Heavy metals and thiol compounds in Mucor racemosus and Articulospora tetracladia

Fungi in Freshwaters: Prioritising Aquatic Hyphomycetes in Conservation Goals

Deprivation of protection for aquatic hyphomycetes is disturbing because they are key players in freshwater ecosystems across the globe. To attain a more holistic conservation paradigm for biodiversity in freshwaters, it is necessary to broaden our ecological perception of microfungi, mainly in aquatic hyphomycetes. A considerable groundwork still needs to be accomplished in progressing towards conserving aquatic hyphomycetes. Overcoming the paucity of information regarding the rare and endangered species, biogeography and above all, a global biodiversity database, would be a significant contribution in the initiation of an overarching conservation strategy for aquatic hyphomycetes. Being aware that the biodiversity decline in freshwaters is alarming, here we seek to explore why biodiversity data of aquatic hyphomycetes are missing. This article closely examines the threats to the biodiversity of aquatic hyphomycetes and freshwater ecosystems. Moving forward, we advocate a structured approach to gaining a thorough understanding to embrace aquatic hyphomycetes biodiversity into the conservation strategies. Including aquatic hyphomycetes in the conservation objectives may attract more funding opportunities for global surveys to initiate a fungal inclusive conservation era. Fungal conservation ventures can profit from interdisciplinary collaborations and cutting-edge science and technology, leading to informed decision making for biodiversity assessment and management.

Use of soil fungi in the biosorption of three trace metals (Cd, Cu, Pb): promising candidates for treatment technology?

Trace metal contamination is a widespread and complex environmental problem. Because fungi are capable of growing in adverse environments, several fungal species could have an interesting potential in remediation technologies for metal contaminated environments. This study proposes to test the ability to tolerate and biosorb three trace metals (Cd, Cu and Pb) of 28 fungal isolates collected from different soils. First, a tolerance assay in agar medium was performed. Each isolate was grown in the presence of Cd, Cu, and Pb at different concentrations. Then, we exposed each soil fungus to 50 mg L^-1 of Cd, Cu, or Pb during 3 days in liquid medium. Parameters such as biomass production, pH, and biosorption were evaluated. The results showed that responses to metal exposure are very diverse even with fungi isolated from the same soil sample, or belonging to the same genera. Several isolates could be considered as good metal biosorbents and could be used in future mycoremediation studies. Among the 28 fungi tested, Absidia cylindrospora biosorbed more than 45% of Cd and Pb, Chaetomium atrobrunneum biosorbed more than 45% of Cd, Cu, Pb, and Coprinellus micaceus biosorbed 100% of Pb.

Biochemical response of Rhodotorula mucilaginosa and Cladosporium herbarum isolated from aquatic environment on iron(III) ions

The objective of the paper was to determine the influence of iron(III) ions on the growth and metabolism of fungi commonly occurring in waters: the yeast Rhodotorula mucilaginosa and filamentous fungus Cladosporium herbarum. Cells of R. mucilaginosa were shown to absorb the most iron(III) ions at a concentration of 1 mg/L iron(III) ions. Yeast cells showed a considerable increase in the content of proteins and monosaccharides, as well as biomass growth. At higher concentrations of iron(III) ions, the yeast limited the intake of iron(III) ions, and a decrease in the basic metabolites in cells was observed, as well as an increase in the secretion of such metabolites into the medium. Moreover, the activity of antioxidant enzymes increased in the fungal cells, suggesting that iron(III) ions have a toxic effect. Simultaneously, even at high concentrations of iron(III) ions in the medium, no decrease in the yeast biomass was recorded. It seems therefore that the potentially pathogenic R. mucilaginosa will likely be present in waters moderately contaminated with iron(III) ions. It can be useful as a water quality bioindicator. A considerably higher capacity for the biosorption of iron(III) ions was recorded for the filamentous fungus C. herbarum. Defensive mechanisms were observed for C. herbarum, which were manifested in a substantial increase in the content of proteins and monosaccharides, as well as an increase in the activity of antioxidant enzymes, particularly under the influence of high concentrations of iron(III) ions. Moreover, it was evidenced that in the filamentous fungus, iron(III) ions limited the extracellular secretion of metabolites. These results suggest that the fungus can actively accumulate iron(III) ions and therefore eliminate them from the aquatic environment. It can be useful in water treatment processes, which has a significant impact on water ecology.

