Biochemical mechanism of phytoremediation process of lead and cadmium pollution with Mucor circinelloides and Trichoderma asperellum

Isolation, morpho-physiological and molecular characterization, phylogenetic analysis of Trichoderma asperellum in Bangladesh

The experiment was conducted at the Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh to identify T. asperellum in a countrywide screening program and to evaluate its antagonistic effect against several soil borne pathogens. Samples were collected from the rhizosphere soil of 49 different crops in 107 different locations in Bangladesh, especially, considering the several isolates of T. asperellum for purification. Based on morphological and physiological features, fifteen isolates were selected. Of these, the isolates of TR27 and TR45 were grown and sporulated at 40 °C except all the isolates with 35 °C, and particularly, showing a decrease of mycelial growth across all the isolates for increasing pH. Meanwhile, T. asperellum showed significant antagonistic effects against Fusarium oxysporum, Sclerotium rolfsii and Pythium aphanidermatum, resulting in reducing foot and root rot, collar rot and damping off diseases, respectively. Four isolates were selected for molecular characterization among 15 isolates in terms of higher mycelial growth and spore density in-vitro condition, isolates of (TR27) Sadar, Moulvibazar (Rice), (TR45) Sadar, Mymensingh (Sweet gourd), (TR70) Chapra, Chapai Nawabganj (Sesame) and (TR85) Nayanpur, Lalmonirhat (Maize) were studied at ITS and TEF region. Isolates of TR45, TR70 and TR85 were observed with 98% homology, and TR27 exhibited 88% in their respective closest isolates at ITS sequences. Isolates of TR27 and TR85 also exerted their respective nearest homology (96%), while TR45 showed 99%, and 93% homology with TR70 in TEF sequences. Isolates TR45, TR70 and TR85 were evidently determined as T. asperellum of 100% bootstrap value, and TR27 isolate was also recognized with 72% bootstrap value in the phylogenetic tree. However, complementary effects of significant superior homology and the greatest bootstrap value in the identification of T. asperellum were found as noteworthy. In the phylogenetic analysis, magnificent differentiation among the Trichoderma isolates within and among the groups of closely related species was observed in Tef1 region than reflecting maximum variability in the isolates of rDNA at ITS region, whereas demonstrating a higher transversion ratio and evolutionary divergence.

Effective soil remediation with fungal Co-inoculation and king grass for robust cadmium and chromium phytoextraction

Bioremediation, an economical and environmentally friendly approach, provides a sustainable solution for mitigating heavy metal contamination in soils. This study identifies four fungal strains-Trichoderma harzianum DAA8, Trichoderma reesei DAA9, Rhizomucor variabilis DFB3, and Trichoderma asperellum LDA4-that exhibit tolerance to cadmium (Cd) and chromium (Cr). These strains were isolated from soils impacted by heavy metal contamination in mining regions. Rigorous examinations of these strains led us to determine their Minimum Inhibitory Concentrations (MICs) and optimal absorption-reduction conditions. Our microscopic data and GC-MS analysis indicate that these strains can accumulate Cd and Cr by generating compounds, such as ketones and imines, in heavy metal environments. We evaluated the remediation efficacy of both single and co-cultures of Rhizomucor variabilis DFB3 and Trichoderma asperellum LDA4 in conjunction with king grass, a plant known for its heavy metal accumulation capabilities. Our findings indicated an impressive 41.9% increase in plant biomass and 47.2% and 64.4% increase in Cd and Cr accumulation respectively. The removal rates of Cd and Cr were 16.5% and 19.0%, respectively, following the co-inoculation of Rhizomucor variabilis DFB3 and Trichoderma asperellum LDA4. These rates represent increases of 37.1% and 33.7% compared to the removal rates achieved with king grass alone. This study not only advances strategies to manage Cd-Cr contamination but also sets a pathway for efficient heavy metal soil remediation using a microbial-plant combined technique.

Response of a simulated aquatic fungal community to nanoplastics exposure and functional consequence on leaf decomposition

Nanoplastics pose a potential threat to a wide variety of aquatic organisms. Despite the awareness of this existing hazard, the impact of nanoplastics on natural fungal communities remains a research gap. In this study, five dominant fungi species, isolated from a stream ecosystem, were used to explore the effects of different nano-polystyrene (nano-PS) particles concentrations on a simulated fungal community. Specifically, the evaluation was conducted regarding the fungal growth, reproductivity, structural composition, and ecological function in leaf litter decomposition. A 15-day exposure experiment showed that 100 μg/L nano-PS significantly reduced the microcosm pH. The extracellular enzyme activities of β-glucosidase, leucine-aminopeptidase, and peroxidase were significantly promoted by nano-PS exposure for 5 days or 15 days. Total sporulation rate significantly decreased after the 15-day exposure to 1 and 100 μg/L nano-PS and significantly increased under 10 μg/L nano-PS. In contrast, nano-PS concentrations had no effects on fungal biomass. In addition, the reduced relative abundance of Geotrichum candidum lowered its contribution to leaf decomposition, resulting in a decreased litter decomposition rate of a 24.5-27.9 % after exposure. This suggests that 1-100 μg/L nano-PS inhibited leaf decomposition by inhibiting fungal reproduction and reducing the contribution of specific fungal species. In addition, the findings highlight the importance of exploring the potential mechanisms of the interaction between nanoplastics and fungal species.

Proteomics analysis of resistance mechanism of Trichoderma harzianum under U(VI) stress

Trichoderma harzianum has a certain resistance to Hexavalent Uranium (U(VI)), but its resistance mechanism is unknown. Based on proteomics sequencing using DIA mode, differentially expressed proteins (DEPs) of Trichoderma harzianum under U(VI) stress were identified. GO enrichment, KEGG annotation analysis and DEPs annotation were performed. The results showed that 8 DEPs, 8 DEPs and 15 DEPs were obtained in the low-dose, medium-dose and high-dose groups, respectively. The functional classification of GO demonstrated that DEPs were associated with 17 molecular functions, 5 biological processes, and 5 cellular components. Furthermore, DEPs were enriched in transport and catabolism, energy metabolism, translation, and signal transduction. These findings showed that Trichoderma harzianum was significantly changed in protein expression and signaling pathway after U(VI) exposure. Therefore, these results have provided Trichoderma harzianum with a theoretical background that can be applied to environmental cleanup.

