Filamentous Soil Fungus Research Articles

First Report of Trichoderma afroharzianum Causing Seed Rot on Maize in Italy.

Maize (Zea mays L.) is a cereal crop of great economic importance in Italy; production is currently of 60,602,320 t, covering 588,597 ha (ISTAT 2021). Trichoderma species are widespread filamentous fungi in soil, well known and studied as biological control agents (Vinale et al., 2008). Seeds of a yellow grain hybrid (class FAO 700, 132 days) were collected in September 2020 from an experimental field located in Carmagnola (TO, Italy: GPS: 44°53'11.0"N 7°40'60.0"E) and tested with blotter test (Warham et al., 1996) to assess their phytosanitary condition. Over the 400 seeds tested, more than 50% showed rotting and development of green mycelium typical of the genus Trichoderma. Due to the high and unexpected percentage of decaying kernels, ten colonies were identified by morphological and molecular methods. Single conidia colonies of one Trichoderma (T5.1) strain were cultured on Potato Dextrose Agar (PDA) for pathogenicity tests, and on PDA and Synthetic Nutrient-Poor Agar (SNA) for morphological and molecular identification. The colonies grown on PDA and SNA showed green, abundant, cottony, and radiating aerial mycelium, and yellow pigmentation on the reverse. Colony radius after 72 h at 30°C was of 60-65 mm on PDA and of 50-55 mm on SNA. The isolates produced one cell conidia 2.8 - 3.8 µm long and 2.1 - 3.6 µm wide (n=50) on SNA. Conidiophores and phialides were lageniform to ampulliform and measured 4.5 - 9.7 µm long and 1.6 - 3.6 µm wide (n=50); the base measure 1.5 - 2.9 µm wide and the supporting cell 1.4 - 2.8 µm wide (n=50). The identity of one single-conidia strain was confirmed by sequence comparison of the internal transcribed spacer (ITS), the translation elongation factor-1α (tef-1α), and RNA polymerase II subunit (rpb2) gene fragments (Oskiera et al., 2015). BLASTn searches of GenBank using ITS (OL691534) the partial tef-1α (OL743117) and rpb2 (OL743116) sequences of the representative isolate T5.1, revealed 100% identity for rpb2 to T. afroharzianum TRS835 (KP009149) and 100% identity for tef-1α to T. afroharzianum Z19 (KR911897). Pathogenicity tests were carried out by suspending conidia from a 14-days old culture on PDA in sterile H2O to 1×106 CFU/ml. Twenty-five seeds were sown in pots filled with a steamed mix of white peat and perlite, 80:20 v/v, and maintained at 23°C under a seasonal day/night light cycle. Twenty primary ears were inoculated, by injection into the silk channel, with 1 ml of a conidial suspension of strain T5.1 seven days after silk channel emergence (BBCH 65) (Pfordt et al., 2020). Ears were removed four weeks after inoculation and disease severity, reaching up to 75% of the kernels of the twenty cobs, was assessed visually according to the EPPO guidelines (EPPO, 2015). Five control cobs, inoculated with 1 ml of sterile distilled water were healthy. T. afroharzianum was reisolated from kernels showing a green mold developing on their surface and identified by resequencing of tef-1α gene. T. afroharzianum has been already reported on maize in Germany and France as causal agent of ear rot of maize (Pfordt et al. 2020). Although several species of Trichoderma are known to be beneficial microorganisms, our results support other findings that report Trichoderma spp. causing ear rot on maize in tropical and subtropical areas of the world (Munkvold and White, 2016). The potential production of mycotoxins and the losses that can be caused by the pathogen during post-harvest need to be explored. To our knowledge this is the first report of T. afroharzianum as a pathogen of maize in Italy.

Trichoderma asperellum Secreted 6-Pentyl-α-Pyrone to Control Magnaporthiopsis maydis, the Maize Late Wilt Disease Agent.

