Safe utilization of heavy-metal-contaminated farmland by mulberry tree cultivation and silk production

Safe utilization and remediation potential of the mulberry-silkworm system in heavy metal-contaminated lands: A review

Mulberry cultivation and silkworm rearing hold a prominent position in the agricultural industries of many Asian countries, contributing to economic growth, sustainable development, and cultural heritage preservation. Applying the soil-mulberry-silkworm system (SMSS) to heavy metal (HM)-contaminated areas is significant economically, environmentally, and socially. The ultimate goal of this paper is to review the main research progress of SMSS under HM stress, examining factors affecting its safe utilization and remediation potential for HM-contaminated soils. HM tolerance of mulberry and silkworms relates to their growth stages. Based on the standards for HM contaminants in various mulberry and silkworm products and the bioconcentration factor of HMs at different parts of SMSS, we calculated maximum safe Cd and Pb levels for SMSS application on contaminated lands. Several remediation practices demonstrated mulberry's ability to grow on barren lands, absorb various HMs, while silkworm excreta can adsorb HMs and improve soil fertility. Considering multiple factors influencing HM tolerance and accumulation, we propose a decision model to guide SMSS application in polluted areas. Finally, we discussed the potential of using molecular breeding techniques to screen or develop varieties better suited for HM-contaminated regions. However, actual pollution scenarios are often complex, requiring consideration of multiple factors. More large-scale applications are crucial to enhance the theoretical foundation for applying SMSS in HM pollution risk areas.

Effect of red and blue light supplementation on the efficacy of Noccaea caerulescens in decontaminating metals and alleviating leaching risk

This study was conducted to investigate the impact of supplementing blue and red light on the biomass yield, metal uptake, contaminant purification, and the alleviation of leaching risks by Noccaea caerulescens, a well-known hyperaccumulator of Cd and Zn. As previously reported for the closely related Thlaspi arvense, N. caerulescens retarded the leaching of Cd and Zn but aggravated the leaching of Pb and Cu, because the species mobilized all metals in soil but only extracted Cd and Zn. Monochromic red light reduced the leaching of Pb and Cu by 13.8% and 1.3%, respectively, but simultaneously weakened Cd phytoremediation by reducing shoot biomass. Our results demonstrated that a small proportion of blue light (10%) could eliminate the negative effect of monochromatic red light on plant shoot growth. However, root biomass decreased by 14.3%, 26.2%, 21.4%, and 61.9% as the percentage of blue light increased from 10 to 100%. Noccaea caerulescens generated the most biomass and accumulated the highest metal concentrations, except for Pb, when the ratio of red to blue light was 1:1. In addition, leachate volume was significantly reduced under the 10% and 50% blue light treatments compared to other light treatments. Therefore, light supplementation with a suitable proportion of blue light can enhance metal purification by N. caerulescens and alleviate potential leaching risk during phytoremediation.

Integrative analysis of microbiota and metabolomics in chromium-exposed silkworm (Bombyx mori) midguts based on 16S rDNA sequencing and LC/MS metabolomics

The gut microbiota, a complex ecosystem integral to host wellbeing, is modulated by environmental triggers, including exposure to heavy metals such as chromium. This study aims to comprehensively explore chromium-induced gut microbiota and metabolomic shifts in the quintessential lepidopteran model organism, the silkworm (Bombyx mori). The research deployed 16S rDNA sequence analysis and LC/MS metabolomics in its experimental design, encompassing a control group alongside low (12 g/kg) and high (24 g/kg) feeding chromium dosing regimens. Considerable heterogeneity in microbial diversity resulted between groups. Weissella emerged as potentially resilient to chromium stress, while elevated Propionibacterium was noted in the high chromium treatment group. Differential analysis tools LEfSe and random forest estimation identified key species like like Cupriavidus and unspecified Myxococcales, offering potential avenues for bioremediation. An examination of gut functionality revealed alterations in the KEGG pathways correlated with biosynthesis and degradation, suggesting an adaptive metabolic response to chromium-mediated stress. Further results indicated consequential fallout in the context of metabolomic alterations. These included an uptick in histidine and dihydropyrimidine levels under moderate-dose exposure and a surge of gentisic acid with high-dose chromium exposure. These are critical players in diverse biological processes ranging from energy metabolism and stress response to immune regulation and antioxidative mechanisms. Correlative analyses between bacterial abundance and metabolites mapped noteworthy relationships between marker bacterial species, such as Weissella and Pelomonas, and specific metabolites, emphasizing their roles in enzyme regulation, synaptic processes, and lipid metabolism. Probiotic bacteria showed robust correlations with metabolites implicated in stress response, lipid metabolism, and antioxidant processes. Our study reaffirms the intricate ties between gut microbiota and metabolite profiles and decodes some systemic adaptations under heavy-metal stress. It provides valuable insights into ecological and toxicological aspects of chromium exposure that can potentially influence silkworm resilience.