Community-based mechanisms underlying the root cadmium uptake regulated by Cd-tolerant strains in rice (Oryza sativa. L)

In recent years, the problem of Cd pollution in paddy fields has become more and more serious, which seriously threatens the safe production of food crops and human health. Using microorganisms to reduce cadmium pollution in rice fields is a green, safe and efficient method, the complicated interactions between the microbes in rice roots throughout the process of cadmium absorption by rice roots are poorly understood. In this investigation, a hydroponic pot experiment was used to examine the effects of bacteria R3 (Herbaspirillum sp) and T4 (Bacillus cereus) on cadmium uptake and the endophytic bacterial community in rice roots. The results showed that compared with CK (Uninoculated bacterial liquid), the two strains had significant inhibitory or promotive effects on cadmium uptake in rice plant, respectively. Among them, the decrease of cadmium content in rice plants by R3 strain reached 78.57-79.39%, and the increase of cadmium content in rice plants by T4 strain reached 140.49-158.19%. Further investigation showed that the cadmium content and root cadmium enrichment coefficient of rice plants were significantly negatively correlated with the relative abundances of Burkholderia and Acidovorax, and significantly positively correlated with the relative abundances of Achromobacter, Agromyces and Acidocella. Moreover, a more complex network of microbes in rice roots inhibited rice plants from absorbing cadmium. These results suggest that cadmium uptake by rice plants is closely related to the endophytic bacterial community of roots. This study provides a reference scheme for the safe production of crops in cadmium contaminated paddies and lays a solid theoretical foundation for subsequent field applications.

Autochthonous strains of Trichoderma isolated from tannery solid waste improve phytoextraction potential of heavy metals by sunflower

This research work was aimed at isolating and demonstrating the significant potential of autochthonous fungi for phytoextraction of hazardous metals in metal polluted soil using Helianthus annuus. Four multi-metal resistant strains of Trichoderma were selected from a total of 21 strains isolated from tannery polluted soil and tannery solid waste. Autochthonous Trichoderma strains were used singly and in the form of consortium (TC). Sunflower was grown in pots for 90 days having eight different amendments of tannery polluted soil with and without Trichoderma inoculation. Growth and biochemical attributes of the plants were observed along with metal content extract by different plant parts. The results revealed that TC enhanced shoot length, shoot dry weight, and metal uptake as compared to single specie inoculation. Similarly, BCF (72.8-118.23%) and TF were significantly pronounced in shoots of H. annuus grown with TC at 40% amended soil. The biochemical analysis of the plants showed that Trichoderma strains boosted the enzymatic (catalase, peroxidase, and superoxide dismutase) antioxidants in the plants. The use of indigenous fungi with metal accumulating plants like sunflower can help to alleviate metal contamination from industrial sites and can make the soil cultivable for energy crops.

Effects of cadmium (Cd) on fungal richness, diversity, and community structure of Haplic Cambisols and inference of resistant fungal genera

Cadmium (Cd) is one of the most toxic and widely distributed pollutants in mining sites of Northeast China, and how Cd contamination may affect the fungal characteristics of the zonal Haplic Cambisols is still unknown. The study aims to investigate the richness and diversity of fungal community in Haplic Cambisols in response to Cd treatments and to infer Cd-resistant fungal genera. Haplic Cambisol was treated with different concentrations of CdCl₂·2.5H₂O solution (0 mg kg^-1, 1 mg kg^-1, 5 mg kg^-1, 25 mg kg^-1, and 50 mg kg^-1, expressed as CK, T1, T2, T3, and T4, respectively), and fungal community was analyzed by high-throughput sequencing technology at 30 days, 60 days, or 80 days after Cd treatment (expressed as d30, d60, and d80, respectively). The results showed that Cd treatment usually increased the richness and diversity indices, the variation of diversity index under different Cd concentrations was not obvious, and different Cd incubation times had an inhibitory effect on fungal richness, but the diversity first increased and then decreased. Besides, Ascomycota and Mortierellomycota having the highest abundance in Haplic Cambisols showed the most pronounced changes under Cd treatment. Accordingly, Cd-resistant fungi were also found, such as Aspergillus, Fusarium, Penicillium, and Trichoderma, especially Aspergillus, which had relatively high abundance. The results obtained in this study had potentially significant findings for soil biodiversity and Cd bioremediation.

Mucor circinelloides: a model organism for oleaginous fungi and its potential applications in bioactive lipid production

Microbial oils have gained massive attention because of their significant role in industrial applications. Currently plants and animals are the chief sources of medically and nutritionally important fatty acids. However, the ever-increasing global demand for polyunsaturated fatty acids (PUFAs) cannot be met by the existing sources. Therefore microbes, especially fungi, represent an important alternative source of microbial oils being investigated. Mucor circinelloides—an oleaginous filamentous fungus, came to the forefront because of its high efficiency in synthesizing and accumulating lipids, like γ-linolenic acid (GLA) in high quantity. Recently, mycelium of M. circinelloides has acquired substantial attraction towards it as it has been suggested as a convenient raw material source for the generation of biodiesel via lipid transformation. Although M. circinelloides accumulates lipids naturally, metabolic engineering is found to be important for substantial increase in their yields. Both modifications of existing pathways and re-formation of biosynthetic pathways in M. circinelloides have shown the potential to improve lipid levels. In this review, recent advances in various important metabolic aspects of M. circinelloides have been discussed. Furthermore, the potential applications of M. circinelloides in the fields of antioxidants, nutraceuticals, bioremediation, ethanol production, and carotenoids like beta carotene and astaxanthin having significant nutritional value are also deliberated.