Simple SummaryThe maize (Zea mays L.) late wilt disease, caused by the fungus Magnaporthiopsis maydis, is considered the most severe threat to commercial maize production in Israel and Egypt. Various control strategies have been inspected over the years. The current scientific effort is focusing on eco-friendly approaches against the disease. The genus Trichoderma, a filamentous soil and plant root-associated fungi, is one of the essential biocontrol species, demonstrating over 60% of all the listed biocontrol agents used to reduce plant infectious diseases. They produce different enzymes and elicit defense responses in plants, playing a significant role in biotic and abiotic stress tolerance, hyphal growth, and plant growth promotion. Trichoderma asperellum was found to have biocontrol ability and protect crops against various plant pathogenic fungi, including the maize late wilt disease causal agent. This research aimed at isolating and identifying T. asperellum secondary metabolites with antifungal action against M. maydis. From T. asperellum growth medium, the 6-Pentyl-α-pyrone secondary metabolite was isolated and identified with high potent antifungal activity against M. maydis. This compound previously exhibited antifungal activities towards several plant pathogenic fungi. Achieving clean and identified T. asperellum active ingredient(s) secreted product(s) is the first step in revealing their commercial potential as new fungicides. Follow-up studies should test this component against the LWD pathogen in potted sprouts and the field.Late wilt disease (LWD) is a destructive vascular disease of maize (Zea mays L.) caused by the fungus Magnaporthiopsis maydis. Restricting the disease, which is a significant threat to commercial production in Israel, Egypt, Spain, India, and other countries, is an urgent need. In the past three years, we scanned nine Trichoderma spp. isolates as biological control candidates against M. maydis. Three of these isolates showed promising results. In vitro assays, seedlings pathogenicity trials, and field experiments all support the bio-control potential of these isolates (or their secretions). Here, a dedicated effort led to the isolation and identification of an active ingredient in the growth medium of Trichoderma asperellum (P1) with antifungal activity against M. maydis. This Trichoderma species is an endophyte isolated from LWD-susceptible maize seeds. From the chloroform extract of this fungal medium, we isolated a powerful (approx. 400 mg/L) active ingredient capable of fully inhibiting M. maydis growth. Additional purification using liquid chromatography–mass spectrometry (LC–MS) and gas chromatography–mass spectrometry (GC–MS) separation steps enabled identifying the active ingredient as 6-Pentyl-α-pyrone. This compound is a potential fungicide with high efficiency against the LWD causal agent.

Soil Saprobic Fungi Differ in Their Response to Gradually and Abruptly Delivered Copper

The overwhelming majority of studies examining environmental change deliver treatments abruptly, although, in fact, many important changes are gradual. One example of a gradually increasing environmental stressor is heavy metal contamination. Essential heavy metals, such as copper, play an important role within cells of living organisms but are toxic at higher concentrations. In our study, we focus on the effects of copper pollution on filamentous soil fungi, key players in terrestrial ecosystem functioning. We hypothesize that fungi exposed to gradually increasing copper concentrations have higher chances for physiological acclimation and will maintain biomass production and accumulate less copper, compared to fungi abruptly exposed to the highest copper concentration. To test this hypothesis, we conducted an experiment with 17 fungal isolates exposed to gradual and abrupt copper addition. Contrary to our hypothesis, we find diverse idiosyncratic responses, such that for many fungi gradually increasing copper concentrations have more severe effects (stronger growth inhibition and higher copper accumulation) than an abrupt increase. While a number of environmental change studies have accumulated evidence based on the magnitude of changes, the results of our study imply that the rate of change can be an important factor to consider in future studies in ecology, environmental science, and environmental management.

