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ABSTRACT. Soil filamentous fungi from Ny-Alesund, Spitsbergen, were studied. A total of 30 fungal isolates were identified by morpho-taxonomy, and the identity of some morpho-taxonomically complex isolates was authenticated by [...]

Abstract: Roots encounter a plethora of microorganisms in the soil environment that are either deleterious, neutral, or beneficial to plant growth. Root endophytic fungi are ubiquitous. These include dark septate [...]

The effects of long-term elevated atmospheric CO2 on root production and microbial activity, biomass, and diversity in a chaparral ecosystem in southern California are examined. The fungal biomass is correlated with cellulose and amylase activities, which indicates that fungi are responsible for the stimulation of enzymatic activity in the free air CO2 enrichment (FACE) treatment.

The effects of artificial defoliation of pines in a mixed pine-spruce forest on the composition of the fungal community in a forest soil is determined using denaturing gradient gel electrophoresis (DGGE) and Biolog filamentous-fungus plates. The results indicate that combined genetic physiological assessments of the soil fungal community are needed to accurately access the effect of disturbance on indigenous microbial systems.

Soil microbes may affect the way exotic invasive plants interact with native neighbors. We investigated the effects of soil fungi on interactions between the invasive weed Centaurea maculosa (spotted knapweed) and six species native to the intermountain prairies of the northwestern United States. We also compared the effect of C. maculosa on the composition of the soil microbial community to that of the native species. In the field, fungicide (Benomyl) reduced AM mycorrhizal colonization of C. maculosa roots by >80%. Fungicide did not significantly reduce non-AM fungi. When grown alone, the biomass of C. maculosa was not affected by the fungicide application. However, depending on the combination of native competitor and fungicide, C. maculosa biomass varied from 10-fold decreases to 1.9-fold increases. In untreated soils, C. maculosa grew larger in the presence of Festuca idahoensis or Koeleria cristata than when alone. When fungicide was applied these positive effects of Festuca and Koeleria on C. maculosa did not occur. A third native grass, Pseudoroegneria spicata, had much stronger competitive effects on C. maculosa than Festuca or Koeleria, and fungicide reduced the competitive effects of Pseudoroegneria. Fungicide increased Centaurea biomass when competing with the forb Gallardia aristata. However, fungicide did not affect the way two other forbs; Achillea millefolium and Linum lewisii, interacted with C. maculosa. Rhizosphere microbial communities in the root zones of the three native bunchgrass species differed from that of C. maculosa. However, despite the strong effects of soil fungi in field interactions and differences in microbial community composition, soil biota from different plant rhizospheres did not affect the growth of C. maculosa in the absence of native competitors in greenhouse experiments. Our results suggest that successful invasions by exotic plant species can be affected by complex and often beneficial effects of local soil microbial communities. These effects were not manifest as simple direct effects, but become apparent only when native plants, invasive plants, and soil microbial communities were interacting at the same time. Key words: Centaurea; communities; competition; fungi; invasive exotics; mutualism; mycorrhizae; phospholipid fatty acids (PLFA); rhizosphere; soil microbes; spotted knapweed; weeds.

Cell wall-degrading enzymes of Trichoderma atroviride strain P1 are regulated by other substances besides carbon catabolites and fungal cell wall components. This fungus occurs in soil and some strains have antifungal properties.

The ectomycorrhizal fungi Dermocybe phoenecius and Inocybe sp. were found in thermal soils in Yellowstone National park but not in forest soils. These fungi could therefore be used to bioremediate acidic soil such as that found in mine tailings and coal spoils.

Pseudomonas putida that has been genetically modified to produce the antifungal compound phenazine-1-carboxylic acid can suppress fungal growth in soil rhizospheres. The Antifungal compound is produced by the phz gene from Pseudomonas fluorescens 2-79.

Data are presented which indicate that the hydroxamate iron chelator produced by Agrobacterium rhizogenes K84 may be identical to a previously described antimicrobial substance called ALS84. Many bacterial and fungal siderophores have antimicrobial activity.

Researchers have discovered a bacterium belonging to the Cytophaga-Flexibacter-Bacteroides phylogroup that is associated with the mycelium of the mycorrhizal fungus Tuber borchii Vittad. This bacterium has not been previously described.

