A nonpathogenic Fusarium oxysporum strain enhances phytoextraction of heavy metals by the hyperaccumulator Sedum alfredii Hance

Bio-organic fertilizer promoted phytoremediation using native plant leymus chinensis in heavy Metal(loid)s contaminated saline soil

Heavy metal(loid)s (HMs) contaminated saline soil appeared around the world, however, remediation regarding these collected from field conditions remains unknown. Native plants cultivation and bio-organic fertilizer (BOF) application were two efficient tools for soil amelioration. Herein, a pot experiment was conducted to examine the feasibility of a native plant (Leymus chinensis) for phytoremediation, and investigate the impacts of lignite based bio-organic fertilizer (LBOF) and manure based bio-organic fertilizer (MBOF) on phytoremediation of the soil contaminated by Pb, Cd, As, Zn, Cu, Ca²⁺, and SO₄^2-. The results demonstrated the effectiveness of L. chinensis and highlighted the positive impacts of BOF according to the improved plant growth, HMs phytostabilization, salt removal, and soil properties. LBOF and MBOF changed soil microbiome to assist phytoremediation in addition to physiological modulation. Having enhanced fungal and bacterial richness respectively, LBOF and MBOF recruited various plant growth promoting rhizobacteria with different functions, and shifted microbial co-occurrence networks and keystone taxa towards these different but beneficial forms. Structural equation models comprehensively reveled the strategy discrepancy of LBOF and MBOF to regulate the plant biomass, HMs uptake, and soil salt. In summary, L. chinensis coupled with BOF, especially LBOF, was a effective strategy to remediate HMs contaminated saline soil.

Rhodococcus qingshengii facilitates the phytoextraction of Zn, Cd, Ni, and Pb from soils by Sedum alfredii Hance

The enhanced heavy metal (HM) phytoextraction efficiency of hyperaccumulating plants via plant-growth-promoting microbes has been proposed as an effective strategy to remove HMs from contaminated soil. Nevertheless, it remains unclear whether catabolizing the abscisic acid (ABA) in hyperaccumulating plants via rhizobacteria can facilitate HM phytoextraction. In the present study, a hyperaccumulator, Sedum alfredii Hance, inoculated with an ABA-catabolizing bacterium Rhodococcus qingshengii, showed higher concentrations of Zn, Cd, Ni, and Pb in the contaminated paddy-grown plant shoots by 35%, 63%, 49%, and 49%, and in plants grown in mine soils by 112%, 105%, 46%, and 49%, respectively, than in the control_{bacteria-free} plants. However, no significant changes were observed in Cu content between these plants. Furthermore, parameters indicating phytoremediation potential, including the translocation factor (TF) and bioconcentration factor (BCF), revealed that bacterial inoculation could markedly increase the efficacy of Zn, Cd, Ni, and Pb phytoextraction from the soil. Notably, the bioavailabilities of HMs in soils were not influenced by R. qingshengii; however, the expression of transporters related to the uptake of these HMs, including SaIRT1, SaZIP1, SaZIP2, SaZIP3, SaNramp1, SaNramp3, SaNramp6, SaHMA2, and SaHMA3, was upregulated. These findings indicate that R. qingshengii inoculation could increase the HM-uptake ability of plants by catabolizing ABA and may provide a promising strategy for enhancing the phytoremediation efficacy in HM-contaminated soils.

Characterization of copper stress response in Fusarium tricinctum M6: A metal-resistant microorganism isolated from an acid mine drainage-affected environment

Acid mine drainage-affected environments are interesting microbial niches for the isolation of metal-resistant microorganisms. In this sense, the aim of the present work is to isolate and characterize metal-resistant microorganisms from sediments of an abandoned gold mine located in San Luis (Argentina). For these purposes, the metal removal capacity and the microelemental composition of the biomass exposed to metals were evaluated. Likewise, proteomic techniques were applied to understand the removal and resistance mechanisms. Fusarium tricinctum M6 was isolated and identified as tolerant to Cu(II), Fe(II) and Cr(VI). When faced with 40 µg mL-1 Cu(II), the growth was affected by 60% and the removal capacity was 30-35%. Copper was found uniformly distributed in the biomass (5.23% w/w) and variations in the proportion of other biomass constituent elements were detected. When exposed to Cu(II), F. tricinctum M6 showed differential expression of intra and extracellular proteins involved in different metabolic processes. A large number of proteins with metal ion binding sites were detected both at intra and extracellular levels. The results obtained in the present work indicated bioadsorption of the metal on the cell surface and an important readjustment of the protein expression to counteract the stress produced by Cu(II).

