Correlation of mycelial growth rate with other phenotypic characters in evolved genotypes of Aspergillus nidulans

Fungal populations can adapt to their environment by the generation and fixation of spontaneous beneficial mutations. In this study we examined whether adaptation, measured as an increased mycelial growth rate, has correlated responses in the filamentous fungus Aspergillus nidulans with several other metric characters that could be important fitness components (colony forming units, germination speed, and biomass formation). Studying 60 populations that had evolved over 800 generations by experimental evolution, we find that only mycelial growth rate increased during adaptation to growing on solid medium. We further found that among evolved strains colony forming units is negatively correlated with mycelial growth rate and that colony forming units and biomass formation show a positive correlation. Our results give insight into changes in fungal phenotype as a result of adaptation and suggest that mycelial growth rate is the only available target of selection.     

Improvement of heavy metal biosorption by mycelial dead biomasses (Rhizopus arrhizus, Mucor miehei and Penicillium chrysogenum): pH control and cationic activation

Abstract: Fungal mycelial by-products from fermentation industries present a considerable affinity for soluble metal ions (e.g. Zn, Cd, Ni, Pb, Cr, Ag) and could be used in biosorption processes for purification of contaminated effluents. In this work the influence of pH on sorption parameters is characterized by measuring the isotherms of five heavy metals (Ni, Zn, Cd, Ag and Pb) with Rhizopus arrhizus biomass under pH-controlled conditions. The maximum sorption capacity for lead was observed at pH 7.0 (200 mg g^-l), while silver uptake was weakly affected. The stability of metal-biosorbent complexes is regularly enhanced by pH neutralization, except for lead. A transition in sorption mechanism was observed above pH 6.0. In addition, comparison of various industrial fungal biomasses ( R. arrhizus, Mucor miehei and Penicillium chrysogenum indicated important variations in zinc-binding and buffering properties (0.24, 0.08 and 0.05 mmol g^−l, respectively). Without control, the equilibrium pH (5.8, 3.9 and 4.0) is shown to be related to the initial calcium content of the biosorbent, pH neutralization during metal adsorption increases zinc sorption in all fungi (0.57, 0.52 and 0.33 mmol g-l) but an improvement was also obtained (0.34, 0.33 and 0.10 mmol g⁻¹) by calcium saturation of the biomass before heavy metal accumulation. Breakthrough curves of fixed bed biosorbent columns demonstrated the capacity of the biosorbent process to purify zinc and lead solutions in continuous-flow systems, and confirmed the necessity for cationic activation of the biosorbent before contact with the heavy-metal solution.     

Influence of humidity on production of pelleted fungal inoculum

One of the practical problems in scaling-up the production of fungal inocula for environmental applications is how to provide essential humidity for fungal growth. Pelleted solid substrate was used as a fungal biomass carrier. It was coated with alginate or agar hydrogels that contained mycelial fragments of the white-rot fungi Trametes versicolor or Irpex lacteus. To follow fungal growth and formation of mycelial coat over pelleted substrate, the fluorescein-diacetate hydrolysing activity (FDA) assay and visual inspection were used. Both fungi were able to overgrow the pelleted substrate in 5–6 days, at a relative humidity (RH) of 86.3% or higher. The enrichment of alginate hydrogel with nutrients or coating of pelleted substrate with more hydrophilic agar hydrogel enabled I. lacteus to overgrow the pellets at a lower RH of 83.6%. Fungal inocula produced at lower RH possessed lower final moisture contents and had greater mechanical strength. Conditioning of T. versicolor mycelial fragments, by a 3-h incubation in fresh growth medium, enhanced fungal growth over the pelleted substrate. A mathematical model was used to simulate and to explain moisture distribution in a hydrogel-coated pellet and the formation of mycelial coat, for various conditions of fungal inocula production.     