Diffusion and enrichment of high-risk antibiotic resistance genes (ARGs) via the transmission chain (mulberry leave, guts and feces of silkworm, and soil) in an ecological restoration area of manganese mining, China: Role of heavy metals

This study investigated the diffusion and enrichment of antibiotic resistance genes (ARGs) and pathogens via the transmission chain (mulberry leaves - silkworm guts - silkworm feces - soil) near a manganese mine restoration area (RA) and control area (CA, away from RA). Horizontal gene transfer (HGT) of ARGs was testified by an IncP a-type broad host range plasmid RP4 harboring ARGs (tetA) and conjugative genes (e.g., korB, trbA, and trbB) as an indicator. Compared to leaves, the abundances of ARGs and pathogens in feces after silkworms ingested leaves from RA increased by 10.8% and 52.3%, respectively, whereas their abundance in feces from CA dropped by 17.1% and 97.7%, respectively. The predominant ARG types in feces involved the resistances to β-lactam, quinolone, multidrug, peptide, and rifamycin. Therein, several high-risk ARGs (e.g., qnrB, oqxA, and rpoB) carried by pathogens were more enriched in feces. However, HGT mediated by plasmid RP4 in this transmission chain was not a main factor to promote the enrichment of ARGs due to the harsh survival environment of silkworm guts for the plasmid RP4 host E. coli. Notably, Zn, Mn, and As in feces and guts promoted the enrichment of qnrB and oqxA. Worriedly, the abundance of qnrB and oqxA in soil increased by over 4-fold after feces from RA were added into soil for 30 days regardless of feces with or without E. coli RP4. Overall, ARGs and pathogens could diffuse and enrich in environment via the sericulture transmission chain developed at RA, especially some high-risk ARGs carried by pathogens. Thus, greater attentions should be paid to dispel such high-risk ARGs to support benign development of sericulture industry in the safe utilization of some RAs.

Phytoremediation as a potential technique for vehicle hazardous pollutants around highways

With the synchronous development of highway construction and the urban economy, automobiles have entered thousands of households as essential means of transportation. This paper reviews the latest research progress in using phytoremediation technology to remediate the environmental pollution caused by automobile exhaust in recent years, including the prospects for stereoscopic forestry. Currently, most automobiles on the global market are internal combustion vehicles using fossil energy sources as the primary fuel, such as gasoline, diesel, and liquid or compressed natural gas. The composition of vehicle exhaust is relatively complex. When it enters the atmosphere, it is prone to a series of chemical reactions to generate various secondary pollutants, which are very harmful to human beings, plants, animals, and the eco-environment. Despite improving the automobile fuel quality and installing exhaust gas purification devices, helping to reduce air pollution, the treatment costs of these approaches are expensive and cannot achieve zero emissions of automobile exhaust pollutants. The purification of vehicle exhaust by plants is a crucial way to remediate the environmental pollution caused by automobile exhaust and improve the environment along the highway by utilizing the ecosystem's self-regulating ability. Therefore, it has become a global trend to use phytoremediation technology to restore the automobile exhaust pollution. Now, there is no scientific report or systematic review about how plants absorb vehicle pollutants. The screening and configuration of suitable plant species is the most crucial aspect of successful phytoremediation. The mechanisms of plant adsorption, metabolism, and detoxification are reviewed in this paper to address the problem of automobile exhaust pollution.

