Pentacyclic Cytochalasins and Their Derivatives from the Endophytic Fungus Phomopsis sp. xz-18.

Eight new cytochalasins 1-8 and ten known analogs 9-18 were isolated from the endophytic fungus Phomopsis sp. xz-18. The planar structures of the cytochalasins were determined by HR-ESI-MS and NMR analysis. Compounds 1, 2, 9 and 10 were 5/6/6/7/5-fused pentacyclic cytochalasins; compounds 3 and 4 had conjugated diene structures in the macrocycle; and compound 6 had a ß,γ-unsaturated ketone. The absolute configuration of 6 was confirmed for the first time by the octant rule. The acid-free purification process proved that the pentacyclic system was a natural biosynthetic product and not an acid-mediated intramolecular cyclized artifact. The new compounds did not exhibit activities against human cancer cell lines in cytotoxicity bioassays or antipathogenic fungal activity, but compounds 1, 3 and 4 showed moderate antibacterial activity in disk diffusion assays.

Polyhydroxy p-Terphenyls from a Mangrove Endophytic Fungus Aspergillus candidus LDJ-5.

Six undescribed polyhydroxy p-terphenyls, namely asperterphenyllins A-F, were isolated from an endophytic fungus Aspergillus candidus LDJ-5. Their structures were determined by NMR and MS data. Differing from the previously reported p-terphenyls, asperterphenyllin A represents the first p-terphenyl dimer connected by a C-C bond. Asperterphenyllin A displayed anti-influenza virus A (H1N1) activity and protein tyrosine phosphatase 1B (PTP1B) inhibitory activity with IC50 values of 53 µM and 21 µM, respectively. The anti-influenza virus A (H1N1) activity and protein tyrosine phosphatase 1B (PTP1B) inhibitory activity of p-terphenyls are reported for the first time. Asperterphenyllin G exhibited cytotoxicity against nine cell lines with IC50 values ranging from 0.4 to 1.7 µM. Asperterphenyllin C showed antimicrobial activity against Proteus species with a MIC value of 19 µg/mL.

Characterization and bioremediation potential of nickel-resistant endophytic bacteria isolated from the wetland plant Tamarix chinensis.

Wetlands have been proposed as a sink for pollutants such as heavy metals. Wetland plants play a significant role in the phytoremediation of heavy metals. Here, we isolated and characterized three novel nickel (Ni)-resistant endophytic bacteria (NiEB) from the wetland plant Tamarix chinensis. The NiEB were identified as Stenotrophomonas sp. S20, Pseudomonas sp. P21 and Sphingobium sp. S42. All isolates tolerated 50 mg L-1 Ni, with isolates S20 and P21 being more tolerant to Ni at up to 400 mg L-1. Moreover, isolate S42 removed 33.7% of nickel sulfate from the water by forming white precipitates. The three isolates exhibited different plant growth-promoting (PGP) traits related to the production of indole acetic acid (IAA), siderophores and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Phytotoxicity studies revealed that the growth of the wetland plants in a high Ni concentration (200 mg L-1) recovered after co-incubation with isolate S42. Overall, this study presents the first report of NiEB isolation from wetland plants and provides novel insights into the diverse functions of endophytic bacteria in a plant host with the potential to improve Ni phytoremediation.

Tolerance of dark septate endophytic fungi (DSE) to 1 agrochemicals in vitro / Tolerancia de hongos endofíticos septados oscuros a agroquímicos in vitro

Abstract Dark septate endophytes (DSE) are a heterogeneous group of fungi, mostly belonging to the Phylum Ascomycota, that are involved in a mutualistic symbiosis with plant roots. The aim of this study is to evaluate the behavior of two strains of DSE isolated from wheat roots of two cropping areas in the province of Buenos Aires, Argentina, against some agrochemicals. Of all the isolates obtained, two strains were identified as Alternaria alternata and Cochliobolus sp. These DSE were found to be tolerant to glyphosate, carbendazim and cypermethrin when evaluated at the recommended agronomic dose (AD), 2 AD and, in some cases, 10 AD. This work contributes to the study of the biology of this group of fungi and their tolerance in the presence of xenobiotics widely used in agriculture.© 2019 Asociaci´on Argentina de Microbiolog´ıa. Published by Elsevier Espa˜na, S.L.U. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/bync-nd/4.0/).