Identifying the Specific Root Microbiome of the Hyperaccumulator Noccaea brachypetala Growing in Non-metalliferous Soils

Noccaea brachypetala is a close relative of Noccaea caerulescens, a model plant species used in metal hyperaccumulation studies. In a previous survey in the Catalan Pyrenees, we found two occidental and two oriental N. brachypetala populations growing on non-metalliferous soils, with accumulated high concentrations of Cd and Zn. Our hypothesis was that the microbiome companion of the plant roots may influence the ability of these plants to absorb metals. We performed high-throughput sequencing of the bacterial and fungal communities in the rhizosphere soil and rhizoplane fractions. The rhizobiomes and shoot ionomes of N. brachypetala plants were analyzed along with those from other non-hyperaccumulator Brassicaceae species found at the same sampling locations. The analyses revealed that microbiome richness and relative abundance tended to increase in N. brachypetala plants compared to non-hyperaccumulator species, regardless of plant location. We confirmed that the root compartment is a key factor in describing the community composition linked to the cohabiting Brassicaceae species, and the rhizoplane fraction contained the specific and rare taxa associated with each species. N. brachypetala plants harbored a similar relative abundance of fungi compared to the other plant hosts, but there was a notable reduction in some specific taxa. Additionally, we observed an enrichment in the hyperaccumulator rhizoplane of previously described metal-tolerant bacteria and bacteria involved in nitrogen cycling. The bacteria involved in the nitrogen cycle could contribute indirectly to the hyperaccumulator phenotype by improving soil quality and fertility. Our results indicate that N. brachypetala captures a particular prokaryotic community from the soil. This particular prokaryotic community may benefit the extraction of metal ions and/or improve plant nutrition. Our research identified satellite groups associated with the root niche of a hyperaccumulator plant that may assist in improving biological strategies in heavy metal remediation.

Enhanced phytoremediation of PAHs and cadmium contaminated soils by a Mycobacterium

This study investigated Fire Phoenix (Festuca L.) and Echinacea purpurea (L.) Moench inoculated with a Mycobacterium strain N12 in remediation of soils contaminated with both polycyclic aromatic hydrocarbons (PAHs) and cadmium (Cd). Plant growth and PAH and Cd removal were monitored in 60, 120, and 150 days after transplanting. Results showed that Fire Phoenix plants grown in soil containing 200 mg/kg PAHs and 15 mg/kg Cd inoculated with N12 were able to remove 76.3% PAHs compared to removal of 68.3% of PAHs by the plants without N12 inoculation. On day 150, the underground biomass of Fire Phoenix plants grown in soil inoculated with N12 increased 59.40% compared to that without N12 inoculation. The enhanced removal of PAH by Fire Phoenix and N12 was related to the improved rhizosphere microbial activities. However, inoculation of N12 to E. purpurea grown soil did not significantly improve the removal of PAHs and Cd. Our results showed that phytoremediation of PAHs and Cd can be enhanced by a Mycobacterium strain N12, especially when PLFA concentrations of bacteria and fungi exceeded 60% of the initial concentrations, but the enhancement is plant species dependent.

Indigenous strain Bacillus XZM assisted phytoremediation and detoxification of arsenic in Vallisneria denseserrulata

The symbiosis between Vallisneria denseserrulata and indigenous Bacillus sp. XZM was investigated for arsenic removal for the first time. It was found that the native bacterium was able to reduce arsenic toxicity to the plant by producing higher amount of extra cellular polymeric substances (EPS), indole-3-acetic acid (IAA) and siderosphore. Interestingly, V. denseserrulata-Bacillus sp. XZM partnership showed significantly higher arsenic uptake and removal efficiency. The shift in FT-IR spectra indicated the involvement of amide, carboxyl, hydroxyl and thiol groups in detoxification of arsenic, and the existence of an arsenic metabolizing process in V. denseserrulata leaves. The scanning electron microscopy (SEM) images further confirmed that the bacterium colonized on plant roots and facilitated arsenic uptake by plant under inoculation condition. In plant, most of the arsenic existed as As(III) (85%) and was massively (>77%) found in vacuole of particularly leaves cells. Thus, these findings are highly suggested for arsenic remediation in the constructed wetlands.