Influences of elevated O3 and CO2 on Cd distribution in different Festuca arundinacea tissues

It is necessary to reveal the responses of the biomass production and metal accumulation capacity of different plants to the variations of atmospheric conditions and soil metals, with the acceleration of urbanization and industrialization. In the present study, a series of experiments were designed to study the individual and interactive influences of O₃ and CO₂ fumigation on the biomass yield, variation in different leaf types, distribution of cadmium (Cd) in various tissues, and phytoremediation efficiency of Festuca arundinacea using open top chambers. The results found that an elevated O₃ content of 80 ppb, a potential O₃ content predicted for 2050, decreased the total dry mass of F. arundinacea and increased the proportion of falling leaf tissues of the species significantly. Under the same ambient CO₂ levels, O₃ fumigation increased the Cd concentrations in the roots and the fresh, mature, senescent, and dead leaf tissues by 27.8%, 133.3%, 94.4%, 125.3%, and 48.6%, respectively. An elevated CO₂ content (550 ppm) promoted the biomass yield of F. arundinacea, particularly in the falling leaf tissues. The results of the combined O₃ and CO₂ treatment showed that CO₂ fumigation alleviated the negative effects of O₃ on plant growth and increased the accumulation capacity in different plant tissues. Significantly more Cd was accumulated in senescent and dead leaves under the synergistic action of CO₂ and O₃, suggesting that the phytoremediation effect on F. arundinacea using the falling leaves harvesting method could be improved under the future atmospheric environment of high CO₂ and O₃ levels.

Safe utilization of cadmium- and lead-contaminated farmland by cultivating a winter rapeseed/maize rotation compared with two phytoextraction approaches

Compared with phytoextraction, growing suitable crops may be a more profitable and practical approach for managing contaminated farmland, especially when there are multiple pollutants. In this 5-year field study, the phytoaccumulator Hylotelephium spectabile, the high-biomass species amaranth (Amaranthus hypochondriacus), and a winter rapeseed/maize rotation crop were cultivated on farmland contaminated with cadmium (Cd) and lead (Pb). Over 4 consecutive years, the annual Cd uptake and extraction efficiency of H. spectabile was 117.6 g hm^-2 and 2.36%, respectively. The Cd extraction efficiency of amaranth was equivalent to that of H. spectabile because of its high biomass, and it extracted more Pb (660-2210 g hm^-2) from the soil than did H. spectabile. However, neither of these species was able to remediate contaminated farmland rapidly and inexpensively, even with enhancing strategies such as variety screening and the addition of fertilizers and a chelating agent. A safe utilization approach to cultivate rapeseed instead of wheat significantly reduced the carcinogenic and noncarcinogenic risks. The concentrations of heavy metals in rapeseed oil were below the limits specified in the Chinese national food standard, and the heavy metal concentrations in the byproducts (rapeseed meal and straw) were below the limits specified in Chinese national standards for organic fertilizer and feed. The cost of safe utilization was one-quarter that of phytoextraction, and the net economic benefit was 33.5%-123.5% higher than that of wheat crops. Therefore, the rapeseed/maize rotation is a profitable and feasible approach for the safe utilization of Cd- and Pb-contaminated farmland on the northern plains of China.

Effect of light combination on the characteristics of dissolved organic matter and chemical forms of Cd in the rhizosphere of Arabidopsis thaliana involved in phytoremediation

Light, one of the most important natural resources for plant species, significantly influences the biomass yield and nutrient uptake capacity in plants. Light sources with different spectra combinations can impact the bioavailability, toxicity, and solubility of heavy metals in soils by altering the concentrations and fractionations of soil dissolved organic matter (DOM). A series of light irradiation treatments were performed to evaluate the influence of red, yellow, and blue lights on the characteristics of DOM in the rhizosphere soils of Arabidopsis thaliana. The results showed that monochromatic red light significantly raised the levels of DOM and proportions of hydrophilic fractionations in the rhizosphere of A. thaliana relative to the control, while monochromatic blue light had the opposite effect. Moreover, the proportions of hydrophobic acid, which can mobilize Cd effectively, also raised with increasing doses of red light, which stimulated Cd mobilization. The application of yellow light not only increased the levels of hydrophobic acid in monochromatic red light treatment but also decreased the proportion of hydrophobic fractions in monochromatic blue light treatment, partially weakening the negative impacts of pure blue light on soil Cd activation. Moreover, DOM from the combined red, yellow, and blue lights resulted in a significantly stronger Cd extraction efficiency than the other light irradiation treatments, consequently enhancing the Cd phytoextraction efficiency of A. thaliana. The findings of this study demonstrated that a suitable light combination could enhance the phytoremediation effect of A. thaliana by activating soil Cd, and this method can be extrapolated to the real field, where light irradiation can be easily applied and modulated.