Resumen Los endófitos septados oscuros (DSE) son un grupo heterogéneo de hongos que participan de una simbiosis mutualista con raíces de plantas, perteneciendo principalmente al Phylum Ascomycota. El objetivo de este estudio fue aislar DSE de raíces de trigo proveniente de dos áreas de cultivo de la provincia de Buenos Aires y evaluar el comportamiento de dos cepas de DSE aisladas de raíces de trigo frente a algunos agroquímicos en dos áreas de cultivo de la provincia de Buenos Aires. De todos los aislamientos obtenidos se seleccionaron dos cepas que se identificaron como Alternaria alternata y Cochliobolus sp. Se encontró que estos DSE son tolerantes al glifosato, el carbendazim y la cipermetrina, evaluados a las dosis agronómicas recomendadas (AD), a 2x AD y, en algunos casos, a 10x AD. Este trabajo contribuye al conocimiento de la biología de este grupo de hongos y su tolerancia a xenobióticos ampliamente utilizados en la agricultura.

Combined use of Enterobacter sp. MN17 and zeolite reverts the adverse effects of cadmium on growth, physiology and antioxidant activity of Brassica napus.

The objective of the study was to evaluate role of zeolite and Enterobacter sp. MN17 on Cd uptake, growth, physiological and biochemical responses of Brassica napus on Cd-contaminated soil. A sandy clay loam soil in plastic pots was spiked with Cd (0 and 80 mg kg-1) and amended with zeolite (0 and 10 g kg-1). Seeds of B. napus were inoculated with Enterobacter sp. MN17. Both inoculated and non-inoculated seeds of B. napus were sown and plants were harvested after 60 days of growth and data were collected. Although sole application of zeolite and seed inoculation reverted adverse effects of Cd in B. napus plants, the combined use resulted in even higher growth and physiological responses compared to control plants. The combined use under Cd stress increased plant height, root length, dry biomass of shoot and root up to 32%, 57%, 42% and 64%, respectively compared to control. The different physiological attributes (photosynthetic rate, chlorophyll content, transpiration rate, stomatal conductance) of B. napus were improved from 6% to 137%. Moreover, combined use of zeolite and seed inoculation on Cd-contaminated soil reduced the stress to plants as antioxidant activities decreased up to 25-64%, however enzyme activities were still higher than plants grown on normal soil. Root and shoot analysis of B. napus for Cd content depicted that zeolite and bacterium decreased Cd uptake from soil. It is concluded that combined use of zeolite and strain MN17 reduces Cd uptake from soil and improves physiological and biochemical responses of B. napus which is helpful to alleviate Cd toxicity to plants.

Effects of CO2 application coupled with endophyte inoculation on rhizosphere characteristics and cadmium uptake by Sedum alfredii Hance in response to cadmium stress.

Comparative impact of CO2 application and endophyte inoculation was investigated on the growth, rhizosphere characteristics, and cadmium (Cd) absorption of two ecotypes of Sedum alfredii Hance in response to Cd stress under hydroponic or rhizo-box culture conditions. The results showed that both CO2 application and endophyte inoculation significantly (P < 0.05) promoted plant growth (fresh weight and dry weight), improved root morphological properties (SRL, SRA, SRV, ARD and RTN) and exudation (pH, TOC, TN, soluble sugar and organic acids), changed Cd uptake and distribution of both ecotypes of S. alfredii. Meanwhile soil total and DTPA extractable Cd in rhizo-box decreased by biofortification treatments. Superposition biofortification exhibits utmost improvement for the above mentioned parameters, and has potential for enhancing phytoremediation efficiency of hyperaccumulator and sustaining regular growth of non-hyperaccumulator in Cd contaminated soils.

Cinnamic acid as an inhibitor of growth, flavonoids exudation and endophytic fungus colonization in maize root.