Most ectomycorrhizal fungi can develop a relationship with different host plants. Of 28 ectomycorrhizal fungal species isolated from a forest in Yellowstone National Park, less than 5% of the fungi were specific to a particular host plant.

Anastomosis between hyphae from individually germinated spores of arbuscular mycorrhizal (AM) fungi have been monitored through use of time-lapse video-enhanced microscopy, both light- and epifluorescence-based. Anastomosis formation and nuclear and protoplasmic exchange were observed when hyphae originated from the same spore and from different spores of the same isolate of three Glomus species. It appears that genetic exchange may take place through intermingling of nuclei in anastomosis formation.

Research was conducted to examine distribution and activity patterns of Pseudomonas fluorescens in the root environment of barley plants. Results show that at normal soil moisture levels the bacteria formed microcolonies around the plant roots with differing viability and activity characteristics.

The antagonistic fungus Trichoderma harzianum does not affect growth and phosphorus uptake by the external mycelium of Glomus intraradices. In contrast, it is G intraradices which adversely affects T. harzianum. These were gleaned from an investigation of the interaction between G intraradices and T harzianum in soil and how such interaction affects growth and activity. Direct interference from roots was avoided with the use of a compartmented growth system with root-free soil compartments. Results showed that the presence of T harzianum does not reduce living hyphal biomass andhyphal (super 33)P transport but the presence of external mycelium of G intraradices hindered T harzianum population development and beta-glucuronidase activity.

There are significant differences in production of aflatoxin B1 and cyclopiazonic acid (CPA) by the L-strain soil isolates from Aspergillus flavus among regions along a transect extending from eastern New Mexico through Georgia to eastern Virginia. This was gleaned from an examination of soil isolates from A flavus to determine whether A flavus populations from different geographic regions differ in production of aflatoxin B1 and CPA.Results affirm the geographic differences found in production of aflatoxin B1 by A flavus in surveys conducted in Japan and in the US' cotton-growing areas.

Hypotheses revisited Nitrogen emissions to the atmosphere due to human activity remain elevated in industrialized regions of the world and are accelerating in many developing regions (Galloway 1995). Although the [...]

A study was conducted to analyze the genetic and biochemical preparation of a soil isolate of Burkholderia cepacia associated with its production of a unique antibiotic active against a variety of soil fungi. The antibiotic was a new lipopeptide related with the cell membrane. Samples to be assayed were prepared in a vacuum centrifuge while positive-mode fast atom bombardment mass spectrometry was carried out with the JEOL SX/SX 102A tandem mass spectrometer.

Although Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young) is widespread in the western USA, reestablishment of this native shrub on disturbed lands by direct seeding is problematic. A number of theories have been proposed to explain this difficulty. Included are the hypotheses that seedlings are unable to obtain adequate moisture and are handicapped by reduced levels of mycorrhizae in perturbed soils. We conducted a greenhouse study to examine the influence of vesicular arbuscular mycorrhizae (VAM) and seedling age on soil moisture stress tolerance of Wyoming big sagebrush seedlings. Results demonstrated greater survival of mycorrhizal seedlings than nonmycorrhizal seedlings as soil dried down past soil water potential values of -2.5 MPa to as dry as -3.8 MPa. For all different aged seedlings tested (30, 45, 60, 90, 120, 150 d), the degree of soil dryness resulting in death of mycorrhizal seedlings was significantly greater (P < 0.01) than that causing death of nonmycorrhizal seedlings. Analysis of variance indicated a significant interaction of seedling age and mycorrhizae on moisture stress tolerance. Experimental data suggest that as sagebrush seedlings age, the beneficial influence of arbuscular mycorrhizae on soil water stress tolerance increases.

Incorporating chipped wood from twigs (CWT) into the soil is an effective and fast way to stimulate bacterial, fungal and actinomycetal populations and to improve soil quality. The microbial stimulating ability of CWT is due to its cellulose content. The CWT's most significant and long-lasting effect was on fungal population with increases of up to 24-fold. The fungi stimulation by CWT appears to be responsible for the increase in the soil's wet-aggregate stability.

