In vitro saprotrophic basidiomycetes tolerance to pendimethalin

Pendimethalin is a dinitroaniline herbicide classified among the persistent-bioaccumulative toxics. In this paper, the tolerance to this herbicide has been studied in isolates of basidiomycetes (10 species including 9 wood-rotting and 1 litter fungi), collected in different areas of the Campania region (South Italy). The isolates were grown on two different agar media, rich and poor for the presence/absence of dextrose and NH₄NO₃, and amended with 0, 100 and 500 ppm herbicide. The mycelial growth was recorded daily, and statistical analysis of fungal growth rates, determined via linear regression, allowed us to compare the hyphal extension of various macrofungi in presence of herbicide. These data represent the adaptation capacity of the fungal organisms to the peculiar environmental situation. In amended agar, all fungi exhibited a certain tolerance to pendimethalin and, normally, the fungal growth decreased with the increasing of pollutant concentration. Nevertheless, in some cases, the difference of ground reflected the different agar media. In fact, the growth of Agrocybe aegerita, in rich agar decreased with the increase of herbicide dose, while in poor agar it increased with the pollutant. Among the examined fungi, A. aegerita was the species which resulted the most tolerant to herbicide, showing growth to about 70% of the control to the highest concentrations of pollutant and for the two different agar media.Scientific relevance of the paperNo published report is available regarding pendimethalin herbicide biodegradation with basidiomycetes; therefore this work represented the first and preliminary investigation as regards. It's directed to determine the fungal tolerance to the pollutant.     

Influence of autoclaved saprotrophic fungal mycelia on proteolytic activity in ectomycorrhizal fungi

The production of proteolytic enzymes by several strains of ectomycorrhizal fungi i.e., Amanita muscaria (16-3), Laccaria laccata (9-12), L. laccata (9-1), Suillus bovinus (15-4), Suillus bovinus (15-3), Suillus luteus (14-7) on mycelia of Trichoderma harzianum, Trichoderma virens and Mucor hiemalis and sodium caseinate, yeast extract was evaluated. The strains of A. muscaria (16-3) and L. laccata (9-12) were characterized by the highest activity of the acidic and neutral proteases. Taking the mycelia of saprotrophic fungi into consideration, the mycelium of M. hiemalis was the best inductor for proteolytic activity. The examined ectomycorrhizal fungi exhibited higher activity of acidic proteases than neutral ones on the mycelia of saprotrophic fungi, which may imply the participation of acidic proteases in nutrition.     

Boron and other elements in sporophores of ectomycorrhizal and saprotrophic fungi

Fungi are usually thought not to have a boron (B) requirement. It is not known if mycorrhizas take up B from low concentrations that are common in forest soils, as fungi might also immobilise B. Here, we studied the B concentrations in sporophores of 49 ectomycorrhizal and 10 saprotrophic fungi to assess whether B is translocated in mycelium or not. Additionally, P and metal concentrations were measured for comparison. Variability both within species and between species was very large, as the lowest measured B concentration was 0.01 mg kg⁻¹ in Amanita muscaria, and the highest was 280 mg kg⁻¹ in Paxillus involutus. There was no clear difference between saprotrophic and mycorrhizal fungi. The majority of species did not accumulate B at more than 0.01–3 mg kg⁻¹, but there were some species that consistently had median concentration values higher than 5–6 mg kg⁻¹ and much higher maximum values, particularly Paxillus involutus, Lactarius necator and several Russula species. Most species increased their B concentration in B fertilised plots, but there were exceptions, particularly Rozites caperatus and Lactarius camphoratus. Boron concentrations did not correlate with those of other elements. In conclusion, B is translocated in the mycelia of most of the studied species. The differences between species may be due to differences in their water use, or carbohydrates used in translocation. It remains to be studied, if B concentrations in mycorrhizas or mycelia in soil are in the same order of magnitude as the larger ones found here, and if this has any effects on the host plants.     

Effect of competitive interactions between ectomycorrhizal and saprotrophic fungi on Castanea sativa performance

In Northeast of Portugal, the macrofungal community associated to chestnut tree (Castanea sativa Mill.) is rich and diversified. Among fungal species, the ectomycorrhizal Pisolithus tinctorius and the saprotroph Hypholoma fasciculare are common in this habitat. The aim of the present work was to assess the effect of the interaction between both fungi on growth, nutritional status, and physiology of C. sativa seedlings. In pot experiments, C. sativa seedlings were inoculated with P. tinctorius and H. fasciculare individually or in combination. Inoculation with P. tinctorius stimulated the plant growth and resulted in increased foliar-N, foliar-P, and photosynthetic pigment contents. These effects were suppressed when H. fasciculare was simultaneously applied with P. tinctorius. This result could be related to the inhibition of ectomycorrhizal fungus root colonization as a result of antagonism or to the competition for nutrient sources. If chestnut seedlings have been previously inoculated with P. tinctorius, the subsequent inoculation of H. fasciculare 30 days later did not affect root colonization, and mycorrhization benefits were observed. This work confirms an antagonistic interaction between ectomycorrhizal and saprotrophic fungi with consequences on the ectomycorrhizal host physiology. Although P. tinctorius is effective in promoting growth of host trees by establishing mycorrhizae, in the presence of other fungi, it may not always be able to interact with host roots due to an inability to compete with certain fungi.     