Effect of Pb-Contaminated Water on Ludwigia stolonifera (Guill. & Perr.) P.H. Raven Physiology and Phytoremediation Performance

A laboratory experiment was led to examine the lead bioaccumulation capacity of Ludwigia stolonifera (Guill. & Perr.) exposed to various Pb concentrations (0, 10, 25, 50, and 100 mg/L) for 1, 3, 5, and 7 days. The lead accumulation increased as the metal concentrations in the solution increased and over time, to an extreme accretion of 6840 mg/kg DW(dry weight) at 100 mg/L of lead on the 10 days exposure. The proportion removal efficiency, translocation factor, and bioconcentration factor of the plant were assessed. The maximum bioconcentration factor values (1981.13) indicate that the plant was a Pb hyperaccumulator, and translocation factor values (1.85), which are >1, indicate fit of L. stolonifera for eliminating Pb in Pb-contaminated water. Photosynthetic pigments were decreased with increase of Pb concentration and time exposure. Total chlorophyll content and Chl a/b ratio lowered to between 46 and 62% at 100 mg/L Pb after 10 days exposure. Protein content and soluble carbohydrate indicated a similar trend, which showed the highest decrease (7.26 and 36.2 mg/g FW(fresh weight), respectively) at 100 mg/L of Pb after 10 days. The activity of the antioxidant enzymes superoxide dismutase, ascorbate, and peroxidase was increased significantly in comparison to the control. The results indicate that L. stolonifera is a newly recognized Pb hyperaccumulator (6840 mg/kg DW), but physiological status indicates that the plant is not tolerant to high Pb concentrations.

A Mini-Review on the Co-growth and Interactions Among Microorganisms (Fungi and Bacteria) From Rhizosphere of Metal-Hyperaccumulators

The co-growth and synergistic interactions among fungi and bacteria from the rhizosphere of plants able to hyper accumulate potentially toxic metals (PTMs) are largely unexplored. Fungi and bacteria contribute in an essential way to soil biogeochemical cycles mediating the nutrition, growth development, and health of associated plants at the rhizosphere level. Microbial consortia improve the formation of soil aggregates and soil fertility, producing organic acids and siderophores that increase solubility, mobilization, and consequently the accumulation of nutrients and metals from the rhizosphere. These microorganism consortia can both mitigate the soil conditions promoting plant colonization and increase the performance of hyperaccumulator plants. Indeed, microfungi and bacteria from metalliferous soils or contaminated matrices are commonly metal-tolerant and can play a key role for plants in the phytoextraction or phytostabilization of metals. However, few works deepen the effects of the inoculation of microfungal and bacterial consortia in the rhizosphere of metallophytes and their synergistic activity. This mini-review aimed to collect and report the data regarding the role of microbial consortia and their potentialities known to date. Moreover, our new data had shown an active fungal-bacteria consortium in the rhizosphere of the hyperaccumulator plant Alyssoides utriculata.

Interactions between pyrene and heavy metals and their fates in a soil-maize (Zea mays L.) system: Perspectives from the root physiological functions and rhizosphere microbial community

The co-occurrence of polycyclic aromatic hydrocarbons (PAHs) and heavy metals in agricultural soils has become a worldwide food crop security concern. Pot experiments, rhizosphere microbial metagenomic sequencing, and root metatranscriptomic sequencing were performed to investigate the interactions among pyrene, Cu, and Cd in a soil-maize (Zea mays L.) system. This study provided direct evidence that the co-presence of PAHs and heavy metals changed the root physiological functions and the rhizosphere microbial community, which subsequently influenced the fate of the contaminants. Co-contamination at low levels tended to enhance the uptake potential and biodegradation performance of the plant, whereas increased contaminant concentrations produced opposite effects. The co-presence of 1000 mg/kg Cu decreased the abundance of Mycobacterium in the rhizosphere and reduced pyrene degradation by 12%-16%. The presence of 400-750 mg/kg pyrene altered the metabolic processes, molecular binding functions, and catalytic activity of enzymes in the maize roots, thus impeding the phytoextraction of Cu and Cd. Competitive absorption between Cu and Cd was observed for the 800-1000 mg/kg Cu and 50-100 mg/kg Cd co-treatment, in which Cu showed a competitive advantage, enhancing its root-to-shoot translocation. These findings provide important information for the production of safe crops and for the development of phytoremediation technologies.

Biostimulants for the Regulation of Reactive Oxygen Species Metabolism in Plants under Abiotic Stress

Global food security for a growing population with finite resources is often challenged by multiple, simultaneously occurring on-farm abiotic stresses (i.e., drought, salinity, low and high temperature, waterlogging, metal toxicity, etc.) due to climatic uncertainties and variability. Breeding for multiple stress tolerance is a long-term solution, though developing multiple-stress-tolerant crop varieties is still a challenge. Generation of reactive oxygen species in plant cells is a common response under diverse multiple abiotic stresses which play dual role of signaling molecules or damaging agents depending on concentration. Thus, a delicate balance of reactive oxygen species generation under stress may improve crop health, which depends on the natural antioxidant defense system of the plants. Biostimulants represent a promising type of environment-friendly formulation based on natural products that are frequently used exogenously to enhance abiotic stress tolerance. In this review, we illustrate the potential of diverse biostimulants on the activity of the antioxidant defense system of major crop plants under stress conditions and their other roles in the management of abiotic stresses. Biostimulants have the potential to overcome oxidative stress, though their wider applicability is tightly regulated by dose, crop growth stage, variety and type of biostimulants. However, these limitations can be overcome with the understanding of biostimulants’ interaction with ROS signaling and the antioxidant defense system of the plants.

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

Simple Summary

The maize (Zea mays L.) late wilt disease, caused by the fungus Magnaporthiopsis maydis, is considered the most severe threat to commercial maize production in Israel and Egypt. Various control strategies have been inspected over the years. The current scientific effort is focusing on eco-friendly approaches against the disease. The genus Trichoderma, a filamentous soil and plant root-associated fungi, is one of the essential biocontrol species, demonstrating over 60% of all the listed biocontrol agents used to reduce plant infectious diseases. They produce different enzymes and elicit defense responses in plants, playing a significant role in biotic and abiotic stress tolerance, hyphal growth, and plant growth promotion. Trichoderma asperellum was found to have biocontrol ability and protect crops against various plant pathogenic fungi, including the maize late wilt disease causal agent. This research aimed at isolating and identifying T. asperellum secondary metabolites with antifungal action against M. maydis. From T. asperellum growth medium, the 6-Pentyl-α-pyrone secondary metabolite was isolated and identified with high potent antifungal activity against M. maydis. This compound previously exhibited antifungal activities towards several plant pathogenic fungi. Achieving clean and identified T. asperellum active ingredient(s) secreted product(s) is the first step in revealing their commercial potential as new fungicides. Follow-up studies should test this component against the LWD pathogen in potted sprouts and the field.

