Showing papers on "Mycelium published in 2003"

Rapid turnover of hyphae of mycorrhizal fungi determined by AMS microanalysis of 14C.

Abstract: Processes in the soil remain among the least well-characterized components of the carbon cycle. Arbuscular mycorrhizal (AM) fungi are ubiquitous root symbionts in many terrestrial ecosystems and account for a large fraction of photosynthate in a wide range of ecosystems; they therefore play a key role in the terrestrial carbon cycle. A large part of the fungal mycelium is outside the root (the extraradical mycelium, ERM) and, because of the dispersed growth pattern and the small diameter of the hyphae (<5 micrometers), exceptionally difficult to study quantitatively. Critically, the longevity of these fine hyphae has never been measured, although it is assumed to be short. To quantify carbon turnover in these hyphae, we exposed mycorrhizal plants to fossil ("carbon-14-dead") carbon dioxide and collected samples of ERM hyphae (up to 116 micrograms) over the following 29 days. Analyses of their carbon-14 content by accelerator mass spectrometry (AMS) showed that most ERM hyphae of AM fungi live, on average, 5 to 6 days. This high turnover rate reveals a large and rapid mycorrhizal pathway of carbon in the soil carbon cycle.

A novel class of secreted hydrophobic proteins is involved in aerial hyphae formation in Streptomyces coelicolor by forming amyloid-like fibrils

Abstract: Streptomycetes exhibit a complex morphological differentiation. After a submerged mycelium has been formed, filaments grow into the air to septate into spores. A class of eight hydrophobic secreted proteins, ChpA-H, was shown to be instrumental in the development of Streptomyces coelicolor. Mature forms of ChpD-H are up to 63 amino acids in length, and those of ChpA-C are larger (+/-225 amino acids). ChpA-C contain two domains similar to ChpD-H, as well as a cell-wall sorting signal. The chp genes were expressed in submerged mycelium (chpE and chpH) as well as in aerial hyphae (chpA-H). Formation of aerial hyphae was strongly affected in a strain in which six chp genes were deleted (DeltachpABCDEH). A mixture of ChpD-H purified from cell walls of aerial hyphae complemented the DeltachpABCDEH strain extracellularly, and it accelerated development in the wild-type strain. The protein mixture was highly surface active, and it self-assembled into amyloid-like fibrils at the water-air interface. The fibrils resembled those of a surface layer of aerial hyphae. We thus conclude that the amyloid-like fibrils of ChpD-H lower the water surface tension to allow aerial growth and cover aerial structures, rendering them hydrophobic. ChpA-C possibly bind ChpD-H to the cell wall.

Contribution of six arbuscular mycorrhizal fungal isolates to water uptake by Lactuca sativa plants under drought stress

Abstract: It is currently accepted that, along with nutrients, arbuscular mycorrhizal (AM) fungi also transport water to their host plant. However, the quantity of water supplied and its significance for plant water relations remain controversial. The objective of this work was to evaluate and compare the ability of six AM fungi to alter rates of root water uptake under drought stress conditions. Soil drying rates of uninoculated control plants of comparable size and nutritional status and mycorrhizal plants were recorded daily. Lactuca sativa plants colonized by Glomus coronatum, G. intraradices, G. claroideum and G. mosseae depleted soil water to a higher extent than comparably sized uninoculated control plants or plants colonized by G. constrictum or G. geosporum. The differences ranged from 0.6% volumetric soil moisture for G. mosseae-colonized plants to 0.95% volumetric soil moisture for G. intraradices-colonized plants. These differences in soil moisture were equivalent to 3-4.75 ml plant -1 day -1 , respectively, and could not be ascribed to differences in plant size, but to the activity of AM fungi. The AM fungi tested in this study differed in their effectiveness to enhance plant water uptake from soil. This ability seems to be related to the amount of external mycelium produced by each AM fungus and to the frequency of root colonization in terms of live and active fungal structures.