Fungal endophyte Phomopsis liquidambari biodegrades soil resveratrol: a potential allelochemical in peanut monocropping systems

BACKGROUND

Most allelochemicals are secondary products released from root excretions or plant residues that accumulate in continuous cropping systems and cause severe decline in peanut yield. Resveratrol is a plant-derived stilbene that is released from peanut residues and accumulates in the soil; however, its allelopathic effects on peanut production are overlooked. Effective management solutions need to be developed to relieve allelopathy caused by soil resveratrol. Here, the biodegradation of resveratrol by the fungal endophyte Phomopsis liquidambari was investigated in a mineral salt medium and a soil trial. Resveratrol and its metabolites (produced by degradation by P. liquidambari) were detected by high-performance liquid chromatography-mass spectrometry (HPLC-MS).

RESULTS

Resveratrol released from peanut residues reached a maximum concentration of 0.18 μg g^-1 soil in litterbag experiments. Exogenous resveratrol inhibited peanut growth, nodule formation, and soil dehydrogenase activity, and reduced the soil microbial biomass carbon content and bacterial abundance, indicating an allelopathic role in peanut growth. More than 97% of the resveratrol was degraded within 72 and 168 h by P. liquidambari in pure culture and soil conditions, respectively. Resveratrol was first cleaved to 3,5-dihydroxybenzaldehyde and 4-hydroxybenzaldehyde, which were subsequently oxidized into 3,5-dihydroxybenzoic acid and 4-hydroxybenzoic acid, respectively. Fungal resveratrol cleavage oxygenase and the related gene expression were enhanced when P. liquidambari was induced by the resveratrol during the incubation.

CONCLUSION

Our results indicate that the practical application of the fungal endophyte P. liquidambari has strong potential for biodegrading soil resveratrol, which can cause allelopathy in peanut continuous cropping systems. © 2019 Society of Chemical Industry.

Enzymatic potential and biosurfactant production by endophytic fungi from mangrove forest in Southeastern Brazil

Microbial activity is the main route for cycling mangrove nutrients. In general, microorganisms have abilities to degrade lignocellulosic compounds. Among the biotechnological potential of the microbiota from mangroves, it is noteworthy about endophytic fungi, which can be considered as effective sources of different bioactive compounds. In this sense, thirty (30) endophytic fungi were isolated from mangrove forest sampling Cananeia, SP, Brazil. These microorganisms were analyzed about their enzymatic activities including: lignin peroxidase EC 1.11.1.14, manganese peroxidase EC 1.11.1.13 and laccase EC 1.10.3.2, as well endo-cellulase EC 3.2.1.4 and endo-xylanase EC 3.2.1.8. Besides that, production of bioactive secondary metabolites like biosurfactant and/or bioemulsifier was also investigated. As results, nineteen (19) isolates were selected about their ligninolytic abilities, nine (9) of them about cellulase activity and thirteen (13) showed xylanase abilities. The fungal isolate named as 3(3), characterized as Fusarium sambucinum, showed a prominent lignin peroxidase (42.4 U L⁻¹) and manganese peroxidase (23.6 U L⁻¹) activities. The isolate 63.1, also related to Fusarium sp. genera, was selected about its laccase activity (41.5 U L⁻¹). From all the investigated fungi, the isolate 47(4) Trichoderma camerunense was selected about its cellulolytic and xylanolytic activities, showing 45.23 and 26.09 U mL⁻¹, respectively. The same fungi also showed biosurfactant ability demonstrated by superficial tension decreasing to 38 mN/m. In addition, fifteen (15) fungi exhibited bioemulsifier activity, with E₂₄ values up to 62.8%.