Abstract

Late wilt disease (LWD) is a destructive vascular disease of maize (Zea mays L.) caused by the fungus Magnaporthiopsis maydis. Restricting the disease, which is a significant threat to commercial production in Israel, Egypt, Spain, India, and other countries, is an urgent need. In the past three years, we scanned nine Trichoderma spp. isolates as biological control candidates against M. maydis. Three of these isolates showed promising results. In vitro assays, seedlings pathogenicity trials, and field experiments all support the bio-control potential of these isolates (or their secretions). Here, a dedicated effort led to the isolation and identification of an active ingredient in the growth medium of Trichoderma asperellum (P1) with antifungal activity against M. maydis. This Trichoderma species is an endophyte isolated from LWD-susceptible maize seeds. From the chloroform extract of this fungal medium, we isolated a powerful (approx. 400 mg/L) active ingredient capable of fully inhibiting M. maydis growth. Additional purification using liquid chromatography–mass spectrometry (LC–MS) and gas chromatography–mass spectrometry (GC–MS) separation steps enabled identifying the active ingredient as 6-Pentyl-α-pyrone. This compound is a potential fungicide with high efficiency against the LWD causal agent.

Accumulation and subcellular distribution of cadmium in rygegrass induced by Aspergillus niger TL-F2 and Aspergillus flavus TL-F3

Although plant growth-promoting fungi can greatly accelerate the ryegrass bioaccumulation of cadmium (Cd), the underlying mechanisms are not yet well documented. Therefore, we performed a 20-days hydroponic experiment to investigate the effects of Aspergillus niger TL-F2 (A. niger TL-F2) and Aspergillus flavus TL-F3 (A. flavus TL-F3) on accumulation/subcellular distribution of Cd by annual ryegrass Dongmu 70 at different Cd concentrations (0, 2.5, and 5 mg L^-1). Results indicated that both fungal strains promoted ryegrass biomass/growth by about 60%. Furthermore, we found that ryegrass roots (17.8-37.1 μg pot^-1) had a significantly higher capability for Cd uptake than the shoots (1.66-5.45 μg pot^-1) (p < 0.05). Of total Cd in ryegrass plants, 44-67% was in soluble form, 24-37% was in cell wall, and 8.5-25.5% was in organelles. Compared with non-fungus ryegrass, cell wall and soluble Cd fractions in fungus-inoculated roots increased and decreased by 13.5-44% and 21.5-26.4%, respectively. Besides, fungus inoculation generally increased the content of cell wall and soluble Cd fractions in ryegrass shoots. Altogether, the study concludes that inoculation of fungus in ryegrass is a promising approach to improve phytoremediation of Cd contaminated environments.Novelty statement Previous study by Han et al. (2018) examined the resistance of ryegrass plant to Cd stress after its inoculation with Aspergillus aculeatus. In this study, using a hydroponic experiment, we examined the effects of co-application of two species of Aspergillus fungi. i.e. A. niger TL-F2 and A. flavus TL-F3 on ryegrass growth/biomass, Cd absorption by ryegrass shoots and roots, and subcellular distribution of Cd in ryegrass roots and shoots.

The Response of the Soil Microbiome to Contamination with Cadmium, Cobalt and Nickel in Soil Sown with Brassica napus

Soil fertility is determined by biological diversity at all levels of life, from genes to entire biocenoses. The aim of this study was to evaluate bacterial diversity in soil contaminated with Cd2+, Co2+ and Ni2+ and sown with Brassica napus. This is an important consideration because soil-dwelling microorganisms support phytoremediation and minimize the adverse effects of heavy metals on the environment. Microbial counts, the influence (IFHM) of Cd2+, Co2+ and Ni2+ on microorganisms, the colony development (CD) index, the ecophysiological diversity (EP) index and genetic diversity of bacteria were determined under controlled conditions. Soil contamination with Cd2+, Co2+ and Ni2+ significantly influenced microbial diversity and increased the values of CD and EP indices. The tested heavy metals decreased the genetic diversity of bacteria, in particular in the phyla Actinobacteria and Proteobacteria. Bacteria of the genera Arthrobacter, Devosia, Kaistobacter, Paenibacillus, Phycicoccus, Rhodoplanes and Thermomonas were identified in both contaminated and non-contaminated soil. These bacteria are highly resistant to soil contamination with Cd2+, Co2+ and Ni2+.

Behaviors of cadmium in rhizosphere soils and its interaction with microbiome communities in phytoremediation

Phytoremediation of cadmium (Cd) contaminated soils by accumulators or hyperaccumulators has received considerable attention. However, there is still limited information about its migration, dynamic characteristics, and interaction with microbial communities in rhizosphere. In this study, the behaviors of Cd in rhizosphere soils in phytoremediation were carefully studied and illustrated. We find that the migration rate of Cd in rhizosphere is higher than the absorption rate of Cd by roots of plants, and Cd in near-rhizosphere moves sluggishly, and near-rhizosphere soils forms a mass pool of Cd for absorption by plants. Additionally, in tall fescue and Indian mustard treatments, shoot biomasses, total extracted Cd and migration rate of Cd in near-rhizosphere soils were comparable. It suggests that shoot biomasses of plants significantly affect their extraction of heavy metals from rhizosphere soils. Biomasses of bacteria significantly increased after phytoremediation, and structures of microbiome communities of soils after phytoremediation reassembled significantly. Furthermore, Indian mustard, even with relative lower root biomasses, could better reassembled the microbiome communities in rhizosphere than tall fescue which possesses a higher developed root system. In the end, analyses of functional microorganisms in rhizosphere soils provide new insights into biological and physiochemical roles of these populations in phytoremediation.