Production of external mycelium by ectomycorrhizal fungi in a norway spruce forest was reduced in response to nitrogen fertilization

Abstract: A field study was carried out to evaluate the influence of N fertilization on the growth of the external mycelium of ectomycorrhizal (EM) fungi in a Norway spruce forest in SW Sweden. Nylon mesh bags filled with sand were buried in the soil for 6-18 months and the ingrowth of mycelium was used as an estimate of EM mycelial growth. Root-isolated, trenched plots were used to estimate background growth of saprotrophic fungi. Mycelial growth of EM fungi in N-treated plots was reduced to c. 50% of that in nonfertilized plots. Local addition of apatite stimulated the EM mycelial growth in N-treated plots. The negative influence of N on the growth of external EM mycelium observed earlier in laboratory studies was confirmed in the present field study. The growth of EM mycelia was not directly related to N concentration in the soil but rather to the N status of the trees, although other factors induced by the N treatment may also have influenced EM mycelial growth. (Less)

The chaplins: a family of hydrophobic cell-surface proteins involved in aerial mycelium formation in Streptomyces coelicolor

Abstract: The filamentous bacterium Streptomyces coelicolor differentiates by forming specialized, spore-bearing aerial hyphae that grow into the air. Using microarrays, we identified genes that are down-regulated in a mutant unable to erect aerial hyphae. Through this route, we identified a previously unknown layer of aerial mycelium surface proteins (the “chaplins”). The chaplins share a hydrophobic domain of ∼40 residues (the “chaplin domain”), and all have a secretion signal. The five short chaplins (ChpD,E,F,G,H) have one chaplin domain, whereas the three long chaplins (ChpA,B,C) have two chaplin domains and a C-terminal “sorting signal” that targets them for covalent attachment to the cell wall by sortase enzyme. Expression of the two chaplin genes examined (chpE, chpH) depended on aerial hyphae formation but not sporulation, and egfp fusions showed their expression localized to aerial structures. Mass spectrometry of cell wall extracts confirmed that the short chaplins localized to the cell surface. Deletion of chaplin genes caused severe delays in aerial hyphae formation, a phenotype rescued by exogenous application of chaplin proteins. These observations implicate the chaplins in aerial mycelium formation, and suggest that coating of the envelope by the chaplins is required for aerial hyphae to grow out of the aqueous environment of the substrate mycelium into the air.

Carbon Export from Arbuscular Mycorrhizal Roots Involves the Translocation of Carbohydrate as well as Lipid

Abstract: Arbuscular mycorrhizal (AM) fungi take up photosynthetically fixed carbon from plant roots and translocate it to their external mycelium. Previous experiments have shown that fungal lipid synthesized from carbohydrate in the root is one form of exported carbon. In this study, an analysis of the labeling in storage and structural carbohydrates after 13 C 1 glucose was provided to AM roots shows that this is not the only pathway for the flow of carbon from the intraradical to the extraradical mycelium (ERM). Labeling patterns in glycogen, chitin, and trehalose during the development of the symbiosis are consistent with a significant flux of exported glycogen. The identification, among expressed genes, of putative sequences for glycogen synthase, glycogen branching enzyme, chitin synthase, and for the first enzyme in chitin synthesis (glutamine fructose-6-phosphate aminotransferase) is reported. The results of quantifying glycogen synthase gene expression within mycorrhizal roots, germinating spores, and ERM are consistent with labeling observations using 13 C-labeled acetate and glycerol, both of which indicate that glycogen is synthesized by the fungus in germinating spores and during symbiosis. Implications of the labeling analyses and gene sequences for the regulation of carbohydrate metabolism are discussed, and a 4-fold role for glycogen in the AM symbiosis is proposed: sequestration of hexose taken from the host, long-term storage in spores, translocation from intraradical mycelium to ERM, and buffering of intracellular hexose levels throughout the life cycle.