Cinnamic acid (CA) is an allelochemical that inhibits the growth of root promoting soil microorganisms. To prevent the growth of soil microbes, CA modulates several metabolic pathways in host plants and soil microbes. The aim of the current study was to investigate the effect of CA on maize root growth, exudation of secondary metabolites and its interaction with beneficial endophyte Pz11. The endophyte Pz11 was isolated from the roots of drought stressed Asphodelus tenuifolius (wild onion). The Pz11 strain was identified as Fusarium culmorum by homology of the internal transcribed spacer (ITS) region of 18 S rDNA sequence. The F. culmorum Pz11 produced phytostimulants and signaling compounds, such as indole-3-acetic acid (IAA), flavonoids and sugars. Moreover, the strain have effectively colonized the roots of maize and subsequently enhanced the growth of its host plants. On the contrary, application of CA has reduced root growth in maize seedlings as well as root colonization ability of F. culmorum Pz11. Also, maize seedlings exposed to CA exude low quantities of flavonoids and polyphenols. In conclusion, CA reduces the maize root growth and exudation of secondary metabolites, which may affects its ability to attract plant growth promoting endophytic fungi.

Extract of Penicillium sclerotiorum an endophytic fungus isolated from Cassia fistula L. induces cell cycle arrest leading to apoptosis through mitochondrial membrane depolarization in human cervical cancer cells.

Seventeen endophytic fungi were isolated from various tissues of Cassia fistula and the ethyl acetate extracts obtained from 21-day cultures of all the endophytic fungal isolates were initially screened for their cytotoxicity against HeLa (human cervical carcinoma) cells using MTT assay. Of these, Penicillium sclerotiorum extract (PSE), significantly affected the viability of HeLa cells in a dose-dependent manner. The extract of P. Sclerotiorum was further analyzed by GC-MS, which showed three compounds, hexadecanoic acid, oleic acid and benzoic acid to be the major active principles in the extracts.The extract was further tested for invitro cytotoxicity against five cancer cell lines. Of the cell lines tested, HeLa cells showed maximum sensitivity followed by A549, while A431 and U251 were moderately sensitive and MCF-7 was insensitive to the treatment. In addition, normal human embryonic kidney cells, HEK293 remained insensitive to the treatment. Furthermore, the mechanism of cytotoxic activity exhibited by PSE was investigated by evaluating cell cycle progression and apoptotic induction in HeLa cells. Cell cycle analysis revealed that the PSE arrested cells at S and G2/M phase of the cell cycle in a dose-dependent manner. Annexin V- Propidium iodide double staining showed that, the extract potentiates apoptosis rather than necrosis in cells. This was supported by the down regulation in the proapoptotic protein BCL2 and up regulation of BAX (BCL2 Associated X), tumor suppressor protein, p53 and Apaf-1 [Apoptotic Peptidase Activating Factor 1]. Loss of mitochondrial membrane potential and a distinct DNA fragmentation pattern observed following the treatment, suggest that the PSE treatment leads to activation of mitochondrial pathway of apoptosis. Further, the extract also exhibited both antioxidant and anti-angiogenic properties. These results indicate that endophytic fungi isolated from medicinal plants may serve as potential sources of the anti-cancerous compounds.

Biodegradation of phenanthrene by endophytic fungus Phomopsis liquidambari in vitro and in vivo.