The bioremediation potential of filamentous fungi in soil contaminated with lead

Population increase resulting from industrial activities has worsened soil contamination with toxic metals. Given the complex dynamics of these pollutants and the complexity of soil matrices, one of the biggest challenges faced by the environmental field lies on developing effective technologies to remediate contaminated soils. Thus, bioremediation may be a decontamination alternative based on using microorganisms. The aims of the current study are to isolate and characterize filamentous fungi with bioremediation potential to be used in soils contaminated with lead. A soil sample was incubated in Sabouraud Caf Agar medium in BOD at 28ºC. CFUs were counted after 72h of incubation; the three most prominently grown colonies were isolated in new plates containing the same medium. Fungi were transferred to liquid submerged fermentation medium with 20 ppm of lead after 24 h of incubation; they remained in shaker incubator at 30°C, 120 rpm, for 120h. Next, the MP-AES analysis was performed to evaluate the final lead concentration. Isolated fungi such as Aspergillus, Penicillium and Trichoderma removed, 56.82%, 66.77% and 75.29% lead ions, respectively, in comparison to the control. Results confirmed the bioremediation potential of these fungi and their possible use in areas contaminated with the herein investigated metal.

Biotransformation and Degradation Pathway of Pyrene by Filamentous Soil Fungus Trichoderma sp. F03

Pyrene, a toxic four-benzene-ring that persists in the ecosystem, is highly resistant to degradation. The goal of the research is to screen, isolate, and identify pyrene-degrading filamentous fungi via the molecular biological identification method. The capabilities of identified isolates in biodegradation and transformation of pyrene were also evaluated. Based on the morphological characterization and sequence alignments, results of neighbor-joining phylogenetic tree from 18S rRNA of F03 revealed that genetic similarity had achieved 99% of homology percentage and identified as Trichoderma sp. Trichoderma sp. F03 was able to degrade pyrene (78%) when culture conditions were set at 100 mg/L initial pyrene concentration in culture medium with pH 5 at 27 °C, the use of glucose as a carbon source and polyethylene glycol sorbitan monooleate as a biosurfactant without agitation. Finally, three metabolites, benzoic acid, 3-hydroxybenzoic acid, and acetic acid, were detected during the pyrene degradation process by using gas chromatography–mass spectrometry (GCMS).

Carboxylesterase activity of filamentous soil fungi from a potato plantation in Mankayan, Benguet

Carboxylesterase activity of filamentous soil fungi from a potato plantation in Mankayan, Benguet

Diversity of filamentous and yeast fungi in soil of citrus and grapevine plantations in the Assiut region, Egypt.

Diversity of filamentous and yeast fungi in soil of citrus and grapevine plantations in the Assiut region, Egypt.

Genome sequence of the filamentous soil fungus Chaetomium cochliodes reveals abundance of genes for heme enzymes from all peroxidase and catalase superfamilies.

BackgroundThe ascomycetous family Chaetomiaceae (class Sordariomycetes) includes numerous soilborn, saprophytic, endophytic and pathogenic fungi which can adapt to various growth conditions and living niches by providing a broad armory of oxidative and antioxidant enzymes.ResultsWe release the 34.7 Mbp draft genome of Chaetomium cochliodes CCM F-232 consisting of 6036 contigs with an average size of 5756 bp and reconstructed its phylogeny. We show that this filamentous fungus is closely related but not identical to Chaetomium globosum and Chaetomium elatum. We screened and critically analysed this genome for open reading frames coding for essential antioxidant enzymes. It is demonstrated that the genome of C. cochliodes contains genes encoding putative enzymes from all four known heme peroxidase superfamilies including bifunctional catalase-peroxidase (KatG), cytochrome c peroxidase (CcP), manganese peroxidase, two paralogs of hybrid B peroxidases (HyBpox), cyclooxygenase, linoleate diol synthase, dye-decolorizing peroxidase (DyP) of type B and three paralogs of heme thiolate peroxidases. Both KatG and DyP-type B are shown to be introduced into ascomycetes genomes by horizontal gene transfer from various bacteria. In addition, two putative large subunit secretory and two small-subunit typical catalases are found in C. cochliodes. We support our genomic findings with quantitative transcription analysis of nine peroxidase & catalase genes.ConclusionsWe delineate molecular phylogeny of five distinct gene superfamilies coding for essential heme oxidoreductases in Chaetomia and from the transcription analysis the role of this antioxidant enzymatic armory for the survival of a peculiar soil ascomycete in various harsh environments.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3111-6) contains supplementary material, which is available to authorized users.