Catalases of Aspergillus fumigatus

Abstract: Upon infection of a host, the pathogenic fungus Aspergillus fumigatus is attacked by the reactive oxygen species produced by phagocytic cells. Detoxification of hydrogen peroxide by catalases was proposed as a way to overcome this host response. A. fumigatus produces three active catalases; one is produced by conidia, and two are produced by mycelia. The mycelial catalase Cat1p was studied previously. Here we characterized the two other catalases, their genes, and the phenotypes of gene-disrupted mutants. CatAp, a spore-specific monofunctional catalase, is resistant to heat, metal ions, and detergent. This enzyme is a dimeric protein with 84.5-kDa subunits. The 749-amino-acid polypeptide exhibits high levels of similarity to the Aspergillus nidulans CatA catalase and to bacterial catalase HPII of Escherichia coli. In spite of increased sensitivity to H2O2, killing of ΔcatA conidia by alveolar macrophages and virulence in animals were similar to the killing of conidia by alveolar macrophages and virulence in animals observed for the wild type. In contrast to the Cat1p and CatAp catalases, the mycelial Cat2p enzyme is a bifunctional catalase-peroxidase and is sensitive to heat, metal ions, and detergent. This enzyme, an 82-kDa monomer, is homologous to catalase-peroxidases of several fungi and bacteria. Surprisingly, mycelium of the double Δcat1Δcat2 mutant with no catalase activity exhibited only slightly increased sensitivity to H2O2 and was as sensitive to killing by polymorphonuclear neutrophils as mycelium of the wild-type strain. However, this mutant exhibited delayed infection in the rat model of aspergillosis compared to infection by the wild-type strain. These results indicate that conidial catalase is not a virulence factor and that mycelial catalases transiently protect the fungus from the host.

Direct nocturnal water transfer from oaks to their mycorrhizal symbionts during severe soil drying

Abstract: Symbiotic mycorrhizal fungi play an important role in the absorption of soil nutrients and water by most plants. It has been suggested that hydraulically lifted water might maintain the integrity of the external mycorrhizal mycelium during drought. We tested this hypothesis in the obligately mycorrhizal species, coast live oak (Quercus agrifolia), using a microcosm system that separated the effects of hydraulic lift in roots from those in the external mycelium. Mycorrhizal oak seedlings were established in microcosms comprising three discrete compartments for (1) upper roots, (2) tap roots, and (3) external fungal mycelium. Eight months after planting, a drought treatment was initiated: irrigation to the upper root and fungal chambers was terminated and only irrigation to the taproot compartment was maintained. After 3, 12, 30, 50, 70 and 80 days of drought, tracers were injected into the taproot compartment at dusk. At dawn the following morning, mycorrhizal hyphae (EM and AM) and spores (AM) in upper root and fungal compartments were extensively labeled with the tracers. In contrast, no labeling was observed when tracers were injected into the taproot compartment during daytime. Nocturnal water translocation from plant to mycorrhizal fungi occurred in association with hydraulic lift. Saprotrophic/parasitic fungi in the microcosms were not labeled, suggesting a direct water transfer from plants to their mycorrhizal mutualists and not to other fungi in the soil. Even after prolonged drought (70-80 days), mycorrhizal hyphae persisted in soils with water potential values as low as -20 MPa. Maintaining mycorrhizal activity through direct water translocation could potentially improve the nutrient status of deep-rooted plants during periods when the fertile upper soil is dry.

Evidence of the production of silver nanoparticles via pretreatment of Phoma sp.3.2883 with silver nitrate

Abstract: Aims: The objective was to demonstrate the size of silver particles produced by the filamentous fungus Phoma sp.3.2883 via adsorption and accumulation, and to confirm that this silver was in a reduced state. Methods and Results: Mycelium was freeze-dried and then shake-cultured in a silver nitrate solution. It was found that up to 13·4 mg of silver was produced per gram of dry mycelium via atomic absorption spectrometer (AAS) analysis. The silver particles adsorbed on the mycelium were observed and measured under transmission electron microscope and their estimated size was 71·06 ± 3·46 nm. Further examination of the particles via X-ray photoelectron spectroscope confirmed that the adsorbed silver particle had been reduced. Conclusion: The frozen mycelium of Phoma sp3.2883 has the potential for use in silver nanoparticle production. Significance and Impact of the Study: Silver nanoparticles could be used in the oil industry as an important catalyst and in the field of human medicine as a bactericide. The fungus Phoma sp3.2883 is a potential biosorbent that could be used for the production of these silver nanoparticles, and may also be useful in waste detoxification and in silver recovery programmes.