Dynamic interactions of Trichoderma harzianum TS 143 from an old mining site in Turkey for potent metal(oid)s phytoextraction and bioenergy crop farming

Despite high pollution risk, the termination of mining practices is not in question in the current era in line with the growing needs of beings. Instead, the rehabilitation by phytoremediation restores the economic and aesthetic values of the damaged locale. Here, potentially toxic elements (PTEs) tolerant 29 Trichoderma isolates from mining sites located foothills of Turkey`s NE Black Sea coast were isolated. The highest tolerant strain (As 1400 mg L^-1, Cd 1200 mg L^-1, Cu 2000 mg L^-1, Pb 2100 mg L^-1, Zn 3000 mg L^-1) was characterized with translation elongation factor1 alpha (tef-1α) barcode and deposited in the GenBank. The PTEs removal strength of novel Trichoderma harzianum TS143 was highest for Pb (58%) and the lowest for As (8.5%) in the order of Pb > Cd > Cu > Zn > As. While bioleaching capacity was highest in Cd with 30%, the lowest was for As (8%). TS143 was found remarkably effective on all the physicochemical parameters in the shoot and root tissues of maize. The increase in the carbohydrate content (33.50%) proves the potential usage of the contaminated maize plants in bioenergy production. Core sustainable agents with their mesh type robust hyphal structure enfolding PTEs such as TS143 contribute to the phytoremediation technology along with potential plant biomass management for the biodiesel industry.

Lead bioaccumulation mediated by Bacillus cereus BPS-9 from an industrial waste contaminated site encoding heavy metal resistant genes and their transporters

This study explores the soil microorganisms for their Lead bioremediation capability. The MIC values of the six Lead resistant bacteria were evaluated, and the AAS studies of these isolates estimated their Lead accumulation percentage. The results showed that the isolate namely Bacillus cereus BPS-9 as identified based on 16S rDNA gene sequences was shown to have the highest Lead accumulation potential (79.26 %) and also selected for bioaccumulation studies. Despite the reduction in growth rate, the superoxide dismutase activity of B. cereus BPS-9 was increased with a rise in the concentration of Lead manifested through increased nitro-blue tetrazolium (NBT) reduction from 3.94 % to 77.48 %. Moreover, the biosorption capacity of B. cereus BPS-9 was 193.93 mg/g and the Langmuir isotherm model showed a value of R² = 0.9. Furthermore, the FTIR analysis also established the role of C-H, C=C, N=N, N-H, and C-O functional groups in Lead adsorption and the SEM micrographs showed that the cells of B. cereus BPS-9 became dense, adhered and distorted after Lead adsorption. Finally, the In-silico results obtained by functional analysis through SEED viewer of the whole genome of B. cereus deciphered the presence of genes encoding heavy metal resistant proteins and transporters for the efflux of heavy metals.

Resistance effect of flavonols and toxicology analysis of hexabromocyclododecane based on soil-microbe-plant system

The toxicity characteristics of HBCD and resistance mechanism of flavonols are investigated based on physiological and metagenomic analysis. Toxicology research of HBCD on Arabidopsis thaliana (Col and fls1-3) not only shows the toxic effect of HBCD on plants, but also indicates that flavonols could improve plant resistance to HBCD, including root length, shoot biomass and chlorophyll content. Analysis of eggNOG and GO enrichment demonstrates that HBCD has toxic effect on both gene expression and protein function, which concentrates on energy production - conversion and amino acid transport - metabolism. Differential expressed genes in flavonols-treated groups indicates that flavonols regulate the metabolism of amino acids, cofactors and vitamins, which is involved in plant defense system against oxidative damage caused by HBCD stress. HBCD is believed to affect the synthesis of proteins via genes expression of ribosome biogenesis process. Flavonols could strengthen the plant resistance and alleviate toxic effect under HBCD stress.

Role of Flavonol Synthesized by Nucleus FLS1 in Arabidopsis Resistance to Pb Stress

Lead (Pb) is an important pollutant of worldwide concern with respect to extensive pollution sources and highly toxic effect. Flavonol can improve plant resistance to abiotic stress and is also responsible for the alleviating effect under Pb stress. The relationship between Pb stress and flavonol and the knowledge about the mechanisms of flavonol function are very limited. Pb affected the energy metabolism process and, thus, inhibited plant growth and development. Flavonol accumulation controlled by FLS1 (flavonol synthase) could alleviate the toxic effect. Importantly, nes (mutant of NES that allows FLS1 to enter the nucleus expression) showed better growth status and lighter oxidative damage than NES (N-terminal nucleus exclusion signal peptide prevents FLS1 from entering the nucleus expression), which indicated that nucleus flavonol synthesized by nucleus FLS1 plays a key role in plant resistance to Pb stress. Although FLS1 signals were detected in the cell membrane, cytoplasm, and nucleus, membrane flavonol, cytoplasm flavonol, and nucleus flavonol were not exercising their function in the corresponding position. The expression of nucleus FLS1 intervened in the total content and composition of flavonol. The results also revealed that nucleus flavonol could regulate the ascorbate metabolism for alleviating the damage on the chloroplast, thus maintaining the photophosphorylation pathway. Our findings provided new insights for the molecular basis of Pb tolerance and response mechanism of the plant.

Bio-detoxification of Jatropha curcas L. cake by a soil-borne Mucor circinelloides strain using a zebrafish survival model and solid-state fermentation

AIMS

The aims of the study were to (i) improve the evaluation criteria of detoxifying Jatropha curcas L. cake (JCC), (ii) isolate and characterize a JCC tolerant strain, (iii) explore its JCC detoxifying potential.

METHODS AND RESULTS

The zebrafish was employed as a survival model to screen the strains capable of detoxifying JCC. A strain identified as Mucor circinelloides SCYA25, which is highly capable of degrading all toxic components, was isolated from soil. Different solid-state fermentation parameters were optimized by response surface methodology. The optimal values for inoculation amount, moisture content, temperature, and time were found to be 18% (1·8 × 10⁶ spores g^-1 cake), 66%, 26, and 36 days, respectively, to achieve maximum detoxification of the JCC (92%). Under optimal fermentation conditions, the protein content of JCC was increased, while the concentrations of ether extract, crude fiber, toxins, and anti-nutritional substances were all degraded considerably (P < 0·05). Scanning electron microscopy and Fourier transform infrared spectrometer analysis revealed that the fermentation process could disrupt the surface structure and improve the ratio of α-helix to β-folding in the JCC protein, which may improve the digestibility when the detoxified JCC is used as a feedstuff.