English

Soil is an oligotrophic medium for fungal growth. F ungi are important component in soil microbiota. Depending on soil depth and nutrient co nditions, the fungal biomass exceeds that of bacteria in almost every soil except rhizosphere so il which is dominated by bacteria. Filamentous fungi in soil degrade organic matter and help in so il aggregation. Some produce substances similar to humic substances and some are capable of forming ectotrophic associations on the root system of forest trees and help in mobilisation of soil phosp horus and nitrogen into plants. Many fungi are biological control agents for plant pathogens and i nsect pests. In Uttarakhand especially in Dehradun District very scanty information is availa ble regarding soil inhabiting microfungi of Agricultural fields. Therefore some agricultural la nds growing Brassica crop were selected to study the composition, dominance and diversity of microfu ngi and physico-chemical properties of the soil inhabited by these fungi. Five agricultural lands viz. Rajawala (RAJ), Bahada rpur(BAH), Bhauwala (BHAU), Telpura (TLP) and Sudhowala (SUDH) were selected. Each land was s urveyed repeatedly to collect soil samples. Soil samples were collected from different depths v0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm. and 2025 cm and composite samples were made for each agri cultural land. For all soil samples examined, pH varied from 6.42± 1.24 to 7.84±1.56; moisture content varied from8.42±1.68 to 10.84±2.16; organic contents varie d from 1.55 to 3.00 and texture varied from sandy to sandy loam. Micronutrients were very high in all the soil samples. A total of 383 colonies of microfungi belonging to 11 genera and 26 species we re isolated. Anamorphic fungi (Deuteromycota) were dominant and represented by 9 genera and 22 sp ecies followed by Zygomycota represented by 2 genera and 4 species. Fungal populations were alw ays highest in surface soil and decreased along with soil-depth. Maximum fungal species were isolat ed from BAH at the depth of 0-10 cm followed by RAZ, whereas the minimum fungal species were iso lated from BHAU, TPR and SUDH at the depth of 15-20 cm. Of the total 26 species recorded , 8 species were of common occurrence, 9 species of frequent, 8 species of moderate and 1 species of rare occurrence respectively. Shanon- Wiever index of species diversity was highe st (2.734) in BAH followed by RAZ (2.686), TLP (2.583) and SUDH (2.553) while it was lowest for BH AU (2.540). Simpson index of diversity also showed identical trends. Highest similarity (84.2%) was observed between RAJ and BAH and lowest (55.6%) between RAJ and TLP. The present investigation will be helpful in docume ntation and conservation as well as in controlling soil borne pathogens. Further, it certainly opens u p a new horizon for the researchers in this interesting and challenging field of soil microfung al biodiversity.

Root Growth, Mycorrhizal Frequency and Soil Microorganisms in Strawberry as Affected by Biopreparations

The aim of the study was to assess the effects of various biopreparations on the growth of the strawberry root system, the number of spores of mycorrhizal fungi, the total number of bacteria in the rhizosphere soil, and the degree of mycorrhizal association in the roots of two strawberry cultivars. The experiment with strawberry plants was established in the spring of 2010 in the Experimental Orchard of the Institute of Horticulture in Dabrowice. The objects of research were “frigo” strawberry plants of the cultivars Elsanta and Elkat. The following experimental combinations were used: control, control NPK (standard NPK fertilization), manure, mycorrhizal preparation Micosat F, Humus UP, Humus Active + Aktywit PM, BioFeed Amin, BioFeed Quality, Tytanit, Vinassa, Florovit Eko, and Florovit Pro Natura. The use of the biopreparation BioFeed Quality resulted in a six-fold increase in root length and a seven-fold increase in root surface area. Compared with NPK fertilization, application of the preparation BioFeed Amin contributed to an eight-fold increase in root volume, and the use of Vinassa increased 24-fold the number of root tips of Elkat strawberry plants. Micosat F and Humus UP caused a five-fold increase in mycorrhizal frequency in the roots of strawberry plants. Micosat F and manure contributed to a two- and four-fold increase, respectively, in the number of spores in the rhizosphere soil. Application of the preparations Humus UP, BioFeed Amin and Florovit Eko doubled the total number of bacteria and filamentous fungi in the rhizosphere soil of strawberry plants of the cultivars Elsanta and Elkat in comparison with NPK fertilization. Fertilization with the biopreparations intensified the growth of the root system and increased the number of spores of AM fungi, mycorrhizal frequency, and the total number of bacteria and filamentous fungi in the soil.