Early Events in the Fusarium verticillioides-Maize Interaction Characterized by Using a Green Fluorescent Protein-Expressing Transgenic Isolate

Abstract: The infection of maize by Fusarium verticillioides can result in highly variable disease symptoms ranging from asymptomatic plants to severe rotting and wilting. We produced F. verticillioides green fluorescent protein-expressing transgenic isolates and used them to characterize early events in the F. verticillioides-maize interaction that may affect later symptom appearance. Plants grown in F. verticillioides-infested soil were smaller and chlorotic. The fungus colonized all of the underground parts of a plant but was found primarily in lateral roots and mesocotyl tissue. In some mesocotyl cells, conidia were produced within 14 to 21 days after infection. Intercellular mycelium was detected, but additional cells were not infected until 21 days after planting. At 25 to 30 days after planting, the mesocotyl and main roots were heavily infected, and rotting developed in these tissues. Other tissues, including the adventitious roots and the stem, appeared to be healthy and contained only a small number of hyphae. These results imply that asymptomatic systemic infection is characterized by a mode of fungal development that includes infection of certain tissues, intercellular growth of a limited number of fungal hyphae, and reproduction of the fungus in a few cells without invasion of other cells. Development of visibly rotted tissue is associated with massive production of fungal mycelium and much less organized growth.

Influence of a Bacillus sp. on physiological activities of two arbuscular mycorrhizal fungi and on plant responses to PEG-induced drought stress.

Abstract: The effects of bacterial inoculation (Bacillus sp.) on the development and physiology of the symbiosis between lettuce and the arbuscular mycorrhizal (AM) fungi Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe and Glomus intraradices (Schenck and Smith) were investigated. Plant growth, mineral nutrition and gas–exchange values in response to bacterial inoculation after PEG–induced drought stress were also evaluated. In AM plants, inoculation with Bacillus sp. enhanced fungal development and metabolism, measured as succinate dehydrogenase (SDH) and alkaline phosphatase (ALP) activities, more than plant growth. Under non-stressed conditions, G. intraradices colonization increased all plant physiological values to a higher extent when in dual inoculation with the bacterium. Under stress conditions, the bacterium had an important stimulatory effect on G. intraradices development. Under such conditions, the effects of the bacterium on photosynthetic rate, water use efficiency (WUE) and stomatal conductance of lettuce plants differed with the fungus species. Plant-gas exchange was enhanced in G. intraradices- and reduced in G. mosseae-colonized plants when co-inoculated with Bacillus sp. Thus, the effects of each fungus on plant physiology were modulated by the bacterium. Stress was detrimental, particularly in G. intraradices-colonized plants without the bacterium, reducing intra and extraradical mycelium growth and vitality (SDH), as well as plant-gas exchange. Nevertheless, Bacillus sp. inoculation improved all these plant and fungal parameters to the same level as in non-stressed plants. The highest amount of alive and active AM mycelium for both fungi was obtained after co-inoculation with Bacillus sp. These results suggest that selected free-living bacteria and AM fungi should be co-inoculated to optimize the formation and functioning of the AM symbiosis in both normal and adverse environments.

In situ identification of intracellular bacteria related to Paenibacillus spp. in the mycelium of the ectomycorrhizal fungus Laccaria bicolor S238N.

Abstract: Bacterial proliferations have recurrently been observed for the past 15 years in fermentor cultures of the ectomycorrhizal fungus Laccaria bicolor S238N, suggesting the presence of cryptic bacteria in the collection culture of this fungus. In this study, intracellular bacteria were detected by fluorescence in situ hybridization in combination with confocal laser scanning microscopy in several collection subcultures of L. bicolor S238N. They were small (0.5 μm in diameter), rare, and heterogeneously distributed in the mycelium and were identified as Paenibacillus spp. by using a 16S rRNA-directed oligonucleotide probe initially designed for bacteria isolated from a fermentor culture of L. bicolor S238N.