Effects of micro-/nano-hydroxyapatite and phytoremediation on fungal community structure in copper contaminated soil

Micro-/nano-hydroxyapatite (MHA/NHA) has been used to reduce the concentration of available heavy metals and increase soil pH in the remediation of heavy metal-contaminated soils. However, little is known about the effects of MHA and NHA on soil fungal communities and function. In this study, fungal community composition was characterized from copper-contaminated soils amended with MHA, NHA and three other classic amendments combined with Elsholtzia splendens during a 3-year immobilization experiment. High-throughput sequencing results showed that applications of MHA increased the richness and diversity of the fungal community, which was opposite the results of NHA. SIMPER analysis indicated that both the relative abundance of fungi associated with biosorption and plant growth promotion increased, whereas the relative abundance of fungi related to bioleaching and potential pathogens decreased after applying MHA. Redundancy (RDA) analysis revealed that the soil pH was a crucial environmental factor in the succession of fungal communities. In addition, the results of functional prediction via FUNGuild suggested that the application of MHA had the potential to reduce the risk of pathogens infecting animals and plants in the soil but that NHA had some environmental risks. Overall, fungal community showed a synergistic effect of immobilization with the test amendments, and MHA was better for the remediation of heavy metal-contaminated soils than the other test amendments.

Promotion of the root development and Zn uptake of Sedum alfredii was achieved by an endophytic bacterium Sasm05

Endophyte-assisted phytoremediation has gained increasing attention. However, the interacting mechanisms of endophytes and metal hyperaccumulators are still not clear. An endophytic bacterium Pseudomonas fluorescens Sasm05 inoculation promoted Sedum alfredii Hance rooting and root development, in which the specific root length (SRL) and average number of root tips (ART) increased to 2.09- and 3.35-fold, respectively. Sasm05 inoculation promoted plant growth, increased the chlorophyll content, and elevated Zn uptake of plant at excess Zn supply. At 200 μM Zn treatment level, Sasm05 inoculation increased plant biomass and the chlorophyll content by more than 40%, and root Zn content by 40%. Furthermore, Sasm05 inoculation upregulated the expression of the Zn transporter SaIRT1 to 3.43-fold in the roots, while another transporter SaNramp1 expression was increased to 38.66-fold in the roots and 7.53-fold in the shoots. Time course study showed the best effects of Sasm05 on plant biomass and the chlorophyll content were detected at 30 d, while for Zn content at 3 d. These results firstly provided molecular evidences of endophytic bacteria in facilitating host plant Zn uptake, which will absolutely benefit the understanding of interacting mechanisms between hyperaccumulators and their endophytes.

Bacterial communities of three plant species from Pb-Zn contaminated sites and plant-growth promotional benefits of endophytic Microbacterium sp. (strain BXGe71)

The endophytic bacterial community of two hyperaccumulators (Arabis alpine, Dysphania ambrosioides) and Veronica ciliate was investigated by Illumina sequencing technology. In addition, the culturable endophytic bacteria (EB) were isolated and their plant-growth promotion capabilities were studied. A dataset consisting of 221,075 filtered high-quality and classifiable unique 16S rDNA gene tags, and an average of 36,846 tags with a mean length of 464-bp for each sample was generated. In total, 10801 different operational taxonomic units (OTUs) were detected, belonging to 18 bacterial phyla, 41 classes, 91 orders, 135 families, and 215 genera. Pseudomonas was the most dominant genus in both shoots and roots of the two hyperaccumulators, making up 81.56% and 81.13%, 41.60% and 77.06% of the total number of OTUs, respectively. However, both Chao 1 and Shannon indices of EB of the two hyperaccumulators were significantly lower than those of V. ciliate (P <. 05), except the Shannon index of D. ambrosioides shoots. The endophytic bacterial community of roots and shoots of A. alpine showed greater similarity with that of D. ambrosioides roots (12 km away), and clustered to one group in dendrogram, in clear contrast to that of V. ciliate, which grew closer to A. alpine (60 m away). Combining results of soil and plant analyses, we suggest that the soil properties, especially heavy metal concentration, may influence the plants endophytic bacterial community composition. Pot experiments showed that the strain BXGe71 (Microbacterium sp.) from A. alpine significantly enhanced host plants' growth under multi-heavy metal (HM) stress (P < .05, t-test).