This study was designed to examine the role of vesicular-arbuscular mycorrhizae (VAM) and microsites on the growth of pioneer species. Flat, rill, near-rock, and dead lupine microsites were created in plots in barren areas of the Pumice Plain of Mount St. Helens. VAM propagules were added to the soil in half of the plots. Six pioneer species were planted into both VAM and non-VAM inoculated microsites. Plants in dead lupine microsites were greater in biomass than those in flat, rill, and near-rock microsites. Significant effects of VAM on plant biomass did not occur. Microsites continue to be important to plant colonization on the Pumice Plain, but VAM do not yet appear to play an important role. This may be due to limited nutrient availability and the facultatively mycotrophic nature of the colonizing plant species. It is unlikely that VAM play an important role in successional processes in newly emplaced nutrient-poor surfaces. Key words: lupine; microsites; Mount St. Helens; pioneer species; vesicular-arbuscular mycorrhizae; volcanoes.

A study was conducted on a rhizosphere isolate obtained from field-grown sugar beet, Stenotrophomonas maltophilia W81. The findings indicate that the ability of S maltophilia W81 to protect sugar beet from Pythium-mediated damping-off can be attributed to the production of a extracellular protease. The results also suggest that protease production may be useful in the construction of novel, genetically modified biocontrol inoculants.

1 Rhizosphere populations of free-living bacteria and fungi associated with particular co-occurring plants were characterized to examine patterns of microbial community structure in natural plant communities. Soil was collected from three co-occurring perennial plant pairs in an undisturbed field at Smoot Hill Biological Reserve, Pullman, Washington, USA, and from three different perennial plant pairs in an old-field community in Durham, North Carolina, USA. 2 Bacteria and fungi isolated from these rhizosphere soils were tested for their ability to utilize various carbon substrates, their tolerance of antibiotics, and their sensitivity to osmotic and metal stresses. Multivariate analysis of physiological characteristics showed that rhizosphere microbial populations associated with particular plant pairs were significantly different from one another. Plots of the first and second linear discriminative functions from a canonical analysis showed clustering of bacterial and fungal physiological characteristics according to plant pair. 3 Replicates of particular plant pairs were planted into both greenhouse and field experiments to test whether bacterial community structure was influenced by different plant pairs. Repeated profile analyses showed that initially similar rhizosphere bacterial communities differentiated in both the greenhouse and field experiments and that these differences were associated with plant pairs. 4 The data suggest structure in rhizosphere populations of free-living bacteria and fungi can be influenced by plants. They provide a first step in understanding the link between the structure and function of natural plant and microbial communities. Keywords: multivariate analysis of variance, perennial grasses, soil bacteria and fungi, substrate utilization assay

Microbiological research using fatty acid signature 16:1omega5 analysis shows that soil phosphorus levels affect the distribution of the arbuscular mycorrhizal fungus in root systems. Neutral lipid fatty acid 16:1omega5 levels are roughly equivalent to spore numbers. Phospholipid fatty acid 16:1omega5 levels equate to hyphal length. Evidence suggests that storage structures use less carbon at high phosphate levels.

A study was conducted to qualitatively and quantitatively determine the mycorrhizal status and spatial/temporal variations in propagules of arbuscular mycorrhizal fungi (AMF). A semiarid ecosystem in southeastern Spain was chosen as the study site. Results indicated that the indigenous inoculum levels of AMF are not enough to support a broad revegetation program when an additional mycorrhizal inoculum is unavailable.

1 A glasshouse study was conducted to determine the effects of three variables (sand burial, arbuscular mycorrhizal (AM) fungi and endoparasitic root nematodes) and their interactions on the growth of Ammophila breviligulata Fern. seedlings. We tested the hypotheses that burial allows A. breviligulata to escape from plant-parasitic nematodes and that inoculation with AM fungi is another factor capable of ameliorating the detrimental effects of nematodes to the plant. 2 Seedlings were grown in [Gamma]-irradiated, sterile sand and treated in a factorial manner with 5 cm of sand burial, rhizosphere inoculation with AM fungi and rhizosphere inoculation with plant-parasitic nematodes. Both AM fungi and nematodes originated from field populations of A. breviligulata. 3 Burial stimulated the foliar growth rate of plants in all combinations except when plants had been infected with nematodes prior to burial. The root dry weight was significantly reduced when nematode infected plants were buried. AM fungi improved the foliar growth rate and root dry weight of buried plants infected with nematodes. We therefore rejected the hypothesis that burial allows escape from plant-parasitic nematodes. 4 AM fungi are capable of reducing plant susceptibility to plant-parasitic nematodes and must be considered when assessing the influence of plant-parasites on the vigour of natural A. breviligulata populations. Keywords: arbuscular mycorrhizal fungi, burial in sand, plant vigour, plant-parasitic nematodes, sand dunes

A research on the effect of peanut and corn cultivation on the population of Aspergillus flavus and Aspergillus parasiticus in three fields during three different years in southwestern Georgia shows that with enough rainfall during the growing season, the soil populations of A. parasiticus and A. flavus remains constant. A. flavus develops rapidly after harvesting when drought has afflicted the corn crop, but peanut seeds are in general more susceptible to these fungi.