Copper and zinc affect the activity of plasma membrane H+-ATPase and thiol content in aquatic fungi

Aquatic hyphomycetes are the major microbial decomposers of plant litter in streams. We selected three aquatic hyphomycete species with different abilities to tolerate, adsorb and accumulate copper and zinc, and we investigated the effects of these metals on H+-ATPase activity as well as on the levels of thiol (SH)-containing compounds. Before metal exposure, the species isolated from a metal-polluted stream (Heliscus submersus and Flagellospora curta) had higher levels of thiol compounds than the species isolated from a clean stream (Varicosporium elodeae). However, V. elodeae rapidly increased the levels of thiols after metal exposure, emphasizing the importance of these compounds in fungal survival under metal stress. The highest amounts of metals adsorbed to fungal mycelia were found in the most tolerant species to each metal, i.e. in H. submersus exposed to copper and in V. elodeae exposed to zinc. Short-term (10 min) exposure to copper completely inhibited the activity of H+-ATPase of H. submersus and V. elodeae, whilst zinc only led to a similar effect on H. submersus. However, at longer exposure times (8 days) the most metal-tolerant species exhibited increased H+-ATPase activities, suggesting that the plasma membrane proton pump may be involved in the acclimation of aquatic hyphomycetes to metals.

Synthesis of silver nanoparticles using haloarchaeal isolate Halococcus salifodinae BK3

Numerous bacteria, fungi, yeasts and viruses have been exploited for biosynthesis of highly structured metal sulfide and metallic nanoparticles. Haloarchaea (salt-loving archaea) of the third domain of life Archaea, on the other hand have not yet been explored for nanoparticle synthesis. In this study, we report the intracellular synthesis of stable, mostly spherical silver nanoparticles (AgNPs) by the haloarchaeal isolate Halococcus salifodinae BK3. The culture on adaptation to silver nitrate exhibited growth kinetics similar to that of the control. NADH-dependent nitrate reductase was involved in silver tolerance, reduction, synthesis of AgNPs, and exhibited metal-dependent increase in enzyme activity. The AgNPs preparation was characterized using UV-visible spectroscopy, XRD, TEM and EDAX. The XRD analysis of the nanoparticles showed the characteristic Bragg peaks of face-centered cubic silver with crystallite domain size of 22 and 12 nm for AgNPs synthesized in NTYE and halophilic nitrate broth (HNB), respectively. The average particle size obtained from TEM analysis was 50.3 and 12 nm for AgNPs synthesized in NTYE and HNB, respectively. This is the first report on the synthesis of silver nanoparticles by haloarchaea.

Pretreatment hepatoprotective effect of the marine fungus derived from sponge on hepatic toxicity induced by heavy metals in rats

The aim of this study was to evaluate the pretreatment hepatoprotective effect of the extract of marine-derived fungus Trichurus spiralis Hasselbr (TS) isolated from Hippospongia communis sponge on hepatotoxicity. Twenty-eight male Sprague-Dawley rats were divided into four groups (n = 7). Group I served as −ve control, group II served as the induced group receiving subcutaneously for seven days 0.25 mg heavy metal mixtures, group III received (i.p.) TS extract of dose 40 mg for seven days, and group IV served as the protected group pretreated with TS extract for seven days as a protection dose, and then treated with the heavy metal-mixture. The main pathological changes within the liver after heavy-metal mixtures administrations marked hepatic damage evidenced by foci of lobular necrosis with neutrophilic infiltration, adjacent to dysplastic hepatocytes. ALT and AST measurements show a significant increase in group II by 46.20% and 45.12%, respectively. Total protein, elevated by about 38.9% in induction group compared to the −ve control group, in contrast to albumin, decreased as a consequence of metal administration with significant elevation on bilirubin level. The results prove that TS extract possesses a hepatoprotective property due to its proven antioxidant and free-radical scavenging properties.