Phenanthrene, as a widespread polycyclic aromatic hydrocarbons (PAHs) contaminant in vitro and in vivo of plant, has the characteristics of carcinogenicity, teratogenicity and mutagenicity. This work aimed to explore the phenanthrene metabolic mechanism by Phomopsis liquidambari in vitro, as well as the bioremediation ability through P. liquidambari-rice combination. This strain was able to use phenanthrene as source of carbon and energy to grow, more than 77% of added 50 mg L-1 phenanthrene was removed after 10 d in MSM. We identified the metabolic products via HPLC-MS and proposed two possible degradation pathways. Phenanthrene was firstly combined with oxygen to become phenanthrene 9,10-oxide, and then degraded to 9-phenanthrol, followed by oxidization to 9,10-dihydroxyphenanthrene. In addition, that epoxide (phenanthrene 9,10-oxide) was also hydrolyzed to phenanthrene trans-9,10-dihydrodiol, and then dehydrogenized to 9,10-dihydroxyphenanthrene, which was further degraded to 9,10-phenanthrenequinone; during this metabolic pathway, the changes of P450 monooxygenase, epoxide hydrolase, dehydrogenase and catechol 2,3-dioxygenase activities and their corresponding gene transcription levels were closely related. What's more, P. liquidambari could combine with rice to eliminate phenanthrene accumulated in vivo of rice seedlings, and the removal rate in inoculation treatment represented a significant difference (increased 25.68%) compared with uninoculation treatment after cultivation 30 d. Therefore, we concluded that P. liquidambari could not only respond to phenanthrene pollution stress in vitro but also exert a mitigation effect on plants accumulated phenanthrene. This work provides a foundation for applying endophytic fungi to PAHs bioremediation in vitro and in vivo.

Effects of a dark septate endophyte (DSE) on growth, cadmium content, and physiology in maize under cadmium stress.

Dark septate endophytes (DSE) are widely distributed in plant roots grown in stressful habitats, especially in heavy metal-polluted soils. But little is known about the physiological interactions between DSE and plants under heavy metal stress. In the present study, the growth, Cd content, and physiological response of Zea mays L. to a root-colonized DSE, Exophiala pisciphila, were analyzed under Cd stress (0, 5, 10, 20, and 40 mg/kg) in a sand culture experiment. Under high Cd (10, 20, and 40 mg/kg) stress, the DSE colonization in roots increased the maize growth, kept more Cd in roots, and decreased Cd content in shoots. The DSE colonization improved the photosynthesis and induced notable changes on phytohormones but had no significant effect on the antioxidant capability in the maize leaves. Moreover, there were significant positive correlations between the gibberellic acid (GA) content and transpiration rate, zeatin riboside (ZR) content, and photosynthetic rate in maize leaves. These results indicated that the DSE's ability to promote plant growth was related to a decrease on Cd content and the regulation on phytohormone balance and photosynthetic activities in maize leaves.

Impact of endophytic colonization patterns on Zamioculcas zamiifolia stress response and in regulating ROS, tryptophan and IAA levels under airborne formaldehyde and formaldehyde-contaminated soil conditions.

Deeper understanding of plant-endophyte interactions under abiotic stress would provide new insights into phytoprotection and phytoremediation enhancement. Many studies have investigated the positive role of plant-endophyte interactions in providing protection to the plant against pollutant stress through auxin (indole-3-acetic acid (IAA)) production. However, little is known about the impact of endophytic colonization patterns on plant stress response in relation to reactive oxygen species (ROS) and IAA levels. Moreover, the possible effect of pollutant phase on plant stress response is poorly understood. Here, we elucidated the impact of endophytic colonization patterns on plant stress response under airborne formaldehyde compared to formaldehyde-contaminated soil. ROS, tryptophan and IAA levels in the roots and shoots of endophyte-inoculated and non-inoculated plants in the presence and absence of formaldehyde were measured. Strain-specific quantitative polymerase chain reaction (qPCR) was used to investigate dynamics of endophyte colonization. Under the initial exposure to airborne formaldehyde, non-inoculated plants accumulated more tryptophan in the shoots (compared to the roots) to synthesize IAA. However, endophyte-inoculated plants behaved differently as they synthesized and accumulated more tryptophan in the roots and, hence, higher levels of IAA accumulation and exudation within roots which might act as a signaling molecule to selectively recruit B. cereus ERBP. Under continuous airborne formaldehyde stress, higher levels of ROS accumulation in the shoots pushed the plant to synthesize more tryptophan and IAA in the shoots (compared to the roots). Higher levels of IAA in the shoots might act as the potent driving force to relocalize B. cereus ERBP from roots to the shoots. In contrast, under formaldehyde-contaminated soil, B. cereus ERBP colonized root tissues without moving to the shoots since there was a sharp increase in ROS, tryptophan and IAA levels of the roots without any significant increase in the shoots. Pollutant phase affected endophytic colonization patterns and plant stress responses differently.