Degradative properties of two newly isolated strains of the ascomycetes Fusarium oxysporum and Lecanicillium aphanocladii

Two ascomycete strains were isolated from creosote-contaminated railway sleeper wood. By using a polyphasic approach combining morpho-physiological observations of colonies with molecular tools, the strains were identified as Fusarium oxysporum Schltdl. (IBPPM 543, MUT 4558; GenBank accession no. MG593980) and Lecanicillium aphanocladii Zare & W. Gams (IBPPM 542, MUT 242; GenBank accession no. MG593981). Both strains degraded hazardous pollutants, including polycyclic aromatic hydrocarbons, anthraquinone-type dyes, and oil. Oil was better degraded by F. oxysporum, but the aromatic compounds were better degraded by L. aphanocladii. With both strains, the degradation products of anthracene, phenanthrene, and fluorene were 9,10-anthraquinone, 9,10-phenanthrenequinone, and 9-fluorenone, respectively. During pollutant degradation, F. oxysporum and L. aphanocladii produced an emulsifying compound(s). Both fungi produced extracellular Mn-peroxidases, enzymes possibly involved in the fungal degradation of the pollutants. This is the first report on the ability of L. aphanocladii to degrade four-ring PAHs, anthraquinone-type dyes, and oil, with the simultaneous production of an extracellular Mn-peroxidase.

The Effects of the Endophytic Bacterium Pseudomonas fluorescens Sasm05 and IAA on the Plant Growth and Cadmium Uptake of Sedum alfredii Hance

Endophytic bacteria have received attention for their ability to promote plant growth and enhance phytoremediation, which may be attributed to their ability to produce indole-3-acetic acid (IAA). As a signal molecular, IAA plays a key role on the interaction of plant and its endomicrobes. However, the different effects that endophytic bacteria and IAA may have on plant growth and heavy metal uptake is not clear. In this study, the endophytic bacterium Pseudomonas fluorescens Sasm05 was isolated from the stem of the zinc (Zn)/cadmium (Cd) hyperaccumulator Sedum alfredii Hance. The effects of Sasm05 and exogenous IAA on plant growth, leaf chlorophyll concentration, leaf Mg²⁺-ATPase and Ca²⁺-ATPase activity, cadmium (Cd) uptake and accumulation as well as the expression of metal transporter genes were compared in a hydroponic experiment with 10 μM Cd. The results showed that after treatment with 1 μM IAA, the shoot biomass and chlorophyll concentration increased significantly, but the Cd uptake and accumulation by the plant was not obviously affected. Sasm05 inoculation dramatically increased plant biomass, Cd concentration, shoot chlorophyll concentration and enzyme activities, largely improved the relative expression of the three metal transporter families ZRT/IRT-like protein (ZIP), natural resistance associated macrophage protein (NRAMP) and heavy metal ATPase (HMA). Sasm05 stimulated the expression of the SaHMAs (SaHMA2, SaHMA3, and SaHMA4), which enhanced Cd root to shoot translocation, and upregulated SaZIP, especially SaIRT1, expression to increase Cd uptake. These results showed that although both exogenous IAA and Sasm05 inoculation can improve plant growth and photosynthesis, Sasm05 inoculation has a greater effect on Cd uptake and translocation, indicating that this endophytic bacterium might not only produce IAA to promote plant growth under Cd stress but also directly regulate the expression of putative key Cd uptake and transport genes to enhance Cd accumulation of plant.

Structural and functional variability in root-associated bacterial microbiomes of Cd/Zn hyperaccumulator Sedum alfredii