Reproduction of aquatic hyphomycetes at low concentrations of Ca2+, Zn2+, Cu2+, and Cd2+

Maple leaf disks were conditioned in a stream for three weeks and then aerated for 2 d in distilled water to induce fungal sporulation. The release of aquatic hyphomycete spores increased when the water was supplemented with low concentrations of Ca(2+) (5 µg/L), Zn(2+) (2.5 µg/L), Cu(2+) (0.5 µg/L), or Cd(2+) (0.125 µg/L). Higher supplement concentrations inhibited sporulation. Over the concentration range used, the sporulation response was generally best described by a quadratic regression, suggesting a biphasic or hormetic response. A similar pattern was found with the number of fungal species as the dependent variable. Anguillospora filiformis and Anguillospora longissima were generally least inhibited by metal supplements, and Ca(2+) was the least and Cd(2+) the most toxic metal. Combinations of metals had a more severe effect on fungal sporulation than predicted from addition of the effects of the metals in isolation. The biological significance of the hormetic response is unclear; however, acknowledging it is clearly relevant for establishing guidelines or recommendations in toxicology.

Effects of heavy metals on production of thiol compounds and antioxidant enzymes in Agaricus bisporus

In a pre-experiment, Agaricus bisporus mycelia grown in PDL medium were found to have a substantial ability to tolerate and accumulate heavy metals. In the study, we investigated changes in the contents of soluble protein and thiol compounds as well as the activities of antioxidant enzymes caused by copper, zinc, lead, and cadmium (nitrate salts) in mycelia of A. bisporus during short-and long-term exposure. Results showed that high-level metal concentrations significantly decrease the contents of soluble protein after long-term exposure, Cu and Zn concentrations significantly increase the thiol compounds levels after long-term exposure, while high-level Cd significantly decrease thiol compounds after long-term exposure. Additionally, SOD activities were significantly increased after long-term exposure to metals, especially to Cd. The CAT activities were enhanced after long-term exposure to low-level Cu and high-level Zn, and enhanced after short-and long-term exposure to high-level Pb. The POD activities were significantly increased after long-term exposure to metals, and increased after short-term exposure to Cd and high-level Pb.

Effects of metals on growth and sporulation of aquatic fungi

Aquatic hyphomycetes are a relevant group of fungi that play a crucial role as intermediaries between plant detritus and invertebrates in clean or metal-polluted streams. In this study, we investigated the effects of Zn, Cu, Ni, and Cd on the growth and sporulation of several aquatic hyphomycete species. Effects of these metals on growth were assessed in solid and liquid media with different compositions [1% malt extract (ME) and a mineral medium supplemented with vitamins and 2% glucose (MK)], and fungal sensitivity to metals was compared. The exposure to Zn or Cd inhibited the sporulation of Heliscus submersus and Tricladium chaetocladium, with these effects being stronger in the latter species. In solid medium, mydelial growth was linear, and, in most cases, metals negatively affected fungal growth. The sensitivity of aquatic hyphomycetes to metals, assessed as the metal concentration inhibiting biomass production in 50% (EC(50)), showed that Ypsilina graminea and Varicosporium elodeae were the most resistant species to Zn, while Alatospora acuminata, H. submersus, and Flagellospora curta appeared to be the most resistant fungus to Cu. Generally, lower toxicity of Zn or Cu than Ni or Cd was found. However, EC(50) values were about 20 times higher in solid than in liquid medium. Changes in nutrient supplies to fungi affected metal toxicity, as shown by higher EC(50) values in MK than ME. Complementarily, fungal tolerance to metals varied with fungal species as well as metal type.