Black, Caspian Seas and Central Asia Silk Association (BACSA) for the Future of Sericulture in Europe and Central Asia

Simple Summary

This paper describes the 16-years long activity of the Black Caspian Seas and Central Asia Silk Association, which was founded in 2005 to revive the sericultural activity in the area indicated by its own denomination. The reasons why this Association was established are described as a direct consequence of the decline in the sericulture agroindustry following the collapse of the Soviet Union and the world cocoon/raw silk decrease of production (except for China and India) since the 90s of the 20th century. Therefore, the enlargement of its membership to countries outside of the boundaries of the geographical area is outlined as well as its internal organization and the actions performed to promote the interaction among the member countries, especially the biyearly conferences. The international scenario is depicted to explain the criticalities experienced in promoting sericultural activities in the region, as well as the opportunities offered by the new applications of the silk, silk proteins and mulberry derivatives.

Abstract

The history and recent activities of the Black Caspian Seas and Central Asia Silk Association are presented in this paper: the countries that participated in its foundation, the FAO’s action to revitalize sericulture in Eastern Europe and Central Asia, the following widening of the Association geographical limits of to enclose other European countries, which were not well-represented in other similar organizations. Some statistical data are illustrated for a better description of the scenario in which the BACSA executive board acted: the world silk production quantity and the relative production of BACSA countries in respect to the Chinese expansion. The themes treated in the BACSA conferences are reported to explain which matters the Executive Board considered the most relevant for the relaunch of this activity in relationships to the international challenges in the subsequent years; the project proposals that were presented to international donors are summarized. A SWOT (Strengths, Weaknesses, Opportunities, Threats) analysis is shown, where key-factors in determining the strengths and weaknesses of this organization and its member countries for a successful re-establishment of sericulture, are considered. In addition, future trends of sericulture with regard to innovative productions and the Green Deal are examined.

Pb contaminated soil influence on aboveground biomass and bioactive compounds in leaves of mulberry

This study investigated the effects of soil lead (Pb), biochar, and partial root zone drought (PRD) on mulberry (Morus alba L.) branches and leaves biomass, Pb accumulation, and bioactive compounds including 1-deoxynojirimycin (DNJ) and flavonoids. Three-factor pot experiments were conducted with biochar, PRD, and soil Pb at four concentration levels (0, 50, 200, and 800 mg kg^-1). Results revealed that mulberry aboveground biomass did not decrease significantly across the soil Pb levels. Pb concentration of mulberry leaves do not increase significantly when soil Pb was 200 mg kg^-1; however, it significantly accumulated under 800 mg kg^-1. There was a dose-effect between the Pb concentration in branches and the soil Pb levels. Mulberry leaf flavonoids were affected by the interaction of soil Pb and biochar. The interaction between two of the three factors significantly affected leaves DNJ concentration. The combination of biochar and PRD maintained the biomass of mulberry and did not significantly increase Pb in leaves under 200 mg kg^-1 soil Pb concentration. In summary, mulberry has a higher resistance to soil Pb stress, and it can be planted in moderate Pb-contaminated soils for no loss of biomass and can safely harvest the branches and leaves.Novelty statementAn economic benefit is a key to the practical application and sustainability of phytoremediation. Based on this, we studied the effects of soil Pb on biomass, Pb accumulation, and bioactive substance concentration of harvesting organs in mulberry.Phytoremediation is not isolated, and techniques, such as soil amendments and water management also play a role. In this study, we found that biochar and partial root-zone irrigation had a synergistic effect on the response of mulberry to soil Pb, which could be co-applied in the phytoremediation of lead-contaminated soil.The concentration of heavy metals is the key to ensuring product safety in heavy metal contaminated soil. We found that Pb concentration in leaf and stem of mulberry did not significantly increase under 200 mg kg^-1 soil Pb, while increased at 800 mg kg^-1 soil Pb. Therefore, planting mulberry on 200 mg kg^-1 Pb contaminated soil can safely harvest branches and leaves.