Interactions between roots and microbes affect plant's resistance to abiotic stress. However, the structural and functional variation of root-associated microbiomes and their effects on metal accumulation in hyperaccumulators remain poorly understood. Here, we characterize the root-associated microbiota of a hyperaccumulating (HP) and a non-hyperaccumulating (NHP) genotype of Sedum alfredii by 16S ribosomal RNA gene profiling. We show that distinct microbiomes are observed in four spatially separable compartments: the bulk soil, rhizosphere, rhizoplane, and endosphere. Both the rhizosphere and rhizoplane were preferentially colonized by Proteobacteria, and the endosphere by Actinobacteria. The rhizosphere and endophytic microbiomes were dominated by the family of Sphingomonadaceae and Streptomycetaceae, respectively, which benefited for their survival and adaptation. The bacterial α-diversity decreases along the spatial gradient from the rhizosphere to the endosphere. Soil type and compartment were strongest determinants of root-associated community variation, and host genotype explained a small, but significant amount of variation. The enrichment of Bacteroidetes and depletion of Firmicutes and Planctomycetes in the HP endosphere compared with that of the NHP genotype may affect metal hyperaccumulation. Program PICRUSt predicted moderate functional differences in bacterial consortia across rhizocompartments and soil types. The functional categories involved in membrane transporters (specifically ATP-binding cassette transporters) and energy metabolism were overrepresented in endosphere of HP in comparison with NHP genotypes. Taken together, our study reveals substantial variation in structure and function of microbiomes colonizing different compartments, with the endophytic microbiota potentially playing an important role in heavy metal hyperaccumulation.

The effects of endophytic bacterium SaMR12 on Sedum alfredii Hance metal ion uptake and the expression of three transporter family genes after cadmium exposure

A hydroponic experiment was conducted to investigate the effects of an endophytic bacterium SaMR12 on Sedum alfredii Hance metal ion accumulation, chlorophyll concentration, and the expression of three metal transporter families, zinc-regulated transporters, iron-regulated transporter-like protein (ZIP); natural resistance-associated macrophage protein; and heavy metal ATPase (HMA) at different Cd treatment levels. The results showed that at relatively low Cd conditions (≤25 μM), SaMR12 demonstrated a 19.5-27.5% increase in Fe, a 46.7-90.7% increase in Zn, and a 7.9-43.7% increase in Cu content in the shoot and elevated expression of SaIRT1, SaZIP3, SaHMA2, and SaNramp3 in the shoot and SaZIP1, SaHMA2, SaNramp1, and SaNramp3 in the root. At high Cd conditions (100 and 400 μM), SaMR12 demonstrated a 16.4-18.5% increase in leaf chlorophyll concentration, a 18.9-23.2% increase in Fe, and a 15.4-17.5% increase in Mg content in the shoot and elevated expression of SaZIP3, SaNramp6, SaHMA2, and SaHMA3 in the shoot and SaZIP3, SaNarmp1, SaNarmp3, and SaNarmp6 in the root. These results indicated that SaMR12 can elevate essential metal ion uptake and regulate the expression of transport genes to promote plant growth and enhance Cd tolerance and uptake to improve Cd accumulation up to 118-130%.

Enhanced Cd extraction of oilseed rape (Brassica napus) by plant growth-promoting bacteria isolated from Cd hyperaccumulator Sedum alfredii Hance

Four plant growth-promoting bacteria (PGPB) were used as study materials, among them two heavy metal-tolerant rhizosphere strains SrN1 (Arthrobacter sp.) and SrN9 (Bacillus altitudinis) were isolated from rhizosphere soil, while two endophytic strains SaN1 (Bacillus megaterium) and SaMR12 (Sphingomonas) were identified from roots of the cadmium (Cd)/zinc (Zn) hyperaccumulator Sedum alfredii Hance. A pot experiment was carried out to investigate the effects of these PGPB on plant growth and Cd accumulation of oilseed rape (Brassica napus) plants grown on aged Cd-spiked soil. The results showed that the four PGPB significantly boosted oilseed rape shoot biomass production, improved soil and plant analyzer development (SPAD) value, enhanced Cd uptake of plant and Cd translocation to the leaves. By fluorescent in situ hybridization (FISH) and green fluorescent protein (GFP), we demonstrated the studied S. alfredii endophytic bacterium SaMR12 were able to colonize successfully in the B. napus roots. However, all four PGPB could increase seed Cd accumulation. Due to its potential to enhance Cd uptake by the plant and to restrict Cd accumulation in the seeds, SaMR12 was selected as the most promising microbial partner of B. napus when setting up a plant-microbe fortified remediation system.