CONCLUSIONS

Our results indicate that M. circinelloides SCYA25 is able to detoxify JCC and improve its nutritional profile, which is beneficial to the safe utilization of JCC as a protein feedstuff.

SIGNIFICANCE AND IMPACT OF THE STUDY

The newly identified M. circinelloides SCYA25 detoxified JCC in a safe manner to provide a potential alternative to soybean meal for the feed industry. These results also provide a new perspective and method for the toxicity evaluation and utilization of JCC and similar toxic agricultural by-products.

MIST: a Multilocus Identification System for Trichoderma

Due to the rapid expansion in microbial taxonomy, precise identification of common industrially and agriculturally relevant fungi such as Trichoderma species is challenging. In this study, we introduce the online multilocus identification system (MIST) for automated detection of 349 Trichoderma species based on a set of three DNA barcodes. MIST is based on the reference databases of validated sequences of three commonly used phylogenetic markers collected from public databases. The databases consist of 414 complete sequences of the nuclear rRNA internal transcribed spacers (ITS) 1 and 2, 583 sequence fragments of the gene encoding translation elongation factor 1-alpha (tef1), and 534 sequence fragments of the gene encoding RNA polymerase subunit 2 (rpb2). Through MIST, information from different DNA barcodes can be combined and the identification of Trichoderma species can be achieved based on the integrated parametric sequence similarity search (blastn) performed in the manner of a decision tree classifier. In the verification process, MIST provided correct identification for 44 Trichoderma species based on DNA barcodes consisting of tef1 and rpb2 markers. Thus, MIST can be used to obtain an automated species identification as well as to retrieve sequences required for manual identification by means of phylogenetic analysis.IMPORTANCE The genus Trichoderma is important to humankind, with a wide range of applications in industry, agriculture, and bioremediation. Thus, quick and accurate identification of Trichoderma species is paramount, since it is usually the first step in Trichoderma-based research. However, it frequently becomes a limitation, especially for researchers who lack taxonomic knowledge of fungi. Moreover, as the number of Trichoderma-based studies has increased, a growing number of unidentified sequences have been stored in public databases, which has made the species identification more ambiguous. In this study, we provide an easy-to-use tool, MIST, for automated species identification, a list of Trichoderma species, and corresponding sequences of reference DNA barcodes. Therefore, this study will facilitate the research on the biodiversity and applications of the genus Trichoderma.

The great potential for phytoremediation of abandoned tailings pond using ectomycorrhizal Pinus sylvestris

To explore the potential of ectomycorrhizal (ECM) Pinus sylvestris (P. sylvestris) utilizing in the phytoremediation of a combined heavy metal contaminated tailings pond, Pisolithus sp.1(P1)-. Pisolithus sp.2 (P2)-. Cenococcum geophilum (Cg)-. Laccaria sp. (L1)- ECM, and non-ectomycorrhizal (NM) P. sylvestris were planted separately in lead (Pb)-zinc-(Zn)-cadmium-(Cd)-combined polluted soil, collected from a tailings pond. After four months, growth, photosynthetic parameters, nutrient and heavy metal levels of the plants were evaluated. The physical and chemical properties and enzyme activities of soil before and after ECM plants planting were also investigated. The results showed that inoculation with ECM fungi improved the survival rates of host plants by increasing the biomass, photosynthesis (photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), intercellular CO₂ concentration (Ci)), and mineral nutrients (phosphorus (Pi), magnesium (Mg), iron (Fe), calcium (Ca)), while it decreased the transfer factors of Cd, Pb, and Zn. In addition, ECM P. sylvestris significantly accumulated much more Cd, Pb, and Zn than NM seedlings, while it reduced pH and the availability of heavy metals (DTPA-Cd, DTPA-Pb, DTPA-Zn) in soil and increased activity of soil enzymes (acid phosphatase, alkaline phosphatase, urease). Therefore, the ECM symbionts have the great potential for phytoremediation of abandoned tailings pond, and this study provides a theoretical basis and application premise for the phytoremediation of abandoned tailings pond.

Indigenous Bacteria Have High Potential for Promoting Salix integra Thunb. Remediation of Lead-Contaminated Soil by Adjusting Soil Properties

Salix integra Thunb., a fast-growing woody plant species, has been used for phytoremediation in recent years. However, little knowledge is available regarding indigenous soil microbial communities associated with the S. integra phytoextraction process. In this study, we used an Illumina MiSeq platform to explore the indigenous microbial composition after planting S. integra at different lead (Pb) contamination levels: no Pb, low Pb treatment (Pb 500 mg kg^–1), and high Pb treatment (Pb 1500 mg kg^–1). At the same time, the soil properties and their relationship with the bacterial communities were analyzed. The results showed that Pb concentration was highest in the root reaching at 3159.92 ± 138.98 mg kg^–1 under the high Pb treatment. Planting S. integra decreased the total Pb concentration by 84.61 and 29.24 mg kg^–1, and increased the acid-soluble Pb proportion by 1.0 and 0.75% in the rhizosphere and bulk soil under the low Pb treatment compared with unplanted soil, respectively. However, it occurred only in the rhizosphere soil under the high Pb treatment. The bacterial community structure and microbial metabolism were related to Pb contamination levels and planting of S. integra, while the bacterial diversity was only affected by Pb contamination levels. The dominant microbial species were similar, but their relative abundance shifted in different treatments. Most of the specific bacterial assemblages whose relative abundances were promoted by root activity and/or Pb contamination were suitable for use in plant-microbial combination remediation, especially many genera coming from Proteobacteria. Redundancy analysis (RDA) showed available nitrogen and pH having a significant effect on the bacteria relating to phytoremediation. The results indicated that indigenous bacteria have great potential in the application of combined S. integra-microbe remediation of lead-contaminated soil by adjusting soil properties.