Fungal lipid accumulation and development of mycelial structures by two arbuscular mycorrhizal fungi

Abstract: We monitored the development of intraradical and extraradical mycelia of the arbuscular mycorrhizal (AM) fungi Scutellospora calospora and Glomus intraradices when colonizing Plantago lanceolata. The occurrence of arbuscules (branched hyphal structures) and vesicles (lipid storage organs) was compared with the amounts of signature fatty acids. The fatty acid 16:1omega5 was used as a signature for both AM fungal phospholipids (membrane constituents) and neutral lipids (energy storage) in roots (intraradical mycelium) and in soil (extraradical mycelium). The formation of arbuscules and the accumulation of AM fungal phospholipids in intraradical mycelium followed each other closely in both fungal species. In contrast, the neutral lipids of G. intraradices increased continuously in the intraradical mycelium, while vesicle occurrence decreased after initial rapid root colonization by the fungus. S. calospora does not form vesicles and accumulated more neutral lipids in extraradical than in intraradical mycelium, while the opposite pattern was found for G. intraradices. G. intraradices allocated more of its lipids to storage than did S. calospora. Thus, within a species, the fatty acid 16:1omega5 is a good indicator for AM fungal development. The phospholipid fatty acid 16:1omega5 is especially suitable for indicating the frequency of arbuscules in the symbiosis. We propose that the ratio of neutral lipids to phospholipids is more important than is the presence of vesicles in determining the storage status of AM fungi.

The production of ectomycorrhizal mycelium in forests: Relation between forest nutrient status and local mineral sources

Abstract: Due to acid rain and nitrogen deposition, there is growing concern that other mineral nutrients, primarily potassium and phosphorus, might limit forest production in boreal forests. Ectomycorrhizal (EcM) fungi are important for the acquisition of potassium and phosphorus by trees. In a field investigation, the effects of poor potassium and phosphorus status of forest trees on the production of EcM mycelium were examined. The production of EcM mycelium was estimated in mesh bags containing sand, which were buried in the soil of forests of different potassium and phosphorus status. Mesh bags with 2% biotite or 1% apatite in sand were also buried to estimate the effect of local sources of nutrients on the production of EcM mycelium. No clear relation could be found between the production of EcM mycelium and nutrient status of the trees. Apatite stimulated the mycelial production, while biotite had no significant effect. EcM root production at the mesh bag surfaces was stimulated by apatite amendment in a forest with poor phosphorus status. The contribution of EcM fungi to apatite weathering was estimated by using rare earth elements ( REE) as marker elements. The concentration of REE was 10 times higher in EcM roots, which had grown in contact with the outer surface of apatite-amended mesh bags than in EcM roots grown in contact with the biotite amended or sand-filled mesh bags. In a laboratory study, it was confirmed that REE accumulated in the roots with very low amounts (<1 %) translocated to the shoots. The short-term effect of EcM mycelium on the elemental composition of biotite and apatite was investigated and compared with biotite- and apatite-amended mesh bags buried in trenched soil plots, which were free from EcM fungi. The mesh bags subjected to EcM fungi showed no difference in chemical composition after 17 months in the field. This study suggests that trees respond to phosphorus limitation by increased exploitation of phosphorus-containing minerals by ectomycorrhiza. However, the potential to ameliorate potassium limitation in a similar way appears to be low. (Less)

P uptake by arbuscular mycorrhizal hyphae: effect of soil temperature and atmospheric CO2 enrichment

Abstract: Mycorrhizas are ubiquitous symbioses that may have an important role in the movement of C from air to soil. Studies on the effects of climate change factors on mycorrhizas have been concentrated on the effects of atmospheric [CO2] whereas temperature effects have been neglected. Based on previous results showing no effect of varying atmospheric [CO2] on the development and P uptake of the arbuscular mycorrhizal fungi (AMF) colonizing plants growing in controlled conditions, we hypothesized that soil temperature would have a higher impact on AMF development and nutrient uptake than the effects of [CO2] on the host plant. Pea plants were grown in association with either a single isolate of Glomus caledonium or AMF from field soil in factorial combination with the corresponding current (10 °C) or elevated (15 °C) soil temperatures at current (350 p.p.m) or elevated (700 p.p.m) atmospheric [CO2]. 33P uptake by extraradical AMF hyphae was measured independently from root P uptake in a root exclusion compartment. Intraradical colonization developed well at both soil temperatures and almost duplicated from 10 to 15 °C. Extraradical mycelium developed only at 15 °C in the root exclusion compartment and hyphal P uptake could therefore be studied at 15 °C only. Hyphal P uptake differed markedly between inoculum types, but was not altered by growing the host plants at two atmospheric [CO2] levels. No significant [CO2] × soil temperature interactions were observed. The results suggested that, in the system tested, AMF development and function is likely more influenced by the temperature component of climate change than by its [CO2] component. We suggest that much more attention should be paid to temperature effects in future studies.