Genomics and proteomics combined analysis revealed the toxicity response of silkworm Bombyx mori to the environmental pathogen Bacillus cereus ZJ-4

Bacterial contamination has caused a major public health problem worldwide. Bacillus cereus is a conditional environmental pathogenic bacteria that can cause food poisoning. Whether environmental pathogens can cause widespread transmission in the insect kingdom is unclear. In this study, a Bacillus cereus ZJ-4 was isolated from the hospital environment of Zhenjiang City, Jiangsu Province, China. It was fatal by injection into the silkworm hemolymph. To investigated the potential toxic factors of ZJ-4 and clarified the toxicity response mechanism of silkworm by the ZJ-4 infection. Then, the whole genome of ZJ-4 was sequenced, and the immune mechanism of silkworm fat body to ZJ-4 pathogen was studied by HE pathological section and proteomics. Bacterial genome sequencing indicated that ZJ-4 had 352 drug resistance genes and 6 virulence genes. After 36 h of subcutaneous puncture with ZJ-4 suspension, the pathological changes were obviously found in HE pathological sections of fat body tissue. Comparative proteomic results indicated that differentially expressed proteins are mainly involved in stress reactions, biological regulation, and innate immunity. The qRT-PCR analysis showed that the expressions of β-GRP, Spaetzle, MyD88, Tube and Dorsal genes in Toll pathway were up-regulated, while Pell and Cactus genes were down-regulated; in the antimicrobial peptide pathway, Glv2, Lzm, Mor, and Leb3 genes were up-regulated, while attacin1 and defensin genes were down-regulated; Sod gene was up-regulated, while Cat gene was down-regulated in the antioxidant pathway; Ldh, Sdh, and Mdh genes were down-regulated in glucose metabolism pathway. These results indicated that ZJ-4 can damage the innate immune pathway of silkworm, and also affect the normal immune function of fat body cells.

In-depth transcriptome unveils the cadmium toxicology and a novel metallothionein in silkworm

Heavy metal pollution has gradually become a major global issue. It is so far reaching in part because heavy metals are absorbed by soil and affect almost all species via ecological cycles. Silkworms (Bombyx mori) are poisoned by heavy metals through a soil-mulberry-silkworm system, which inhibits larval growth and development and leads to a decrease in silk production. In the present study, we performed transcriptome sequencing of larval midgut with cadmium exposure to explore the toxicological mechanism of heavy metal, and found that the following potential pathways may be involved in cadmium infiltration: endocytosis, oxidative phosphorylation, and MAPK signaling. Moreover, we identified a novel metallothionein in silkworm, which is inhibited by cadmium exposure and able to improve heavy metal tolerance in B. mori cell lines and Escherichia coli. We also generated a transgenic silkworm strain overexpressing metallothionein and the result showed that metallothionein observably enhanced larval viability under cadmium exposure. This study used RNA sequencing to reveal a mechanism for cadmium toxicology, and identified and functionally verified BmMT, offering a new potential heavy metal-tolerant silkworm variety.

Pollution characteristics of livestock faeces and the key driver of the spread of antibiotic resistance genes

The increasing prevalence of antibiotic resistance genes (ARGs) in livestock and poultry faeces has attracted considerable amounts of attention. However, in the actual breeding environment, the key driver of the spread of ARGs and which bacteria are involved remain unclear. This study investigated 19 antibiotics and 4 heavy metals in 147 animal faeces. The results showed that piglet faeces exhibited the highest levels of antibiotics and heavy metals. Twelve ARGs, 4 mobile genetic elements (MGEs) and bacterial communities of piglet faeces from 6 pig farms were further assessed to determine the key driver and relevant mechanism of the spread of ARGs. Sulphonamides (SAs) explained 36.5% of the variance (P < 0.05) of the bacterial community and were significantly related to 8 genes (P < 0.01), indicating that SAs dominated the spread of ARGs and should be tightly supervised. Structural equation modelling (SEM) indicated that SAs increased the abundance of ARGs via two pathways: horizontal transfer of ARGs (involving 10 genera) and vertical transfer of ARGs (involving 26 genera). These results improve our understanding of the potential hosts involved in the spread of ARGs, suggesting that monitoring of the above potential hosts is also important in animal feeding practice.