Bioaugmentation-assisted phytoremediation of lead and salinity co-contaminated soil by Suaeda salsa and Trichoderma asperellum

The combined application of plant Suaeda salsa and indigenous fungus Trichoderma asperellum on the treatment of a lead (Pb) and salinity (Na⁺ and Ca²⁺) co-contaminated soil was investigated by a flowerpot experiment. As demonstrated by plant growth and selected antioxidant parameters, S. salsa was able to tolerate and grow in the co-contaminated soil, especially bioaugmented with T. asperellum, which promoted plant growth (9-23% and 5-13% increases for plant height and fresh weight, respectively) and appeared to alleviate plant oxidative damage (7-85% and 7-49% decreases for plant malondialdehyde and peroxidase levels, respectively). The SDS-PAGE fingerprints indicated that the total protein contents of S. salsa were affected under Pb and salinity stresses. The interactions of Na⁺ and Ca²⁺ ions on the phytotoxicity of Pb remained hormesis phenomenon that low-dose alleviation and high-dose enhancement. The analysis of phytoextraction parameters and bioavailability demonstrated that Pb was mainly concentrated in plant roots and poorly translocated, indicating the phytostabilization served as a major repair pathway. On the contrary, the Na⁺ and Ca²⁺ ions were concentrated in plant by the following order: shoot > root. Moreover, bioaugmentation of planted soil with T. asperellum generally led to the 9-42%, 13-58%, and 19-30% decreases of plant Pb, Na⁺, and Ca²⁺ concentrations and translocations, respectively, as well as a 6-21% decrease of soil Pb bioavailability. This study provided a bioaugmentation-assisted phytoremediation technique to make up the deficiencies of the long-term remediation for heavy metals and salinity.

Spatial distribution and risk assessment of heavy metals in contaminated paddy fields - A case study in Xiangtan City, southern China

An extensive investigation on spatial distribution and environmental risk assessment based on total content and fractions of heavy metals, as well as the cancer risk of Cd from seven adjacent contaminated paddy fields at Xiangtan City, southern China, was conducted in this study. A total of 63 soil samples were analyzed for soil physical properties and concentrations of eight heavy metals (Cd, Cr, Co, Cu, Mn, Ni, Pb, Zn). The results showed that concentrations of metals except for Cr, Mn and Ni exceeded the background values to varying degrees, and particularly, content of Cd was as 57.4-612 times higher than background values. Principal components analysis and correlation analysis revealed three groups: industry activities for Cd and Zn; natural sources mainly for Cu, Pb, Ni and Cr, with some slight anthropogenic activities for Cu and Pb accumulation; and manganese ore associated with cobalt for Co and Mn. Combined with different indices, Cd and Zn were the major contributors to the ecological risk, and cancer risk of Cd indicated an unacceptable degree in this area. Altogether, results from this study will facilitate a better understanding of metals distribution characteristics and provide a scientific basis for further comprehensive management for these paddy fields. Combination of functional microbial agent and plants promises to be a feasible and effective remediation method for cadmium pollution in the study area.

Optimization of combined phytoremediation for heavy metal contaminated mine tailings by a field-scale orthogonal experiment

The combined application of plant, microorganism, and amendment on the phytoremediation of heavy metals was optimized as a remediation technique for mine tailings by a field-scale orthogonal (L₁₆) experiment, aimed to achieve the maximum of phytoremediation effect. Soybean, M. Circinelloides, and A3 amendment (organic fertilizer: rice husk: biochar: ceramsite = 1:1:2:1) were recommended as the best plant, microorganism, and amendment materials, respectively. With the combined plant, microorganism, amendment application, effective fractions of Cu, Zn, Pb, Cd, Mn were immobilized for decreased bioavailability, indicating the phytostabilization served as a major repair pathway. Plant length and biomass in the treatments were significantly higher than that in the control, indicating their phytoremediation potentials were enhanced. The final contents of heavy metals in soil were decreased, and the removal rates of soil heavy metals were in the order of Pb＞Cd＞Cu＞Zn＞Mn. Temporal variations of soil microorganism populations indicated that the abundance of soil microorganism in the treatments was significantly higher than that in the control, and bacteria became the dominant microbial species. Results showed that the soil organic matter and catalase, urease, phosphatase activities of the treatments were all significantly higher than that of the control. This study provided optimized combined plant, microorganism, amendment materials in the enhanced phytoremediation field to make up the deficiencies of the long-term phytoremediation for heavy metals.

The Effects of Different Lead Pollution Levels on Soil Microbial Quantities and Metabolic Function with/without Salix integra Thunb. Planting

Background and Objectives: Salix integra Thunb., a fast-growing woody species, has been used in phytoremediation in recent years. It has the potential to accumulate high amounts of lead (Pb) in its growth, however, its effects on soil microbial community structure and function during its phytoextraction processes are not well understood, especially at different pollution levels. Materials and Methods: In our study, we set unplanted and planted Salix integra in areas with four levels of Pb treatments (0, 500, 1000, and 1500 mg/kg). After six months of planting, the rhizospheric soil, bulk soil, and unplanted soil were collected. Soil properties and microbes participating in nitrogen and phosphorus cycling were measured, following standard methods. Microbial metabolic functions were assessed using a Biolog-ECO microplate. Results: The bacteria (nitrogen-fixing bacteria, ammonifying bacteria, inorganic phosphorus-solubilizing bacteria, and nitrosobacteria) all increased in the 500 mg/kg treatment and decreased in the 1500 mg/kg treatment compared with the 0 mg/kg treatment, especially in rhizospheric soil. The microbial metabolisms decreased along with the increase of Pb levels, with the exception of the rhizospheric soil with a 500 mg/kg treatment. The metabolic patterns were relative to the pollution levels. The utilization of carbohydrates was decreased, and of amino acids or fatty acids was increased, in the 500 mg/kg treatment, while the opposite occurred in the 1500 mg/kg treatment. The values of soil properties, microbial quantities, and metabolic activities were higher in rhizospheric than bulk soil, while the differences between bulk and unplanted soil were different among the different Pb treatments. The soil properties had little effect on the microbial quantities and metabolic activities. Conclusions: S. integra planting and Pb levels had an interactive effect on the microbial community. In general, S. integra planting promoted microbial quantities and metabolic activity in rhizospheric soil. Lower Pb pollution increased microbial quantities and promoted the utilization of amino acids or fatty acids, while higher Pb concentrations decreased microbial quantities and metabolic activities, and promoted the utilization of carbohydrates.