The effect of tree-root exudates on the growth rate of ectomycorrhizal and saprotrophic fungi

Summary The object of this investigation was the promotion by root exudates of the growth rate of ectomycorrhizal fungi, discovered by Elias Melin in 1954. Eight ectomycorrhizal and ten non-mycorrhizal species were used as test fungi in the experiments. Different species often reacted differently: none of the eight isolated strains of Suillus luteus were promoted by pineroot exudate, whereas the growth rates of all seven strains of S. granulatus were increased. Among the other ectomycorrhizal species, S. variegatus, Laccaria bicolor, Pisolithus tinctorius and Thelephora terrestris, each represented by only one, two or three strains, usually reacted to the pine root exudate with an increased growth rate; S. bovinus and Paxillus involutus did not respond at all. Hitherto, studies of root-exudate effects on fungi have been based exclusively on the responses of ectomycorrhizal species; in the present study saprotrophic fungi were also used as test organisms. Seven out of ten saprotrophic species reacted with markedly accelerated growth when exposed to a pineroot exudate. Melin's assumption that a constituent of the root exudate, the M-factor, could replace the exudate growth-promoting activity was verified. By means of TLC fraction it was found that the fatty acid palmitic acid alone caused an increase in growth rate equal to that of the pine-root exudate. In line with previously published data by Gogala (1970), we also showed that certain cytokinins, especially isopentenylaminopurine, could act as substitutes for the total root exudate. Thus both palmitic acid and isopentenylaminopurine are able to function as M-factors equivalent to a root exudate.     

The effect of pH on the growth of saprotrophic and ectomycorrhizal ammonia fungi in vitro

Some saprotrophic and ectomycorrhizal fungi produce reproductive structures, preferably in slightly alkaline to neutral forest soil. This research examines the growth of these "ammonia fungi" in liquid medium at various pH values. In the first experiment, the capacity of six buffers was examined to select appropriate buffers for stabilizing pH in the neutral-to-alkaline range by culture of three species of the ammonia fungi in media initially adjusted to pH 7, 8 or 9. The highest buffering capacity was shown in 2-(N-morpholino) ethanesulfonic acid (MES) at pH 7, and N, N-bis (2-hydroxyethyl) glycine (Bicine) and N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) at pH 8 and 9. In the second experiment, the growth of 15 strains of both saprotrophic and ectomycorrhizal ammonia fungi was tested on the medium initially adjusted to pH 3, 4, 5, 6 or 7 with MES, or to pH 8 or 9 buffered with Bicine. Many of the saprotrophic species grew well at pH 7 or 8; the ectomycorrhizal species showed optimum growth at pH 5 or 6. The pH suitable for the in vitro growth of these fungi was correlated with the pH of forest soil where these fungi occur.     

Spore wall traits of ectomycorrhizal and saprotrophic agarics may mirror their distinct lifestyles

Although fungal spores are tiny compared to plant seeds, their morphological variability is enormous, which points toward selective forces. We investigated the frequency of ornamentation, thick walls, pigmentation and germ pores of spores of ectomycorrhizal and saprotrophic agarics. We hypothesised that these traits are shaped by the needs of these distinct lifestyles. All traits showed a strong phylogenetic signal; we therefore applied a phylogenetically informed statistical analysis. There was a significantly higher occurrence of spore ornamentation in ectomycorrhizal agarics and a higher occurrence of thick-walled spores in saprotrophic agarics. The interplay between thick-walled and pigmented spores and the occurrence of germ pores was only significant for saprotrophs. We argue that ornamentation is probably important to ectomycorrhizal fungi for dispersal by soil invertebrates, whereas pigmented thick walls and germ pores would be more advantageous for predominantly r-selected saprotrophic agarics exposed to hazardous environments and in need of quick germination success.     

Insights into nitrogen and carbon dynamics of ectomycorrhizal and saprotrophic fungi from isotopic evidence