Ornamental plants for the phytoremediation of heavy metals: Present knowledge and future perspectives

Environmental matrices are polluted with the plethora of contaminants, and among these, the concerns related to heavy metals (HMs) are also included. Due to the low cost in a long-term application and environmental friendliness, the use of biological remediation has gained significant attention in recent decades. The use of ornamental plants (OPs) in the field of phytoremediation is scarcely reported, and the impacts of HMs on OPs have also not been investigated in great depth. The OPs mediated HMs remediation can simultaneously remove contaminants and bring improvement in aesthetics of the site. The biomass of OPs produced after such activities can be used and sold as pot plants, cut flowers, essential oils, perfumes, air fresheners production, metal phytomining, and feedstock in silk production. The OPs also present a lower risk of HMs bioaccumulation compared to crop plants. This review focuses on the current knowledge of HMs toxicity to OPs, their applicability advantages, methods to improve the tolerance of OPs with incremented HMs uptake, challenges in the field, and future application perspectives. The case studies realted to practical application of OPs, from China, Iran, India, Oman, Pakistan, and Turkey, were also discussed. This work fetches the inter-disciplinary features and understanding for the sustainable treatment of HMs in a new novel way, to which no previous review has focused.

Building a stable and accurate model for heavy metal detection in mulberry leaves based on a proposed analysis framework and laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used to rapidly detect heavy metals in mulberry leaves. For the purpose of increasing detection stability and accuracy, a novel analysis framework consisting of a Kohonen self-organizing map (SOM), a variable selection method using the successive projection algorithm (SPA) and uninformative variable elimination (UVE), and a consensus modeling strategy was proposed for processing LIBS data to determine copper (Cu) and chromium (Cr) content. Results showed that the best regression model for Cu and Cr content achieved the residual predictive deviation (RPD) values of 10.0494 and 8.3874, respectively, and root mean square error of prediction (RMSEP) values of 110.4550 and 41.4561, respectively. The proposed strategy provides a high-accuracy and rapid alternative to the traditional method for monitoring heavy metals in mulberry leaves, which could guarantee the quality of mulberry leaves and potentially be used in food-related industries.

Physiological responses of Morus alba L. in heavy metal(loid)-contaminated soil and its associated improvement of the microbial diversity

Woody plants have considerable application potential in the phytoremediation schemes, owing to their long-lived large biomass and prosperous root systems in heavy metal(loid)-contaminated soil. Under greenhouse conditions, the physiological response characteristics and phytoremediation possibility of Morus alba L. and its associated improvement of the bacterial and arbuscular mycorrhizal fungal (AMF) diversities in heavy metal(loid) co-contaminated soils were investigated. The results showed that the cultivated M. alba L. plant exhibited significant tolerance against the heavy metal(loid)s in co-contaminated soil and that the microbial diversities were improved notably. The contents of malondialdehyde (MDA) in M. alba L. leaves decreased with cultivation from 90 to 270 days, while the superoxide dismutase, peroxidase and catalase activities were maintained at normal levels to eliminate the production of lipid peroxides. The chemical compositions (e.g. amino acids, carbohydrates and proteins) in the root of M. alba L. fluctuated slightly throughout the cultivation period. Meanwhile, Cd, Pb and Zn were majorly concentrated in the M. alba L. roots, and the maximum contents were 23.4, 7.40 and 615.5 mg/kg, respectively. According to the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis results, the influence of M. alba L. on the rhizosphere AMF community was greater than that on the bacteria community. Meanwhile, the bacterial and AMF Shannon diversity indexes in the contaminated soil were enhanced by 18.7-22.0% and 7.14-16.4%, respectively, with the presence of M. alba L. Furthermore, the correlations between the availability of As, Cd, Pb, and Zn and Shannon diversity indexes of the bacterial and AMF communities were significantly (p < 0.05) positive with the phytoremediation of M. alba L. Therefore, M. alba L. can be suggested as a potential plant candidate for ecological remediation and for simultaneously improving the activity and diversity of microorganisms in contaminated soils.