Improved coverage of fungal diversity in polluted groundwaters by semi-nested PCR

Traditional methods used for studying communities of aquatic hyphomycetes are based on the detection and identification of their asexual spores under a microscope. These techniques limit detection to aquatic fungi present in sufficient quantity and capable of sporulating under laboratory conditions. Our objective was to develop a molecular approach to detect and monitor all types of fungi (i.e. strictly or facultatively aquatic) in harsh habitats (i.e. groundwater wells and heavily polluted surface water) where fungal biomass may become limited. We developed a semi-nested PCR protocol for fungal 18S ribosomal RNA genes coupled to subsequent analysis of the PCR products by Temperature Gradient Gel Electrophoresis (TGGE) to monitor the fungal community structure in aquatic habitats characterized by a pollution gradient. Our TGGE-protocol was compared with the traditional morphological approach and revealed a higher diversity in groundwaters and in some polluted surface waters. Thus, PCR-TGGE is a promising alternative in particular in habitats with low fungal biomass. The dynamics of fungal biomass and sporulation rates during the first weeks of leaf colonization showed that habitats with adverse ecological conditions allow only reduced fungal growth, which might subsequently impact upper trophic levels and thus interfere with key ecological processes of leaf decomposition.

Effects of heavy metals on the production of thiol compounds by the aquatic fungi Fontanospora fusiramosa and Flagellospora curta

The aquatic hyphomycetes Fontanospora fusiramosa and Flagellospora curta isolated from a clean and a metal-contaminated site, respectively, were tested for the production of thiol compounds when exposed to Cd, Zn, and Cu for short- and long-term periods. After 8 days, control cultures of F. curta had a total thiol (T-SH) concentration in mycelia of 3.46 +/- 0.37 micromol g(-1) dry mass, which was 2.4 times greater than that of F. fusiramosa. In both species, nonprotein (NP-SH) and protein-bound (PB-SH) thiols accounted for 30% and 70% of T-SH, respectively. F. curta increased the production of thiol compounds, namely NP-SH, more rapidly than F. fusiramosa when exposed to Cd or Zn. The greater increases in either NP-SH or PB-SH occurred in F. fusiramosa after long-term exposure to all metals; in this case, the increases of PB-SH overwhelmed those of NP-SH. Long-term exposure to metals also increased the mycelial protein concentration.

Metal-binding proteins and peptides in the aquatic fungi Fontanospora fusiramosa and Flagellospora curta exposed to severe metal stress

The production of thiol-containing proteins/peptides and its role in metal-binding was examined in the aquatic hyphomycetes Fontanospora fusiramosa and Flagellospora curta exposed to Cu, Cd, or Zn at concentrations inhibiting the biomass production in 80%. Heat-treated cell-free extracts were separated by size-exclusion chromatography and the thiol and metal content in the fractions was determined. F. curta, the species tolerant to metals, showed higher absolute levels of thiol compounds, which bound higher amounts of Cu and Cd than F. fusiramosa. Peptides with very low molecular weight (<9 kDa), most likely glutathione and phytochelatins, were the major Cu- and Zn-binding components in both species of aquatic hyphomycetes. In most cases, proteins with high molecular weight (>26 kDa) were induced by metal ions and they were the major Cd-binding component in both species. Proteins with characteristics of metallothioneins were also induced by exposure to metals in both species, but they showed a minor role in metal-binding, suggesting they might have other functions in fungal cells.

Species-specific Cd-stress response in the white rot basidiomycetes Abortiporus biennis and Cerrena unicolor

The effect of cadmium (Cd) on fungal growth, Cd bioaccumulation and biosorption, and on the formation of potential heavy metal response indicators such as thiols, oxalate, and laccase was investigated in the white rot fungi Cerrena unicolor andAbortiporus biennis. Only the highest Cd concentration employed (200 microM) inhibited growth of C. unicolor, whereas already lower Cd concentrations caused decreasing mycelia dry weights in A. biennis. Cd biosorption onto the mycelial surface was the predominant Cd sequestration mechanism in C. unicolor. Surface-bound and bioaccumulated Cd concentrations were essentially in the same range in A. biennis, leading to considerably higher intracellular Cd concentrations in A. biennis than in C. unicolor. Oxalate and laccase were produced by both of the fungal strains and their extracellular levels were elevated upon Cd exposure. Oxalate concentrations and laccase titres were considerably higher in C. unicolor than in A. biennis. Both fungi responded to increasing Cd concentrations by increasing intracellular amounts of thiol compounds (cysteine, gamma-glutamylcysteine, glutathione in both its reduced and oxidized form) but Cd application increased the amounts of thiols to a higher extend in A. biennis. Taken together, these species-specific responses towards Cd suggest that C. unicolor possesses a more efficient system than A. biennis to keep intracellular Cd concentrations low.