The increase in tiller numbers, leaf stage, shoot and root dry matter and P, Zn and Cu uptake by the wheat plants grown on eroded, infertile soils, from three landscape positions in eastern Washington, shows that the incubation of vesicular-arbuscular mycorrhizal (VAM) fungi improves the nutrient uptake of plants in infertile soils. This indicates that VAM innoculation can be beneficial to wheat production in eroded soils.

Previous research has shown the effectiveness of methyl bromide soil fumigation in eliminating soil pathogens and other undesirable soil organisms. However, the method often kills desirable organisms such as vesicular arbuscular mycorrhizal fungi (VAMF). The effect of methyl bromide fumigation on plant accumulation of 14 elements is studied while plant colonization by VAMF after fumigation is analyzed.

Randomly primed PCR and tRNA-PCR using consensus primers help evaluate the genetic variability among Paecilomyces lilacinus isolates from soil, nematodes or insects. The genotypes exhibit a high degree of variability. Cluster or multivariate analysis does not reveal any well-defined phenetic groups or relationship with the host or geographical origin. A subsample of 12 Paecilomyces lilacinus isolates, two Paecilomyces fumosoroseus isolates, one Paecilomyces amoenoroseus isolate and three Paecilomyces fasinosus isolates subjected to PCR with four consensus tRNA gene primer pairs exhibits the presence of a monophyletic group that contained most of the Paecilomyces lilacinus isolates.

Capsella bursa-pastoris (L.) Medikus (Brassicaceae) was sampled in lawn and waste habitats from three Ohio sites in April, May, June and July 1992. Vesicular-arbuscular mycorrhizal (VAM) fungi colonization was determined for 30 individuals per date/site/habitat by examining root subsamples for the presence of internal fungal structures. The mean percent colonization of VAM fungi in lawn habitats (35%) was over twice that in waste habitats (15%). This suggests that the dense mycorrhizal matrix offered by the lawn habitat influences the development of VAM in this typically nonmycorrhizal species. No arbuscules were observed in the 7200 root segments examined; however, internal hyphae, vesicles and chlamydospores were common. These results suggest that the surrounding community's root matrix can influence colonization of VAM fungi in roots of typically nonmycorrhizal plants.

Biochemical and immunological studies reveal that U. reesii is the closest relative of C. immitis among the onygenaceae. The identical positive tube precipitin antibody reaction in the immuno diffusion assays. The equal levels of glucanase activity of U. reesii and C. immitis provide further evidence of relatedness. The amino acid sequence data reveal that C. immitis and U. reesii form a monophyletic pair.

Studies on Trichoderma harzianum isolates from mushroom compost reveal the presence of three major groups, with the group 2 isolates, which are aggressive colonizers, being the dominant group. The random amplified polymorphic DNA analysis confirms the three groups based on restriction fragment length polymorphism analysis. There are three distinct rDNA internal transcribed spacers (ITS) designated ITS 1, 2 and 3.

An analysis of Dominican amber showed the presence of large vegetative mycelia common to the genus Nocardia. The mycelium are presumed to have grown in the resin, suggesting an anaerobic or facultative life form similar to the nocardioform actinomycetes Nocardia or Pseudonocardia. Sporomorphs with spiral surface structures were also detected in the amber. The presence of soil particles correlates with Nocardia being a soil organism and suggests a similar habitat for Nocardioformis. Further analysis shows that the actinomycete thrived in an organically rich terrestrial habitat.

The induction of the cellulase system of Trichoderma reesei was investigated. The results of chromatographic and electrophoretic separations, and recombination experiments, showed that the multienzyme system induced by scoured cotton was more effective compared with that by Solka Floc, and suggested that an alkaline endoglucanase was important in the degradation of crystalline cellulose.