Toxicity response of silkworm intestine to Bacillus cereus SW7-1 pathogen

Bacillus cereus is a foodborne pathogen that causes gastrointestinal disease in hosts. The interactions between pathogenic bacteria and silkworms (Bombyx mori L.) involve complex processes. This study aimed to investigate the potential genetic traits of B. cereus SW7-1 and profile the toxicity response of silkworm intestine upon infection by the SW7-1 pathogen. Bacterial genome sequencing and polymerase chain reaction (PCR) detection indicated that B. cereus SW7-1 possesses multiple antibiotic-resistant genes and nine virulence factor genes. Then, silkworm larvae were infected with SW7-1. Comparative transcriptomic analysis revealed that 273 differentially expressed genes (DEGs) with known functions were successfully annotated to the silkworm reference genome. Specifically, 18 DEGs were up-regulated, and 255 DEGs were down-regulated. Compared with the control group, the treated group revealed down-regulated DEGs that are related to stress reactions, immunity, autophagy and apoptosis, DNA replication, ribosomal stress, and carbohydrate metabolism. Quantitative real time PCR analysis showed that many key genes in the Toll pathway, immune deficiency pathway, Janus kinase/signal transducers and activators of transcription pathway, and melanization reaction were up-regulated. Thus, B. cereus SW7-1 pathogen could damage the silkworm intestine, as confirmed by the histological section assay. In addition, SW7-1 can affect the normal physiological functions of intestinal cells. This study contributes toward an improved understanding of the toxicity response of silkworm to the B. cereus pathogen and provides new insights into the molecular mechanisms of the complex interactions between pathogenic microbes and silkworms.

A critical prospective analysis of the potential toxicity of trace element regulation limits in soils worldwide: Are they protective concerning health risk assessment? - A review

Trace elements (TEs) may have toxic effects to plants and humans; thus, countries and organizations impose maximum allowable regulation limits of their concentrations in soils. Usually such limits are placed in different categories according to soil use, soil properties or based on both attributes. However, some countries have regulation limits irrespective of differentiation in soil properties. In this review, we aimed at collecting TE regulation limits in soils from major countries and organizations around the globe, and critiquing them by assessing potential human health risks in the case of soils attaining the maximum allowable values. We explored the soil-to-human pathway and differentiated among three major exposures from TEs, i.e., residential, industrial and agricultural. We observed the existence of problems concerning TE regulation limits, among which the fact that limits across countries do not regulate the same TEs, not even a minimum number of TEs. This indicates that countries do not seem to agree on which regulation limits of TEs pose a high risk. Also, these regulation limits do not take into account TE mobility to neighbouring environment interphases such as plant, especially edible, and water matrices. Moreover, limits for same TEs are vastly diverse across countries; this indicates that those countries have conflicting information concerning TE-related health risks. Subsequently, we addressed this problem of diversity by quantifying resultant risks; we did that by calculating human health risk indices, taking into consideration the cases in which the highest allowable TE limits are attained in soil. Arsenic limits were found to generate a relatively high hazard quotient (HQ_i, accounting for human intake over the maximum allowable oral reference dose for that same TE), indicating that its risk tends to be underestimated. Other TE limits, such as those of Cd, Cu, Ni, Pb, and Zn typically result in low HQ_i, meaning that limits in their cases are rather overprotective. Our approach reveals the need of reducing diversity in regulation limits by drafting soil legislations of worldwide validity, since risks are common across countries. We suggest that new directions should strategically tend to (a) reduce limits of TEs with underestimated contribution to health risk (such as As), (b) cautiously increase limits of TEs that currently cause minor health risks, (c) quantify TE risks associated with uptake to edible plants and potable water, and (d) consider multi-element contamination cases, where risks are cumulatively enhanced due to TE synergism.

Complementarity of co-planting a hyperaccumulator with three metal(loid)-tolerant species for metal(loid)-contaminated soil remediation

Co-planting with multiple plant species has great value for the remediation of soil co-contaminated with metal(loid)s. A pot experiment has been conducted to study the growth, phytoextraction of metal(loid) and complementarity by co-planting Pteris vittata L. with three metal(loid)-tolerant species with large biomass (namely Arundo donax L., Morus alba L., and Broussonetia papyrifera L.) on soil co-contaminated with As, Cd, Pb, and Zn. The results showed that the co-planting can favor the growth and uptake of As in hyperaccumulator P. vittata L., and improve comprehensive extraction of metal(loid). The total biomass and content of As in the roots of P. vittata L. under the co-planting system were significantly (p < 0.05) improved by 117.5% and 122.0%, respectively, compared with that in monoculture, while the content of As, Cd, Pb and Zn in the tissues of A. donax L., M. alba L. and B. papyrifera L. was slightly increased. The comprehensive accumulation amounts for As, Cd, Pb, and Zn by the four plants co-planting in contaminated soil were higher than that in part of plant's monoculture. Moreover, availability of As, Cd, and Zn in the contaminated soil was decreased in the co-planting system, meanwhile soil urease and acid phosphatase activities in soil significantly (p < 0.05) promoted as compared to the monocultures. The results suggested that positive interaction between hyperaccumulator and three metal(loid)-tolerant species can effectively enhance the growth of P. vittata L., regulate the comprehensive metal(loid)s accumulation capacity, and improve the environmental quality of contaminated soil, which drives high phytoremediation potential for metal(loid)s-contaminated soil by the co-planting.