Heavy metals have different effects on mycelial morphology of Achlya bisexualis as determined by fractal geometry

The morphological response, as measured by changes to mycelial area, radial extension and border fractal dimension, of the oomycete Achlya bisexualis to Cu, Co, Hg, Zn and Cd at concentrations of between 0.05 and 3 mM is described. All of the metals decreased mycelial area and radial extension. Border fractal dimension increased in the presence of Cu, Co and Hg with individual hyphae extending out beyond the mycelial margin. In the presence of 3 mM Hg these hyphae displayed spiral growth. Zn and Cd had no effect on border fractal dimension. We suggest that all of the metals slow growth and that Cu, Co and Hg may also disrupt the relationship between tip growth and branching at the edge of the mycelium.     

Statistical analysis of structural and kinetic characteristics of fungal colony growth with Trichoderma viride PERS.: S.F. Gray

The mycelial colonies of Trichoderma viride were grown between two thin cellophane films for exact measurements. The results obtained testify to the fact that in a mature colony the average length of intercalary cells, the average number of intercalary cells in an internode and the average internode length are stable. At this stage of morphogenesis the mean internode length is shown to be equal to the product of the average intercalary cell length and the average number of intercalary cells in an internode. The coefficients of variation of the internode length and the number of intercalary cells in an internode are found to be equal. The length of an intercalary cell and duration of the doubling cycle of an apical cell of T. viride obey the law of Gamma distribution. According to our observations, the Gamma distribution is typical for the length and duration of the doubling cycle of any bacterial cells and cells of any multicellular organisms.     

Cellular automata simulations of fungal growth on solid substrates

Growth of filamentous fungi on the surface of cereal grains is a critical aspect of solid substrate fermentation (SSF). Numerous mathematical models have been developed to describe various aspects of fungal growth in SSF. These models consider hyphal geometry and nutrient availability as determinants of colony morphology and fungal physiological state. This work describes the use of cellular automata (CA) as an alternative method of modeling fungal growth. CA models reliant on a very limited set of rules or "knowledge base" display a rich array of behaviors that mimic fungal growth. By incorporating probablistic growth rules into CA models, colony characteristics such as biomass accumulation rate, colony radial growth rate, mycelial density and fungal differentiation are readily generated.     

被内生真菌侵染的禾草提取液对真菌的抑制作用

以带有与不带有Neotyphodium属内生真菌的醉马草Achnatherum inebrians、披碱草Elymus dahuricus和野大麦Hordeum brevisubulatum的草粉浸提液对细交链孢Alternaria alternata、根腐离蠕孢Bipolaris sorokiniana、燕麦镰孢Fusarium avenaceum和绿色木霉Trichoderma viride进行了抑菌活性研究。结果表明:披碱草、醉马草和野大麦草粉浸提液对细交链孢、根腐离蠕孢、燕麦镰孢和绿色木霉的菌落生长、孢子萌发率和芽管长度均有一定的抑制作用。而披碱草中的Neotyphodium可显著增强披碱草草粉浸提液对细交链孢、燕麦镰孢、绿色木霉菌落生长及对细交链孢和根腐离蠕孢孢子萌发及燕麦镰孢芽管长度的抑制作用;醉马草中的Neotyphodium显著增强了醉马草草粉浸提液对燕麦镰孢、绿色木霉菌落生长和芽管长度,以及细交链孢、根腐离蠕孢和燕麦镰孢孢子萌发的抑制作用;野大麦中的Neotyphodium显著增强了野大麦草粉浸提液对绿色木霉菌落生长、孢子萌发和芽管长度的抑制作用。     

Biosorption of cadmium(II), lead (II) and copper(II) with the filamentous fungus Phanerochaete chrysosporium

The biosorption from artificial wastewaters of heavy metals (Cd(II), Pb(II) and Cu(II)) onto the dry fungal biomass of Phanerochaete chryosporium was studied in the concentration range of 5-500 mg l(-1). The maximum absorption of different heavy metal ions on the fungal biomass was obtained at pH 6.0 and the biosorption equilibrium was established after about 6 h. The experimental biosorption data for Cd(II), Pb(II) and Cu(II) ions were in good agreement with those calculated by the Langmuir model.     