The thermophilic fungus Scytalidium thermophilum had a salutary effect on mycelial growth of Agaricus bisporus. The growth enhancement was apparently due to carbon dioxide production by S. thermophilum, rather than any intrinsic quality of this fungus. The higher growth rate was the effect of a higher rate of hyphal extension and does not seem to be related to the rate of biomass increase of the mycelium.

The induction of the lysyl-tRNA synthetase system or LysU, inducible lysine decarboxylase and inducible arginine decarboxylase is temperature-dependent in Escherichia coli when grown in broth to a pH of 5.5 or lower. Coordinate induction of these enzymes, as well as other peptides such as the heat-shock peptides HtpG and HtpM, suggest that these make up part of a stimulon which is induced in a temperature-dependent manner at low pH.

A diverse population of vesicular-arbuscular mycorrhizal fungi (VAMF) was found in the test system. Root length and VAMF colonization correlated positively at all soil depths. VAMF colonization and activity was affected by crop rotation. Colonization and total root length of soybean and sorghum was decreased when soybean was grown preceding the test crop. Colonization of the test crops was greatest in unfertilized soil. The use of manure as fertilizer reduced colonization and arbuscule formation but produced the greatest yields. An active VAMF-plant association was shown by the large number of arbuscules associated with colonization.

The role of lectins in the interaction between Trichoderma spp. and soil-borne plant pathogenic fungi was examined. In the system developed, nylon fibers simulated fungal hyphae. The nylon fibers were treated with either concanavalin A or LSR, a lectin produced by Sclerotium rolfsii. Treatment of nylon fibers with the lectins resulted in apparent recognition by Trichderma harzianum, which coiled and formed hooks around treated fibers. Therefore, treatment of nylon fibers with lectins can simulate living hyphae and change the behavior and morphogenesis of filamentous fungi.

Water repellence in soils may occur as a result of direct drilling practices. Soil samples were subjected to slow drying under conditions of high humidity to study the factors contributing to seasonal water repellence. Soil samples were treated with a dilute thymol solution in place of deionized water, after which water repellence and fungal growth were recorded. Water repellence inhibited infiltration when water was applied with a 40 mm suction. The study indicates that direct drilling favors microbial growth and water repellence.

Microbiological research shows that the soil-inhabiting microorganism Fusarium proliferatum can degrade lignin. Synthetic, natural and carbon-14 labelled lignin was used in comparative studies to ascertain degrading activity. Mineralization production occurs during primary metabolism. Residual products are also produced. The production process involves both depolymerization and polymerization activity.

Transformed root cultures of three nonmycotrophic and one mycotrophic plant species stimulated germination and hyphal growth of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus etunicatum in a gel medium. Roots of the mycotrophic species supported continued hyphal exploration after 3 to 4 weeks and encouraged appressoria formation by Glomus etunicatum. The carrot roots gave rise to spatial information perceived by the fungus, but the non mycotrophic roots did not.

A greenhouse trial was used to evaluate the impact of transgenic white spruce [Picea glauca (Moench) Voss] containing the endochitinase gene (ech42) on soil fungal biomass and on the ectendomycorrhizal fungi Wilcoxina spp. The results indicated that the higher level of chitinolytic activity in root exudates and root tissues from ech42-transformed lines does not alter the soil fungal biomass or the development of ectendomycorrhizal symbiosis involving Wilcoxina spp.

Exploratory research on the presence of actinomycetes in surface-sterilized roots was performed. There were 28 plant species used, and the roots of all species were found to harbor actinomyces. Most of the 499 actinomycetes isolated were Streptococcus strains. Streptomycete hyphal growth inside the cortical cells was revealed by scanning electron microscopy. These growths were surrounded or partially coated by a mucilaginous layer.

Horizontal transfer of the Tn916 gene, which includes a gene that codes for tetracycline resistance in soil populations, was investigated using Bacillus subtilis as the vector. The percentage of tetracycline-resistant organisms in the experimental soils significantly increased, reaching up to 60% after the fourth day. All recipients were identified as actinomycetes, including three genera, namely, Streptomyces, Actinomadura and Kineosporia. These actinomycetes have not previously been reported to be Tn916 recipients.

Studies have shown that two model plant species, Arabidopsis thaliana and Medicago truncatula, have maintained resident soil fungal populations, but are unable to maintain nonresident soil fungal populations. Root exudates are established as a mechanism through which a plant is able to regulate soil fungal community composition.