Effects of Cd- and Pb-resistant endophytic fungi on growth and phytoextraction of Brassica napus in metal-contaminated soils

Metal-resistant endophytic fungi from roots improved phytoremediation efficacy of host plants; however, the effects of endophytic fungi from plant aerial parts on host plants are unknown. The aim of this study was to develop a feasible method to screen fungal endophytes from stems and roots of Brassica napus and to investigate effects of the endophytic fungi on growth and phytoremediation efficiency of the plant. Endophytic Fusarium sp. CBRF44, Penicillium sp. CBRF65, and Alternaria sp. CBSF68 with different traits were isolated from roots and stems of rapes grown in a metal-contaminated soil. Fusarium sp. CBRF44 (resistant to 5 mM Cd and 15 mM Pb, isolated from roots) and Alternaria sp. CBSF68 (resistant to 1 mM Cd and 10 mM Pb, isolated from stems) could produce indole-3-acetic acid (IAA) and siderophore; Penicillium sp. CBRF65 (tolerate 2 mM Cd and 20 mM Pb, isolated from roots) could not produce IAA and siderophore but showed the highest phosphate-solubilizing activities. Fusarium sp. CBRF44 and Penicillium sp. CBRF65 significantly increased the rape biomass and promoted the extraction efficacy of Pb and Cd, while Alternaria sp. CBSF68 did not show similar results. Penicillium sp. CBRF65 and Fusarium sp. CBRF44 could be frequently recovered from inoculated rape roots, while Alternaria sp. CBSF68 was scarcely recovered. The results indicate that the colonizing capacity of endophytic fungi in roots is important to improve phytoremediation efficacy of host plants.

The Effects of Various Amendments on Trace Element Stabilization in Acidic, Neutral, and Alkali Soil with Similar Pollution Index

Many studies have examined the application of soil amendments, including pH change-induced immobilizers, adsorbents, and organic materials, for soil remediation. This study evaluated the effects of various amendments on trace element stabilization and phytotoxicity, depending on the initial soil pH in acid, neutral, and alkali conditions. As in all types of soils, Fe and Ca were well stabilized on adsorption sites. There was an effect from pH control or adsorption mechanisms on the stabilization of cationic trace elements from inorganic amendments in acidic and neutral soil. Furthermore, acid mine drainage sludge has shown great potential for stabilizing most trace elements. In a phytotoxicity test, the ratio of the bioavailable fraction to the pseudo-total fraction significantly affected the uptake of trace elements by bok choy. While inorganic amendments efficiently decreased the bioavailability of trace elements, significant effects from organic amendments were not noticeable due to the short-term cultivation period. Therefore, the application of organic amendments for stabilizing trace elements in agricultural soil requires further study.

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.

Trichoderma sp. PDR1-7 promotes Pinus sylvestris reforestation of lead-contaminated mine tailing sites

Vegetation is critical to stabilize and remediate mine tailing sites, but plant growth is often poor due to toxicity from heavy metal(loid)s (HMs). A non-symbiotic endophytic fungus, Trichoderma sp. PDR1-7, isolated from Pb-contaminated mine tailing soil, exhibited both high tolerance to HMs and desirable plant growth-promoting characteristics. PDR1-7 promoted HM solubilization in mine tailing soil and removed significant amounts of Pb and other HMs from liquid media containing single and multiple metals. Pb removal efficiency increased with initial pH from 4 to 6 and with Pb concentration from 100 to 125 mg L(-1). Inoculating soil with PDR1-7 significantly increased nutrient availability and seedling growth, chlorophyll and protein contents, as well as antioxidative enzyme (superoxide dismutase) activity. A decrease in malondialdehyde indicated less oxidative stress. HM concentrations were much higher in Pinus sylvestris roots when PDR1-7 was present. These observations suggest the utility of Trichoderma sp. PDR1-7 for pine reforestation and phytoremediation of Pb-contaminated mine soil.

Improved plant growth and Zn accumulation in grains of rice (Oryza sativa L.) by inoculation of endophytic microbes isolated from a Zn Hyperaccumulator, Sedum alfredii H