Is the plant-associated microbiota of Thymus spp. adapted to plant essential oil?

We examined whether the microbiota of two related aromatic thyme species, Thymus vulgaris and Thymus citriodorus, differs in relation to the composition of the respective essential oil (EO). A total of 576 bacterial isolates were obtained from three districts (leaves, roots and rhizospheric soil). They were taxonomically characterized and inspected for tolerance to the EO from the two thyme species. A district-related taxonomic pattern was found. In particular, high taxonomic diversity among the isolates from leaves was detected. Moreover, data obtained revealed a differential pattern of resistance of the isolates to EOs extracted from T. vulgaris and T. citriodorus, which was interpreted in terms of differing chemical composition of the EO of their respective host plants. In conclusion, we suggest that bacterial colonization of leaves in Thymus spp. is influenced by the EO present in leaf glandular tissue as one of the selective forces shaping endophytic community composition.

Euphorbia milii-native bacteria interactions under airborne formaldehyde stress: Effect of epiphyte and endophyte inoculation in relation to IAA, ethylene and ROS levels.

Better understanding of plant-bacteria interactions under stress is of the prime importance for enhancing airborne pollutant phytoremediation. No studies have investigated plant-epiphyte interactions compared to plant-endophyte interactions under airborne formaldehyde stress in terms of plant Indole-3-acetic acid (IAA), ethylene, reactive oxygen species (ROS) levels and pollutant removal efficiency. Euphorbia milii was inoculated with native plant growth-promoting (PGP) endophytic and epiphytic isolates individually to investigate plant-endophyte compared to plant-epiphyte interactions under continuous formaldehyde fumigation. Under airborne formaldehyde stress, endophyte interacts with its host plant closely and provides higher levels of IAA which protected the plant against formaldehyde phytotoxicity by lowering intracellular ROS, ethylene levels and maintaining shoot epiphytic community; hence, higher pollutant removal. However, plant-epiphyte interactions could not provide enough IAA to confer protection against formaldehyde stress; thus, increased ROS and ethylene levels, large decrease in shoot epiphytic population and lower pollutant removal although epiphyte contacts with airborne pollutant directly (has greater access to gaseous formaldehyde). Endophyte-inoculated plant synthesized more tryptophan as a signaling molecule for its associated bacteria to produce IAA compared to the epiphyte-inoculated one. Under stress, PGP endophyte interacts with its host closely; thus, better protection against stress and higher pollutant removal compared to epiphyte which has limited interactions with the host plant; hence, lower pollutant removal.

Effect of endophytic Bacillus cereus ERBP inoculation into non-native host: Potentials and challenges for airborne formaldehyde removal.

Phytoremediation could be a cost-effective, environmentally friendly approach for the treatment of indoor air. However, some drawbacks still dispute the expediency of phytotechnology. Our objectives were to investigate the competency of plant growth-promoting (PGP) endophytic Bacillus cereus ERBP (endophyte root blue pea), isolated from the root of Clitoria ternatea, to colonize and stabilize within Zamioculcas zamiifolia and Euphorbia milii as non-native hosts without causing any disease or stress symptoms. Moreover, the impact of B. cereus ERBP on the natural shoot endophytic community and for the airborne formaldehyde removal capability of non-native hosts was assessed. Non-native Z. zamiifolia was effectively inoculated with B. cereus ERBP through soil as the most efficient method of endophyte inoculation. Denaturing gradient gel electrophoresis profiling of the shoot endophytic community verified the colonization and stability of B. cereus ERBP within its non-native host during a 20-d fumigation period without interfering with the natural shoot endophytic diversity of Z. zamiifolia. B. cereus ERBP conferred full protection to its non-native host against formaldehyde phytotoxicity and enhanced airborne formaldehyde removal of Z. zamiifolia whereas non-inoculated plants suffered from formaldehyde phytotoxicity because their natural shoot endophytic community was detrimentally affected by formaldehyde. In contrast, B. cereus ERBP inoculation into non-native E. milii deteriorated airborne formaldehyde removal of the non-native host (compared to a non-inoculated one) as B. cereus ERBP interfered with natural shoot endophytic community of E. milii, which caused stress symptoms and stimulated ethylene biosynthesis. Non-native host inoculation with PGP B. cereus ERBP could bear potentials and challenges for airborne formaldehyde removal.