Influence of a Ni, Cu and Cd on the number of filamentous fungi in soil with poplar sprout clones M1, PE19/66 and B229

For more than three hundred years heavy metals in addition to pesticides in the last fifty years, represent quantitatively, the most widespread pollutants in the environment. The total concentrationof heavy metals in the living environment is not reflected directly on the degree of their availability to microorganisms, which further complicates an accurate assessment of the risk that heavy metals have in areas where they are present. It is important to point out influence of heavy metals on antibiotic properties of microorganisms. During the experimental work the research was carried out examining the impacts of the specified concentrations of NI, Cu, Cd on the number of microorganisms in the soil with 3 clones of poplar plantations. According to the obtained experimental results, the influence of Ni, Cu, Cd on the number of molds in the soil may lead to an increase in their numbers which is placed in close correlation with the corresponding poplar clones.

Cloning, annotation and expression analysis of mycoparasitism-related genes in Trichoderma harzianum 88

Trichoderma harzianum 88, a filamentous soil fungus, is an effective biocontrol agent against several plant pathogens. High-throughput sequencing was used here to study the mycoparasitism mechanisms of T. harzianum 88. Plate confrontation tests of T. harzianum 88 against plant pathogens were conducted, and a cDNA library was constructed from T. harzianum 88 mycelia in the presence of plant pathogen cell walls. Randomly selected transcripts from the cDNA library were compared with eukaryotic plant and fungal genomes. Of the 1,386 transcripts sequenced, the most abundant Gene Ontology (GO) classification group was "physiological process". Differential expression of 19 genes was confirmed by real-time RT-PCR at different mycoparasitism stages against plant pathogens. Gene expression analysis revealed the transcription of various genes involved in mycoparasitism of T. harzianum 88. Our study provides helpful insights into the mechanisms of T. harzianum 88-plant pathogen interactions.

Filamentous Soil Fungi from Ny-Ålesund, Spitsbergen, and Screening for Extracellular Enzymes

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 ITS1-5.8S and ITS2 rDNA domain sequence similarity. The isolates belonged to 19 species under 14 genera ( Acremonium , Arthrinium , Aspergillus , Cladosporium , Corynespora , Emericella , Geomyces , Mortierella , Mucor , Myrothecium , Penicillium , Phialophora , Preussia , Xylaria ). To the best of our knowledge, Acremonium roseolum , Aspergillus aculeatus , Emericella nidulans , and Preussia sp. are the first northernmost records from Arctic soils. The viable fungal count in different soil samples varied from 0.5 • 10 4 to 2.0 • 10 5 g -1 . Species richness in different soil samples was also calculated. Mortierella was one of the most dominant genera in Arctic soils. A temperature tolerance study was carried out for all the isolates, and representative species were screened for their extracellular enzyme activity (amylase, cellulase, phosphatase, and pectinase) at 4˚C and 20˚C. Among the 30 isolates, seven showed cellulolytic activity, two were phosphate solubilizers, three had amylolytic activity, and only one showed pectinolytic activity on solid media. CMCase (β1, 4-endoglucanase) activity was quantified in seven isolates that exhibited positive activity during preliminary screening. The records of enzyme activity for amylases, pectinases, and cellulases are the first from the fungi of Spitsbergen. The present study indicates the dominance in Ny-Alesund of cellulolytic strains, which may serve as potent decomposers in Arctic tundra. These isolates may be used to facilitate the mineralization of cellulolytic wastes generated by human activities in colder hilly areas across the world, including the Himalayas in India.