Preparation and Characterization of Nanoporous Activated Carbon Derived from Prawn Shell and Its Application for Removal of Heavy Metal Ions

The aim of this study was to optimize the adsorption performance of activated carbon (AC), derived from the shell of Penaeus vannamei prawns, on heavy metal ions. Inexpensive, non-toxic, and renewable prawn shells were subjected to carbonization and, subsequently, KOH-activation to produce nanoporous K-Ac. Carbonized prawn shells (CPS) and nanoporous KOH-activated carbon (K-Ac) from prawn shells were prepared and characterized by FTIR, XRD, BET, SEM, and TEM. The results showed that as-produced K-Ac samples were a porous material with microporous and mesoporous structures and had a high specific surface area of 3160 m²/g, average pore size of about 10 nm, and large pore volume of 2.38 m³/g. Furthermore, batches of K-Ac samples were employed for testing the adsorption behavior of Cd²⁺ in solution. The effects of pH value, initial concentration, and adsorption time on Cd²⁺ were systematically investigated. Kinetics and isotherm model analysis of the adsorption of Cd²⁺ on K-Ac showed that experimental data were not only consistent with the Langmuir adsorption isotherm, but also well-described by the quasi-first-order model. Finally, the adsorption behaviors of as-prepared K-Ac were also tested in a ternary mixture of heavy metal ions Cu²⁺, Cr⁶⁺, and Cd²⁺, and the total adsorption amount of 560 mg/g was obtained.

Characterization of three Pb-resistant fungi and their potential Pb2+ ions adsorption capacities

Bioremediation is preferred in heavy metal remediation, and the high-performance microbe is of prime importance. In the present research, three Pb-resistant microbes were isolated and growth characteristics and adsorption capacities were evaluated. The results showed that R. oryzae SD-1, T. asperellum SD-5, and M. irregularis SD-8 can grow well under 100 mg L^-1 Pb²⁺ ions stress. There is a higher minimum inhibitory concentration (MIC) of Pb but lower MICs of Cd and Zn in T. asperellum SD-5. However, there were similar MICs of Cu among the three microbes. R. oryzae SD-1 exhibited a higher adsorption capacity and removal rate relative to the other two microbes under various Pb²⁺ ion levels. The Langmuir equation was fitted for the adsorption capacity of T. asperellum SD-5 and M. irregularis SD-8, and their maximum adsorption capacities were approximately 456.62 mg g^-1 and 93.62 mg g^-1. Moreover, the Elovich equation and the double constant equation can describe the adsorption process of Pb²⁺ ions in Pb-resistant microbes well. The strongest adsorption capacity under lower Pb²⁺ ion level was observed in M. irregularis SD-8, while the strongest adsorption capacities under higher Pb²⁺ ion levels were seen in R. oryzae SD-1 and T. asperellum SD-5. Therefore, three novel Pb-resistant microbes may be used as efficient, easily cultivated materials for Pb-contaminated soil remediation.

Physiological responses of Suaeda glauca and Arabidopsis thaliana in phytoremediation of heavy metals

The over discharge of mine tailing cause consequent heavy metal pollution. Phytoremediation as one of the most viable and efficient method for this problem has aroused much attention. In this research, the growth and physiological responses of Suaeda glauca and Arabidopsis thaliana plants were investigated, and the soil conditions (pH and enzyme activity) were evaluated further under varied levels of cadmium (Cd), lead (Pb) and manganese (Mn). The results showed that heavy metals could inhibit the growth of plants. The fresh weight and photosynthetic pigments contents of Suaeda and Arabidopsis decreased with the increased concentration of Cd, Pb and Mn. As a monitoring plant, growth status of Arabidopsis showed good dose-effect when treated by heavy metals. S. glauca showed better tolerance capacity for Cd, Pb and Mn, when compared with Arabidopsis. Moreover, the physical and chemical properties of soil were significantly improved after phytoremediation. The soil catalase activity decreased with increased concentration of metal treatments, which showed similar regularity with microbial community. Changes of microbial community could not only indicate the soil environment but also suggest that S. glauca plants had better influences on the soil microbial environment. The introduction of plants resulted in a 0.5-0.8 units change in soil pH compared with the initial pH level. The present study provided the potential of S. glauca plants for phytoremediation in contaminated soil. Microbial community of Suaeda and Arabidopsis were evaluated and showed different regularity because of the rhizosphere effect. Soil microorganisms played an important role in the process of bioremediation. Meantime the main problems about physical and chemical properties of mine tailings were improved. It could be of great significance to the large-scale resource utilization and economical remediation of mine tailings.

Soil sustainable utilization technology: mechanism of flavonols in resistance process of heavy metal

The soil ecosystem is critical for agricultural production, affecting many aspects of human health. Soil has more unknown biodiversity and edaphic parameters than any other ecosystem especially when polluted. Metagenomics and metatranscriptomics were applied to research on toxicological characteristics of Pb and resistance mechanism of flavonols. Rhizosphere microorganisms-plants system, a unified system closely related to soil environment was taken as research object. Results emphasize gene expression changes in different test groups. Gene ontology enrichment and eggNOG showed that Pb has a toxic effect on gene and protein function which concentrated on ATPase and ATP-dependent activity. Differentially expressed genes in the flavonols group indicated that flavonols regulate amino acid transport and other transportation process related to Pb stress. Kegg analysis represents that Pb interferences energy production process via not only the upstream like glycolysis and tricarboxylic acid (TCA) circle but also oxidative phosphorylation process, which can also produce reactive oxygen species and impact the eliminating process. Flavonols have shown the ability in alleviating toxic effect of Pb and improving the resistance of plants. Flavonols can recover the electronic transmission and other process in TCA and oxidative phosphorylation via ascorbic acid-glutathione metabolism. Flavonols activated antioxidative process and non-specific immunity via vitamins B₂-B₆ metabolism.