Cadmium removal capacities of filamentous soil fungi isolated from industrially polluted sediments,in La Plata (Argentina)

Aspergillus terreus, Cladosporium cladosporioides, Fusarium oxysporum, Gliocladium roseum, Penicillium spp., Talaromyces helicus and Trichoderma koningii were isolated from heavily polluted streams near an industrial area in La Plata, Argentina. The fungi were obtained from sediments with 0.25–0.50 mg Cd/l and they were isolated in cadmium-basal medium. They were then cultivated to evaluate their Cd detoxification abilities. The biomass developed in static assays represented 5–53% of the yield of stirred cultures, for the different fungal species, although the cadmium absorption were similar in both cases. These soil fungi represented 50% of the total isolates and their mycelial growth was conspicuous in these polluted sediments. Although bacteria have been mentioned as active microorganisms against heavy metals, the mycelial fungi were able to develop a significantly higher mass to sequestrate more metals. Thus, they could be used in remediation biotechnology to improve the Cd detoxification of chronically contaminated habitats.     

Stimulation of Mycelial Growth of Endothia parasitica by Heavy Metals

Of 16 metal cations tested on agar medium, only copper and iron stimulated mycelial growth of Endothia parasitica in relatively high concentrations. Similarly enhanced growth was produced in high (32%) glucose concentrations and also when the fungus was grown on cellophane placed over the agar surface. E. parasitica secreted large amounts of oxalate that precipitated primarily as calcium oxalate at the periphery of the fungal colony, causing an opaque halo in the medium. Mycelial growth was retarded greatly when calcium oxalate accumulated, but retardation was reversed by copper and iron salts that prevented accumulation of the calcium oxalate crystals. E. parasitica grew well on media containing copper oxalate and copper-calcium oxalate but grew poorly with calcium oxalate as the carbon source and was inhibited by sodium oxalate in the medium. The specificity by which only copper and iron salts stimulated mycelial growth suggested that the metal and oxalate ions interact to form specific oxalate complexes that reverse the inhibition of simple oxalate salts. This probably accounts for enhanced growth in the presence of otherwise toxic levels of metals and oxalate. The stimulation did not occur in liquid cultures.     

Production of fungal biomass protein using microfungi from winery wastewater treatment

This study was carried out to investigate the production of fungal biomass protein (FBP) in treatment of winery wastewater using microfungi. Three fungal strains, Trichoderma viride WEBL0702, Aspergillus niger WEBL0901 and Aspergillus oryzae WEBL0401, were selected in terms of microbial capability for FBP production and COD reduction. T. viride appeared to be the best strain for FBP production due to high productivity and less nitrogen requirement. More than 5 g/L of fungal biomass was produced in shake fermentation using T. viride without nitrogen addition, and by A. oryzae and A. niger with addition of 0.5-1.0 g/L (NH4)2SO4. The FBP production process corresponded to 84-90% COD reduction of winery wastewater. Fungal biomass contained approximately 36% protein produced by two Aspergillus strains, while biomass produced by T. viride consisted of 19.8% protein. Kinetic study indicated that maximum fungal cell growth could be achieved in 24h for T. viride and 48 h for A. oryzae and A. niger. Current results indicated that it could be feasible to develop a biotechnological treatment process integrated with FBP production from the winery waste streams.     

Comparison of biomass allocation in ectomycorrhizal and nonmycorrhizal Douglas fir seedlings of similar nutrition and overall size

Biomass allocation in 6-month-old ectomycorrhizal Douglas fir seedlings was compared to that in nonmycorrhizal seedlings of the same age, nutrient status and total biomass. Seedlings colonized by Rhizopogon vinicolor had the same distribution of biomass between roots, stems and needles, but only 56% of the total length of roots (including mycorrhizal branches) compared to nonmycorrhizal seedlings. Laccaria laccata had no effect on distribution of biomass or root length of seedlings. The results for Rhizopogon provide direct evidence that the process of ectomycorrhizal colonization can significantly affect plant biomass allocation by one or more mechanisms not directly related to altered nutrition or overall plant size.     