Expressed sequence tags-based identification of genes in a biocontrol strain Trichoderma asperellum

Trichoderma asperellum, a filamentous soil fungus, is an effective biocontrol agent against many fungal plant pathogenic species. In the present study, we investigated the biological control properties of the strain T.asperellum T4. T.asperellum fermentation products significantly decreased the ability of Rhizoctonia solani and Sclerotinia sclerotiorum to infect rice and soybean, respectively. To further elucidate the biocontrol mechanisms of T.asperellum at the molecular level, a cDNA library was constructed from its mycelium. In total, 3114 expressed sequence tags (ESTs) were generated, which represented 1,554 unigenes, including 354 contigs and 1,200 singletons. Among these unigenes, 731 represented known genes while 823 were novel genes. Forty-six unigenes potentially involved in biocontrol processes were identified from the EST collection. Among them, the expressions of 16 genes were studied, and 15 genes were highly differentially regulated during confrontation with 2 phytopathogens, suggesting that they play roles in the T.asperellum response to phytopathogens. Our study may provide helpful insight in the mechanism of biocontrol by T.asperellum T4 against plant pathogens.

Adaptive Melanin Response of the Soil Fungus Aspergillus niger to UV Radiation Stress at “Evolution Canyon”, Mount Carmel, Israel

BackgroundAdaptation is an evolutionary process in which traits in a population are tailored by natural selection to better meet the challenges presented by the local environment. The major discussion relating to natural selection concerns the portraying of the cause and effect relationship between a presumably adaptive trait and selection agents generating it. Therefore, it is necessary to identify trait(s) that evolve in direct response to selection, enhancing the organism's fitness. “Evolution Canyon” (EC) in Israel mirrors a microcosmic evolutionary system across life and is ideal to study natural selection and local adaptation under sharply, microclimatically divergent environments. The south-facing, tropical, sunny and xeric “African” slope (AS) receives 200%–800% higher solar radiation than the north-facing, temperate, shady and mesic “European” slope (ES), 200 meters apart. Thus, solar ultraviolet radiation (UVR) is a major selection agent in EC influencing the organism-environment interaction. Melanin is a trait postulated to have evolved for UV-screening in microorganisms. Here we investigate the cause and effect relationship between differential UVR on the opposing slopes of EC and the conidial melanin concentration of the filamentous soil fungus Aspergillus niger. We test the working hypothesis that the AS strains exhibit higher melanin content than strains from the ES resulting in higher UV resistance.Methodology/Principal FindingsWe measured conidial melanin concentration of 80 strains from the EC using a spectrophotometer. The results indicated that mean conidial melanin concentration of AS strains were threefold higher than ES strains and the former resisted UVA irradiation better than the latter. Comparisons of melanin in the conidia of A. niger strains from sunny and shady microniches on the predominantly sunny AS and predominantly shady ES indicated that shady conditions on the AS have no influence on the selection on melanin; in contrast, the sunny strains from the ES displayed higher melanin concentrations.Conclusions/SignificanceWe conclude that melanin in A. niger is an adaptive trait against UVR generated by natural selection.

Interactions between a plant growth-promoting rhizobacterium, an AM fungus and a phosphate-solubilising fungus in the rhizosphere of Lactuca sativa

This study evaluated the interactions between the inoculation with an arbuscular mycorrhizal fungus, Glomus intraradices Schenck & Smith, a plant growth-promoting rhizobacterium, Bacillus subtilis, and a filamentous soil fungus, Aspergillus niger, with respect to their effects on growth of lettuce plants and on indicators of biological soil quality (microbial biomass C, water-soluble C and carbohydrates and dehydrogenase, urease, acid phosphatase and benzoyl argininamide hydrolyzing protease activities). Water-soluble carbohydrates and microbial biomass were increased only in the rhizosphere soil of G. intraradices-plants. Rhizosphere soil from all microbial inoculation treatments had significantly higher dehydrogenase activity than the control soil, particularly in the soil inoculated with B. subtilis (about 21% higher than control soil). Inoculation with A. niger or B. subtilis increased significantly the urease, protease and phosphatase activities of the rhizosphere soil of the lettuce plants. The foliar P and K contents increased significantly with the B. subtilis or G. intraradices inoculation, alone or in combination. The most effective co-inoculation was observed in the combined treatment of inoculation with G. intraradices and B. subtilis, which synergistically increased plant growth compared with singly inoculated (about 77% greater with respect to the control plants).

