract: Arbuscular mycorrhizal (AM) symbioses are known to play a role in increased resistance of plants against soilborne pathogens. Mechanisms involved in this phenomenon are not yet well understood. This work investigates possible roles of endoproteolytic activities in bioprotection of Pisum sativum roots by Glomus mosseae against Aphanomyces euteiches. First, it is demonstrated that bioprotection occurs only in pre-mycorrhizal plants. Second, endoproteolytic activities were analysed qualitatively and quantitatively during AM symbiosis, in plants infected with either zoospores or mycelium of A. euteiches, and in mycorrhizal plants infected with the pathogen. In mycorrhizal symbiosis a progressive increase in endoproteolytic activities was observed following root colonization by G. mosseae. By contrast, in roots inoculated with A. euteiches, a drastic increase in endoproteolytic activities was observed which was correlated with the amount of pathogen occurring in roots. Qualitative differences were seen among the endoproteolytic activities detected in roots inoculated with zoospores or mycelium. The constitutive as well as mycorrhizal and pathogen-induced activities were further characterized as ‘trypsin-like’ serine endoproteases. Interestingly, in a situation of bioprotection, only low levels of the activities normally associated with the infection by A. euteiches were detected, suggesting that the synthesis of these proteins is directly linked to the growth or virulence of the pathogen.
TL;DR: The results indicate that the genetic control of aerial mycelium formation is more complex than previously recognized and support the idea that a high proportion of bld genes are directly or indirectly involved in the production of substances that are exchanged between cells during morphological differentiation.
Abstract: Morphogenesis in the bacterium Streptomyces coelicolor involves the formation of a lawn of hair-like aerial hyphae on the colony surface that stands up in the air and differentiates into chains of spores. bld mutants are defective in the formation of this aerial mycelium and grow as smooth, hairless colonies. When certain pairs of bld mutants are grown close to one another on rich sporulation medium, they exhibit extracellular complementation such that one mutant restores aerial mycelium formation to the other. The extracellular complementation relationships of most of the previously isolated bld mutants placed them in a hierarchy of extracellular complementation groups. We have screened for further bld mutants with precautions intended to maximize the discovery of additional genes. Most of the 50 newly isolated mutant strains occupy one of three of the previously described positions in the hierarchy, behaving like bldK, bldC, or bldD mutants. We show that the mutations in some of the strains that behave like bldK are bldK alleles but that others fall in a cluster at a position on the chromosome distinct from that of any known bld gene. We name this locus bldL. By introducing cloned genes into the strains that exhibit bldC or bldD-like extracellular complementation phenotypes, we show that most of these strains are likely to contain mutations in genes other than bldC or bldD. These results indicate that the genetic control of aerial mycelium formation is more complex than previously recognized and support the idea that a high proportion of bld genes are directly or indirectly involved in the production of substances that are exchanged between cells during morphological differentiation.