Stress response in two strains of the aquatic hyphomycete Heliscus lugdunensis after exposure to cadmium and copper ions

Biochemical responses to cadmium (Cd2+) and copper (Cu2+) exposure were compared in two strains of the aquatic hyphomycete (AQH) Heliscus lugdunensis. One strain (H4-2-4) had been isolated from a heavy metal polluted site, the other (H8-2-1) from a moderately polluted habitat. Conidia of the two strains differed in shape and size. Intracellular accumulation of Cd2+ and Cu2+ was lower in H4-2-4 than in H8-2-1. Both strains synthesized significantly more glutathione (GSH), cysteine (Cys) and gamma-glutamylcysteine (gamma-EC) in the presence of 25 and 50 microM Cd2+, but quantities and rates of synthesis were different. In H4-2-4, exposure to 50 microM Cd2+ increased GSH levels to 262% of the control; in H8-2-1 it increased to 156%. Mycelia of the two strains were analysed for peroxidase, dehydroascorbate reductase, glutathione reductase and glucose-6-phosphate dehydrogenase. With Cd2+ exposure, peroxidase activity increased in both strains. Cu2+ stress increased dehydroascorbate reductase activity in H4-2-4 but not in H8-2-1. Dehydroascorbate reductase and glucose-6-phosphate dehydrogenase activities progressively declined in the presence of Cd2+, indicating a correlation with Cd2+ accumulation in both strains. Cd2+ and Cu2+ exposure decreased glutathione reductase activity.

Quantification of phytochelatins in plants by reversed-phase HPLC–ESI–MS–MS

An on-line HPLC-ESI-MS-MS method has been developed for determination of glutathione and phytochelatins (PC) in plant tissues. For sample pretreatment, dithiothreitol (DTT) must be added at the very beginning, as an anti-oxidant. Optimization of instrumental conditions i.e. composition of HPLC mobile phase, ionization efficiency of the electrospray interface, and MS-MS detection in the multiple ion-monitoring mode, are the central aspects of this work. A polystyrene-packed column was found to be superior to a standard silica-packed reversed-phase column. A concave quadratic gradient of ammonium formate buffer and acetonitrile was found to be optimum. The limits of quantitation were 0.2 micromol kg(-1) plant tissue for glutathione and PC. The method has been applied to analysis of tissue samples from Vicia faba grown in Cd-containing nutrient solutions.

Cadmium induces a novel metallothionein and phytochelatin 2 in an aquatic fungus

Cadmium stress response was measured at the thiol peptide level in an aquatic hyphomycete (Heliscus lugdunensis). In liquid culture, 0.1 mM cadmium increased the glutathione (GSH) content and induced the synthesis of additional thiol peptides. HPLC, electrospray ionization mass spectrometry, and Edman degradation confirmed that a novel small metallothionein as well as phytochelatin (PC2) were synthesized. The metallothionein has a high homology to family 8 metallothioneins (http://www.expasy.ch/cgi-bin/lists?metallo.txt). The bonding of at least two cadmium ions to the metallothionein was demonstrated by mass spectrometry (MALDI MS). This is the first time that simultaneous induction of metallothionein and phytochelatin accompanied by an increase in GSH level has been shown in a fungus under cadmium stress, indicating a potential function of these complexing agents for in vivo heavy metal detoxification. The method presented here should be applicable as biomarker tool.

Cadmium and zinc response of the fungi Heliscus lugdunensis and Verticillium cf. alboatrum isolated from highly polluted water