Ultrastructure and properties of Paecilomyces lilacinus spores.

Strains of the filamentous soil fungus Paecilomyces lilacinus are currently being developed for use as biological control agents against root-knot, cyst, and other plant-parasitic nematodes. The inoculum applied in the field consists mainly of spores. This study was undertaken to examine the size, ultrastructure, and rodlet layers of P. lilacinus spores and the effect of the culture method on structural and functional spore properties. A rodlet layer was identified on aerial spores only. Other differences noted between aerial spores and those produced in submerged culture included the size and appearance of spores and thickness of spore coat layers when examined with transmission electron microscopy. The two spore types differed in UV tolerance, with aerial spores being less sensitive to environmentally relevant UV radiation. Also, viability after drying and storage was better with the aerial spores. Both spore types exhibited similar nematophagous ability.

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.

Assessment of fungal–bacterial development in a successional shortgrass steppe by direct integration of chloroform-fumigation extraction (FE) and microscopically derived data

An active cytoplasm (AC) approach for characterization of soil fungi and bacteria is proposed, in which information on biovolume and biovolume contents is directly integrated. This AC method was developed to provide information on limited cytoplasm occurrence in an extended hyphal network which is characteristic of the non-discrete filamentous soil fungi. In this procedure, fumigation extraction (FE) derived carbon is allocated proportionally to the cytoplasm-containing biovolumes (fungal, inactive and active bacteria) followed by identification of the proportion of FE-derived carbon allocated to hyphal lengths and the active bacteria, considered to be the active cytoplasm. This approach was used during 1995 (summer and autumn samplings) to characterize three northeastern Colorado shortgrass steppe sites of different ages since cultivation, in comparison with an uncultivated site. Based on FE, the sites had similar extractable C contents. In contrast, the microscopic analyses indicated that fungal hyphal lengths increased significantly from the early successional to the uncultivated site at both samplings, while the functional (cytoplasm-filled) hyphal volume decreased. In comparison, the bacterial total and active numbers did not show distinct changes related to succession. Using this AC approach, the active fungal–bacterial cytoplasm was found to become more bacterial with succession in this shortgrass steppe ecosystem. By estimating active cytoplasm occurrence in fungal and bacteria in relation to succession, this approach provided unique information on fungal–bacterial community changes, particularly related to hyphal development and cytoplasm maintenance, which is not given by the independent use of biovolume or FE carbon-based analyses.

Photoreactivation of UV‐lnactivated Spores of Trichoderma harzianum

Abstract— Photoreactivation in the filamentous soil fungus Trichoderma harzianum is of interest because its blue, UVA photoreceptors (cryptochromes) may share homology with DNA photolyases. Furthermore, this organism antagonizes, by mycoparasitism, a number of soil‐borne pathogens. Photoreactivation is thus important as one of the factors that may contribute to survival in the field. Exposure of asexually produced spores (conidia) to UVC inhibits germination. Nongerminating spores either do not swell or are inhibited later in germination, swelling but failing to put out a germ tube. Both types of inhibition can be reversed by photoreactivation with visible and UVA (320‐400 nm) light, restoring high germination percentages. Conidia of mutants lacking the normal greenish pigmentation are more sensitive to UVC (200‐280 nm) than wild‐type conidia but photoreactivation still occurs. The action spectrum for photoreactivation indicates that T. harzianum has a DNA photolyase with a pterin as second chromophore. The most effective wavelengths for photoreactivation correspond to valleys, rather than peaks, in the action spectrum for photoinduction of sporulation. Furthermore, mutants with defects in photoinduction of sporulation (dimY) are not defective in photoreactivation. Induction of sporulation and DNA photorepair, while sharing parts of the blue/UVA spectrum, are different, by spectroscopic, kinetic and genetic criteria.