Biological Control of Pathogens Causing Root Rot Complex in Field Pea Using Clonostachys rosea Strain ACM941.

Abstract: Pea root rot complex (PRRC), caused by Alternaria alternata, Aphanomyces euteiches, Fusarium oxysporum f. sp. pisi, F. solani f. sp. pisi, Mycosphaerella pinodes, Pythium spp., Rhizoctonia solani, and Sclerotinia sclerotiorum, is a major yield-limiting factor for field pea production in Canada. A strain of Clonostachys rosea (syn. Gliocladium roseum), ACM941 (ATCC 74447), was identified as a mycoparasite against these pathogens. When grown near the pathogen, ACM941 often was stimulated to produce lateral branches that grew directly toward the pathogen mycelium, typically entwining around the pathogen mycelium. When applied to the seed, ACM941 propagated in the rhizosphere and colonized the seed coat, hypocotyl, and roots as the plant developed and grew. ACM941 significantly reduced the recovery of all fungal pathogens from infected seed, increased in vitro seed germination by 44% and seedling emergence by 22%, and reduced root rot severity by 76%. The effects were similar to those of thiram fungi...

Symbiotic Status, Phosphate, and Sucrose Regulate the Expression of Two Plasma Membrane H+-ATPase Genes from the Mycorrhizal Fungus Glomus mosseae

Abstract: The establishment of the arbuscular mycorrhizal symbiosis results in a modification of the gene expression pattern in both plant and fungus to accomplish the morphological and physiological changes necessary for the bidirectional transfer of nutrients between symbionts. H + -ATPase enzymes play a key role establishing the electrochemical gradient required for the transfer of nutrients across the plasma membrane in both fungi and plants. Molecular analysis of the genetic changes in arbuscular mycorrhizal fungi during symbiosis allowed us to isolate a fungal cDNA clone encoding a H + -ATPase, GmPMA1 , from Glomus mosseae (BEG12). Despite the high conservation of the catalytic domain from H + -ATPases, detailed analyses showed that GmPMA1 was strongly related only to a previously identified G. mosseae ATPase gene, GmHA5 , and not to the other four ATPase genes known from this fungus. A developmentally regulated expression pattern could be shown for both genes, GmPMA1 and GmHA5. GmPMA 1 was highly expressed during asymbiotic development, and its expression did not change when entering into symbiosis, whereas the GmHA5 transcript was induced upon plant recognition at the appressorium stage. Both genes maintained high levels of expression during intraradical development, but their expression was reduced in the extraradical mycelium. Phosphate, a key nutrient to the symbiosis, also induced the expression of GmHA 5 during asymbiotic growth, whereas sucrose had a negative effect. Our results indicate that different fungal H + -ATPases isoforms might be recruited at different developmental stages possibly responding to the different requirements of the life in symbiosis.

Correlation of the properties of several lignocellulosic substrates to the crop performance of the shiitake mushroom Lentinula edodes

