Nutritional influence on fungal colony growth and biomass distribution in response to toxic metals

This work examines nutritional influence on fungal colony growth and biomass distribution in response to toxic metals. In low-substrate solid medium, 0.1 mM Cd, Cu and Zn caused a decrease in radial expansion of both Trichoderma viride and Rhizopus arrhizus. However, as the amount of available carbon source (glucose) increased, the apparent toxicity of the metals decreased. These metals also affected the overall length of the fungal mycelium and branching patterns. In low-nutrient conditions, T. viride showed a decrease in overall mycelial length and number of branches in response to Cu, resulting in an extremely sparsely branched colony. Conversely, although Cd also reduced overall mycelial length to about one-third of the control length, the number of branches decreased only slightly which resulted in a highly branched colony with many aberrant features. Cu and Cd induced similar morphological changes in R. arrhizus. A large-scale mycelial-mapping technique showed that disruption of normal growth by Cu and Cd resulted in altered biomass distribution within the colony. When grown on metal-free low-substrate medium, T. viride showed an even distribution of biomass within the colony with some allocation to the periphery. However, Cu caused most of the biomass to be allocated to the colony periphery, while in the presence of Cd, most biomass was located at the interior of the colony. These results imply that such alterations of growth and resource allocation by Cu and Cd may influence success in locating nutrients as well as survival, and that these metals have individual and specific effects on the growing fungus.

Negative fungal chemotropism to toxic metals

Hyphal growth responses of Geotrichum candidum, Gliocladium roseum, Humicola grisea and Trichoderma viride to Cu and Cd were studied using a simple tessellated agar tile system. Negative chemotropic behaviour of hyphae, which included curling and growth away from metal-containing domains, occurred in all species and with both metals. Both toxic metal and sucrose concentrations in the medium modulated the magnitude of the negative chemotropic effects observed. In general, greater concentrations of metals led to a higher level of negative chemotropism in response to Cu and Cd, which could be reduced with increasing concentrations of sucrose in the medium. This suggests that resource availability affects the ability of these fungi to grow into metal-laden domains.

Changes to water repellence of soil caused by the growth of white-rot fungi: studies using a novel microcosm system

A microcosm system is described which permits assessment of the progressive growth of filamentous fungi through soil. We report on its application to measure the effects of Coriolus versicolor and Phanerochaete chrysosporium upon the sorptivity and water repellence of a mineral soil, measured using a miniature infiltration device. Both fungal species caused moderate sub-critical repellence. Since the pore structure was unaffected, the repellence was probably due to hydrophobic substances of fungal origin. This is the first report of changes in soil repellence caused by the growth of potential xenobiotic bioremediating fungi. The potential consequences are discussed.

Predicting relapse to substance abuse as a function of personality dimensions

The goal of the present study was to determine whether personality traits are related to return to heavy drinking or drug use following treatment for substance abuse. Personality characteristics of one hundred and eight patients residing on an inpatient substance abuse treatment program were assessed. Personality traits were examined using the 5-factor model of personality as measured by the NEO-Personality Inventory. These patients were then followed for 1 year after discharge from the treatment program. These substance abuse patients scored higher than the NEO-Personality Inventory normative sample on the personality domains of Neuroticism and Conscientiousness. A survival analysis showed that Neuroticism and Conscientiousness from the NEO-Personality Inventory were significant predictors of relapse. Odds ratios showed that the risk of relapsing was greatest for those patients who were both low in conscientiousness and high in neuroticism. The relevance of these two broad personality dimensions to the development and maintenance of addiction is discussed. Treatment implications for patients who possess these personality risk factors are outlined.

Broad-scale analysis of soil microbial community DNA from Upland grasslands

We have applied a broad-scale approach to the analysis of DNA extracted from soils which support characteristic grasslands at an upland site in the UK. To test for the degree of coherence between microbial and vascular communities, grasslands were characterised as 'improved', 'semi-improved', or 'unimproved', according to the degree of management they had received and consequent botanical composition. Microbial DNA was extracted directly from the grassland soils and analysed by three techniques: (i) thermal denaturation, which profiles the guanine and cytosine (G + C) base distribution within the community; (ii) cross hybridisation of the DNA which measures the degree of similarity between the samples; (iii) measurement of reassociation kinetics of denatured DNA, which provides a measure of the complexity of the DNA. Thermal denaturation revealed significant differences in the %G + C composition of the communities. DNA from the improved soil had the highest median %G + C value, whilst that from the unimproved soil had the lowest. The relative distribution of G + C bases also differed significantly between the samples from the three grasslands. Cross hybridisation of DNA from the different soils also indicated significant differences in the degree of similarity between the DNA from the grasslands, with unimproved showing 59% similarity to improved. Indices from the cross hybridisation assay suggested that, in terms of complexity, the samples ranked unimproved > semi-improved > improved. Reassociation kinetics supported this conclusion, but the rates of reassociation were such that less than 40% reassociation occurred over a 31-day period, thus preventing calculation of C(o)t1/2.