Environmental stress and elicitors enhance taxol production by endophytic strains of Paraconiothyrium variabile and Epicoccum nigrum.

This study examined the effect of different elicitors (seven, different concentrations) and environmental factors (water activity (aw), pH) on taxol production by strains of two endophytic fungi, Paraconiothyrium variabile and Epicoccum nigrum, isolated from temperate yew trees. A defined liquid broth medium was modified with elicitors, solute aw depressors at different pH values. For P. variabile, the best elicitor was salicylic acid at 50mg/l which gave a taxol yield of 14.7±4.8µg/l. The study of synergistic effects between elicitor, aw and pH on taxol production showed that the highest yield of taxol (68.9±11.9µg/l) was produced under modified ionic stress of 0.98aw (KCl) at pH 5 when supplemented with 20mg/l of salicylic acid. For E. nigrum, serine was the best elicitor which increased yield significantly (29.6 fold) when KCL was used as the aw depressor (0.98aw) at pH 5.0 with 30mg/l of serine. The maximum taxol yield produced by E. nigrum was 57.1±11.8µg/l. Surface response models were used to build contour maps to determine the conditions for maximum and marginal conditions for taxol yield in relation to the best elicitor and aw, and the best pH for the first time. This will be beneficial for identifying key parameters for improvement of taxol yields by endophytic fungi.

Effects of Tricyclazole on Cadmium Tolerance and Accumulation Characteristics of a Dark Septate Endophyte (DSE), Exophiala pisciphila.

Exophiala pisciphila is a cadmium-tolerant fungus, and produces 1,8-dihydroxynaphthalene melanin which can be inhibited by tricyclazole. Tricyclazole at higher levels (20 and 40 µg mL−1) reduced the growth and sporulation of E. pisciphila, but toxicity was not observed at a low concentration (2.5 µg mL−1). Under cadmium (Cd) stress (50, 100 and 200 mg L−1), 2.5 µg mL−1 of tricyclazole reduced fungal growth and sporulation. These reduces indicated a decrease on Cd tolerance of E. pisciphila. For both the 0 and 2.5 µg mL−1 tricyclazole treatments, Cd was associated mostly with cell walls and was extracted by 2 % acetic acid and 1 M NaCl. The FTIR spectra of the E. pisciphila mycelia were similar for both 0 and 2.5 µg mL−1 tricyclazole treatments, which showed hydroxyl, amine, carboxyl and phosphate groups. Thus inhibition of melanin synthesis by tricyclazole did not change Cd accumulation characteristics in E. pisciphila. Results suggested that melanin played a protective role for E. pisciphila against Cd stress, but inhibition of melanin synthesis did not have a remarkable impact on Cd accumulation in E. pisciphila.

Subcellular distribution and chemical forms of cadmium in a dark septate endophyte (DSE), Exophiala pisciphila.

Our objective was to understand the cadmium (Cd) tolerance mechanisms by investigating the subcellular distribution, chemical forms of Cd and adsorptive groups in the mycelia of Exophiala pisciphila. We grew E. pisciphila in the liquid media with increasing Cd concentrations (0, 25, 50, 100, 200, and 400 mg L(-1)). Increased Cd in the media caused a proportional increase in the Cd uptake by E. pisciphila. Subcellular distribution indicated that 81 to 97% of Cd was associated with the cell walls. The largest amount and proportion (45-86%) of Cd was extracted with 2% acetic acid, and a concentration-dependent extraction was observed, both of which suggest that Cd-phosphate complexes were the major chemical form in E. pisciphila. A large distribution of phosphate and Cd on the mycelia surface was observed by scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). The precipitates associated with the mycelia were observed to contain Cd by transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX). Fourier transform infrared (FTIR) identified that hydroxyl, amine, carboxyl, and phosphate groups were responsible for binding Cd. We conclude that Cd associated with cell walls and integrated with phosphate might be responsible for the tolerance of E. pisciphila to Cd.