Abstract: Two selected Lentinula edodes strains (S4080 and SIEF0231) were cultivated on oak-wood sawdust (OS), wheat straw (WS) and corn-cobs (CC) substrates in order to examine the influence of those residues on mycelium growth and on basidiomata production. For both strains, mycelial growth measurements conducted in ‘race tubes’ demonstrated faster colonization of OS and WS media. Lag-phase and complete colonization periods were correlated to mycelium extension rates in the three substrates tested. Similar patterns of pH and electrical conductivity (Ec) changes were detected in all media and for all strains tested; the pH decreased steadily throughout the colonization process to reach values of 4.49–5.06; Ec increased by the end of mycelium colonization, and it presented the highest and lowest values in the WS and OS media respectively. In addition, a negative correlation was established between final salt content of the substrates and mycelium extension rates. Subjecting fully colonized substrates to a cold-shock treatment resulted in fruiting 58–65 days after inoculation in tubes; WS and CC promoted earlier sporophore initiation than OS. Monitoring CO2 emissions by strain SIEF0231 in pilot-scale cultivation on synthetic blocks, revealed higher respiration rates from OS and CC than from WS, which were further correlated with substrate colonization rates. Among residues colonized by the same strain, WS appeared to promote earliness and crop productivity (BE 54.17%) by presenting shorter cropping periods and equal yield distribution among flushes, while on OS and CC maximum yields were obtained within the first two flushes. Moreover, heavier basidiomata were produced by WS and OS substrates.

A Phytophthora infestans G-protein beta subunit is involved in sporangium formation.

Abstract: The heterotrimeric G-protein pathway regulates cellular responses to a wide range of extracellular signals in virtually all eukaryotes. It also controls various developmental processes in the oomycete plant pathogen Phytophthora infestans, as was concluded from previous studies on the role of the G-protein alpha-subunit PiGPA1 in this organism. The expression of the P. infestans G-protein beta-subunit gene Pigpb1 was induced in nutrient-starved mycelium before the onset of sporangium formation. The gene was hardly expressed in mycelium incubated in rich growth medium. The introduction of additional copies of Pigpb1 into the genome led to silencing of the gene and resulted in transformants deficient in PiGPB1. These Pigpb1-silenced mutants formed very few asexual spores (sporangia) when cultured in rye sucrose medium and produced a denser mat of aerial mycelium than the wild type. Partially Pigpb1-silenced mutants showed intermediate phenotypes with regard to sporulation, and a relatively large number of their sporangia were malformed. The results show that PiGPB1 is important for vegetative growth and sporulation and, therefore, for the pathogenicity of this organism.

Biosorption of metal ions with Penicillium chrysogenum.

Abstract: Biosorption of metal ions with Penicillium chrysogenum mycelium is described in this article. Alkaline pretreatment was used to remove proteins and nucleic acids from cells, and this treatment increased the adsorption capacities, for Cr3+ from 18.6 mg g−1 to 27.2 mg g−1, for Ni2+ from 13.2 mg g−1 to 19.2 mg g−1, for Zn2+ from 6.8 mg g−1 to 24.5 mg g−1. The adsorption of metal ions was strongly pH dependent. The mycelium could beused for large-scale removal of Cr3+ from tannery wastewater. The results show that this inexpensive mycelium adsorbent has potential in industry because of its high adsorption capacity. The main chelating sites are amino groups (−NH2) of chitosan in the mycelium. A new model is established, which describes the relation of adsorption of metal ions on pH according to amino group chelating with metal ions and H+. The relative errors of simulation for Cu2+, Ni2+, Zn2+, and Cr3+ are 4.66%, 5.45%, 11.55%, and 1.69%, respectively.

Soil and rhizosphere microorganisms have the same Q(10) for respiration in a model system

Abstract: We compared the Q10 relationship for root-derived respiration (including respiration due to the root, external mycorrhizal mycelium and rhizosphere microorganisms) with that of mainly external ectomycorrhizal mycelium and that of bulk soil microorganisms without any roots present. This was studied in a microcosm consisting of an ectomycorrhizal Pinus muricata seedling growing in a sandy soil, and where roots were allow to colonize one soil compartment, mycorrhizal mycelium another compartment, and the last compartment consisted of root- and mycorrhiza-free soil. The respiration rate in the bulk soil compartment was 30 times lower than in the root compartment, while that in the mycorrhizal compartment was six times lower. There were no differences in Q10 (for 5-15°C) between the different compartments, indicating that there were no differences in the temperature relationship between root-associated and non-root-associated organisms. Thus, there are no indications that different Q10 values should be used for different soil organism, bulk soil or rhizosphere-associated microorganisms when modelling the effects of global climate change.