Effect of pollutants on the ergosterol content as indicator of fungal biomass

Ergosterol content was determined in 20 white-rot fungi isolates and the values ranged from 2380 to 13 060 μg g⁻¹ fungal biomass. Significant changes of ergosterol content according the physiological stage for Bjerkandera adusta 4312 and Coriolopsis gallica 8260 were found, showing the highest values during the stationary phase. However, in the case of Phanerochaete chrysosporium 3642, no changes were detected during growth. The effect of pollutants, such as heavy metals and fungicides, on the ergosterol content of C. gallica was determined. Heavy metals (Cu 80 ppm, Zn 50 ppm or Cd 10 ppm) and fungicides (thiram 3 ppm or pentachlorophenol 1.5 ppm) at concentrations that reduce the metabolic activity between 18% and 53% (pollutant-stressed cultures) did not affect the ergosterol content. Only the fungicide zineb (25 ppm) reduced significantly the ergosterol content in biomass basis. In soil experiments with Cu (80 ppm) or thiram (10 ppm) after 15 and 30 days of incubation, the ergosterol content in soil was linearly correlated to the fungal biomass C in both polluted and control soil cultures. The ergosterol content was independent of the presence or the absence of pollutants. Thus, these results indicate that ergosterol can be a useful indicator for fungal biomass in polluted soils, and can be applied for monitoring bioremediation processes.     

不同浓度壳聚糖对炭黑曲霉和硫色镰刀菌生长和发育的影响

【背景】壳聚糖是广泛存在于甲壳动物的一种多糖,具有广谱的抗真菌活性,但壳聚糖是否影响炭黑曲霉(Aspergillus carbonarius)和硫色镰刀菌(Fusarium sulphureum)生长和发育尚未见报道。【目的】明确不同浓度壳聚糖对A. carbonarius和F. sulphureum生长和发育的影响。【方法】通过在PDA培养基中添加不同浓度壳聚糖,测定两种真菌的菌落直径、生物量和菌丝干重,观察产孢量、孢子萌发和芽管长度,比较抑菌的差异。【结果】壳聚糖处理可显著改变两种真菌的菌落形态,处理浓度越高菌落皱缩和变形越明显;壳聚糖还可以有效抑制两种真菌的菌落生长、菌丝干重和菌丝生物量,抑制效果呈明显的浓度依赖,对F. sulphureum的抑制效果更好。壳聚糖可抑制两种真菌的产孢量、孢子萌发和芽管伸长,处理浓度越高抑制效果越好,对F. sulphureum的抑制效果更为明显。壳聚糖对A. carbonarius和F. sulphureum的EC₅₀值分别为0.12 mg/mL和0.075 mg/mL。【结论】壳聚糖可有效抑制A. carbonarius和F. sulphureum的生长发育,抑制效果呈浓度依赖,F. sulphureum对壳聚糖更为敏感。     

Effect of cadmium on growth of potentially pathogenic soil fungi

The effect of Cd on the mycelial growth of some potentially pathogenic soil fungi was investigated. Sixty-four strains from twenty-five fungal species were tested for their susceptibility to Cd. Final colony diameter, radial growth rate and final dry mass of mycelium (for Cd: 1–200 ppm) were measured. EcD₅₀ values were calculated from these parameters. The intra- and interspecific variability in the results obtained is presented. Among the keratinolytic fungal group, the genera Arthrographis, Trichophyton and Chrysosporium (including the Chrysosporium anamorph of Aphanoascus reticulisporus) were the most resistant to Cd. T. mentagrophytes was the most sensitive of all Trichophyton species tested. Among the nonkeratinolytic fungal group, the genera Pseudallescheria, Absida and Rhizopus were highly resistant to Cd. Strains of Aspergillus were more resistant to Cd than strains of Penicillium. Zygomycetes were more resistant to Cd than Ascomycetes with Fungi Imperfecti. Nonkeratinolytic fungi showed higher resistance to Cd than keratinolytic fungi. The two last differences resulted from the extremely high EcD₅₀ values for R. oryzae and A. corymbifera. This revised version was published online in June 2006 with corrections to the Cover Date.     