This study is to investigate the possibility of zinc (Zn) biofortification in the grains of rice (Oryza sativa L.) by inoculation of endophytic strains isolated from a Zn hyperaccumulator, Sedum alfredii Hance. Five endophytic strains, Burkholderia sp. SaZR4, Burkholderia sp. SaMR10, Sphingomonas sp. SaMR12, Variovorax sp. SaNR1, and Enterobacter sp. SaCS20, isolated from S. alfredii, were inoculated in the roots of Japonica rice Nipponbare under hydroponic condition. Fluorescence images showed that endophytic strains successfully colonized rice roots after 72 h. Improved root morphology and plant growth of rice was observed after inoculation with endophytic strains especially SaMR12 and SaCS20. Under hydroponic conditions, endophytic inoculation with SaMR12 and SaCS20 increased Zn concentration by 44.4% and 51.1% in shoots, and by 73.6% and 83.4% in roots, respectively. Under soil conditions, endophytic inoculation with SaMR12 and SaCS20 resulted in an increase of grain yields and elevated Zn concentrations by 20.3% and 21.9% in brown rice and by 13.7% and 11.2% in polished rice, respectively. After inoculation of SaMR12 and SaCS20, rhizosphere soils of rice plants contained higher concentration of DTPA-Zn by 10.4% and 20.6%, respectively. In situ micro-X-ray fluorescence mapping of Zn confirmed the elevated Zn content in the rhizosphere zone of rice treated with SaMR12 as compared with the control. The above results suggested that endophytic microbes isolated from S. alfredii could successfully colonize rice roots, resulting in improved root morphology and plant growth, increased Zn bioavailability in rhizosphere soils, and elevated grain yields and Zn densities in grains.

Role of sulfur assimilation pathway in cadmium hyperaccumulation by Sedum alfredii Hance

Sedum alfredii Hance is a promising cadmium (Cd) hyperaccumulating plant recently identified in China. However, the physiological and molecular mechanisms underlying Cd accumulation, which differentiate hyperaccumulating ecotype (HE) from non-hyperaccumulating ecotype (NHE) has not been elucidated yet. A hydroponic experiment was conducted to investigate the role of sulfur assimilation pathway in Cd hyperaccumulation by the S. alfredii Hance, by analyzing gene expression pattern in sulfur assimilation pathway and the concentration of some sulfur containing compounds. The results show that, sulfur assimilation pathway was affected by Cd differently in HE and NHE S. alfredii Hance. The gene expression pattern of sulfur assimilation pathway was regulated differently in HE and NHE plants, especially the nicotianamine synthase (NAS). NAS transcript levels in root of HE was 141-fold higher than NHE, while in shoots of HE only 0.31-fold higher than NHE. In HE roots, NAS expression level was maximum 3171-fold higher than shoots, while in NHE plants roots NAS expression level was maximum 45.3-fold higher than shoots. In HE plant roots, sulfur, cysteine and methionine concentrations increased 30%, 46% and 835% respectively, by Cd treatment, but in NHE plants roots, sulfur concentration increased less than 1%, cysteine and methionine concentrations decreased 78.5% and 13.3% respectively, by Cd. Cd exposure increased glutathione levels by 142% in HE but less than 10% in NHE plant roots.

Bioremediation of Cd-DDT co-contaminated soil using the Cd-hyperaccumulator Sedum alfredii and DDT-degrading microbes

The development of an integrated strategy for the remediation of soil co-contaminated by heavy metals and persistent organic pollutants is a major research priority for the decontamination of soil slated for use in agricultural production. The objective of this study was to develop a bioremediation strategy for fields co-contaminated with cadmium (Cd), dichlorodiphenyltrichloroethane (DDT), and its metabolites 1, 1-dichloro-2, 2-bis (4-chlorophenyl) ethylene (DDE) and 1, 1-dichloro-2, 2-bis (4-chlorophenyl) ethane (DDD) (DDT, DDE, and DDD are collectively called DDs) using an identified Cd-hyperaccumulator plant Sedum alfredii (SA) and DDT-degrading microbes (DDT-1). Initially, inoculation with DDT-1 was shown to increase SA root biomass in a pot experiment. When SA was applied together with DDT-1, the levels of Cd and DDs in the co-contaminated soil decreased by 32.1-40.3% and 33.9-37.6%, respectively, in a pot experiment over 18 months compared to 3.25% and 3.76% decreases in soil Cd and DDs, respectively, in unplanted, untreated controls. A subsequent field study (18-month duration) in which the levels of Cd and DDs decreased by 31.1% and 53.6%, respectively, confirmed the beneficial results of this approach. This study demonstrates that the integrated bioremediation strategy is effective for the remediation of Cd-DDs co-contaminated soils.