The successful use of natural abundances of carbon (C) and nitrogen (N) isotopes in the study of ecosystem dynamics suggests that isotopic measurements could yield new insights into the role of fungi in nitrogen and carbon cycling. Sporocarps of mycorrhizal and saprotrophic fungi, vegetation, and soils were collected in young, deciduous-dominated sites and older, coniferous-dominated sites along a successional sequence at Glacier Bay National Park, Alaska. Mycorrhizal fungi had consistently higher δ¹⁵N and lower δ¹³C values than saprotrophic fungi. Foliar δ¹³C values were always isotopically depleted relative to both fungal types. Foliar δ¹⁵N values were usually, but not always, more depleted than those in saprotrophic fungi, and were consistently more depleted than in mycorrhizal fungi. We hypothesize that an apparent isotopic fractionation by mycorrhizal fungi during the transfer of nitrogen to plants may be attributed to enzymatic reactions within the fungi producing isotopically depleted amino acids, which are subsequently passed on to plant symbionts. An increasing difference between soil mineral nitrogen δ¹⁵N and foliar δ¹⁵N in later succession might therefore be a consequence of greater reliance on mycorrhizal symbionts for nitrogen supply under nitrogen-limited conditions. Carbon signatures of mycorrhizal fungi may be more enriched than those of foliage because the fungi use isotopically enriched photosynthate such as simple sugars, in contrast to the mixture of compounds present in leaves. In addition, some ¹³C fractionation may occur during transport processes from leaves to roots, and during fungal chitin biosynthesis. Stable isotopes have the potential to help clarify the role of fungi in ecosystem processes. Received: 7 January 1998 / Accepted: 9 November 1998     

Nitrogen availability affects saprotrophic basidiomycetes decomposing pine needles in a long term laboratory study

Fungi, especially basidiomycetous litter decomposers, are pivotal to the turnover of soil organic matter in forest soils. Many litter decomposing fungi have a well-developed capacity to translocate resources in their mycelia, a feature that may significantly affect carbon (C) and nitrogen (N) dynamics in decomposing litter. In an eight-month long laboratory study we investigated how the external availability of N affected the decomposition of Scots pine needles, fungal biomass production, N retention and N-mineralization by two litter decomposing fungi – Marasmius androsaceus and Mycena epipterygia. Glycine additions had a general, positive effect on fungal biomass production and increased accumulated needle mass loss after 8 months, suggesting that low N availability may limit fungal growth and activity in decomposing pine litter. Changes in the needle N pool reflected the dynamics of the fungal mycelium. During late decomposition stages, redistribution of mycelium and N out from the decomposed needles was observed for M. epipterygia, suggesting autophagous self degradation.     

The quantity and structure of the saprotrophic bacterial complex of the mycorhizosphere and hyphosphere of symbiotrophic basidiomycetes

The impact of symbiotrophic basidiomycetes on the abundance and structure of the soil saprotrophic bacterial complex of the mycorhizosphere and hyphosphere of 10 species of symbiotrophic basidiomycetes in natural conditions is studied. Compared to the reference soil, one can observe a significant increase in bacterial abundance in the mycirhizosphere and hyphosphere of basidiomycetes. The analysis of the taxonomical structure of bacterial complexes showed that Pseudomonas prevail in the mycorhyzosphere and Bacillus, in the rhizosphere and reference soil. Bacterial complexes of the hyphosphere and those in reference soil showed greater similarity to each other than either of them does to the mycorhizosphere. This fact implies the selective impact of the mycorhizosphere on soil bacteria.     

Charcoal filter paper improves the viability of cryopreserved filamentous ectomycorrhizal and saprotrophic Basidiomycota and Ascomycota

We assessed viability of 18 strains of filamentous ectomycorrhizal and saprotrophic basid-iomycetes and ascomycetes after cryopreservation with a novel technique based on charcoal filter paper strips (CFS). The results indicate that axenic fungal cultures grown on CFS recovered from freezing within a few days, even though none survived cryopreservation by the conventional straw method. Fungal growth on CFS was more vigorous, with morphological differentiations such as rhizomorphs and an increased amount of aerial mycelia compared to the unamended culture media. Accordingly CFS allows the cryopreservation of a wide range of rare and important ectomycorrhizal and saprotrophic fungi, which hitherto were difficult to revive from liquid nitrogen storage with the conventional and widely applied straw technique.     

Comparison of the thiol-dependent antioxidant systems in the ectomycorrhizal Laccaria bicolor and the saprotrophic Phanerochaete chrysosporium

Sequencing of the Laccaria bicolor and Phanerochaete chrysosporium genomes, together with the availability of many fungal genomes, allow careful comparison to be made of these two basidiomycetes, which possess a different way of life (either symbiotic or saprophytic), with other fungi. Central to the antioxidant systems are superoxide dismutases, catalases and thiol-dependent peroxidases (Tpx). The two reducing systems (thioredoxin (Trx) and glutathione/glutaredoxin (Grx)) are of particular importance against oxidative insults, both for detoxification, through the regeneration of thiol-peroxidases, and for developmental, physiological and signalling processes. Among those thiol-dependent antioxidant systems, special emphasis is given to the redoxin and methionine sulfoxide reductase (Msr) multigenic families. The genes coding for these enzymes were identified in the L. bicolor and P. chrysosporium genomes, were correctly annotated, and the gene content, organization and distribution were compared with other fungi. Expression of the Laccaria genes was also compiled from microarray data. A complete classification, based essentially on gene structure, on phylogenetic and sequence analysis, and on existing experimental data, was proposed. Comparison of the gene content of fungi from all phyla did not show huge differences for multigenic families in the reactive oxygen species (ROS) detoxification network, although some protein subgroups were absent in some fungi.