Production of lactic acid and fungal biomass by Rhizopus fungi from food processing waste streams

This study proposed a novel waste utilization bioprocess for production of lactic acid and fungal biomass from waste streams by fungal species of Rhizopus arrhizus 36017 and R. oryzae 2062. The lactic acid and fungal biomass were produced in a single-stage simultaneous saccharification and fermentation process using potato, corn, wheat and pineapple waste streams as production media. R. arrhizus 36017 gave a high lactic acid yield up to 0.94-0.97 g/g of starch or sugars associated with 4-5 g/l of fungal biomass produced, while 17-19 g/l fungal biomass with a lactic acid yield of 0.65-0.76 g/g was produced by the R. oryzae 2062 in 36-48 h fermentation. Supplementation of 2 g/l of ammonium sulfate, yeast extract and peptone stimulated an increase in 8-15% lactic acid yield and 10-20% fungal biomass.     

Growth, root and leaf structure, and biomass allocation in Leucanthemum vulgare Lam. (Asteraceae) as influenced by heavy-metal-containing slag

Effects of heavy metal contamination on growth, leaf turnover, biomass allocation and leaf and root structure of Leucanthemum vulgare Lam. were investigated. Plants were grown in two outdoor experiments, for 5 weeks or for 3 months, respectively, on sand with different additions of slag containing elevated levels of heavy metals, especially Cu and Ni. In the 3-month experiment nutrients were provided as composted manure, in the 5-week experiment as a solution. Slag contamination reduced plant growth, biomass allocation to roots, specific root length and specific leaf area, while root tissue density and leaf dry matter content increased. Fine root diameter increased, whereas coarse root diameters showed a non-significant decreasing trend. Toxicity of slag was lower in the 3-month experiment, probably due to organic matter in the substrate. We conclude that heavy metals in the soil around Cu–Ni smelters may, besides directly reducing growth of the plants, increase their susceptibility to other stresses such as drought, by reducing the root length to leaf area ratio. Fine and coarse roots show distinct responses, indicating that different root diameter classes should be regarded separately to fully understand stress responses of root systems.     

Fungal biomass associated with decaying leaf litter in a stream

Summary Fungal biomass, measured as ergosterol content, was determined on alder leaf litter incubated during autumn in a softwater Pyrenean stream. The ergosterol content of the leaf litter increased rapidly to a maximum of 462 μg/g detrital dry mass. Ergosterol contents of aquatic Hyphomycetes grown in shake culture were typically ≤5 mg/g mycelial dry mass. Using the corresponding ergosterol-to-biomass conversion factor of 200, peak fungal mass accounted for 9.2% of total system mass, or 10.2% of leaf dry mass. For the period of highest activity (incubation days 7–28), net fungal production on leaf litter was estimated as 2.3 mg d⁻¹ g⁻¹ leaf mass. A conservative estimate of the growth efficiency for the same period was 105 mg mycelial mass per gram leaf mass degraded, assuming that non-leaf organic matter did not constitute an important carbon source supporting fungal production.     

Quantifying dynamic resource allocation illuminates foraging strategy in Phanerochaete velutina

Saprotrophic woodland fungi forage for mineral nutrients and woody resources by extension of a mycelial network across the forest floor. Different species explore at different rates and establish networks with qualitatively differing architecture. However, detailed understanding of fungal foraging behaviour has been hampered by the absence of tools to quantify resource allocation and growth accurately and non-invasively. To solve this problem, we have used photon-counting scintillation imaging (PCSI) to map and quantify nutrient allocation and localised growth simultaneously in heterogeneous resource environments. We show that colonies spontaneously shift to an asymmetric growth pattern, even in the absence of added resources, often with a distinct transition between the two growth phases. However, the extent of polarisation was much more pronounced and focussed in the presence of an additional cellulose resource. In this case, there was highly localised growth, often at the expense of growth elsewhere in the colony, and marked accumulation of ¹⁴C-AIB in the sector of the colony with the added resource. The magnitude of the response was greatest when resource was added around the time of the endogenous developmental transition. The focussed response required a metabolisable resource, as only limited changes were seen with glass fibre discs used to mimic the osmotic and thigmotropic stimuli upon resource addition. Overall the behaviour is consistent with an adaptive foraging strategy, both to exploit new resources and also to redirect subsequent foraging effort to this region, presumably with an expectation that the probability of finding additional resources is increased.