Characterization of cadmium-resistant endophytic fungi from Salix variegata Franch. in Three Gorges Reservoir Region, China.

The community and Cd-resistance of endophytic fungi from roots of Salix variegata Franch. collected from the water-level-fluctuation zone of Three Gorges Reservoir Region, China, were investigated. A total of 53 strains were isolated and identified to 13 morphotaxa, in which Chromosporium, Fusarium and Gonatobotrys were dominant genera. Among them, 27 isolates were selected to measure their resistance to 0.02 mg ml(-1) Cd(2+) and 11 were growth stimulated (Tolerance index>100%). Of these active isolates, four dark septate endophyte (DSE) isolates (Paraphaeosphaeria sp. SR46, Pyrenochaeta sp. SR35, Rhizopycnis vagum SR37 and R. vagum SR44) were further tested for minimum inhibitory concentrations (MICs) against Cd and SR46 was found to be the most tolerant isolate with MIC of 0.39 mg ml(-1). Additionally, the maximum uptake values of these DSEs ranged from 3.01 to 7.89 mg g(-1), but there was no significant correlation between metal uptake with fungal biomass and metal tolerance. Subsequently, a pot experiment was conducted for investigating the impact of SR46 on corn seedlings in Cd-enriched soil. The results obtained suggested that SR46 reduced the Cd bioaccumulation of plant under low (100 mg kg(-1)) Cd stress and enhanced the Cd translocation from root zone to aerial parts under high (200 mg kg(-1)) Cd stress. Besides, it promoted plant growth without Cd stress. These findings indicated S. variegata harbors an endophytic fungal flora showing a high genetic diversity as well as a high level of metal resistance to Cd that has potential values in cadmium cycling and restoration of plant, soil and water system.

Tolerance and antioxidant response of a dark septate endophyte (DSE), Exophiala pisciphila, to cadmium stress.

The growth, oxidative damage and antioxidant response of Exophiala pisciphila ACCC32496, a dark septate endophyte isolated from an abandoned lead-zinc mining area, were measured at cadmium (Cd) concentrations of 0, 25, 50, 100, 200 and 400 mg L(-1). The EC50 values of E. pisciphila ACCC32496 to Cd were 332.2 mg L(-1) after 30 days on solid medium and 111.2 mg L(-1) after 7 days in liquid medium. Cd stress markedly stimulated the production of superoxide anion, H2O2 and malondialdehyde in the fungal mycelia. The activities of superoxide dismutase and catalase reached their maxima at 100 mg L(-1) Cd. The glutathione and non-protein thiol contents, along with the total antioxidant capability, reached their maxima at 50 mg L(-1) Cd. Low Cd concentrations induced a noticeable increase in antioxidant defense, while high Cd concentrations decreased the antioxidant defense.

Effects of plant stress signal molecules on the production of wilforgine in an endophytic actinomycete isolated from Tripterygium wilfordii Hook.f.

The endophytic actinomycete F4-20 was isolated from Tripterygium wilfordii Hook.f. and was confirmed to produce wilforgine, a secondary metabolite discovered in its host. F4-20 showed a close phylogenetic relationship to Streptomyces species. To seek elicitors that may enhance the production of wilforgine in F4-20, four plant stress molecules were applied to the in vitro liquid cultures. Results showed that methyl jasmonate (MeJA), salicylic acid (SA), and hydrogen peroxide (H2O2) inhibited bacterial growth, whereas glutathione (GSH) treatment significantly increased bacterial growth. The wilforgine contents in the mycelia of F4-20 were reduced by MeJA and GSH but were induced by SA and H2O2. When added in the end of the culture period (7 day), 1 mM SA and 5 mM H2O2 resulted in 69.35 ± 1.71 and 71.80 ± 3.35 µg/g DW of wilforgine production, 1.55 and 1.60 fold to that of control (44.83 ± 1.35 µg/g DW), respectively. Though this improved production was about 6.5 times lower than that of the natural root (454.00 µg/g dry root bark), it provided an alternative method for the production of valuable plant secondary metabolites.