Aggregation and collapse of fungal wall vesicles in hyphal tips: a model for the origin of the Spitzenkörper

The intracellular origins of polarity and branch initiation in fungi centre upon a localization in the supply of fungal wall constituents to specific regions on the hyphal wall. Polarity is achieved and maintained by accumulating secretory vesicles, prior to incorporation into the wall, in the form of an apical body or Spitzenkörper. However, neither the mechanisms leading to this accumulation nor the initiation of branching, are as yet understood. We propose a mechanism, based on experimental evidence, which considers the mechanical properties of the cytoskeleton in order to explain these phenomena. Cytoskeletal viscoelastic forces are hypothesized to be responsible for biasing vesicles in their motion, and a mathematical model is derived to take these considerations into account. We find that, as a natural consequence of the assumed interactions between vesicles and cytoskeleton, wall vesicles aggregate in a localized region close to the tip apex. These results are used to interpret the origin of the Spitzenkörper. The model also shows that an aggregation peak can collapse and give rise to two new centres of aggregation coexisting near the tip. We interpret this as a mechanism for apical branching, in agreement with published observations. We also investigate the consequences and presumptive role of vesicle—cytoskeleton interactions in the migration of satellite Spitzenkörper. The results of this work strongly suggest that the formation of the Spitzenkörper and the series of dynamical events leading to hyphal branching arise as a consequence of the bias in vesicle motion resulting from interactions with the cytoskeleton.

Direct extraction of microbial community DNA from humified upland soils

This paper describes a protocol effective at extracting high yields of high-purity microbial community DNA from humified soils. DNA was extracted from soil by lysozyme, SDS and freeze-thaw lysis, precipitated and then subjected to a double caesium chloride density gradient centrifugation stage before concentrating and washing. Evaluation using three soils yielded up to 30 micrograms DNA g-1 dry soil, with absorbance ratios at 260:230 nm and 260:280 nm of 1.6-2.0. The DNA extracted from the three soils was digested by four restriction enzymes and a 16S rDNA eubacterial product was amplified by PCR. These tests indicated that the DNA obtained by the protocol was sufficiently pure for molecular biological analysis.

Broad-Scale Approaches to the Determination of Soil Microbial Community Structure: Application of the Community DNA Hybridization Technique

Broad-scale approaches seek to integrate information on whole microbial communities. It is widely recognized that culture techniques are too selective and unrepresentative to allow a realistic assessment of the overall structure of microbial communities. Techniques based on fatty acid or metabolic profiles determine the phenotypic composition of the community. Complementary information about the genotypic structure of soil microbial communities necessitates analysis of community DNA. To determine broad-scale differences in soil microbial community structure (i.e., differences at the whole community level, rather than specific differences in species composition), we have applied a community hybridization technique to determine the similarity and relative diversity of two samples by cross hybridization. In previous studies this assay failed with whole-soil community DNA. Usable hybridization signals were obtained using whole-soil DNA, in this study, by digesting the DNA with restriction enzymes before the labeling with a random-primer reaction. The community hybridization technique was tested using a graded series of microbial fractions, increasing in complexity, all isolated from the same soil sample. This demonstrated that single bacterial species and a mixture of cultivable bacteria were less complex and only 5% similar to whole-community DNA or bacteria directly extracted from the soil. Extracted bacterial and whole-community DNA were 75% similar to each other and equally complex. When DNA was extracted from four different agricultural soils, their similarities ranged from 35 to 75%. The potential usefulness of community hybridization applied to soil microbial communities is discussed.

EVIDENCE ON THE PATHWAYS OF PHOSPHORUS TRANSFER BETWEEN VESICULAR - ARBUSCULAR MYCORRHIZAL PLANTS

Mycorrhizal hyphae can link one root to another, and it is possible that phosphorus passes from plant to plant by these links. We present evidence on whether this 'direct transfer pathway' is the major route between mycorrhizal plants, or whether most phosphorus passes from the roots of one plant to the soil before being taken up by the other plant's roots or its associated mycorrhizal hyphae (the 'soil pool pathway'). The time-course of loss of ³² P from Lolium perenne L. roots to solution was measured after ³² P had been fed to leaves. Another experiment indicated that the amount of ³² P lost to soil was not influenced by mycorrhizal infection. ³² P was applied to soil in which Plantago lanceolata L., mycorrhizal or non-mycorrhizal, was growing and the time-course of uptake determined. Using these results, two alternative models, the 'direct transfer model' and the 'soil pool model', were used to predict the time-course and amount of ³² P transfer from L. perenne to P. lanceolata. The predictions were then compared with measured transfers between these two species presented here and in a previous paper. The soil pool model's predictions of both amount and time-course of transfer gave the better fit to observation. The evidence thus suggests that direct hyphal links between roots are not important in phosphorus transfer between these plants.

Effect of furosemide on urinary kallikrein excretion in patients with essential hypertension

The effect of furosemide on urinary kallikrein excretion was studied in 10 patients with essential hypertension and 9 normal volunteer subjects. After intravenous administration of furosemide and 2 hours of upright posture, urine volume (UV), urinary sodium (UNaV) and potassium (UKV) excretion, plasma renin activity (PRA), plasma aldosterone concentration (PAC) and urinary kallikrein markedly increased. However, the augmentation of urinary kallikrein in patients with essential hypertension (1.50 +/- 0.19 EU/2 hr) was less remarkable than that in normal subjects (2.33 +/- 0.24 EU/2 hr), although the same degrees of response were observed in PRA and PAC. The increments of UV, UNaV and UKV in patients with essential hypertension were also significantly lower than in normal subjects. Significant positive relations were found between urinary kallikrein and UV or UNaV in both hypertensive and normotensive groups, but there was no such correlation before fursemide administration. It is likely that diuresis and natriuresis induced by furosemide are somehow associated with an increase in urinary kallikrein excretion. Blunted response of urinary kallikrein in essential hypertension may suggest an abnormality in the renal kallikrein-kinin system in this disease.