Phytoextraction of Cd from a contaminated soil by tobacco and safe use of its metal-enriched biomass

Successful phytoextraction produces a large quantity of contaminated biomass, which will cause secondary pollution unless properly treated. This study investigated the disposal of contaminated tobacco biomass after phytoextraction. We detected significantly high Cadmium concentrations in tobacco, especially in their stems and leaves. From the latter, nearly all the Cd and nicotine were removed by extractions with 0.5% HCl + 70% ethanol, and the nicotine completely recovered via steam distillation, whereas the protein content remained unaffected in the leaves, thus making them safe for use as animal feed. The highest biochar yield was 47%, obtained after slow pyrolysis at 300 °C. In this case, the biochar contained the highest amount of nutrients and metals. From stem biochar, 87% of Cd and a large amount K along with several other elements were extracted by deionized water at pH 1. After acid-extraction, metals were formed precipitation and then separated from the K-enriched solution when the pH was adjusted to 11 by using drops of 40% KOH. Therefore, with improved technology to remove metals and recover nutrients and nicotine from biomass, tobacco is an ideal candidate as profit yielding crop for use in phytoextraction while also providing renewable resources.

Intercropping efficiency of four arsenic hyperaccumulator Pteris vittata populations as intercrops with Morus alba

Soils that are slightly or moderately contaminated with arsenic (As) can be safely utilized by intercropping As hyperaccumulator Pteris vittata with cash crops. Introducing hyperaccumulators into crop planting systems results in the alleviation of the adverse effects of As and competition effect for resources. The balance between these two effects determines intercropping efficiency. The effect of using different hyperaccumulator populations on such balance is the focus of this study. Through a tank experiment, four P. vittata populations were compared on the basis of their intercropping efficiencies and physiological and morphological characteristics. The evaluation of the intercropping efficiency of P. vittata was mainly based on the capabilities of the species to promote growth and decrease As concentrations in intercropped Morus alba. Two populations of P. vittata were appropriate for intercropping with M. alba, with the alleviation effect of As harm as the main effect on the intercropping system. These populations showed extensive root overlap with M. alba and efficient uptake of bioavailable As, thus depleting As in the rhizosphere and lowering As risk. After different P. vittata populations were used, varied interspecific interactions were observed. Root overlap and aboveground morphological parameters are the key factors determining intercropping efficiency among P. vittata populations.

Remediation of Arsenic contaminated soil using malposed intercropping of Pteris vittata L. and maize

Intercropping of arsenic (As) hyperaccumulator and cash crops during remediation of contaminated soil has been applied in farmland remediation project. However, little is known about the fate of As fractions in the soil profile and As uptake within the intercropping plants under field condition. In this study, As removal, uptake, and translocation were investigated within an intercropping system of Pteris vittata L. (P. vittata) and maize (Zea mays). Results indicated that the concentration of As associated with amorphous Fe (hydr)oxides in the 10-20 cm soil layer was significantly lower under malposed intercropping of P. vittata and maize, and As accumulation in P. vittata and biomass of P. vittata were simultaneously higher under malposed intercropping than under coordinate intercropping, leading to a 2.4 times higher rate of As removal. Although maize roots absorbed over 13.4 mg kg^-1 As and maize leaves and flowers accumulated over 21.5 mg kg^-1 As (translocation factor higher than 1), grains produced in all intercropping modes accumulated lower levels of As, satisfying the standard for human consumption. Our results suggested that malposed intercropping of a hyperaccumulator and a low-accumulation cash crop was an ideal planting pattern for As remediation in soil. Furthermore, timely harvest of P. vittata, agronomic strategies during remediation, and appropriate management of the above ground parts of P. vittata and high-As tissues of cash crops may further improve remediation efficiency.