The aquatic hyphomycete Heliscus lugdunensis and the terrestrial fungus Verticillium cf. alboatrum, both isolated from a highly polluted surface water, were investigated for their tolerance against Cd and Zn. Hl-H4 showed a 50% growth inhibition at 0.1 mM Cd, whereas at 0.7 mM Cd the growth of Va-H4 was only reduced by 30%. The fungi also showed a remarkable difference in their Zn-tolerance. The growth of Va-H4 was not inhibited at 1 mM Zn, whereas for Hl-H4 no growth occurred above 0.3 mM Zn. The biosorption and accumulation capacities for Cd or Zn of both fungi differed between the fungal species. In a 0.1 mM Cd-medium Hl-H4 biosorbed 15-fold and accumulated 39-fold more Cd than Va-H4. Exposure to 0.3 mM Zn resulted in a 13-fold higher biosorption and 11-fold higher accumulation for Hl-H4 than Va-H4. As glutathione (GSH) is known to be involved in the phytochelatin synthesis and other stress related processes we investigated its synthesis. Both fungi increased their synthesis of GSH in response to Cd. For Hl-H4 a concentration of 0.0125 mM Cd, corresponding to an intracellular Cd content of 2.1 nmol Cd mg(-1) dw, increased the GSH content, whereas Va-H4 only responded with a higher production of GSH at 1 mM Cd and a concomitant intracellular Cd content of 22.5 nmol Cd mg(-1) dw. An increased GSH synthesis under Zn-stress was only detectable for Va-H4 (20 mM).

Effects of zinc on leaf decomposition by fungi in streams: studies in microcosms

The effect of zinc on leaf decomposition by aquatic fungi was studied in microcosms. Alder leaf disks were precolonized for 15 days at the source of the Este River and exposed to different zinc concentrations during 25 days. Leaf mass loss, fungal biomass (based on ergosterol concentration), fungal production (rates of [1-14C]acetate incorporation into ergosterol), sporulation rates, and species richness of aquatic hyphomycetes were determined. At the source of the Este River decomposition of alder leaves was fast and 50% of the initial mass was lost in 25 days. A total of 18 aquatic hyphomycete species were recorded during 42 days of leaf immersion. Articulospora tetracladia was the dominant species, followed by Lunulospora curvula and two unidentified species with sigmoid conidia. Cluster analysis suggested that zinc concentration and exposure time affected the structure of aquatic hyphomycete assemblages, even though richness had not been severely affected. Both zinc concentration and exposure time significantly affected leaf mass loss, fungal production and sporulation, but not fungal biomass. Zinc exposure reduced leaf mass loss, inhibited fungal production and affected fungal reproduction by either stimulating or inhibiting sporulation rates. The results of this work suggested zinc pollution might depress leaf decomposition in streams due to changes in the structure and activity of aquatic fungi.

The role of thiol species in the hypertolerance of Aspergillus sp. P37 to arsenic

Aspergillus sp. P37 is an arsenate-hypertolerant fungus isolated from a river in Spain with a long history of contamination with metals. This strain is able to grow in the presence of 0.2 M arsenate, i.e. 20-fold higher than the reference strain, Aspergillus nidulans TS1. Although Aspergillus sp. P37 reduces As(V) to As(III), which is slowly pumped out of the cell, the measured efflux of oxyanions is insufficient to explain the high tolerance levels of this strain. To gain an insight into this paradox, the accumulation of acid-soluble thiol species in Aspergillus sp. P37 when exposed to arsenic was compared with that of the arsenic-sensitive A. nidulans TS1 strain. Increasing levels of arsenic in the medium did not diminish the intracellular pool of reduced glutathione in Aspergillus sp. P37, in sharp contrast with the decline of glutathione in A. nidulans under the same conditions. Furthermore, concentrations of arsenic that were inhibitory for the sensitive A. nidulans strain (e.g. 50 mM and above) provoked a massive formation of vacuoles filled with thiol species. Because the major fraction of the cellular arsenic was present as the glutathione conjugate As(GS)3, it is plausible that the arsenic-hypertolerant phenotype of Aspergillus sp. P37 is in part due to an enhanced capacity to maintain a large intracellular glutathione pool under conditions of arsenic exposure and to sequester As(GS)3 in vacuoles. High pressure liquid chromatography analysis of cell extracts revealed that the contact of Aspergillus sp. P37 (but not A. nidulans) with high arsenic concentrations (> or =150 mM) induced the production of small quantities of a distinct thiol species indistinguishable from plant phytochelatin-2. Yet, we argue that phytochelatins do not explain arsenic resistance in Aspergillus, and we advocate the role of As(GS)3 complexes in arsenic detoxification.